General information[ Contribute ]

Welcome to the biggest source on Acoustat on the web. Find out about the Acoustat history, discuss with fellow hifi-enthusiasts in the forums or download a manual to repair or modify your equipment.

The technology of full-range-element electrostatic loudspeakers by James Strickland, President of Acoustat Corporation. (PDF, 1.2 MB, 6 pages)

A factory tour (by Andy Szabo, March 2002)

Marco Visona (November 2000): I want to inform my friends Acoustat lovers that Acoustat is now a brand owned by a Chinese company (sigh, sigh). The Italians has went to China, after a long and terrible trip and they sold brand, technology and repairing skills. This is not necessarily a damage, maybe the Chinese will restore our beloved brand.

Malcolm Dean (November 2001): Business Credit Management UK lists a voluntary liquidation of Acoustat last year: 14/01/99, Acoustat Ltd 02.00 pm Bristol Drew Dunn replied on the above information (November 2001): The "Acoustat, Ltd" that Malcolm Dean mentioned made environmental controls for workplace acoustic management. I don't think that it's our beloved Acoustat, the speaker manufacturer.

Jim Curry (November 22, 2004): Southeastern Transformers of Miramar, FL was acquired by Galaxy Transformer in 1998, and subsequently relocated to South Jersey. Southeastern was one of the original transformer suppliers for the Acoustat product line. Today, Galaxy Transfomer & Magnetics still sells replacement transformers. Galaxy Transformers website is:

James Wong (March 3, 2005) The Acoustat brand has once more emerged from its ashes. The "Acoustat, Ltd" brand is now in Chinese hands. The information is a bit sketchy as most of the site is in Chinese. More to follow!

Nemish Mehta (March 29, 2005): Acoustat is indeed in Chinese hands and is being made again. I have come across this brand recently (in China!!) and have bought some models (probably renamed from the Spectra series). Only have a feel for the lineage through several forums.

I would like to discuss with Andy Szabo et al., whether worth resurrecting. The new amps are not really great. I assumed that ESL manufacture was a high tech operation but looking at the pictures that Andy has posted, perhaps the Chinese can make high end ESL's utilising low labour costs!

Nemish Mehta (February 18, 2010): The speakers being made were not simialr to the old Spectras as far as I was able to tell. Since 2009 I have not heard from the Chinese manufacturer, possibly as there was little or no market in the UK for these products. In 2008, I closed down my importing from China. The Chinese website also does not seem to have been updated since 2008. This is a shame as I still get occasional emails from people who have the old Spectras and need repairs, refurbishment, etc. I usually point them to this forum so anybody still working with these speakers - please update with your details!

Yann Zeeuwe (July 1, 2010): The Chinese Acoustat website has been offline since June 1, 2010. Their email address doesn't seem to work anymore either.

milan puncer (September 27, 2014): hello
I am looking to purchase THYRISTOR for acoustat model x servo driver amplifier.
Please somebody help.
Kind regards from MIlan

He (February 28, 2015): i own a model 3 Acoustat set of speakers that were given to me 25 years ago and have been boxed and bubble wrapped. I recently tried to hook them up to a fairly high end Sony 333es receiver (80 watts per channel) and no sound or hum. I am not sure if I need a formal power amp to power it or whether it could be 2 blown fuses together which seems unlikely. Any suggestions would be much appreciated!

greg (May 4, 2015): Has anyone here from the USA built the ER Audio Acorn ESLs? Or the Mini Panels?

Jim CURRY (June 1, 2015): Just to update all those Acoustat enthusiasts.....Galaxy Transformer is continuing production on the Acoustat transformers with the expert assistance of Mike Savuto. The needs are being filled through the Southern NJ facility. While we have manufacturing in China, the Acoustat line is built solely in the US. Thank you for your continued support.

Kathy (November 10, 2016): Is there a way to get in touch with Andy Szabo. My husband Michael Vardaman used to work with him, and would love to get in touch with him.

History[ Contribute ]

Barry Wilkinson (March 2000): The financial difficulties referred to in the article below (by John Doe) took place in the early 80's . I can still remember the cover of the issue of Stereophile announcing that acoustat was returning from the dead (yes a Phoenix was on the cover) and that David Hafler had rescued them. Then later in the 80's, Hafler sold his Company (including Acoustat) to Rockford-Fosgate, but it was not in financial difficulty, at the time of sale. Hafler became a division of R-F , but under Haflers Management and when he retired Jim Strickland took over as head of the Hafler division.

John Doe (April 2000): This company was originally based in Florida in the USA. My experience with them started in 1982 when I purchased a set of their Model 2+2 speakers. At the time, Acoustats were a rather tall speaker (almost 240 cm ! ) whose design consisted of an array of stacked electrostatic panels (one above the other) in multiple groupings. For example, the 1+1s were the smallest, then came the 2+2s, 3+3s, etc.. These speakers, in my opinion, were some the best sounding speakers available at the time. However, they had a few not-so-inconsequential problems : they required amplifiers with very high current delivery capability at very low impedance (down to less than 1 ohm in some cases). They were also very inefficient (82 to 84 dB with 1w @ 1m), and tended be a bit "beamy" sounding in the upper octaves (progressive narrowing of the radiation pattern with the increase of frequency). In the late 1980s, Acoustat was experiencing serious financial difficulties and was eventually absorbed by the Rockford Fosgate Corp. (the car audio people) who also happened to own the Hafler Company. By the way, David Hafler was also the brains behind the original Dynaco company, who are back in business building reasonably good solid state and tubed home components in the USA. Rockford relocated Acoustat to their own facilities in Arizona and invested a sizable pile of money into the research and development of an entire new line of hybrid and full-range speakers, which upon introduction, became known as the Acoustat Spectra Series. These speakers did not rely on physically placing the adjacent panels at an angel to each other to rectify the narrowing of radiation in the higher frequencies, but rather achieved this remedy electrically (hence, the name Spectra). There were initially three models available:

About three years later, two larger models were introduced:

Another interesting aspect of the Spectra line was that they were a Two way system, with half or more of the panels doing low frequency duty only, whereas the older Plus series was strictly full range. About a year before Rockford realized that there was no future for them in the high-end home audio field, a cosmetically updated series was made available, the 2200, 3300, 4400 and 6600, and the Spectra 11 was replaced with the Spectra 1100, which featured a built-in eight or ten inch dynamic woofer. This was not a subwoofer. Acoustat did have a line of two real subwoofer units which perfectly matched their ESL's, but were not entirely necessary. Acoustats can make bass on their own....REAL bass that you can Feel ! Rockford Fosgate also introduced a line of amplifiers under their Hafler name called the TransNova XL series. These amps were supposed to have simplified the choosing of amplification for the Acoustats because at that time, any amps which suitable to drive these speakers were extremely expensive.

The TransNovas were more stable with the very low impedance found in the Ells, and had a large current output capability and huge heatsinks. Personally, I never liked the sound of these amps, and I have always used Classe electronics to drive my speakers. I have found them to be very musical and extremely durable and reliable. I have also used Sonic Frontiers amps with my Acoustats. My choice of amplification is also tempered by the fact that I live in Canada, and non-Canadian components such as Krell or Mark Levinson are much less affordable here. As far as I can ascertain, Rockford killed the Acoustat division in 1993. In 1995 (approximately) the Acoustat name resurfaced as a division of the Italian firm Audio Physic. They are building electrostatic speakers in Italy which are based on the Spectra design principals. However, when I contacted them, I was told in no uncertain terms that they had NO intentions of ever exporting these interesting speakers to North America. They were intended for sale in certain parts of Europe ONLY! Audio Physic is selling only their dynamic speaker line outside of Europe.

Mike Savuto (July 2000): The first model manufactured by Acoustat was the Acoustat X, made from late 1976 until early 1980. The "X" designation was actually stylized from the electrical representation of an electrostatic speaker design as shown in the manuals. This is the floor standing speaker with the panels in a Walnut trimmed cabinet with the Servo-Charged amplifiers in the bottom of the cabinet and the removable "pegboard" back. They retailed for $1995.

The Monitor 4 came out in late 1978 or early 1979 at about $2995. Acoustat made it available as a DIY kit to upgrade Acoustat X's as well at a very reasonable price, $750. The original Monitor 4 was the "Wing" design with solid Mahogany (black grill cloth) or Oak (white grill cloth) top and bottom caps on a separate base as shown in the pictures on the ESL website.

In 1980 the Monitor 4 cosmetics were changed so that the "Wing" extended to the floor, doing away with the separate base. It was now a monolith design. This is the design shown in the Owners and Service Manual also made available during that time.

The Model X was superceded during that same time by a Monitor 3 with the monolith cosmetics similar to that of the revised Monitor 4. Also in 1980 the first Magnetic-Kinetic (MK-121) interface was introduced. For a time the Monitor 3 and 4 were available with the Servo-Charged amplifiers and the same panel configuration with the MK-121 interface designated as "Model 3 or 4".

In December of 1981 the last Servo-Charged amplifiers were built. All subsequent models utilized the MK-121, and later the Spectra, interface and amplifiers of the owners choice. One source of confusion is that every Servo-Charged amplifier, until very close to the end of production, had "Acoustat Model X" on the serial number sticker. The amplifiers were all the same basic design for each model. The model designation of the speaker array itself was never indicated on the speaker "cabinet" or the Servo-Charged amplifiers. During the time when the MK-121 was being introduced, and the Servo-Charged Amplifiers were being phased out, an excellent article was produced by a short lived audiophile publication, whose name escapes me, that tested and compared the sonics of two designs and officially announced the passing of the Servo-Charged amplifiers. The King was dead.

Hafler home page (January 2001): James C. Strickland, Vice President - Engineering, received his degree in 1963 from the university of Miami. Jim taught physics and mathematics from 1963-1969, while also pursuing development of electrostatic loudspeakers. Jim started his electronic design career with MCI-Sony in 1969. Shortly after becoming Vice President of Engineering there, he developed both analog and digital circuitry for professional multi-track tape recording machines. His work on the digital Automatic Locator and the digital and analog controls of the JH-100 tape decks allowed this series to become the most widely used multi-track machine in the world. In 1984, Acoustat was merged into Hafler, with Jim remaining as Chief Engineer for Acoustat. He developed the SPECTRA drive principle for electrostatic loudspeakers and the IRIS system of digital-analog remote control - ultimately yielding another patent for Rockford, which acquired Hafler in 1987.

Phil Porcari (Februari 2002): As an owner of Acoustat speakers I can tell you that they are sadly no longer being manufactured. The last company I know of who made them was the Rockford Corp. in Tucson.

A Historical Overview (Andy Szabo, march 2002)

The Robot Underground (November 5, 2004): I worked for a summer for Lightning Audio. At that time the accessories brand was being absorbed by Rockford Corp and I got a tour of the RF facilities. One thing that was mentioned was that when RF bought Acoustat, the guy that wrote the contract forgot to place reponsibility for repair on Acoutat speakers to the Italian company that had bought the brand. When I called for info on my Spectra 11 power supplies, the tech confirmed what I had heard. That contract guy was so fired. RF is still responible for build on speakers that had a lifetime warranty. RF tech support: 800-669-9899.

Forum topics[ Add new topic ]

  • Need to find 75k Ohm replacement resistors - Ryan on 2016-06-03 19:53:27

    I have obtained yet another pair of acoustat speakers. This time spectra 44s with one bad interface. I took a look inside the bad interface and the 75k Ohm resistors are clearly charred and have left black marks on the PCB. The 680k resistors look to be ok but I have 4 extra from a left over spectra 1100 interface that had the 680k resistors doubled up in place of the 330k ones. The problem is that I have no idea where to find 75k resistors that are good for audio use and 5 watts. I looked on mouser and digikey and did not find anything that I identified as a suitable replacement. Any help would be greatly appreciated.


    AcoustatAnswerMan (2016-07-17 12:40:57)

    Try looking for Vishay ROX series, in a range of 3-5 watts. Finding the exact 75k ohm might be the hardest part, may have to look at paralleling two 150k ohm. Resistance rating is not super critical. Wattage is not the key specification need a high voltage rating of least 5 kV. Newark Electronics (among others) carries the ROX series.

    AcoustatAnswerMan (2016-09-03 13:15:10)

    Check out this eBay auction.

  • For Sale, 66/6600 (trying the post again) - Eli Hollander on 2016-02-19 22:56:45

    I have put together a Spectra 66/6600, using a proper 6600 transformer, upgraded premium caps and components, and a rigid composite wood frame. The black socks are in very good shape, as are the bases and the electronics. The speaker sound great.

    I also have JL Audio 113 Subwoofer and a pair of Antique Sound Labs Cadenza Mono-Blocks 845 tube (also, with upgrade caps, etc.) amps for sale, and I am open to making an attractive "package deal".

    I am selling my equipment because of my creeping hearing handicap that is preventing me from enjoying music listening that has been an important part of my life. Now it's time to have this wonderful equipment become a part of yours.

    I am in central California and would strongly prefer not to ship the speakers (nor any of the equipment). Thank you.

    Eli Hollander

  • For Sale, 66/6600 (trying the post again) - Eli Hollander on 2016-02-19 22:56:03

    I have put together a Spectra 66/6600, using a proper 6600 transformer, upgraded premium caps and components, and a rigid composite wood frame. The black socks are in very good shape, as are the bases and the electronics. The speaker sound great.

    I also have JL Audio 113 Subwoofer and a pair of Antique Sound Labs Cadenza Mono-Blocks 845 tube (also, with upgrade caps, etc.) amps for sale, and I am open to making an attractive "package deal".

    I am selling my equipment because of my creeping hearing handicap that is preventing me from enjoying music listening that has been an important part of my life. Now it's time to have this wonderful equipment become a part of yours.

    I am in central California and would strongly prefer not to ship the speakers (nor any of the equipment). Thank you.

    Eli Hollander

  • For sale, Acoustat 66/6600 - Eli Hollander on 2016-02-19 22:40:20

    I have a pair Spectra 66/6600's in great shape, black (socks in very good shape), that I put together with proper 6600 transformers, etc.

    The frame is made of wood composit. All the caps have been replaced with premium high quality caps.

    I am selling the speakers because of my progressive hearing disability, making my music listening days a thing of the past.

    I also have a JL Audio 113 Subwoofer for sale as a part of the system, along with a pair of Antique Sound Lab Cadenza Mono-Blocks 845 tube amps for sale and will consider an attractive "package deal".

    I'm located in central California and would definitely prefer to not ship the speakers.

    Eli Hollander

  • pr. MK 121-C's, the gift of a friend! - chris on 2016-01-13 21:48:58

    Purchased new back in the 80's by my buddy, they are 94 inches tall; and I tried sticking a cheap 6 amp fuse or a lower rated one in the one that had a broken fuse set-up, which I bypassed with an automotive fuse-holder. It kept blowing the non-recommended fuses I was sub'ing in. Also, the spkr that I presumed to have issues ran hot in the pre-amp and sounded weaker than the ok spkr. I was testing them with a 100w per ch. Yamaha receiver, and they sounded weak and wouldn't get real loud.
    So I got the amps from the guy who gave me them (the MK's, 2+2's, I think)..a PS 200 watts per ch. and a Conrad Johnson pre, but nothing with equalizers, and it sounded sharper but didn't get loud with the Conrad Johnson near max'd at 3/4+ on the Vol-knob (violins sounding rather tasty like you can feel the cat-gut of the strings when the Hungarian is dragging the bow across them, pulling double and triple-stops).

    Today I finally went and put the recommended 6 amp slo-blo in - everybody went to Disneyland - and went back to the Yama-ha-ha, and it sounds much better - I don't understand why - and does not blow the fuse. The pre to the spkr with my kustom-installed fuse holder does not show arcing in the darkness, but if I rub the back of my knuckles on the 3" grey resistors, I get a little electrical sensation off my knuckle-hairs from it (!but nothing like when I grabbed the connector-terminals that time). It still gets warm but not hot like it did, and I've been playing them for a couple hours now, and the sound seems improved. The spkr that seems to have no issues runs cold on its pre-amp, and together they sound balanced, although they are picky about the source I give to them, having especially tender feelings for 78 rpm records recorded onto the casettes, like, for example, RUSSIAN FOLK SONGS (in Russian) by Alexander Kipnis with Balalaika Orchestra. They are somewhat antagonistic to Elvis through my 8-Track player..The Guitar Man! I can switch to the Dynaco bookshelf's, which have a very excellent sound from any source whatsoever (what great spkrs they are).

    These MK 121-c's are clean and original with just a triangle of the black formica or whatever, knicked off one front corner of the left spkr base, about 3/4 of an inch per angle. The grill cloths are in very good condition with not one cat-claw indiscretion being detectable. They also like Woody Herman very much for the most part..particularly whenever Phil Nastico, or Bill Chase steps up to the front.

    They are out in a Mayflower moving van converted to a man-cave/ art studio in back of the house right now as there is no room for them in the house..until I give it some thought, maybe. I still have to make room out there for a Hammond B-3K and matching Leslie coming soon! chrisinbigbear
    PS: Claw-foot bathtub in the dk-rm. area for washing the prints --

  • Identifying Acoustat speakers - Vegar Hansen on 2015-06-01 08:40:18

    HI. I have 5 Acoustatspeakers but are not able to identify them. The firs one has a 6" bass on top, black pianolack.

    And the other one has the label on the back; it says:Z1100A, those I need panels for so if anyone knows where to get i please let me know. If you need pictures I will gladly send them on mail.

    Best regards
    Vegar Hansen

  • Wire connection to panel - LutherG on 2015-04-13 15:51:59


    I have a pair of Acoustat Monitor 4 speakers and want to know how the wire connexion are made to the panels? Does anyone know of a repair procedure for reconnecting a wire to a panel?

    Thanks and kind regards,


  • Photos of modified Acoustat Speakers - MrAcoustat on 2015-02-28 14:30:42

    MrAcoustat (2015-02-28 14:32:05)

  • - Supajit on 2014-11-23 15:09:25

    Where can I find this spare part "TTA ULT2 ?

  • Why are the interfaces not grounded? - Hank on 2014-04-09 21:07:37

    I bought a pristine pair of Model 3's with "A" interfaces a few months ago. I have parts to upgrade/replace caps, resistors and diodes. I also have a pair of power line filters to install. However, I noticed that the interface power cords are only 2-wire - not grounded. Anyone know why?

  • Sudden decibel diminishment and slight low pitch 'whistle'??? - CineDave on 2014-02-12 06:36:03

    Currently and out of nowhere one of my Spectra 33s is experiencing diminished output and a slightly low-pitched hissy whistle (if you will).

    As for the decibel reduction it is no more than 1db or so. The trouble seems to be emanating from the middle panel.
    Some of the midrange information is a bit recessed and not as forward in presentation as the other panel. The final confirmation was determined using various mono recordings.

    In terms of troubleshooting I've swapped everything except panels (likely the one thing I should have swapped first) cables, wall warts, preamps, amps etc. No changes have been made to the system or the room.

    I've experienced this phenomenon in the past. The resolution turned out being getting into the interface, cleaning/Deoxiting the terminal pins, sub switch and speaker connections...or so it seems. I also gave the the hair dryer treatment just in case as they were due.

    Now for the hissy whistle. It's very subtle, can only be heard when the room is quiet and disappears st about a foot away or so.
    Strangely, the noise only occurs coming out if the top 1/4 section of the panel. Any lower and it disappears . My only thought is the possibility of it being RF as I live in LA . The panels have picked up faint radio stations in the past.

    I'm sure both interfaces would benefit from a recapping. The only problem being it would be my first ever recap job.

    If any of you recognize these issues, have any advice or possible remedies I'd greatly appreciate your expertise


    AcoustatAnswerMan (2014-03-17 21:17:47)

    My suspicion is that you have some sort of debris caught between stator and diaphragm. This debris is causing a small localized discharge (the hissing sound) and in turn is reducing the overall bias level in that panel, causing the reduced volume. The fact that the hissing sound is very localized reinforces this theory. The debris could be something as small as a bit of dust, a hair, or even an insect wing!

    So the good news is that your interfaces are probably okay. Usually, a problem in the interface would manifest itself equally in all panels. More good news is that you can probably fix the problem without having to replace the panel.

    I suggest you discharge the panel by unplugging it for an hour or so, then gently bang with an open hand on the surface of the effected panel. Quite often, this will be enough to cause the debris to drop out of its offending position. If necessary, try this several times before moving on to the next step.

    If that does not work, you will probably need to pull the grille sock down from the top of the speaker, and with the speaker fully discharged, vacuum both sides of the panel. If available, you can also use a gentle blast of compressed air. (The best method is to use compressed air first, then vacuum.) You may have to repeat this process several times before it works. This is not an entirely uncommon problem, and it can almost always be fixed with the methods described above.

  • 1982 vintage - ROBERTLEE on 2014-01-28 21:22:37

    my right speaker is a lot quieter than my left

    I have exchanged easy solder remove able large electronic components
    from the right speaker

    except the rheostat and difficult to remove circuit components

    still same lower volume

    ROBERTLEE (2014-01-28 21:29:41)

    Correction to sentence - I have exchanged .....
    my right speaker is a lot quieter than my left

    I have exchanged easy solder remove able large electronic components
    from the right speaker using those components from the left speakers
    and soldered those original components from the right to put them to the left
    speakers to see if the left speaker will be the quieter one

    except the rheostat and difficult to remove circuit components

    still same lower volume for the right speaker

    AcoustatAnswerMan (2014-01-31 21:47:56)

    One speaker playing less loud than the other is usually due to a problem in the bias power supply. This consists of the 5 diodes and 5 capacitors that form the voltage quintupler. These are located in the center of the printed circuit board. Your best bet is to replace all 10 components in both speakers.

  • Overheating resistor at RCA input jack - Vince Maida on 2014-01-01 21:36:51

    I am having a problem (Both Channels)with the 4.7 ohm resistor that connects the circuit ground to chassis ground at the RCA input connectors overheating and burning out. I noticed on the Hafler version of the amp that the resistor/capacitor combo has been removed with a direct wire connection from circuit to chassis ground. The problem occurred while bench testing the amp into a 2 ohm load at 75 Watts RMS output. I have not looked into this further but it does not occur when the amp is just idling (DC condition) only under power (AC condition). I suspect a high frequency oscillation since the only other connections from chassis ground to circuit ground are the two 0.1uf caps from the output FETS source to chassis ground and the AC line chord. I have checked all the circuit grounds and have found no open circuits or high resistances (> .05 ohms). Has anyone encountered this and what might be the fix. Thanks for any help.

  • Couple of questions - Eric Noyes on 2013-12-10 00:05:18

    I was recently given a set of model Xs with the MK subwoofer. They are in need of refurbishing but everything seems to be there. I'm in Phoenix and would like to have the tubes checked before turning them on, is the a shop in Phoenix that can do this? I would like to upgrade the board components is there a schematic I can download so we can source the replacement parts? Also is there a downloadable manual? I have been researching the internet for info and all the pictures I have seen have the HF knob and gain knob but mine have an additional knob under the RCA input that has approx 8 detents. Any ideas as to what this controls? Since its not in any other pictures I dont think its going to be in the manual. The knobs all match and looking at the board , it doesnt look to have been modified. I can send a pic if needed. Thanks in advance

  • crossover question - Maziar Hamedi on 2013-11-29 16:09:16

    Hi. I have just bought the spectra 11 and im in heaven. Im loving the sound with my tube monoblocks but i have a WAF problems. So im thinking the woofers have to go and i want to keep the panels. Is there any way i can get the panels to go down to 100hz so that i can have a subwoofer hidden in the room to take over from 100hz down? I have heard that the panels go down to 250 and im not an expert but i have heard of mini dsp and I'm thinking maybe i can do something with that to get the hz down? If anyone has a good ide about how i can replace the woofers with one smaller i would be forever thankful.

  • High Voltage Capacitor - Andy Tomlinson on 2013-07-18 18:41:29

    Hi Andy
    I wanted to replace the high voltage .01uF 6000V capacitors on the secondary of the transformer . I can only find a .015uF 6000v . Would this be an OK replacement? How would if affect the sound

    Mathieu (2013-07-29 14:59:39)


    No problem about replacing the 0.01 for a 0.015...
    The sound will depend upon the capacitor type.
    Originals (the yellow ones) are polyester caps. They reveal a typical 'dry' sound of the old acoustats.
    Most of the Acoustat owner have upgraded these caps against polypropylen ones, which gives a more fluid and natural sounding.


    AcoustatAnswerMan (2013-07-30 20:28:59)

    I disagree with Mathieu on two points.

    A change from .01 to .015 is a 50% change. This will affect the frequency at which the audio transformer's main winding and the bass-boost winding will overlap. Some people may not notice the difference, but I would NOT consider such a large change in value to be a good idea.

    The original 0.01-uF, 6kV capacitors are NOT polyester, they are metalized polypropylene. Not only did I specify these parts in the original design, I also purchased them.

    If there is nothing wrong with the existing capacitors, I would leave them alone. If one or more have failed, I would wait until you can find the proper capacitance value in a high-voltage polypropylene.

    Mathieu (2013-07-31 07:30:41)

    Oh Oh....
    I had wrong infos about the nature of these caps.... Too sure of myself... Thanks for correction.

    I use 0.02uF Polypropylen on my Spectra 2200, and 0.015 Auricap ones on my 1+1.
    Auricap gave impressive improvements. To give a comparison, it was similar to the change of a standard polypropylen cap against a VCap in the last stage of a preamplifier.
    .... But these dicussions about Capacitors qualities are another topic...

    I did not check the Spectra 2200 frequency response curve after the caps change. I will do this soon.
    But I did with the 1+1, and I did not notice any modification of the frequency curve between the 0.01 and the 0.015uf. Pehraps are we talking about 1 db differences, which my measurement system cannot see.

    .... You write about 'double winding' for bass boost on the Spectra transformers.
    Can you tell us more about the way these transfortmers works ?

    Thanks again,

    Thanks for your answers.

    Mathieu (2013-08-01 08:21:34)

    Dear Acoustatsanswerman,

    About The 1+1 Spectra...
    ...Of course this model has never existed, but I want to create it.
    The 1+1 are interesting design objects, and making them sounding in the way of the Spectra's models would be a nice thing.

    I've got already 2 pannels, and will begin the job in next october.
    Pehraps may you give me some advise...

    I intend to separate each pannel in three vertical independant areas :
    - 1/4 full range
    - 1/2 medium
    - 1/4 bass
    The cutoff frequency will be the same as for the Spectra 22 ones.

    - I assume that if Acoustat has never produced this model, there is pehraps a good reason....
    What's you opinion ?
    - Is there a negative effect of separating one stator in three areas ?
    - Is the MK121 interface suitable for that job, or should I use a Spectra 22 interface ?
    (I remarked that the HV resistor of the MK121 is a 50kohm, as the Spectra interface resistor is a 100kohm if I'm correct)


    Ryan Benitez (2013-08-15 23:24:59)

    I don't think a spectra 1+1 will work that way. As I see it the options are half full range and half base with a spectra 22 interface or half full range, half medium range, and a woofer using spectra 11 or 1100 interfaces.

    mathieu (2013-08-16 07:37:53)

    Thanks for your interest in that project
    subwoofer exists already in the system. I dont use the original interface for the low cut, it was replaced by a 0,047 Vcap at the first stage of the power amp. Low cut is about 60Hz. And the subs are active with a room correction.

    I don t understand your option..... Do you mean that I should separate the pannels in two parts instead of three ?

    Ryan Benitez (2013-08-16 16:55:07)

    If by 1+1 you mean 2 panels stacked I consider it a bad idea to break the panels up into 3 ranges. An ESL should be considered both a line array and an open baffle speaker. Because it is line array arrangement and segmentation of the drivers needs to be considered. This is why the spectra 11, 22, 33, and 44 are all segmented the way they are.

    AcoustatAnswerMan (2013-08-16 18:09:19)

    Acoustat never considered making a 3-segment Spectra panel. Changing manufacturing from regular panels to Spectra panels was easy by adding the steps of cutting and securing the stator wires in the middle of each panel half. No additional wire leads were required. Manufacturing three sectors would have been possible, but it would have involved adding more wire leads for the center segment. Modifying an existing Spectra panel is another story. Cutting the additional stator wires and adding more leads would be very difficult and risky, at the very least. Itâs not something I would attempt, and if you read below, there are additional electrical issues that cannot be solved by using existing Acoustat transformers.

    The MK121 interface is unsuited to drive a Spectra system of any configuration. Why? Any full range ESL requires internal electrical equalization to produce a flat acoustic response. The MK121âs equalization is designed for a speaker with constant area per frequency (all area playing full range). The MK2123 (2 and 3 panel Spectra) and MK2146 (4 and 6 panel Spectra) interfaces are designed for a speaker with decreasing area with increasing frequency (variable width). Therefore, the high frequency boost must be greater to achieve a flat response. Since the equalization is largely a function of the transformersâ design, the MK121 cannot be modified to drive a Spectra.

    Using a Spectra MK2123 isnât really a solution, either. The MK2123 has three outputs, whereas a stacked 1+1 configuration would have only 2 segments. Even if you were successful in making 3-segment panels, the equalization wouldnât be correct for that mix of panel areas.

    I agree with Ryan that a 1+1 configuration Spectra would be best accomplished by using a Spectra 11/1100 interface driving two stacked, 2-segment Spectra panels. You will probably want to change the 330K-ohm sector resistors to 150K-ohm to compensate for the doubled load capacitance. This will keep the sector frequency roll-off at the same point.

    Since the 11/1100 interface cannot operate at low frequencies, I do not recommend operation lower in frequency than currently configured. Since the crossover frequency is fairly high (about 150 Hz if I remember correctly) you will probably want to use stereo woofers. This is an intriguing project, and one that Iâve often thought about. Properly done, I think it would make for an outstanding speaker. Might Acoustat have ever produced such a model? Perhaps, but the realities of manufacturing and marketing too many models might have killed the idea. Let me know if you build one!

    AcoustatAnswerMan (2013-08-16 19:08:06)


    Regarding your earlier question about how the Acoustat interfaces work.

    Letâs start with the original MK121. The primaries (inputs) of two push-pull transformers are driven in parallel from the amplifier. One is a large low frequency transformer, driven directly, and the other is a smaller high frequency transformer, driven through a high-pass network. The secondaries (outputs) of these transformers are recombined through a resistor-capacitor network to form the push-pull signal to drive the stators. Adjusting the low frequency boost (for different numbers of panels) is accomplished by selecting one of several primary taps on the low frequency transformer. Itâs a very simple concept, but clever enough that the idea is patented.

    The Spectraâs MK2123 and MK2146 interfaces operate by the same concept, but with a very different implementation. Here, two identical transformers are used, one for each phase (one for push, one for pull). The primaries are driven in parallel from the amplifier. There are two secondaries on each transformer, one for high frequencies, and one for low frequencies. These are combined through a resistor-capacitor network to drive the full range sectors directly. The other two sectors are driven through resistors that work against the capacitance of the panels to roll-off the low frequencies. Adjusting the low frequency boost (for different numbers of panels) is accomplished by selecting one of several secondary taps on each transformerâs low frequency winding.

    A major advantage to this second implementation is that each transformer is exposed to only half of the total peak-to-peak push-pull voltage, so there is much less chance of high voltage arc-over.

    Ryan Benitez (2013-08-17 04:08:09)

    What I am interested in is if the woofer section could be done open baffle. I am fairly confident that the spectra 11/1100 crossover is about 250 Hz. I was thinking that the SEAS W22EX001 or HiVi M8N should be able to crossover to a sealed or IB subwoofer smoothly at around 80 Hz but there may be advantages to the sealed box that I have not yet considered. Also I would like to experiment with crossover points to see if the imaging in noticeable affected. The passive filter used a 6 dB rolloff for the panel and 12 dB rolloff for the woofer. Using 24 dB active crossovers should allow a little bit of flexibility to move the crossover down a bit.

    AcoustatAnswerMan (2013-08-20 17:31:10)


    I cannot offer any good advice: your questions about woofer design might get a better answer if posted in the subwoofer section of the website There's lots of bright and clever folks who frequent that forum.

    mathieu (2013-08-20 20:49:04)

    i never could have a good result with a so high roll off frequency.
    when they are well optimized, electrostat can supply enough energy down to 50-70Hz.
    then, two good sub's make sense. But high cut at 100-150Hz destroys the coherence of many musical signals.
    I use such high roll off when high sound level is needed only.

    how low can drive the Spectra 11 interface ? could it go down to 60hz without damage in a 1+1 Spectra configuration ?


    AcoustatAnswerMan (2013-08-20 23:21:55)


    As stated earlier, I would not operate the Spectra 11/1100 interface lower in frequency that currently configured. The transformer is not designed for low frequencies. Core saturation can occur (creating distortion) and even possible damage to the transformer.

    mathieu (2013-08-20 23:57:26)

    That s sad.... Thanks for that precision.
    Backe to the 3 area pannel.....
    If I m correct,
    The Mk2123 used with a 2x three area pannel connected in parrallel would be suitable
    configuration if the sum of the surfaces are the same than for the spectra 22.
    That s why I proposed the following :
    - 1/4 full range
    - 1/2 medium
    - 1/4 bass
    The cutoff frequency will be the same as for the Spectra 22 ones. 
    Is this proposal acceptable ?


    Ryan Benitez (2013-08-21 02:27:40)

    Might life be much more simple you you just get or make a spectra 44? I belive it is the mk2146 that you will need.

    mathieu (2013-08-21 11:02:36)

    You are 100% right !
    Im in the process to build a pair... The MK2146 are there and the 8 pannels are onto modification.
    Target is begin 2014, time to prepare everything and to machine the aluminium frame.

    .... The 1+1 spectra is something else.... I m thinking about it since long ago...


    AcoustatAnswerMan (2013-08-22 16:29:51)


    You are correct that the panel sectoring as described will maintain the same panel area per sector, and therefore the sector roll-off frequencies will remain the same.

    However, there is another aspect that troubles me. Although the total area per sector will remain the same, you have re-arranged that area in a way quite different than the Spectra 22 configuration. From the listening position, your ears mainly hear the cross-section of the array in the same horizontal plane. And when looked at that way, the arrangement of sectors, and therefore their corresponding width in that horizontal plane, is quite different than the 22. How much of a difference this will make, I am not sure. But it could be that the resulting frequency response and the 'electrical curve' will not be as satisfying as you hope. I wish I could be more certain of what will happen, and I'm certainly open to alternate opinions.

    Personally, I would be more inclined to use an MK2123 interface driving a stacked pair of two-sector panels, with the LF-only output disconected. Yes, you would need to change one of the sector resistors to keep the roll-off frequencies the same. By using the full-range interface, your crossover point to a woofer could be much lower, thereby avoiding some of the problems in using the Spectra 11/1100 limited-range interface.

    mathieu (2013-08-23 04:09:24)

    That s a nice idea ! This one never came to my mind...
    That can be a first step , easy to build.
    Many thanks I ll keep you informed.

    Roy A. Esposito (2013-09-06 12:08:36)

    Hello Friends --

    This is just to let you know that my email contact
    has recently changed. It seems AT&T/Yahoo could no
    longer support my very old email address.
    For those of you requiring fantastic restorations
    and upgrading of Acoustat MK and Spectra Interfaces
    and Acoustat Power Amplifiers and Preamplifiers
    my new email address is

    (please notice the dots/periods between the words)

    Email is the preferred method for initial contact with me
    for Acoustat Service and questions.

    Thank you for your continued friendship, kind comments and reviews,
    and support of my work.

    All the Best,
    Roy A. Esposito

    Mathieu (2014-04-29 12:26:10)

    Dear all,

    Now both 1+1 spectra and Spectra 44 are ready.
    I kept the original 'spectra' pannel configuration for the 1+1s, using the MK2123. Pannels have been modified from standard to spectra whithout any trouble. I made the frequency cuttof with Caddock 100Kohm resistors. I aloso modified the Resistors of the MK2123 interface from 1001 to 75kohm (better medium frequency level).

    I built the spectra 44 with respect to the original sketches, changed only the resistors for caddocks, 0,01uF caps for auricaps, and the HV source comes from ERAudio Australia.

    Both speakers have 'plus' and 'minus' : The Spectra 44 delivers a smooth and pleaseant sound, with a very large possible sound level. The 1+1s are more focused and sharp, but more aggressive. Basically the 1+1s are less pleasant that the spectra 44. Measurement curves show that the sonic equilibrium is far different for each speaker and confirm the listening impression.
    First I will finish the setting of the spectra 44
    ... then I intend to keep on going with the 1+1s... I build new pannels divided in three section in respect with the original spectra configuration (30% treeble / 50 mide / 30% bass).

    note for : I made a first test with the spectra 1100 transformer and an low cut at 150 hz : doesn't gives a nice result, the connection between the subwoffer and the esl at 150Hz is still a problem.


    Mathieu (2014-04-29 12:29:10)

    And another question for Acoustatanswermanâ¦
    I don't remember the exact resaon for the 1ohm resistor on most of the Acoustat models â¦
    Is that a way to protect the amplifiers against the low impedance of the speaker ?

    AcoustatAnswerMan (2014-04-30 01:40:02)

    Yes, the 1-ohm resistor keeps the very-low frequency impedance from dipping too low. Keeping this part in-circuit is highly recommended, as many amplifiers will not behave well without it (especially if the amplifier has any DC-offset on its output).

    Mathieu (2014-04-30 11:44:22)

    Ok it is clear to me now,

    - Another thing I don't well understand is the way that you designed the HV interface of the speakers.
    For example I measured the response curve of a MK2123 (spectra 2200) with a 'non spectra' configuration (the two pannel being full range). result is an ascending response curve above 2500Hz, which is confirmed by the listening impression : too much highs.
    Does that means that you designed the transformers for pannels with a 'descending' response, with the idea of a 'compensation' effect ?

    - Then I made some others measurement with variation of the 0,01uF cap from 0,0033 to 0,033uF. The frequency curve becomes completly different⦠The medium range (around 300 Hz) is affected, and i could even use this to improve the frequency curve of the original 1+1.
    ⦠Then I made others measurement with variation of the 100kohm resistor and found that it has also an effect on the SPL curveâ¦.

    Would you be kind enough to give me your email, then I can send to you the curves and you will be able to explain to me what is the relationship between the cap value and the frequency response ?

    AcoustatAnswerMan (2014-05-28 20:05:43)

    I am not surprised that you found the MK2123, driving panels full-area, as having too much high frequency. That would be completely expected. The MK2123 is designed to drive only a small area full range, therefore the HF equalization is intentionally boosted to compensate for the smaller area as compared to lower frequencies. The MK2123 was designed for a specific panel area configuration, and is not likely to work well with other ratios of panel area.

    Changing the values of the coupling resistors and capacitors will certainly have an effect on overall frequency response. The purpose of these components is to sum the outputs of the high and low frequency transformer secondaries. The design of the transformers, and the associated summing components were done for a specific panel configuration, and again, would not be expected to work well for other configurations.

    I cannot advise on specific component value changes and their effect on overall frequency response. If you are interested in modifying an existing design (and I have no problem with that) you are really on your own to make the proper decisions. As the Acoustat Answer Man, my aim is to help owners keep their original speakers running as best possible. Although I am open to discussions about modifications, my opinions and knowledge about alterations are limited.

    Chris Barnard (2014-07-19 03:09:39)

    Hi Acoustatanswerman,

    I have just bought a pair of Spectra 33S with the MK2123 interface and they sound a bit down in the high frequency range.
    I have been told that this is a sympton of the HV diodes and or caps being faulty, but I am unable to find a supplier for these. Can you please suggest a supplier who would post to Australia.

    Also can you tell me what the cross over frequencies are?



    AcoustatAnswerMan (2014-07-19 11:16:52)

    Chris - it is unlikely that the high voltage diodes and capacitors are responsible for any perceived lack of high frequency. These components produce the 5000 volts necessary for the ESL's operation, and if there was a problem in this area, the volume would be reduced equally at all frequencies. That is, the speaker would be less efficient than normal.

    Do you have the speakers correctly oriented with regards to left and right speakers? The high frequencies should be coming off the inner area of each speaker. That is, from the right area of the left speaker, and the left area of the right speaker. Both speakers should be toed-in so that the more-or-less face the listener's position. If possible, the speakers should be placed at least a few feet from the wall behind them. All of these points will affect the perceived HF balance, and I would suggest experimenting with them before blindly replacing components. Unfortunately, there is a lot of what I call 'voodoo' advice out there, not based on a proper scientific understanding of the speaker's operation.

    There are no crossover points as traditionally defined. All of the speaker's area produces low frequencies, less of the area produces mid frequencies, and only a small area produces the highest frequencies. Therefore, the speaker becomes effectively narrower as frequency increases.

    Mathieu (2014-07-20 17:40:37)

    Nice purchase...

    ... The Spectra 33 have a 'big' bass compared to the 22's, as a complete pannel reproduces the lows. It can be only the room which is not large enough ...

    Other possibilty might be the 100+47+10uF caps ? But I never had one failed.

    Or someone modified the internal connections ? Check the internal connections, you should have the orange (not the red) wire connected from the transformer to the 100Kohm HV resistor. The red is not used for the spectra 33.

    Beware also that the pannels are correctly connected (you sould have the connection in the booklet) . An inversion may invert the phase of a section and completly perturb the response curve.

    Great speakers with huge bass...


    Chris Barnard (2014-07-21 05:12:35)

    Thanks for your responses,

    Yes I have them orientated in the room correctly, high freq in the inner section and 1.5m from the rear walls and 300mm from the side walls. My room is not too small, I think being 7m x 4m.

    A few people who are more knowledgeable than I on electrostatics suggested that it is a comon symptom of a low HV output that the treble becomes less extended.

    The MK2123 are factory set, no mods and they have 2 transformers both of which use the orange wire to the resistors.

    BTW: which group of connectors are the front of the panels, Blue or White?

    The reason I ask about crossover points is that I am thinking of Bi-amping them with a crossover before the power amps. I currently have my Tymanpis built this way with my own 50w Class A stereo blocks, but they crossover at 800Hz.



    Mathieu (2014-07-21 07:41:52)

    Tymanpis = Tympanis ?
    I used to set my MG3 exactly the same way with active crossovers... Carver PM1.5 up to 400Hz, then Cary 50W for the mids and highs. Was very nice.

    As said Acoustatanswerman there is no way to do so with the Acoustat. Do you have the possibility to measure the amplitude/frequency response ? I can send to you the measurement for my spectra 2200 and we might pehraps undestand wath's going wrong...


    AcoustatAnswerMan (2014-07-21 12:46:24)

    As correctly mentioned by Mathieu, the Spectra series cannot be biamped. Each of the two transformers is for one phase of the push-pull system, and their primaries are driven in parallel from a single input. The 'crossover' occurs on the secondary, high voltage side of the transformers.

    The blue set of wires are for the rear set of stators, and the white set is for the front.

    I still do not believe that low bias voltage can be responsible for a rolled-off top end. However, if you have access to the necessary equipment, the bias voltage can be measured, and even adjusted somewhat. See instructions copied below.


    Measurement and adjustment of the high voltage bias power supply is vital to the proper operation of the speaker. If an imbalance in playing volume is noted, or any modifications or repairs have been made, the bias power supply should be measured and adjusted if required. Two methods of measurement are provided.

    ⢠This procedure requires specialized equipment and electronic skills. DO NOT attempt this procedure if you are unfamiliar with safe operating practices around high voltage (+5000-volts DC).

    ⢠Do not be concerned about the exact voltage measurements. Due to variable loading effects of different meters, it is impossible to accurately measure the output of the supply. What is important is that both speakers are adjusted to read the same voltage using the same meter.

    ⢠This procedure requires that the interface be disconnected from both the speaker and amplifier. Do not plug in the wall transformer until told to do so.

    ⢠Location '5KV' is the point (used for method #1 only) for measurement of the 5000 volt power supply. Location '5KV' is the circuit pad next to the "+5 KV" label located at the center of the large printed circuit board.

    METHOD #1: (Preferred) Using a high impedance, 1000:1 high voltage probe, and digital voltmeter, connect the ground lead of the probe to chassis ground (at the solder lug attaching the white wire to the chassis). Apply power via the appropriate wall transformer, and allow the system to stabilize for several minutes. Connect the hot lead of the probe to location '5KV'. Adjust the trimmer potentiometer on the PC board until the probe reads approximately 4.3 volts DC.

    METHOD #2: (Alternate) Using a 10 megohm input impedance digital voltmeter, connect the ground (black) lead of the meter to chassis ground (at the solder lug attaching the white wire to the chassis). Apply power via the appropriate wall transformer, and allow the system to stabilize for several minutes. Connect the hot (red) lead of the meter to the red pin-plug terminal (where the panel connections are normally made). DO NOT CONNECT THIS TYPE OF METER TO LOCATION â5KVâ. Adjust the trimmer potentiometer on the PC board until the probe reads approximately 75 volts DC. This reading will correspond to an actual 5000 volts, but the measurement is greatly reduced due to the voltage divider effect of the power supply and voltmeter.

    Chris Barnard (2014-07-22 04:06:59)

    Hi Guys,

    I have with the help of a Tech, measured the HV on the board using a 100Meg Ohm probe, one measured 2.5Kv and the other 1.5kv.
    I assume that the probe has loaded down the actual voltage but one is lower than the other, would that be the diodes?
    And if so where can I buy some?

    When I get the probe again I will follow your procedure thank you.

    Also, I have now used other transformers(from ER Audio Acorns), and run one as I suggested from my Class A bi-amped, and it sounds great, but I would like to get these running properly as standard.



    Mathieu (2014-07-22 15:26:55)

    Good... It seems to me that the setting of the HV is very easy (only a potentiometer in the low voltage area of the interface). Are you living in Perth ? Rob Mc Inlay and I talk time to time and he supplies me with his excellent material and - most of all - advices ! You are in good hands in the Electrostatic world !

    Chris Barnard (2014-07-24 00:28:46)

    Hi Mathieu,

    I live in Melbourne but I have been speaking with Rob on my Acorn project, and yes he is both very knowledgeable and helpful.

    Now that I started this with the Acoustats, another friend wants me to fix his MK2123 supply, I just saw that it has been modified with 7x UF4007 diodes but with a quick test no HV, could be the inverter.


    I would still like to know where I can get the 25g10 or equivelent diodes please.



    Mathieu (2014-07-24 15:26:53)

    Good day Chris,

    ... The answer of the boss is there (2011)
    My 1+1's are working daily with the original diodes changed with 2 1N4007 in serie.
    No problem and I check my HV frequently.
    I also changed the 3300pF caps of the HV ladder for some similar to those below :

    Cost peanuts...

    AcoustatAnswerMan (2014-07-24 23:59:35)

    As mentioned in the link above, the original diodes are a special high voltage type rated at 25-mA, 10-kV. This particular diode has been discontinued by its manufacturer, but other similar ones are available. But be careful on the physical size - some are quite large and you'll have difficulty making a neat installation.

    Although I never tried it myself (since I've never had trouble with the original diodes) I suppose that using two 1N4007 in series would be an acceptable substitute for each original diode.

    However, before replacing parts...have you tried adjusting the HV supply while measuring the output of the supply with an HV probe? I highly recommend that you do this before tampering with the original parts.

    Chris Barnard (2014-07-26 06:17:06)

    Thanks Guys,

    Your advice is much appreciated.

    I haven't tried to adjust mine yet because of my friends power unit (MK2123) has become priority.

    The inverter has no output that I need to investigate.

    Thanks Mathieu, for the links, I will have a look if it turns out that I need them.



    Mathieu (2014-07-28 11:44:44)

    Dear Acoustatanswerman,

    ... My question is about how did you manage to make linear the respone curve of the Spectra's pannels...

    As the surface of the pannel which reproduces the high frequencies is reduced through the 75/680Kohm resistors, the global acoustic panel response curve itself becomes non linear : I measured a progressive loss of about 3db above 3500Hz.

    That means that the Spectra interface compensates this ...
    How did you manage this in the interface ?


    Chris Barnard (2014-07-29 06:06:23)

    Hi Guys,

    I would still like to know the best crossover points for the 3 sections of the Spectre 33, so that if I do bi or tri-amp them I have a place to start.



    Mathieu (2014-07-29 09:49:43)

    The relation between the Resistor value (R) and the cutoff frequency (F3) is a F3=1/(R*K), where K is a constant which includes the capacitance of the panel and others thing I don't know...
    => So the relation is not linear. I could approximate it with F3=400000/R (R in Kohm)

    I also made the acoustic measurement last year,and if I well remember :
    - The 75Kohm resistor provides a cutoff at 5-7 kHz (- 3dB )
    - The 680Kohm resistor provides a cutoff at 400-500 Hz (- 3dB)
    The best would be that I send to you the measurement curves -email-
    Write me an email to, I will send them tonight.

    But pehraps that Acoustatanswerman may give us the magic calculation formula to get directly the value ....


    Mathieu (2014-07-30 08:52:10)

    I had a look to the curves on Spectra44 yesterday evening :
    - The 75Kohm resistor provides a cutoff at 3,5kHz (- 3dB )
    - The 680Kohm resistor provides a cutoff at 600Hz (- 3dB), but the loss of energy begins at 100Hz.

    Chris Barnard (2014-07-30 23:10:48)

    Thanks Mathieu,

    That is what I need, I will send you an email for the curves.


    Mathieu (2014-07-31 07:11:06)

    Good day Chris,

    I sent to you the measurements, photos of 1+1 and Spectra's 44 in process, and also some notes ... Which Acoustatanswerman may check for exactitude ... Thanks !

    First I assume that you know the principle of the Spectra's : each half pannel acts independantly, depending upon the resistor which it is connected to. The resistors R combined with the capacitance of the pannel C act as a delay line due to a variation of the phase angle, and a frequency filter through the relationship Fc = 1/2/pi/RC.

    That's here that there is a trick : every Acoustat speakers do not have the same Capacitance value...

    The Spectra 33 have a single pannel design, and the Spectra 44 and 66 have vertically stacked design.

    => In the 33, there is one half pannel wich acts full range (C/2) , 2 half pannels in parallel for the medium (C), one complete pannel for the bass (C)

    => The 44 uses 2 (two) half pannels for the full range (C), 4 half pannels for the medium (2xC), and two half pannels for the bass (C)

    This is why the resistor used in the 33 and 44 may be different for a single frequency cutoff... Additionnaly the resistors of the medium and bass section are connected in serial.

    In your case of course these resistance hare not usefull for the cutoff effect, but they are NECESSARY for the delay time effect ! So I would not advise that you remove them because your stereo image will be less precise...

    How do you manage to multi-amp the 33's ? Do you use additionnal HV transformers ? Photos ?



    AcoustatAnswerMan (2014-07-31 18:20:21)

    Mathieu and Chris-

    I have been monitoring your conversation, but have not responded since I really don't feel I have much to contribute. But I do have a few comments:

    The final values of the sector resistors were chosen after extensive listening trials, not calculations. Therefore, I cannot tell you the transistion points, because I never knew what they were, nor were they ever documented. Please note I call them transition points, not crossover points, as they are not crossover points as traditionally defined. Please note that the resistors, working against the capacitance of the panels, also provide a time delay to adjacent sectors, which makes the mechanically flat speaker appear as a convex surface (from both sides!). This considerably improves the horizontal dispersion and imaging. SPECTRA is an acronym for Symmetric Pair Electrically Curved TRANSducer.

    Secondly, there is considerable equalization provided by the transformers, and this is all part of the final acoustic reponse curve. Sorry, I do not know what those curves look like. Keep in mind that the transformers are not just simple step-up devices, as they contain seperate high and low frequency secondaries, the outputs of which are re-combined in an R/C network.

    Finally, the idea of trying to triamp the Spectra speaker is ill-advised in my opinion. I'm not saying it can't be done, or that you couldn't end up with something better. But without extensive technical knowledge and considerable resources to design and implement a driving system, I think such an endeavor is doomed to failure. The transformers, R/C combining network, sectoring resistors and the area of each sector all work together as part of an integrated whole. Unlike a traditional tweeter/woofer with crossover system, one cannot merely seperate them and drive each with a different amplifier.

    Chris Barnard (2014-08-01 04:32:13)

    Thanks Acoustatanswerman,

    I take your meaning, but I don't understand the delay and how it is achieved.

    I only look at bi-amping because I have the amps already and they are only 50w each Class A, as well as being my own design and would like to keep using them.

    I have begun testing with bi-amping by using my existing amps set for 1khz crossover, and using High and Low frequency transformers, with a 50k resistor to the Mid.

    This set up sounds great but I plan to adjust the crossover of my amps and then add the resistors to adjust the delays.



    Mathieu (2014-08-01 09:29:52)

    Dear Acoustatanswerman... Your remarks are more than welcome and I'm always impressed by your constant involvement, so may years after Acoustat stopped... Many people love your babes, and with good maintenance, minor mods, good amplifier they still compete with 20K$ speakers. I know we are all gratefull to you for that.

    A small note : Hifi Zenith in Germany confirmed to me that they can change any damaged diaphragm of the Acoustat Pannels, for a 'decent' price. I ve got some old ones with damaged coating and another with a torn diaphrag so I'm quite happy ...

    Chris ! We peharps misunderstood :
    a. If we are right your speakers are Spectra 33 with a MK2123 interface.
    The interface has two identical transformers -one for the rear and one for the front stators- followed with a first HV R/C network, then a second resistance network with separates the main signal in the direction of the 3 pannels. I cannot imagine how to biamp such a system...

    b. We misundersood and your interface is a MK121 with three transformers inside : one for the HV Bias, the other for the bass, the third (smaller) for the treeble. I've no experience with bi-amping of these interfaces but I know it has existed.

    Let me know !

    Chris Barnard (2014-08-04 07:23:40)

    Hi Mathieu,

    I am not using either of the units, I am only using an external HV supply from ER Audio and 2 transformers also from ER Audi, one for (at the moment), above 1khz and one below.

    I realize that the high freq panel is meant to be full range, and I do hear less bass in this configuration, but I intend to change that later.

    Still sounds very good.


    Mathieu (2014-08-04 12:38:01)

    OK I understand...
    The only weakness of this solution is that you lose the SPECTRA effect, means the time delay between the differents half pannels...
    How do you find the listening now ?

    Chris Barnard (2014-08-18 06:45:44)

    Ok, I have had them bi-amped for a week now and they sound very good, but I think with some tweaking they will be great.

    the current configuration is this:

    I have one amp sending full range to one transformer feeding the full range section, and the mid/low section via a 100k ohm resistor.

    Another amp which still has the low pass filter at 900Hz is feeding the Low section.

    I think my next step is to remove the low pass and add the 680k ohm as in the original circuit to hopefully reinstate the Spectra effect.

    Any suggestions?

    BTW: Andy, is it ok to leave the HV on all the time or just say 1 hour before listening?



    mathieu (2014-08-18 08:20:12)

    Looks good...
    How much compared to the others loudspeakers you already have ?
    Once your setting is fully homogeneous you can change the original resistors for some cadock ones. They offer nice improvement.

    AcoustatAnswerMan (2014-08-18 14:35:22)


    The high voltage should be left ON at all times for best performance. Power consumption is minimal. My speakers are on all the time unless I plan on being away for at least a week.

    Smithe912 (2014-08-19 10:00:41)

    Farmville farms even include free gift that is especially designed for the neighbors on their farm visit. cdfkbdecffcgfbeg

    Philip (2014-09-21 20:13:58)

    I have a pair of SPECTRA ll's. I have always enjoyed them until recently. Now they have developed a very "strident" sound to them making then hard or even impossible to listen to. I have checked everything upstream, even trying different electronics and cables but the problem remains. I haven't changed room acoustics either. Does anyone have any ideas as to what could be the problem?

    AcoustatAnswerMan (2014-09-21 22:06:40)

    Nothing in your description of the problem points to a particular known problem. Did both speakers begin to sound bad at the same time? If so, the problem is probably not in the speakers. Although not impossible, it's very unusual for both speakers to develop the same problem at the same time. Unless of course...they were subjected to an abusively loud listening session, or they were subjected to some sort of high volume transient. Is this possibly the case, or perhaps someone else had access to your system when you were not around?

    If the problem exists in only one speaker, try swapping the black-box interface from one speaker to another. If there is a problem with one speaker, the problem will usually follow the interface. In other words, problems of this sort are extremely rare with the panels themselves.

    Another question: does it seem to require more amplifier power to reach the same volume level? Are you sure that the AC power is applied at all times?

    Depending on your answers to these questions, we may be able to pinpoint the problem in your system. Don't give up yet!

    Philip (2014-09-22 15:02:06)

    Thanks for responding! I'll answer your questions in order and hope it will give you a clue as to what might be happening.
    Both speakers slowly began to sound bad equally at the same time. Very strange. The speakers were fine at the beginning of the year. I disconnect eveything even though I have a surge protector
    whenever a thunderstorm is about. We haven't had any real close lightning hits so the EMP effect shouldn't be the issue.
    I do not blast my speakers. I don't like it that loud. I am the only one who operates my system (No one else could figure it out anyway).
    I checked the house a/c and it's fine. Both wall warts are putting out 12 volts. I opened up the back interfaces and cleaned the connectors to the panels.
    Although I haven't checked yet, is it possible for the panels to be dirty/dusty behind the sock? I've had them since 1993. I saw two screws on the top which I suspect will allow me access to the panels.
    If you need to know what my equipment is, please let me know.
    Again, thanks for your help...Without it, I am lost.

    AcoustatAnswerMan (2014-09-22 19:20:06)

    We are talking about the Spectra 11 (eleven), correct? Assuming that's correct...

    I'm still waiting for that AHA! moment...but so far no luck. It is extremely unusual for both speakers to begin failing simultaneously, and the description of the 'bad' sound is not a typical failure mode. My first suspicion would be that the problem lies elsewhere in your system...have you systematically swapped out EVERY component, including the source component? Even then, it's unusual for two electronic channels to fail in the same way, unless a component has faulty power supply that is common to both channels. Tell me about your system components - it might yield a clue.

    Problems with dirty or dusty panels usually cause extraneous noises, like crackling, buzzing, arcing etc. (often whether music is playing or not). I don't think that's the problem in your case. Removing the plate on top of the panel will only reveal very many staples securing the grille cloth. Removing the grille cloth is a real chore, and re-using the old cloth is usually problematic - meaning you'd likely want/need to use new cloth. So I'd leave that alone for now.

    Try this experiment: unplug the AC power from both speakers for a few hours. This elapsed time should allow the charge on the panels to bleed off. Turn on the music: you should hear bass sounds only from the woofer. If you still hear sound from the panels, they need to be discharged longer. Even though the sound from the woofer won't be full range, does it still have the distortion characteristics you describe? If yes, I'm nearly certain the problem is not in the speaker. If the woofer sounds clear (i.e. free from the distortion you describe) then there is probably an issue with the speaker's interface electronics. Keep in mind that this test is not definitive, as the distortion you are hearing may not be present at low frequencies, and/or may not be reproduced well by the woofer.

    That's all I can think of for now. Keep writing - we'll get this problem SOLVED!

    Philip (2014-09-23 18:21:56)

    The speakers are definately SPECTRA ll.

    I have had all of my equipment for quite a few years. My equipment is:

    Turntable..Rega Planar 2 with a modified RB 250 arm. Cartridge is a Dynavector Karat. The Pre-amp is a Dynavector P75.

    CD player......NAD C545BEE
    Pre-amp........Adcom 555ll
    Power amp......Adcom 5500 (200 watts @ 8 ohms, 300 watts @ 4 ohms)
    Line filters...Adcom ACE 515, Monster
    Receiver.......NAD C725BEE (50 watts @ 8ohms)
    Interconnects..KCAG, Alpha Core Goertz
    Speaker cables..Audioquest Bedrock.

    The main reason for the above choices is budget. I was able to get most of this equipment from a dealer several years ago at good price when he was going out of business. I just don't have the deep pockets for Krell and the like.
    To check the Adcom equipment I installed the NAD receiver in its place. The sound improved a bit. I will try the pre-out lines from the NAD into the Adcom power amp and see what happens. That's where I am as of now. I will do the speaker test you suggest too. Forget about taking the "socks" off!

    AcoustatAnswerMan (2014-09-24 19:49:47)

    There's certainly nothing inappropriate about the equipment you list...and in fact it is quite typical of what is used with the Spectra 11.

    The fact that the sound 'improved a bit' tends to support my theory that your speakers are not at fault. But it does bother me that it didn't improve completely, as that suggests there could be more than one problem in the system. OR that a failure in your amplifier might have damaged the speakers. I hate to suggest that, but it can happen, and it should be added to the list of things that might be wrong.

    Philip (2014-09-25 19:43:01)

    What I have done shouldn't work, but it has helped a lot. I took out the KCAG interconnects that I have been using for years between the Dynavector P75 head amp and the NAD receiver(which I am now using instead of the Adcom electronics). I replaced them with Alpha Core Goertz cables and the sound from my records has improved. That confuses me as to why the KCAG cables should slowly become more strident????? I don't know. I have always liked the detail I would get with KCAG.

    Also, is it possible that too much sound absorbing material in the room would kill the mid range of these speakers forcing me to turn them up to fill it in and have the highs out of balance with the mids! I don't know all the technical details, but I know SPECTRA has some thing to do the highs in these speakers. I'm not giving up......yet.

    Thanks for your help..

    Philip (2014-10-05 15:01:03)

    I completely changed the speaker locations and did get rid of all KCAG interconnect cables. That has done the trick. Why? I haven't a clue. Eliminating the old Adcom components changed the sound a little for the better, but I never had a problem with them. Relocating the Acoustats to the longer part of my rectangular shaped room also helped a bit. I can't imagine having the sound stage of these speakers from regular tower type cone speakers unless I spent a lot of $$$$$.

    AcoustatAnswerMan (2014-10-05 16:01:03)

    Interesting...and quite unusual. You might contact Kimber to see if they've had reports about similar changes to the sound of the cables.

    I'm happy to hear you've got your system sounding the way it should again.

    Philip (2014-10-12 14:24:35)

    I hope you are still monitoring this site as I still have problems. It seems that changing everything around helped a bit probably more due to room acoustics than anything else. The speakers continue on thier downward slide and are now very glarey (is there such a word?) and quite strident. They are unlistenable on most music except muted/dull recordings. Even those are harsh. I can get used panels on the internet, but is it the panels or interface? I don't expect you to give a firm answer there just your best guess. My best guess is that these panels were made in Tempe, AZ and have spent their lives in Florida and southern Georgia. That would bring humidity into the picture despite air conditioning. I wonder if the glues and structures have finally given in to the moisture. I don't know. I did visit the Acoustat manufacturing facility when it was in Fort Lauderdale (early eighties)and was quite impressed with their workmanship. Sadly, I couldn't afford them at that time. I don't know if it's worth spending about $250.00 on a set of used panels if the problem is in the interface. I don't think it is, but I have no solid reason to believe that either. Any advice on your part would be greatly appreciated. Don't worry, I won''t bitch and moan if it's not the panels if I did buy them and it didn't correct the problem. That ball is in my court.

    AcoustatAnswerMan (2014-10-13 19:09:27)

    Your issue is almost certainly NOT a problem with the panels. They are not subject to problems with humidity, and are pretty much not affected by anything, nor do they typically degrade over time. When they do act up, it is usually a case of making extraneous noises, and not a degradation of sound quality.

    If you are absolutely convinced the problem lies in the speakers, I suggest you contact Roy Esposito and talk to him about getting the interfaces checked out. No need to send the whole speaker - just the interfaces. His email is See his post earlier in this thread.

    I have just about exhausted my ability to diagnose your problem remotely, so I think contacting Roy is your next step. He worked at the Acoustat factory prior to my joining the company, and he is the go-to guy for Acoustat repairs. I don't do any repairs myself.

    Mathieu (2014-10-15 13:45:13)

    Sure that Roy will find...

    I've go a pair of Spectra 1100. The resistor in serie with the pannel was burnt when I purchased them. Result was an agressive sound coming mainly from the woofer. I replaced it with a 0,5 or 1ohm one (Dale, the ones with the yellow radiator)

    One possibility to test the interface is to disconnect the woofer, and to try the panel alone without the resistor with only the 110uF cap. You can also try without the cap.
    The only important precaution is too listen not too loud, because the HV transformer cannot handle power at low frequency (that the reason for the 110uF cap), and also that your amp will be loaded only with the panel (so a very low impedance). But most modern amplifers accept this.

    If the sound seem back to 'normal', that means that you have a problem with the resistor or the cap. You can easyly check the resistor (0.5ohm if i well remember).
    Otherwise there is something else wrong. But I did never broke any HV transformer neither pannels.

    Another possibility could be that your woofer is dead... You can listen to it alone, and look for abnormal 'crrrr' sound.


    Philip (2014-11-21 14:42:07)

    I sent my interfaces from my SPECTRA ll's to Roy Esposito and he repaired them. First I would like to say is that he does very professional work. i have built many amps when kits were popular and his work is excellent. I know good clean work when I see it. The speakers sound like they're supposed to. They are accurate, detailed and seem to have a wider soundstage. The strident harshness is gone. I can definately recommend Roy Esposito's work ( to anyone who has issues with their Acoustats. I thank him for getting me back my favorite speakers.


    mathieu (2014-11-21 22:03:41)

    Good news., di roy say tout you what was wrong ?

    Philip (2014-11-22 13:34:31)

    He said the voltage going to the panels was about half the value it should have been. Apparently there wasn't enough "juice" to move the speaker panels properly. Roy could explain it in detail much better than me. That's for sure.

  • Pair of Acoustat 2 plus 2 with Transformers for Sale - Kelvin Green on 2013-07-18 18:12:54

    Up for sale is a pair of Acoustat 2+2 electrostatic speakers. This pair is in good working condition. Both come with MK-121-2A Acoustat Medallion Transformer both working. Both bases are in excellent shape, no peeling on the wood, The cloth over lay has some snags in them could use replacing, however is in good shape. Shipping will be a bit of a challenge, huge 8 foot tall , where there's a will, there's a way. Email for shipping or if you want photos. Pick up is preferred.

    Kelvin Green (2013-07-18 18:13:39)

    Up for sale is a pair of Acoustat 2+2 electrostatic speakers. This pair is in good working condition. Both come with MK-121-2A Acoustat Medallion Transformer both working. Both bases are in excellent shape, no peeling on the wood, The cloth over lay has some snags in them could use replacing, however is in good shape. Shipping will be a bit of a challenge, huge 8 foot tall , where there's a will, there's a way. Email for shipping. Pick up is preferred.

    Mathieu (2013-07-29 14:52:13)

    Good day Kelvin,

    These are what I look for....ds,
    I'm owner of a pair of 1+1 a
    What would be you price ? I will of course pay for shipping to Canade (Quebec).

    Best regards ,

    Mathieu (2013-07-29 14:53:22)

    ... and would like to upgrade my system...
    The computer was quicker than I.....

    Kelvin Green (2013-07-29 15:10:36)


    Thanks for the reply. As of lately. One of the transformers went out. I was going to have it fixed and the c mod done but if you like I would sell them as is at a cheaper rate. $600 for the pair. The other one works fine. Shipping would cost somewhere in the area of $300. Freight. Would this work for you? You could also give me a call and we could work out the details. I use paypal also. 858-735-2372


    Kelvin Green (2013-07-29 16:13:53)

    Hi, sent the photos and a test mail, did you receive it. Give me a call back so we can get a verification.
    my email is email me and I can reply to ensure I have it correct.


    AcoustatAnswerMan (2013-07-30 20:44:44)

    A word of advice when shipping any model Acoustat: the bases, interfaces and frames should be disassembled and shipped as separate units. The frame is not designed to withstand the twisting that the heavy interface and base can inflict on the frame. The same holds true even if not shipping the speaker. Unless you are just sliding the speaker across the floor, the speaker should be disassembled before picking it up.

    When I bought my used Spectra 4400's, the previous owner had moved them around quite a bit without disassembling them, and I ended up doing quite a bit of frame repair to fix the damage done by the twisting motion of the heavy interface.

    Mathieu (2013-07-31 05:59:25)

    Many thanks boss,

    You are 100% right,
    Kelvin is now dissasembling the ladies,
    Then a friend of mine will take all necessary care before crossing the ocean...

    Final aim is to modify the pannels (onto Spectra type with welded heads), and to build Spectra 44, as I could not find any in Europe.


  • How do I know what side left and right are? - Ryan Benitez on 2013-04-23 23:31:55

    I know this sounds like a stupid question but I really do need help with this. I thought left means side playing into my left ear but after looking at page 9 and 10 in the spectra 1100 manual I am not so sure. It looks like the back of the speakers being connected L R.
    I look at the placement of of connectors on some of my other gear for clues.

    My Preamp is
    L R

    The back of my amps are
    1. L R
    2. L R
    3. R L
    4. R L
    5. 1 2

    For now I am set up R L from the back so the "Left" speaker plays into my left ear. Please left me know if this is right.


    Acoustat Answer Man (2013-05-27 21:06:25)

    The speaker labelled LEFT should be playing to your left ear. The 'left' and 'right' labels on amplifiers and preamplifiers are really for convenience only, and there is no difference between channels. On source units, like a turntable or CD player, the output labelled 'left' should follow through the system and play through the left speaker.

    The Acoustat Spectra Series speakers are created in mirror-image pairs, so there is a distinct '
    left' and 'right' speaker, and they should be placed as labelled.

    Roy A. Esposito (2013-09-06 12:11:57)

    Hello Friends --

    This is just to let you know that my email contact
    has recently changed. It seems AT&T/Yahoo could no
    longer support my very old email address.
    For those of you requiring fantastic restorations
    and upgrading of Acoustat MK and Spectra Interfaces
    and Acoustat Power Amplifiers and Preamplifiers
    my new email address is

    (please notice the dots/periods between the words)

    Email is the preferred method for initial contact with me
    for Acoustat Service and questions.

    Thank you for your continued friendship, kind comments and reviews,
    and support of my work.

    All the Best,
    Roy A. Esposito

  • Acoustat 3's with Servo Amp question - paul ranieri on 2013-02-11 16:43:09


    I am running 3-panel X's (2-9" and 1-8") 5-wire with basically stock Servo amps and am very pleased. I recently bought a pair of 3's with 3-wire panels to use on the servos because my X's have no frames and are quite unattractive. I have disconnected the MK interfaces and wired the panels to the Servo amps exactly like the X's but the sound is very off. The 3's appear to work okay with the MK interfaces but not nearly as nice as my X's although I do not have an ideal amp to power them. The 3's play at proper listening levels when connected to the servo amps and the frequency response is not compressed but the music is lifeless and the texture of the instruments is gone. Also, the bass is distorted. I am looking for ideas on why there is such a stark difference in the sound as I was told the pre-Spectra panels are interchangeable. Can it be the 3 vs. 5 wire? Any wisdom that can be shared would be appreciated. Also, I have played with the straight vs. curved patterns of the panels and that is not the reason for the difference, at least not the difference I am referring to. Thanks.

    Roy A. Esposito (2013-09-06 12:14:26)

    Hello Friends --

    This is just to let you know that my email contact
    has recently changed. It seems AT&T/Yahoo could no
    longer support my very old email address.
    For those of you requiring fantastic restorations
    and upgrading of Acoustat MK and Spectra Interfaces
    and Acoustat Power Amplifiers and Preamplifiers
    my new email address is

    (please notice the dots/periods between the words)

    Email is the preferred method for initial contact with me
    for Acoustat Service and questions.

    Thank you for your continued friendship, kind comments and reviews,
    and support of my work.

    All the Best,
    Roy A. Esposito

  • Ideal six panel configuration? - Paul Ranieri on 2013-01-02 17:49:38

    Andy et al.,

    I am in the process of refurbishing my Servo amplifiers and have decided I would like to build a custom configuration for six panels per side (it is my understanding that 6 is the max number of panels the Servos can drive properly). My listening room is 16' wide by 22' deep and a 15' cathedral ceiling. I have 4-9" and 2-8" five wire panels so whatever configuration I go with I will need additional panels. My options are 9-9-9 x2 high planar, 9-8-9 x2 high planar, 9-9-9 x2 high convex (angle TBD) and a 9-8-9 x2 high convex. I intend to build a very sturdy steel framework and want the best possible sound and imaging regardless of the sized of the sweet-spot. Any thoughts on panel configuration would be really appreciated, thanks. Also, if anybody has any info on a tube driver/splitter stage for the Servo amps, I would like to know more.


  • Where can I find a replacement for the part labeled TTA-ULT3? - Ryan Benitez on 2012-12-31 05:08:46

    This part that I assume to be the voltage regulator transformer is making an annoying sound that can be slightly muffled by pouring glue on it. Replacing the part would really help the sanity of both myself and my wife. If anyone knows where a replacement can be found I would really appreciate it.


    Acoustat Answer Man (2013-01-06 17:38:20)

    Ryan: Part number TTA-ULT3 is the ultrasonic bias transformer that provides part of the high-voltage step-up necessary for the ESL's operation. As it's name suggests, it operates above typical human hearing so it should NOT be audible. This means that your transformer is either operating below normal frequency for some reason, or it has an odd sub-resonance. I've never encountered this complaint, so I'm poking around in the dark here.

    Finding a replacement part may be difficult, as I haven't seen any for sale from any of the sellers who bought the obsolete Acoustat inventory.

    You might try installing a locking plastic cable tie around the periphery of the transformer's body. This might squeeze the transformer enough to change its vibrational character. You could also try swapping transformers between speakers (be very careful of the bottom pins on the transformer). If the problem moves to the other speaker, then it is the transformer. If the problem stays on the same speaker, then something in the circuit is causing the transformer to misbehave.

    Please let me know your results. I am curious to know the cause of this problem, as I might be able to help other Acoustat owners in the future.

    Ryan Benitez (2013-01-06 18:01:56)

    I measured the voltage with a 1000x probe and got 2.9 volts. I had no complaints about the sound but did the ultrasonic bias upgrade (about $3 in parts from digi-key) and took the transformer off the board that was making sound to pour glue on the bottom side. After the glue dried I reattached the transformer and have not heard the unwanted sound again so far. Also adjusting the voltage on both speakers fixed the 1 dB mismatch between speaker and increased efficiently by about 3 dB.


    Acoustat Answer Man (2013-01-07 00:39:13)

    Great news. The ultrasonic supply can be a little finicky before doing the upgrade, but its operation is very stable after the fix. The real beauty is that the system is both regulated and adjustable. Therefore, the charge can set at a specific point, and once set, it is unaffected by variations in mains voltage.

  • Schematics for Z-1100 - Ales Lesar on 2012-07-23 07:42:54

    I like ESL-s very much. I have Acoustat Z-1200 and Acoustat Z-1100 (new), but i do not like bass (mid-high are OK). I need schematics for these speakers.

    Best regards.


  • Research orientated DIY repair of a pair of Acoustat1+1 - Sylvo Schroeder on 2012-05-02 05:34:05

    I own a pair of 1+1 Acoustat since 1986 and gave me a good service till 2004.I live in India and tried quite a few electronic repair shops for help – no result. Having no knowledge in electronics I studied all parts/its functions of the interface + Biassupply carefully.
    During my research I discovered a German Company who is themselves manufacturers of electrostats.The owner asked me to check the part with am Ohmmeter he had suggested – Bingo – he then send me 2 High Voltage Bias Supplies with plug in power source.
    While waiting for the parts to arrive – I upgraded all of the Caps,Resistors + wires mounted them on a new motherboard - to the very moment I am enjoying my Acoustats rendering more details/soundstage/harmonics (no unwhanted panel noises) than ever before.
    If any one needs well experienced tips on parts suppliers and other problems (no transformers)then drop me a line.

  • Help removing the cover off an Acoustat 2 - Christos on 2012-04-25 23:00:42

    Hi folks,

    I am trying to remove the cloth cover from my Acoustat 2's. I removed the staples on the top and pulled the cover down below the panels, but I cannot figure out how to get it off from there - it is sandwiched between the base and the upper portion of the frame. What am I missing?



    Mark Svien (2013-11-21 11:06:52)

    You have to remove the base, there's another row of staples in between the base and the panel frame. Here's the sequence on Model 3's, yours should be similar.
    Remove the interface. Pull the center pin and ground it to the white/blue posts.
    Remove the connectors from the white and blue posts
    Remove the metal plate from the base
    Remove the 2 screws you find under the plate
    Lay the base and frame flat. Look inside the base and you will see the screws attaching the base to the frame
    Remove the screws and pull the base downward exposing the bottom of the cover and the staples

    Be sure to watch the wires and don't snag them
    Have fun!

  • MK 121C and MK 131B w Sub for sale - Scot on 2012-04-21 12:13:45

    I have a (2) Acoustat MK121C and (2) MK 131B speakers with a matching Acoustat sub for sale. All the speakers are in great shape. $1750 for all of them. Central Texas. Pick up only.

    If interested send an email to and I can send pics and additional info.


  • One speaker has low volume - Chris on 2012-03-09 03:14:12

    Hi, I am having a problem with one of my interfaces attached to a Acoustat Model 4. One channel has very low volume coming from it so I did the following to diagnose it: I started by swapping parts back and forth between the two interfaces and narrowed it down to the high voltage board with the speaker outputs. I replaced the 3300 pf caps, tested the high voltage diodes using a power supply and measuring the voltage drop across it when in series with a 250 ohm resistor and they all checked out. I also measured the 50K ohm resistor and the .01uf capacitors leaving only the 500M ohm resistor which I orded and am waiting on. I was just curious if anyone knows or sees anything I may be overlooking? It is possible I ran a signal through the amp while it wasn't plugged in and I remember someone telling me that it was bad to do and would blow out a particular component. Has anyone herd of this? Thanks in advance for any help, Chris

  • Model 3 interface-low out put - DDT on 2012-02-22 09:07:25

    Decided to break out the Model 3's to see how they compared after having to slum it for a few years with some Spectra 3300. Got them set up and one was producing less output and a tad bit distorted, which increases some with volume.
    Sounded like a fuse-checked those and all was well.
    Swapped interfaces-the problem followed.
    What are the possible culprits?
    What should inspect/meter first?
    I am far more the listener then the Techie but I can manage a thing or 3 so any advice in simplr terms would be greatly appreciated

    PS I run the 3300 with a Bedini 150 mkII, Ai mod 3 pre, Acurus ACD11 Technics 1200mk2, SW1 2xjbl6260

    Andy Szabo - AcoustatAnswerMan (2012-03-04 14:29:11)

    The problem moved with the interface, so your panels should be okay. A reduced playing volume (if occurring equally at all frequencies) is usually caused by low bias voltage. And the most likely culprit is one or more of the capacitors in the high voltage multiplier. I suggest you replace all of them in both speakers (ten total). The diodes in the multiplier can go bad too, but that's not as likely as the capacitors. Note that those diodes are multi-junction high-voltage-types,so cannot be measured with an ohmmeter in the usual manner.

  • Acoustat 2 plus 2, Making a crackling/popping noise at low to medium volume levels - Mat on 2012-02-18 14:29:47


    I recently got a pair of 2 plus 2. They sound right at low volumes, but start breaking up at anything more than low volume. All panels equally. I haven't taken the socks off yet, but they don't appear to have been abused. So I don't know whether to suspect the panels, or the interfaces. Any advice appreciated, thanks!


    For comparison's sake, I also have the Acoustat Spectra 22 and 44 speaker systems. Both pair sound great in my system. I use a TNT 200 that was recently refurbished by Roy Esposito, and tube preamp by Rogue Audio.

  • Making a crackling/popping noise at low to medium volume levels - Mat on 2012-02-08 17:59:22

    Hello, and thanks for the great site. Given the problem stated, crackling/popping at low to medium volume levels, what should I suspect is causing it?

    Thanks in advance,

  • moving these speakers - austin on 2012-01-21 20:26:36

    Please help. Someone needs to move these speakers with this model number on the black electronic box. mk-121-2a. I'm the electrician and have been told that these things have a capacitor that needs to be uncharged before they can be moved. Does this sound familiar to anyone? If this is in fact the case how would one go about safely doing this so as not to damage anything? Any help would be much appreciated.

    Richard (2012-02-02 18:02:07)

    In order to remove the MK-121-2A interface, the first thing to do is to unplug the line power supply plug. Then the upper panel can be opened. BE VERY CAREFUL because the internal high voltage power supply will remain charged at around 4.8KVolts !. In order to discharge the HV power supply, a jumper wire shall be first attached to the chassis (make sure it is a good ground). Then, the red-pink wire at the center of the PCB must be discharged. Attaching the other side of the jumper to the metallic section of a screwdriver is a good way to proceed. Then holding the screwdriver by the insulated handle, the metallic part can be approached and gently put in contact with the red-pink high voltage wire on the PCB, close to the RED connector soldered on the PCB. Make sure you touch the PCB trace for at least 20 seconds, in order to fully discharge any remaining charges. Then, the HV side panel wires can be removed and the interface can be unscrewed from the speaker. Be also very careful not to shock the panel. This is very fragile. Do not lay the panels flat, but rather on their sides in order to reduce the risk of breaking any internal wires. Two persons are usually preferred to move the panels.
    Good Luck. Richard.

  • SUPERTWEETER - Leo Bischof on 2012-01-01 16:27:48

    I see myself very lucky to have purchased a Spectra 66.I have auditioned many High - End speakers and nothing compared to the 66s. The previous owner already did all the available upgrades. Additional upgrades were done: Panels wired with Eichmann Silver wires, Eichmann Speaker terminals, 3 Cerabals support units per speaker and eventually the TOWNSHEND SUPER TWEETERS. I can strongly recommend these S/T as they integrate very well with the Acoustats. I have managed to build a clamp on the inside of the speaker at +/- ear height. They are supplied with there own cabling and have a level adjustment at the back of the unit, so adjustments are easily and quickly done. The supplied speaker cable has to be connected to the speaker cable terminal of the Acoustats and you are already in business, no soldering or removal of panels is necessary. I gladly supply a picture of my set-up. Amplification is the Audio Research Reference Line ( 40 the Ann. Ref, Ref 210 KT 120, Ref 8 CD, Ref 2 phono and Clearaudio Master Ref with Colibri Gold Ref). Good results were also achieved with the Audio Research DS 450 power amp with dynamic power of 1800 watts into 4 ohms. If you want to use valves, you need 250 watts plus, therefore the DS 450 is a cheaper option. My listening room (11m x 6 m) tends to be on the lively side, therefore valves work better for me. In dark sounding rooms, I would definitely prefer the solid state DS 450.
    I visited the Munich Audio Show last year and found nothing which sounded better than the 66.
    The only Speaker which I thought were in a similar class were the Lansche Audio Cobus with a
    Plasma tweeter and a Horn Mid-range at 55000.00 Euros!
    I also had the opportunity to audition a pair of Martin Logan’s CLX with dedicated subs in
    my Listening room. The CLX had slightly more detail in the Mid-range, tops were equal to the
    66s incl S/Tw, but overall the 66s were a far more satisfying speaker and specifically the bass
    reproduction of the 66s against the CLX including subs was far better. The overall bass of the
    CLX incl subs sounded disjointed in comparison and the low bass sounded like it was recorded in
    a different recording environment. Still the CLX is probably one of the very best speakers
    which is available today and I would recommend anybody which has failed to find a used
    Acoustat should audition the CLX , it would be my choice if I would not own a 66.

    MrAcoustat (2012-01-27 16:22:45)

    Hi Leo Bischof if it is possible i would like to get in touch with you here is my e-mail address thank you very much. André MrAcoustat Sévigny.

    PS: My friend Jocelyn Jeanson would like to reach you he own's Spectra 6600s very highly modified here is a photo of me with his speakers.


  • Nylon Shoulder Washers - Andrew Tomlinson on 2011-11-17 02:10:46

    Hi Andy
    Do you know the dimensions of and where to get the plastic inserts/ shoulder washers that are used between screw head and the panel when mounting the panels to the frame.

  • Acoustat owners from Canada & USA - MrAcoustat on 2011-09-19 19:10:33

    Hi my name is André Sévigny from Sainte Catherine Quebec on the south shore of Montreal i have been an owner of Acoustat's since the early 80s i would like to create a club of Acoustat proud owners across Canada & USA so that whe can share our passion for those old but wonderful speakers this way whe can continue the existence of these fine electrostatics you can see the making of my all steel model 1+1s modified by Mr.Jocelyn Jeanson of Kingsbury Quebec Canada in my Flickr photo galery here ( ) hope to see lot's of owners Thank You MrAcoustat

  • Acoustat 1+1 Modified Jocelyn Jeanson - MrAcoustat on 2011-09-16 07:14:09

    Hi i would just like to let you know that i am an Acoustat fanboy since the 1980s i ham the owner of a very special pair of 1+1s they are my sixt pair but my third pair of 1+1s they are all steel frame filled with silice and weigh over 200 pounds each and the interfaces & panels where modified by my friend Jocelyn Jeanson from Kingsbury Quebec Canada there is a saying in the U.S.A. that say's IN GOD WHE TRUST well for ME my friend is not god but i say IN JOCELYN I TRUST those speakers are my pride and joy thank's again Jocelyn for such a great job on these 1984 speakers.

    PS: You may see the whole mod of these speakers in my Flickr Photo Galery.

  • Can someone please help identify? - Chris Marciniak on 2011-09-12 14:48:30

    I have always been a fan of electrostatics and recently acquired a pair of Acoustats for a rather great price. First off, please visit the links below and tell me what kind they are. Please ignore the mess in my garage!!


    How much did they list for when new? RMS rating? Lower end of the frequency response? Are they worth re-habbing?

    Next, what should I do with the 10" woofers that were in the bases? Are they worth re-foaming or would I be better advised to replace them with a newer pair with a better/deeper frequency range?

    Thank you to any and all for the help,


  • ac power supply - greg on 2011-06-21 05:05:43

    during a recent move i lost the wall plug power supplies. any ideas where to find replacements.
    the speaker uses the MK-2123 transformer. thanks

  • Specta 11 Wall wart info - Wolfsong Audio on 2011-06-07 00:36:05

    Hello all,

    I am trying to find a pair of the AC wall warts for a pair of Spectra 11s. I know they are 15V DC and need at least 150 mA. Can I use a 15v ac adapter that has say 500 mA? Will the speaker simply dray the needed current and "overage" is no big deal? Also is there a wattage figure associated with the AC adapter? Not the watts the speaker will handle but a required wattage output for the panel interface? Thanks in advance.


    SJR809 (2011-08-05 04:24:49)


  • In series connection for 8 ohm nominal impedance - Alvaro Vasquez Lopez on 2011-06-02 21:21:48

    Hello, I have four electrostatic speakers ACOUSTAT model 3, and I would like instate all in stereo configuration (3+3), in series connection for 8 ohm nominal impedance.
    My amplifier is BEDINI model 100/100, CD player is MERIDIAN, other electronics are Audio Research.
    I hope some opinion about this idea. I want protect the 121 interfaces.



  • looking for schematic for 2 plus 2 or any information - Randal Weiss on 2011-05-30 03:01:03


    I have had a pair or 2 plus 2 for approx. 25 years. I have been driving the speakers with the same amp (Belles 400) and everything has been great, until 2 years ago. My amp has blown once each year and not when the speakers were being driven hard or anything. The place I took the amp in, said he checked everything and said the amp is/was working fine and maybe the problem was with the speakers. So I took in the transformers for the two speakers. He found that the voltage reading was lower on the right speaker (which is the side that the amp blew each time), so we figure that may fix the problem, but I was hoping if someone had the schematics or something, it would help us to ensure everything is running properly.

    Any help would be appreciated.

    Thanks, Randy

  • 4ohm vs 8 Ohm - Noel on 2011-05-28 07:51:21

    I have a Quicksilver QLA tube amp to run my Acoustats. Should I use the 4ohm or the 8ohm hookup?

    Daniel Q O'Leary (2011-11-11 17:26:16)

    I believe the Acoustat 2+2 is nominally a 4 ohm load, though it varies a bit and can get down to a minimum value that is limited by a 1 ohm resistor.

  • Acoustat 1+1 - Amplifier Maximum Power - Matos on 2011-05-16 23:28:51

    Hi all
    First of all, thanks in advance to all that answer in this great forum.I'm a new owner of acoustat 1+1, MK121C.
    After reading the manual and some posts concerning the maximum power of the amplifier to drive the 1+1, I still have a doubt.
    The speakers are 4ohms. In the manual is writen the minimum power requirements is 100watts but doesn't tell the impedance... (is it 100watts at 4ohms?)

    Andy Szabo answered in some posts that we can drive the 1+1 with care until 250watt (8ohms).
    I would like to know what is the maximum power in 4ohms?
    I have a crown psa-2 that outputs 460watts at 4 ohms and 275watts at 8ohms and would like to now if I can drive them with it or I risks to damage something.
    Thanks again
    Best regards

    MrAcoustat (2011-06-28 14:02:47)

    Hi technicaly i don't know to much BUT i have owned Acoustat's for more than 25 years the 1+1s are the most difficult to drive there around 81-82db they can play loud BUT if you like your volume at rock volume you will be better off with the 2+2s because they are more efficient 85-86db and easier to drive i have owned Spectra 22s - spectra 33s - 2+2s - and three pairs of 1+1S yes they are my favorites but i am not a ROCKER see my Flickr galery here.

  • pop away success? - frank murphy on 2011-05-13 18:29:04

    i have read several accounts of how to solve the occasional popping of panels -vacuuming, compressed air, slapping, and many reports of failing to solve the problem using any and all of these techniques. I have noticed that just placing my hand on the grille cloth hard enough to contact the grid will induce a pop. my question: does anyone know of even one report of success in making to pops go away?

    Mike SA (2012-09-08 21:13:44)

    Yes, any (or combination) of the above will work. I have successfully de-popped both Acoustats and Soundlabs with thorough vacuuming only. Acoustats M-3 have been playing for the last 15 years without popping ever again; Soundlabs A2x I only have for about 6 months and they have been free of pops since day one when they have been vac-ed. I have even been able to increase the bias on them significantly without reintroducing the pops. But, YMMV - you might have a really bad luck of stator insulation being damaged in which case nothing will help except locating the fault and fixing the insulation.

  • looking for documentation - Benjamin on 2011-04-07 00:30:33

    I owned a pair of acoustics z22 yesterday, unfortunately one of them don't work. It would be great if someone could give me the shematic. thanks.

    MrAcoustat (2011-06-28 13:22:49)

    Hi a friend of mine bought a pair of Z-22a Acoustat speakers but is having problems with the adapters could you please tell me if you know WHAT ADAPTER TO USE with these speakers in the back of the speakers it say's 9volt. Thank You very much for your response.

    Andre MrAcoustat Sevigny

  • Acoustat Center Channel Speaker - Eric VanDenBerg on 2011-04-05 22:32:49

    I am interested in creating a center channel using Acoustat speakers. My left and right fronts are Acoustat 2+2's. My center channel is a Magnepan CC3. I have not been satisfied with the bass extension or the SPL level of the CC3 compared to my 2+2's. My room size is 36’ x 63’ with a cathedral ceiling with a peak of 13’. The back 18’ of the room drops down 10’ to a lower level. Between the 2+2’s is a 107” wide by 60” tall screen. When I bring up the idea of a horizontal Magnepan used as a center channel to Wendell Diller of Magnepan, he tells me this is a bad idea. I assume this is due to the dispersion of the reflected sound hitting the floor and the ceiling. I have seen on another post where Andy Szabo says that a horizontal center channel made from Acoustat components is a good one. My questions are:
    1) What compromises will I incur with a horizontal Acoustat center channel?
    2) How can I minimize these compromises?
    3) Would I be better off with an Acoustat 2+2 or a Spectra horizontally for may center channel?
    4) I own a pair of Acoustat Spectra 2’s. If I built a new frame and got rid of the woofers, what would be the best arrangement and placement of the panels and the best way to hook up and set the interface or Interfaces? I would like to use all four panels to try and equal the 2+2’s.
    5) If I had room below my screen? Is there a better vertical combination using my Spectra 2’s, that I should consider?
    Right now the Spectra 2’s are 6 and 7 of my 7.2 system.

  • high frequency response - frank murphy on 2011-04-02 00:21:51

    i am considering an acoustat purchase and while i have heard lots of good things about them i am having trouble finding any data about high frequency response. my suspicion is that there is a serious hf roll off compared for example to magnapans, even the qr versions. does anyone know what the hf response is or where i could find out?

    this is a fabulous site and i thank all of the contributors.

    Frank Murphy

    joshua (2011-04-06 06:23:11)

    i'm sure it varies by model, but i think i read somewhere that usually acoustats go up to 18k. i can barely hear 17k so i guess it doesn't matter.

    one thing probably worth mentioning is that when i used lower powered amps, though really high quality, hf roll off was awful. several hundred wpc opened 'em up, but still wondering if recapping of interface will help the panels hold voltages better and work as they should to improve hf. as soon as my projects are trimmed down, i'll do the recap.

    frank murphy (2011-04-06 14:46:59)

    thanks for the info. i don't hear any higher than that either, but one audio legend has it that unheard harmonics affect the frequencies we do hear. in an area where science, magic and wishful thinking blend seamlessly it's not easy to know what to believe.

    joshua (2011-04-06 17:07:31)

    i know exactly what you're talking about. wish i could hear things with my ears only.

    Eric VanDenBerg (2011-04-06 19:52:49)

    From the Acoustat specifications in their documentation for a Two + Two

    28 - 28K Hz +/- 2 dB

    You can downlaod the documentation on this site.

    frank murphy (2011-04-06 20:11:30)

    hey, thanks, Eric. i found it in the brochure for the 2+2.

  • what is the impedance for these speakers, and anyone used them with MC-240 tube amp? - Joshua on 2011-03-23 20:03:53

    wondering what the nominal impedance is for spectra 11 speakers.

    also, has anyone used them with McIntosh MC240? how do they sound and can the amp handle the speakers?


    Joshua (2011-03-24 18:47:11)

    well, to answer my own questions....i guess they are 4ohm. last night i tried them with the McIntosh MC240 and couldn't help myself from thinking...."this sucks". the MC240 has been 100% restored and working perfectly with other more efficient speakers, but with spectra, it definitely lacked something.....perhaps power.

    hooked 'em up with SAE 2600, and the panels came alive. also, voltages measured off. one side (using 2nd-alternate method of measuring them since i don't have HV prob) measured 45vdc and the other 65vdc. adjusted both to 75vdc and there's a lot of improvement right away.

    i've read many first time users' opinion that described the speakers to have dull mid and high. i think this is due to low power/current amp and bias being off - when everything else checks out.

  • Different versions of interface/crossover? Overall restoration. - Joshua on 2011-03-23 19:41:03


    first, i thank who ever is in charge of this website for running it with all the information that can't be found anywhere else.

    ever since i heard a pair of original Quad ESL speakers years ago, i've been chasing after different electrostatic speakers. just recently came across a pair of spectra 11. they sound ok, but not spectacular, and actually, a lot less impressive than a pair of Quad 57 i have with rebuilt power supply section. i'm wondering if i can make it sound any better with replacing of old caps and mods.

    1. mine came with different boards inside. one is missing a few resistors compared to the other. is there a schematic for updated version?

    2. all the electrolytic caps look stock and i'm wondering if i should replace them with higher quality caps. also if i should increase the value. how much difference do these electrolytic caps make? does it make sense to bypass them with small value high quality film caps?

    3. what other restoration/upgrades are there? i've searched this site and there's only a few suggested that aren't exactly upgrades.

    4. is there a procedure to measure voltages around the interface - in order to make sure that everything's up to spec?

    thank you!

  • Analogue Associates still in business? - Paul Chung on 2011-01-20 03:05:58

    The links on the following page are no longer valid:,-Acoustat-X-Servo-Amp
    I did find a pdf document listing numerous mods:
    However the date of the document is August 1, 2004.
    If they are no longer in business, is there anyone offering restoration/mods of the Servo amps?

    john (2012-04-05 13:59:45)

    I wonder about the same thing, there is Ken Ealey who works on them. You can find him on the net.

    Luther Goodman (2012-09-20 15:39:14)

    I have a pair of Acoustat Monitor 4s that are in need of refurbishing. If anyone knows of someone who is still in the business of refurbishing the speakers and the interfaces please post or send me a link...

    best regards to all

    Luther Goodman (2012-09-20 15:44:18)

    Ken Ealey:



    Ehous (2012-12-23 16:09:15)

    I am almost certain analogue associates is still in business. Reply if you want me to look further into it. I have a heavily modded set of servos. I got most of the specialty parts from Mike. If any one is interested, I am copied ring selling them with a custom balanced input so I can fund the next acoustat build.

    AcoustatAnswerMan (2012-12-28 19:37:56)

    Try contacting Mike Savuto directly at:

    Roy A. Esposito (2013-09-06 12:16:50)

    Hello Friends --

    This is just to let you know that my email contact
    has recently changed. It seems AT&T/Yahoo could no
    longer support my very old email address.
    For those of you requiring fantastic restorations
    and upgrading of Acoustat MK and Spectra Interfaces
    and Acoustat Power Amplifiers and Preamplifiers
    my new email address is

    (please notice the dots/periods between the words)

    Email is the preferred method for initial contact with me
    for Acoustat Service and questions.

    Thank you for your continued friendship, kind comments and reviews,
    and support of my work.

    All the Best,
    Roy A. Esposito

    Michael Savuto (2014-03-26 16:58:53)

    As has been said before, reports of our death are somewhat premature. As of March 26, 2014 Analogue Associates, LLC is alive and well. We are still in love with the Acoustat Direct Drive ServoCharge amplifiers, providing parts, upgrades and service on them as well. The old email address of is also still functional. We all have to keep the Acoustats alive!
    Happy Listening,
    Michael Savuto
    Analogue Associates, LLC

  • restoration of original crossover components - Mauro on 2010-12-09 22:13:49

    I have a pair of electrostatic loudspeakers Acoustat Spectra 11.
    Time ago, I had the bad idea of changing the loudspeakers original crossovers.
    The loudspeaker sound worsened.
    Now, I would like to restore the crossover to the original state.
    I have not the original electrical diagram and I don't know the original values of the changed condensers and inductor.
    I have a photograph of current crossover state.
    If I sent him by e-mail the photo, is there someone who could give me the original value (and/or type) of changed elements?
    Thank you very much.

  • Audio fuses for 2+2 -correct type - Erik Bock on 2010-12-04 23:57:41

    Can anyone help me find the correct type audio fuses for the 2+2: 5 amp slo-blow - 250V?,32V,MDL?,MDQ?,313?,dual-element? Thank you.


  • Model 3 Placement with respect with side walls - Richard on 2010-12-03 19:22:35

    Dear Andy. I have a question regarding the placement of Model 3 with respect with the side walls. I have a long listening room of 34 feet but having only 11 feet large. My actual Acoustat Model 2 are placed at about 14 inches of each side walls and 3 feet from the rear wall, emitting on the long axis. The actual results are very good (listing position is at about 14 feet from speakers). I am considering an upgrade to model 3 and it means that they would be at only 10 inches of each side walls (I have a HDTV in between). I would really appreciate to have your advice regarding the performances of the model 3 in such a configuration i.e.: would it be at least, as good as my actual setup? (NB: The ampl. I have is a NAK PA7 MK2)

    Just a word to let you know that I really appreciate your work and contribution on this site. It is wonderful for Acoustat lovers like us. I very often read your comments and technical notes. Thank you for being here.

    Richard (2012-01-31 18:45:10)

    Dear all, does anyone know if M. Andy Szabo is still active on this forum?

    Many thanks...Richard.

  • Help Identifying C4 & C5 caps in MK-121-2A - Erik Bock on 2010-12-01 20:05:56

    I recently purchased the Model 2+2 speakers with MK-121-2A interfaces. Serial #s 309171 and 309172. Inside, the transformer brown wrapping has a date code? of 090783. I would like to know if C4 & C5 in this interface had the .01uF/6KV polypropylene caps in it or the older Mylar type? The caps themselves are approx. 2.25"x1.1" with (reddish) brown wrap and no identification or markings. Any information would be greatly appreciated.


    Gnnett (2010-12-05 07:58:07)


    I think you will find these are the older caps. The newer ones are longer and skinnier, with yellow plastic wrap.



  • Spectra 44 Transformer Wiring - Grantn on 2010-11-22 10:21:08


    I have a question regarding the wiring of the transformers for the Spectra 44.

    I am wondering if they are able to be wired in series, rather than parallel to achieve an easier load for an OTL amplifier.

    I have sucessfully used an autoformer (the zero) with my 1+1 and an aquaintence had great sucess with Model 6's, by wiring the two MK121 interfaces in series, with a similar OTL to mine.

    I am guessing that if it is possible there would need to be a change to the resistor and capacitor network on the primary side of the transformers.

    Kind Regards


  • Spectra 33 biasing - jared on 2010-11-11 20:20:36

    Hi there, I have a pair of spectra 33's which have the old-style non-ultrasonic power supply and was reading the write up about biasing the power supply. I was wondering how one goes about (or if it is even nessesary) checking the bias and adjusting it if it has drifted. Any info you can give would be useful. Thanks for having such a great rescource for us acoustat owners!

    jared (2010-12-13 01:41:23)

    Any advice would be appreciated, I have them in storage, waiting to relocate them to my new home, which is still a few months away. I would love to run a diagnostic on them before installing them again. Is there a service manual for the mk-2123 interface?

  • Crossing the species - Wanchai on 2007-07-31 07:06:33

    I just bought 8 of standard 9\" panels and 4 of ex soundlab eng. modified 9\" panels.And I ruined the exist. panel of Soundlab m3 by heat air gun.(suggest not to do heat treatment for esl. if no really necessity). The interfaces of Soundlab and Acoustat are nearly the same concept with dividing two ranges of hi & low freq. step up transformers to the stators.I have no idea of what are the figures (size of Soundlab\'s stator transformers are much larger than Acoustat mk121 c_mod.)but they have attenuators for three ranges hi,mid,low in Soundlab m3\'s interfaces.The DC voltage for the mylar is 15 KV (three times higher than Acoustat)with bias attenuator also.My questions are :can I make new frames for 6 panels per side like Acoustat 6 and connect to the Soundlab m3\'s interfaces. Do I need any modification in the circuit of Soundlab to fit to the Acoustat panels? I plan to put 2 mod. panels straight at the middle and 4 standard panels by both sides with angle.What is the suggested angle. Any more advices will be appreciated. I think your reply would be useful for the Sounlab\'s owners whoever have the problems with their panels or Acoustat\'s owners whoever have the problems with their interfaces.

    Andy Szabo (2007-08-03 22:55:23)

    You will need to reduce the bias voltage from 15 KV to 5 KV. I do not recommend any higher than 5 KV for the Acoustat panel. Since I am not familiar with the Soundlab bias power supply, I can not suggest how you would lower the voltage, or even if it can be done. I do not know if the Soundlab audio transformer(s)can handle the capacitance of six Acoustat panels. The standard Acoustat Model Six actually used two MK-121 interfaces per speaker, because the audio transformers are designed to drive four panels maximum. The angle between panels for the Model Six is about 6 degrees. Unless one is intimately familiar with both Acoustat and Soundlab technologies, then this could be a very frustrating project. If you are attempting to mix Acoustat and Soundlab panels in one speaker, this will only serve to complicate matters further (especially if they have different bias voltage requirements, different equalization, etc.) All in all, I can\'t say I would recommend attempting such a combination of different brands. For any brand, the ESL panels and corresponding audio step-up and bias supply are designed as a set, and trying to mix different designs will be very difficult if not impossible. Since you own a bunch of Acoustat panels already, I might suggest trying to find some MK-121 interfaces or servocharge amplifiers to drive them.

  • Acoustat Mk-121-2 interface hum - Chris Terzis on 2010-10-11 20:30:21


    I bought some model 3's and have been enjoying them for a few months. One of the interfaces has a hum. Only heard if music is off and if you go behind the speaker. I tried to plug it into other wall outlets on different circuits - same noise.

    Tried tightening transformer bolts - seemed tight.

    Can anyone suggest anything else - am I stuck with the hum unless I bring them in for service.
    Is there anything else - do it yourself - that I could try first. Interfaces have Solen caps and cardas wiring and posts.

    There are three paper wrapped transformers.

    I can send a picture to an email id?

    Appreciate any help - thank you . Chris

    Chris Terzis (2010-10-12 20:24:56)

    After looking at the interfaces and talking to another Acoustat owner I will be picking up some small rubber washers and installing them between the inside of th steel box and the screws where the transformers are mounted - in the hopes of isolating the transformer that is humming. I will remove the top of the interface box to get access. Before I do this I will also pick up a cheater electrical plug to see if it is a ground loop problem. Any suggestions or ideas ? Thx. Chris

  • Ballpark figure speaker and transformer - Andy Szabo on 2007-08-21 21:22:13

    This answer might be a bit late if you\'ve already put them up for sale on eBay. Based on my observations of Acoustats for sale, I would expect to get at least $500 for the pair, and possibly as much as $1000 (possibly more if you get two buyers bidding against each other). This is assuming, of course, that they are in good working order. Due to their large size, a successful sale often depends on finding the right buyer in the right location. Many sellers won\'t ship the speakers (for good reason), so you probably need to find a local buyer. You may have to list them a few times before you find a buyer who is both motivated and close by. There is definitely a market for your speakers - all Acoustat models enjoy a very good resale value, but the original Model X has a real cult following. And fortunately, with Mike Savuto helping us, repairs and parts are available to keep them running.

    Tom Rood (2010-07-02 09:24:59)

    I have a pair of properly functioning X\'s serial #s 252 and 255. The cosmetics are very good considering their age. grills are undamaged but some nicks in the wood mostly on the back edges.I also have a spare set of transformers.The bottom is missing from one of the servo amps? Don\'t ask! I will be putting them up for sale on Ebay but don\'t really have an idea of what they are worth and am afraid of getting lowballed and not know it.Can you give me a ballpark figure on the speakers and the transformers seperatly? Please and thankyou.

  • Bi Amping - Dave Gallenberger on 2010-10-01 04:24:27

    I recently acquired a set of Spectra 1100s that outlived their owner. They seem to have the wrong woofers. Playing them with a single input, not biamped, they are so bass heavy you can't listen to them. So I built an active crossover adjustable from 100-400 hz 12db/octave. Sounds very nice now. Very rich midrange. The first speaker I have heard that I would replace my Magnepan 2.5Rs with.

    Right or wrong, I have bypassed the crossovers in favor of biamping. The sound seems tighter this way. I'm pretty sure it's OK to bypass the Woofer crossover components. I'm not so sure about the panels high pass cap. I bypassed that too. Could I damage the panels or transformers running this way?

    I'm using an Ampzilla with 400w/ch at 4 ohms for the panels and Son of Ampzilla at 150 w/ch at 4 ohms for the woofer. These amps can drive 2 ohm loads with no problem. I may switch to the Son of Ampzilla and Grandson thinking 400w/ch is a bit much.

  • Pair of Spectra 66's for sale - $1200 - mint - Paul Ranieri on 2013-01-02 20:32:24


    Where are your 66's located?

    John Luecke (2013-02-03 20:27:48)

    I'm interested in the Spectra 66's for sale.
    E-mail me back with a way to contact to arrange
    a way to purchase them.
    Thank you,


    John (2013-02-03 20:40:33)

    Here is an email to contact me

    John (2013-02-03 21:06:20)

    My cell # is 817-229-5558
    in case you would like to contact

  • Converting a late model, five-wire panels 2+2 to 4400 - Eli Hollander on 2010-09-05 08:45:18

    I have a 2+2 with the five-wire panels (I believe they are the same as the Spectra panels).

    If I get a 4400 Spectra interface, will converting the 2+2 framed panels work? I know I will have to break out the wires from the 3-wire connection to the 121-C interface into the Spectra mode. Is the panel wiring similar to the setup of the 2200, except that it's stacked?

    Any advice would be highly appreciated.

    Also, Andy, is it possible to reach you directly for advice?

    Thank you,

  • Upgrade question (medallion) - kim108 on 2010-08-03 08:48:05

    Will the medallion 141 transformer be an upgrade for my non medallion 121c of my Acoustat 3?

  • Modded Edition - MrAcoustat on 2010-08-19 16:43:21

    Please have a look at the Acoustat 1+1s it is a modified pair of 1+1 everything was modified from interfaces to the exterior. Thanks for looking. MrAcoustat

    sylvo (2011-07-06 08:17:17)

    Show me the pics of your Acousat 1plus 1 modded edition

    MrAcoustat (2011-07-06 11:05:03)

    Hi Sylvo, you can see the making of my Acoustat's 1+1s in my Flickr galery here is the link. MrAcoustat

    sylvo (2011-07-07 10:22:47)

    Amazing and thanks for sharing - I see you have a lot of changes in the electonics of the 1+1 - do you share your experience and mod. diagram too?
    Once again - congrats.

    MrAcoustat (2011-07-07 13:16:18)

    Hi Sylvo all mods where done by my friend Jocelyn Jeanson of Kingsbury Quebec, he as been doing mods on Acoustat's for many many years, he's in contact with people across the world, send me your e-mail address and i will put you in contact with him, my e-mail address is, looking forward to hear from you. Andre MrAcoustat Sevigny.

    sylvo (2011-07-08 03:52:33)

    Andre - thanks - email on the way to you.

    Alinda Zhang (2011-12-08 01:24:54)

    Our factory was formed in 1989 as specialists in the manufacture of plastic injection tooling and die-cast tooling.We can offer a complete tool makers solution to all of your plastic injection tooling needs, including:" Product Design "Tool Design "Prototype Tooling "Plastic and Die Cast Injection Tooling"Twin-shot Tooling"Tool Repairs"Jigs and Fixtures"For more information,welcome to visit our website: and my email address is

    MrAcoustat (2012-01-27 20:29:35)

    I'm sorry to all i forgot to include the site where my Acoustat's 1+1s can be seen it is in my Flickr photo galery here pages 5 and 6 -

    MrAcoustat (2012-01-27 20:37:21)

    Alinda Zhang any relation to the beautiful Rachel Zhang of Grant Fidelity ????? ( just curious )

  • Monitor - Don Gold on 2010-08-17 19:00:13

    Does anyone know of a source for a power transformer for the Monitor amplifiers. The servo charged Amp. The amp blew a G.E. 6HB5 and my Guru tells me that I need a new power transformer. Number on the transformer is 2008380. It is T1 on the schematic. It's the big transformer on top. It is believed to be 2500 volts AC with 40 ma current.
    Any help would be appreciated.

  • What mods have been done to my Accoustat model 3 interfaces ? - Chris Terzis on 2010-08-17 15:13:52


    Steve Zeeuwe asked me to post my question here.

    I just acquired a pair of model 3's and they sound lovely.

    I was told that they were heavily modified and have medallion transformers.

    I am hoping someone can help me to identfy the mods.

    Is it possible to send a picture to someone to look at the interfaces.

    My email is

    Thank you


  • will a 70volt commercial amp direct drive the 3 without transformers? - kim108 on 2010-08-03 09:00:21

    will a 70volt commercial amp direct drive the 3 without transformers? I saw on the net where some have the earlier acoustat wit the built in amp sounded better thank the transformer version. I have see several commercial 70 volt amp on eBay.

  • I need help identifing parts in the MK-121- C transformer. - Andrei Tudoran on 2010-07-28 13:25:57

    Dear Mr. Szabo, some years ago you advised me on voltage conversion for my beloved model # 8.
    Until now I enjoyed many years of unequaled sound form my Acoustats.

    Recently I got careless with one of the 4 KMA 200 powering the speakers and blew it.
    After repair, one speaker has much lower volume than the healthy one. I would say, may be as much as 30/40% difference.
    The sound is still crisp & clear. I isolated the problem with one or two of the MK 121 C Medallion transformers powering the speaker.

    Inside the Medallion transformer, on the plate with the butterfly nuts & ground connection ;In the center, there are 5 black power diodes with a white dot on top, surrounded by 5 blue capacitors.

    One of the diodes is defective. They don’t have any markings and I can’t find any schematics.
    Can you please be so kind and provide replacement specifications!

    Greatly appreciated and thanks for your part in making this great speakers.
    Even now after so many years, most people are awed by their sound.


    Andrei Tudoran (2010-07-29 14:21:25)

    Just to let you know , I found one of your older posts where the diodes are discussed.

    Thanks you, If you want to comment on my post, please do !

    Andrei Tudoran (2010-09-22 12:05:28)

    OK, a few month later a I got all the parts replaced the diodes, the transformers are all working.
    Unfortunately, one of the speakers still has an issue.
    When played there is a very noticeable difference in volume between the speakers, on the damaged one,
    the sound is muddy and occasionally sounds like someone is gargling.

    That probably means panel damage. I want to remove the cloth cover and investigate but I am clueless as to what to look for. How to spot a damaged panel or what else can be damaged or broken.

    Al this started when I accidentally removed an audio cable from the preamp while at very high volume.

    Burned one amp, damaged one interface now the panel.

    Anyone can give me some pointers ; greatly appreciated.

    Andrei Tudoran (2011-09-10 09:49:04)

    From the activity in this forum; not too many #8 owners around.

    To complete the above saga; I ended up upgrading all my components and replacing all the panels in one speaker.
    Roy Esposito ( Sounds Like New ) did a fine job upgrading the interfaces.
    Without his help & patient advice, it would have been much more difficult.

    Today, the speakers sound better than anything around; amazing for speakers close to 30 years old.
    Thank you Acoustat.

    Best regards.

    MrAcoustat (2011-10-15 09:58:15)

    Hi Andrei you are right not to many owners of Acoustat 8s of course that's one huge speaker like you i have owned Acoustat's since 1984 six different pairs 2+2s - Spectra 22s - Spectra 33s - and i am on my third pair of 1+1s these are all metal frame and weigh 200 pounds each dollar for dollar NOTHING come's even close to Acoustat's.

    PS: If you want to see pictures here is a link to my Flickr photo galery.

  • Convert a left array into a right one ? - Maurice Chevalier on 2010-07-25 16:52:51

    Hello Andy,

    May be i made a mistake: i already post a similar ask in the "left and right" subject but it was not probably the right place. Sorry.

    I hope you are still reading this forum...
    I recently purchased a used "pair" of Acoustat Spectra 2200.
    They please me but I'm not convinced by their sound stage and i've just discovered your answer to an old question about how to distinguish a left and a right array...
    I didn't found any label to help me except those put by the former owner on the wood plates.
    So i have to be sure i've got a pair or not.
    The high frequencies (actually full range) appear to be coming from the inner edge of the left array but on the "right" one, they come from the outer edge...
    I read on the 22 owner manual that one hole can be found to distinguish right and left arrays:
    "Each is identified by a small hole (3/16" diameter) located in the top metal capture plate. The hole is on the left side of the left array and right side of the right array - when viewed from the listenning side ."
    Is there a "top metal capture plate" on the 2200 ?
    The only hole i found on my pair of 2200 was used to let wires coming from the interface to the array and it was on the same side.
    I'm afraid i own two left arrays...
    Is it possible to convert a left array into a right one ?

    What do you think of that Andy ?

    Best Regards,


    Steve Zeeuwe (2010-07-26 14:40:56)

    Dear Maurice,

    I am pretty sure Andy still reads this forum, just not every day (as you already noticed).

    I hope you have some patience!

    Kind regards,


    Maurice Chevalier (2010-07-27 14:22:18)

    Dear Steve,

    Thank you for these kind words.
    I'm not in a hurry and i have some patience.
    I'm aware that my question is not easy to answer.

    Best regards,


    Maurice Chevalier (2010-10-24 14:29:18)

    Dear Andy and Steeve,

    Do you think i should still wait for an answer to my question, even if it's a negative one ?
    I really enjoy my pair of 2200 but i would like to know how i can improve this situation or if i should look for another "real" pair.

    Thank you so much for your help.

    Best regards,


    Steve Zeeuwe (2010-10-24 16:53:01)

    Dear Maurice,

    Thank you for your patience!

    I will try to contact Andy directly to see if he has the time and will to answer your question. I will let you know as soon as Andy replied to me, but hopefully you will already have your answer by then.

    Kind regards,

    Steve Zeeuwe
    The Audio Circuit

    Andy Szabo (2010-11-01 00:19:24)

    Sorry for the delay in responding - somehow your question escaped my attention. The small metal hole mentioned in the 22 manual does not apply to the 2200, since there is a wooden trim piece on the top of the 2200, instead of the metal plate used on the 22. (The same comment applies to the Models 33/3300.) Based on your description of listening for the position of the full-range sector, you have two left-hand speakers. The speaker on the right side needs to be re-wired into a right speaker.

    I won't say this is easy to do, but it not impossible if you have some mechanical/electrical skill. You will be very happy with the results, I assure you. Go to the Acoustat main page, and scroll down to find the document entitled 'Spectra Sectoring and Color Codes'. This diagram shows the color codes for a right speaker. Note there will be no change to the red-striped bias wire. Basically you'll need to remove the pin-plugs from the connecting wires, and re-sort them into the order shown. To reduce the number of wires that need sorting out at one time, do the white group first, and then the blue group (or vice-versa). Because you'll need to see which panel each wire is coming from, you'll need to pry off the wooden trim and pull the grill cloth up. Most likely you'll want to replace the grille cloth - see the source under 'Available Parts'. My article on refurbishing my Spectra 4400's seems to be missing from the website, but I'll ask the webmaster to get it re-posted under my Technical Bulletins.

    If that is not a sufficient description of the process to get you through it, do write again and I can provide more detailed instructions.

    Maurice Chevalier (2010-11-03 00:20:42)

    Dear Andy and Steve,

    Your reply was one of the best news of the year !
    So it's possible to convert a left array into a right one ! Not easy but possible !
    I can keep my pair and change the socks at the same time.
    I already asked to Ren Jenson for a quote...
    I thank you for the diagram to re-sort the wires and i think your article on the 4400 will be helpfull too.
    I'll tell you what i do as soon as i'm ready with the socks.
    A big thank again !


    Maurice Chevalier (2010-11-18 21:23:59)

    And the Andy's decisive help gave back so much to the "false" pair of Spectra 2200...
    Yes it's possible to re-sort the wires in the order shown on the document.
    A friend of mine came at home with his soldering iron and some silver solder, we spent an afternoon to do that together and we had the joy to discover the changes !
    After some listenings, we decided to place the Spectras on the same virtual line on the ground (carpet).
    And yes, the sound stage and the music are here now !
    No day without listening to them... I'll have to listen again my CDs including those on which I was only listening two or three tracks... because they just go easier from track to track.
    The hard part was probably to follow each wire without mistake. The yellow pins had two wires that we had to separate themselves. I think we did a good job.
    And you know what ? I received yesterday the new socks - genuine ones - for the Spectras professionaly sent by Ren and Shirley... amazing !
    How can I thank Andy and Steeve ?
    May be I could say how can each one here can thank Andy for his so precious help ?

    Andy Szabo (2010-11-19 12:21:08)

    Maurice - Thanks for the follow-up. Your success at getting your speakers fixed is all the thanks I need. My satisfaction comes from helping Acoustat owners keep their speakers running. Working at Acoustat was the most rewarding part of my career, and answering questions on the Audiocircuit helps me to re-live those glory years.

  • found new spectra (more questions) - nikos from Greece on 2006-08-30 15:50:56

    hi again and thanks for your very clarifying answers.I think that the model in the shop is acoustat 1200 after all(Italy period).It is certainly hybrid, though in the TAC site it is not included in the hybrid series. Also I am almost certain that they are not second hand, it is one of those rare cases, small city nobody really cares much,this is not a BMW.About amplifying.My amplifier is TEAC A BX7R which is a very qood quality solid state amplifier but with not the watts that Spectra may need (2 X 70 watts probably almost A class, not sure).Could I have some good sound for the time being until I change my amplifier in the future? Also apart from the set of the speakers what else should also come together with them? external crossover or what else?Any more info you think is necessary for someone not expert at all woud be most welcome. Thanks

    Andy Szabo (2006-09-02 10:46:13)

    I know very little about the Acoustat models made in Italy. I wouldn’t expect there to be an external crossover, but there is almost certainly a wall transformer or separate power supply, or at least an AC power cord. Like all electrostatic loudspeakers, the Acoustat requires an external power source to energize the bias power supply. Your Teac amplifier might be okay as a temporary solution, but the 70-watt rating would not provide enough power to get the most from the speakers. The best way to determine if all the parts are there is to listen to them before you buy, preferably with the particular amplifier you plan to use. If the dealer is unwilling or unable to do that, then you should insist on an at-home trial period, with a money-back guarantee. If the dealer is unwilling to do that, I would say no deal and walk away.

  • Various, 28 Hz? - John Mastroleo on 2004-02-23 22:21:42

    Andy, I have owned my Spectra 44 speakers for 12 yrs. I have two questions. Acoustat\'s add literature for the model 2+ 2 rates the speaker with a maximum output of 115db on musical peaks. This output is given in a room with a dimension of 16\'x24\'. The add goes on and gives a listening distance of 20\' feet from the speakers with the speakers positioned four feet from the front wall. It also gives the maximum power capacity for the speaker of 500 watts. The printed frequency response was given at 28 to 20 plus or minus two db. This add is printed in Stererophile vol 7 issue two. John Holt conducted the review.

    My two questions are how can the speaker achieve 28 hz.frequency response. I measured the SPECTRA panel ( The older panel not the one built in Europe or China.) It has a resonate frequency of 45 hz. How do you get 28 hz out of that? Was the measurement including room gain and taken at the far field of the listening room where you sit? I would like to know how the measurements were taken.

    The other question has to do with the amplitude that is used when measuring any speaker system but specifically the 2 + 2 and model 44. When a speaker manufacturer prints a plus or minus reponse of say 2 db for his speaker at what sound pressure are the speakers measured at. ( 85 ,90 ) Many speaker manufactures take frequency response test with the mike 1 meter from the plane of the speaker but you never see what sound pressure the test is conducted at and you never know how low in amplitude the base range is in relationship to the mid band. If a speaker is tested at say 1 meter and at a 87 db loudness level. To be an acurate rating shouldn\'t the speaker be be able to produce the same amplitude at 28 hz as it is at 1kh? Is there a standard for measuring? How are the Acoustat 2 + 2 and the model 44 measured to achieve the published 28 hz freq response when the panels have a measured resonate frequeny of 45 hz.?

    One last thing the new panel that was designed in 1995 for the European Acoustats makes mention of the new wider dynamic range panels. The Audiostatic Company also talks on their web page of a wide dynamic panel. To do this is the mylor placed further away from the charge so it has to stretch further thus moving more air.?

    Sincerely, John Mastroleo

    Andy Szabo (2004-02-23 22:21:42)

    Hello again John! I remember talking to you many times on the phone back in the good ol\' Acoustat days. You\'ve asked a lot of specific questions about speaker specifications and measurements that I cannot answer, but I will make a few general comments.

    I have always felt that any loudspeaker\'s acoustic specifications are highly suspect. Due to non-standardized methods of measurement, effects of room acoustics, and a liberal dose of marketing hype, I just don\'t give them much credence.

    I was not at Acoustat when those 2+2 measurements were taken and published, so I cannot comment on how they were produced. Personally, I always suspected that the pre-Spectra specifications were … shall we say optimistic?

    Attempts were made to produce more meaningful specifications for the Spectra models. I did most of those measurements myself, and I have a little more faith in the Spectra specifications, but still not much. Part of the problem is that measuring a large-area speaker at one meter will not give an accurate picture of its total output - particularly in the bass region. Taking the measurement at three meters (and extrapolating the numbers back to one meter) can give better results for a large speaker. But, unfortunately, this greater distance increases the likelihood of room acoustics affecting the measurement.

    If I remember correctly, most published speaker measurements are made at 1-watt input: impedance, frequency response, and sensitivity. Maximum SPL levels are very tricky to measure. Measuring peak music levels is difficult (even with a peak-holding meter), and trying to measure with a continuous high-level tone would quickly destroy most speakers.

    I am not familiar with any changes made to the Acoustat panel since the company was sold to the Italians. (I\'d be interested in learning more!) In regards to your question about Mylar spacing, I can make a few comments. If the spacing is increased, dynamic capability may increase slightly, but efficiency would drop dramatically. Electrostatic forces fall off with the square of the distance, so even a slight increase in spacing would significantly reduce efficiency. Since electrostatic speakers have poor efficiency already, a further reduction in efficiency would not be good. When Jim Strickland designed the original panel, I think he arrived at the optimum diaphragm-to-stator spacing, for the materials being used with an air dielectric.

    Acoustat (America) did make one change in the panel that increased dynamic capability, without any negative side effects. The conductive coating was increased in resistivity, which reduced charge migration and localization. This means that the charge distribution over the surface of the panel remains more uniform and hence closer to theoretical operation. The result was a speaker that could play louder without the familiar ”crackles” on bass notes. Panels built with the improved coating can be identified by a bias wire that is yellow with a red spiral stripe.

  • New frames - Ephraim Meyer on 2004-02-23 22:21:42

    Hello, this a question for Andy Szabo. I would like to rebuild my Acoustat 2+2 speakers on a hollow aluminium frame (to be filled afterwards with lead shot or sand). I want to attach the loudspeaker sections directly to the aluminium, and of course use some type of damping material between the aluminium and plastic of the loudspeaker units.My question is if there will be any magnetic interference with the electrostatic field. There will be no wood on the speakers or frames. Thanks in advance, Ephraim Meyer

    Andy Szabo (2004-02-23 22:21:42)

    The electrostatic field is very localized between the stators, so it is unlikely that any sort of metal frame (even steel) would have an adverse effect. Aluminum, by its very nature, is non-magnetic, so I don’t see any problems in that area.

    The biggest concern with a metal frame is shock hazard. It is vital that the panels are insulated from the metal, so that any potential leakage cannot energize the metal. Use some sort of insulating material between the frame and the panel on the mounting surfaces, and allow at least ½â€ between edges of the panels and the frames. You may also want to use some non-metallic (nylon?) screws for mounting the panels. The wires leading to the panel should also be double-insulated along their entire run inside the frame. PVC tubing is a good choice for insulating the wires. The metal frame should also be electrically connected to earth ground, to further safeguard against shock hazard.

    Another concern is resonance. A metal frame will have a considerably higher resonant frequency than a wood frame. Even filled with lead shot or sand, you may have problems with resonance.

    See Izzy Wizzy Audio to gain some more insight into the problems of using metal frames. Please note that I do not necessarily endorse the work represented there, but you may be able to benefit from his experience.

  • Various, changing into 2+2 - Lee Sulka on 2004-02-23 22:21:42

    I am considering modifying my Acoustat model 3s into a 2+2 configuration with some spare panels I have. In order to do this I need to add some length to the red, blue, and white wires that supply the panels. Do you know of a source for this wire or do you have any suggestions for alternatives? Thanks again, Lee.

    Andy Szabo (2004-02-23 22:21:42)

    Newark Electronics ( has a wire that I think would work okay. Their part number 05F1285, it is 22 gauge silver-plated copper wire, with type R790 silicon insulation rated for 20-kV. It\'s not cheap: $126 for a 100-foot roll. This wire is white, so you\'ll need to color-code it with colored markers, tape, or shrink tubing.

    All splices should be soldered and insulated with a double layer of heat shrink tubing. Stagger the splices so that no two splices are directly next to each other.

    A note to all you ”wire-nuts” out there: I DO NOT recommend the use of this wire for the wholesale ”upgrade” of the wiring from the panels to the interface. There is no advantage in making such a change. This wire is to be used only when the existing wires are too short and must be extended, as in the project mentioned above.

    Please note that the Spectra 44/4400 frame drawing shown on this website is NOT the same as the 2+2 frame. Both contain four panels, but the 2+2 holds the panels at a slight angle (9 degrees?) for proper dispersion.

    This sounds like a great project. Have fun!

  • Woofer/Subwoofer solution - Joseph M. Fabricatore on 2004-02-23 22:21:42

    I am interested in adding a SPW-1 to my Spectra 33s. I auditioned an SPW-1 some years ago, but found its addition change the character of the Spectras unpleasantly. Now since I watch DVDs and run the sound through the Spectras, I might want the changed sound, or if anyone has a suggestion for another woofer/subwoofer solution. Responses much appreciated. Joseph M. Fabricatore

    Andy Szabo (2004-02-23 22:21:42)

    Adding any conventional sub-woofer to any pure-ESL system will necessarily involve compromises. I feel safe in making such a blanket statement due to the very different nature of the two types of transducers.

    When Acoustat introduced the SPW-1 for the Spectra series, we felt we did a pretty good job of minimizing the trade-offs associated with adding a conventional woofer to a pure-ESL system. Multiple, small woofers were used to preserve as much “quickness” in the low end as possible. Even so, the quality of bass is not as good as it would be with a pure-ESL system. However, adding the SPW-1 does increase the low-end extension and the dynamic capacity of the system as a whole.

    Certainly, for some applications, adding a subwoofer can increase one\'s enjoyment of the system. If you are using the system for home theater, or are trying to fill a large room with high sound levels, then adding subwoofer can be worth living with the inevitable compromises.

    I suggest you take another look at the SPW-1. They are available on the used market for a reasonable price, and you can always switch the woofer “off” for pure music applications.

    There are many other subwoofers on the market: some of them are quite expensive (and presumably one gets what one pays for). I can\'t offer any particular recommendations.

    I recently added a subwoofer to my Spectra 1100\'s: the Titanic 10” subwoofer from Parts Express ( ). This is a self-powered system available for a very reasonable $350. I\'m quite happy with the system, but remember that the Spectra 1100 already has a woofer covering the bottom octaves. Therefore, adding a subwoofer to this system does not involve the same compromises, because the stock 1100 already has a “woofer-ish” bottom end. I can\'t say how well it would mate to a pure-ESL system.

    Good Luck with your search for a subwoofer – if you find a model that matches particularly well, please let us know!

  • Spectra interface - Joe on 2004-02-23 22:21:42

    Hi Andy, are transformers from a Spectra series the same as in the mk 121-c I\'m the original owner of a pair of 3\'s with mk-121-a interfaces I have access to a pair of spectral 3 interfaces and would like to do a little updating.

    Andy Szabo (2004-02-23 22:21:42)

    The Spectra Interfaces are not compatible with pre-Spectra panels. First, the frame configuration of pre-Spectra models (like your Model 3\'s) is not correct for Spectra. In pre-Spectra models, the panels are arranged in a physical arc to achieve a curved dispersion. The Spectra frames arrange the panels in a flat plane, and the curved dispersion is achieved by electrical means.

    More importantly, your panels are not segmented, as required for Spectra operation. Spectra panels have the stator grids split into vertical halves, and each segment is driven separately by the Spectra interface.

  • MK-2123 Interface - John Scandrol on 2004-02-23 22:21:42

    I have a pair of Acoustat mk-2123 speakers of which one of the voltage amp needs repaired. Do you know where I can get a schematic for these and or who I can contact to get replacement parts?
    Thanks, John.

    Andy Szabo (2004-02-23 22:21:42)

    The MK-2123 is a transformer step-up system and bias power supply, not an amplifier. It is used on the Spectra 22/2200/33/3300 models. A schematic is available on this website, listed under the 2200 or 3300 (same schematic for either model - only the transformer tap is different).

    Some parts are available from electronics distributors. Unfortunately, it is no longer possible to purchase replacement transformers. If you have bad transformers, repair is available from Sounds Like New, listed on this site under ”Refurbishing”. Note that they do not sell parts, so you would need to send the interfaces (not the whole speaker) to them for repair. Tell \'em I sent you!

    Once you have looked at the schematic and done some troubleshooting, I may be able to assist you further with parts sources if you determine the problem is not with the transformer(s).

  • Identification needed - Robert H Lever on 2004-02-23 22:21:42

    Dear Andy, I just purchased a pair of Acoustats. They have been my dream speakers since I heard a pair back in the eighties. I am not sure which model I have- They look like Spectra 22s. They are 5-1/2 ft tall and 1-1/2 ft wide with black grilles and oak frames with brass trim. The interface chassis has this info on them: Rockford Corp. Mk 2123. There is a small 22 sticker near the bottom. The serial numbers are 27031-36 and 37.

    The Speakers are very impressive in many ways although I listened to them after only about 4 hours of charging. I was told they need to charge all night to sound their best. The speakers have a broad peak in the midrange which makes vocalists too prominent. Could this be due to room placement? The speakers are about 3-1/2 ft from a 12 ft wide backwall and about 2 ft in from the side walls. The couch is about 8ft away from the speakers. Are these Spectra 22s? Is it possible to obtain copies of owner or service manuals on these speakers? I would greatly appreaciate any help on the speakers that you could provide. Sincerely, Robert H Lever

    Andy Szabo (2004-02-23 22:21:42)

    The speaker you have is a Spectra 2200, which is the same as a Spectra 22. When Acoustat added the wood and brass trim to the Spectra series, all models went from an XX model number to an XX00 model number. This was a cosmetic change only: the new models were sonically identical. (The exception to this is the Spectra 11 vs. the Spectra 1100, which are two very different speakers.)

    A sales brochure, electrical schematic, impedance graphs, and frame drawings are available on this site for the Spectra 22/2200. Currently, there is no Spectra full-range owner\'s manual available on this site. The Spectra 1100 Owner\'s Manual will be posted soon: this is for a smaller hybrid speaker, but much of this manual\'s content also applies to the full-range speakers. Perhaps one of your fellow Spectra owners could send a copy of the owner\'s manual to our Webmaster. There is one manual that covers the 22, 2200, 33, and 3300.

    Although the speakers do reach full bias voltage within a minute or so, there are slight changes in the sound character for many hours. A full day is generally considered enough for the speaker to reach it\'s full potential, but I have heard some people claim to hear improvements even after several days.

    Room placement can be tricky, and the owner\'s manuals do discuss this at length. My first suggestion would be to place the speakers closer to the rear wall. At 3-1/2 feet, this is farther than most people use, and indeed, a greater distance than most people have the room for! You didn\'t mention how your room is furnished. Floor treatment (carpeted or not), draperies, and furniture type will all have an effect on sound. Hard reflecting surfaces (like glass windows and bare floors) will tend to brighten the sound, and absorbing surfaces (like carpet and upholstery) will tend to soften the sound. Changing the room\'s décor to improve the sound is usually not an option, but be aware that it can have a significant affect on the performance.

    All Spectra models have a left and right panel, so make sure these are oriented correctly. The panels were originally marked ”left” and ”right”, but the labels may have fallen off. The easiest way to be sure is by listening at close range: when set-up correctly, the high frequencies (actually full-range) will appear to be coming from near the inner edge of each speaker, when viewed from the front of the speaker.

    The speakers should be angled inwards, so that they more-or-less face the listening position. Slight differences in this angle can have a dramatic effect, particularly on sound staging, so experimentation is the key to success. Listening distance from each speaker should be roughly the same as the distance between speakers (an equilateral triangle). Again, this is subject to experimentation. Be patient: it may take you a few weeks of listening and making small changes to yield the maximum satisfaction from the speakers. This is all part of the fun of owning esl speakers.

    Once you have determined the final position of the speakers, you may want to consider using spiked feet (if you have carpet) to help stabilize the base and make sure it stays in that position. (I\'m having trouble remembering: did the Spectra 2200 have T-Nuts located on the bottom of the bases to receive screw-in spiked feet?)

  • Difference spectra 11-22 and 1100-2200 - Mathieu Soumireu on 2004-02-23 22:21:42

    My question is very simple, but Acoustat products are not very well known in France : What is the difference between Spectra 11-22 and Spectra 1100-2200 ? Best regards and bravo for your precious association, Mathieu Soumireu

    Andy Szabo (2004-02-23 22:21:42)

    The difference between the Spectra 22 and 2200 is purely cosmetic. The 2200 has a solid-wood trim strip around the around the edge of the panel, with an in-laid polished brass strip. Otherwise, the speakers are identical: the ESL panels and electronics (*) are exactly the same. These same comments hold true when comparing the Spectra 33 vs. 3300, 44 vs. 4400, and 66 vs. 6600.

    (*) The Ultrasonic Bias Power Supply was introduced during the manufacturing life of the Spectra 22/33/44/66. So, it is possible to encounter a 22/33/44/66 with the older mains-powered bias supply, or with the newer low voltage-powered bias supply. All of the 2200/3300/4400/6600 models were manufactured with the Ultrasonic Supply. In any case, the speakers will sound the same regardless of bias supply. That change was made to create a ”universal” speaker that could be used anywhere in the world.

    The differences between the Spectra 11 and 1100 are much more than just cosmetic. Both models use the same ESL panel, step-up transformer, and bias supply. The differences between the two models are significant, and are easiest to present in chart form:

    Feature 11

    woofer cabinet - particleboard w/plastic laminate
    woofer - ”good” 8-inch driver
    bi-amp/bi-wire switch - none
    hi-freq balance switch - none
    panel trim - none
    ESL xover capacitor - electrolytic
    holes for spiked feet - none

    Feature 1100

    woofer cabinet - MDF w/wood veneer
    woofer - ”excellent” 8-inch driver
    bi-amp/bi-wire switch - yes, w/separate woofer inputs
    hi-freq balance switch - yes, high/medium/low
    panel trim - solid wood w/brass trim
    ESL xover capacitor - electrolytic w/polyprop. bypass
    holes for spiked feet - four/speaker (1/4”-20 thread)

    The Spectra 11 was introduced first. It was intended to be an entry-level system, and in order to keep costs low, it had few features and used few premium materials. Due to a demand for better appearance, features, and low-end response, the Spectra 1100 was introduced. Both models were sold concurrently.

  • Repairing amplifiers - Gary Winter on 2004-02-23 22:21:42

    My project: I am repairing the amplifiers from a pair of Acoustat Model X. I am eager to hear them. I\'m having trouble locating any information.

    Can anyone forward any information at all (e.g. owners manuals, service manuals, schematics, alignment instructions)?

    Andy Szabo (2004-02-23 22:21:42)

    See the response to Paul Marino, above.

  • Various, monitor 4 to 1+1 - Alan Kelly on 2004-02-23 22:21:42

    I have reconfigured my Monitor Four speakers to a 1+1 using one wide panel at the bottom and a narrower panel at the top. Does this arrangement make sense ? Or should I stick to using equally wide panels top and bottom ? Which one to use the narrow or the wide ? Can anyone tell me the dimensions of the panels in the 1+1 ? I am listening in a small room otherwise I might have gone to 2+2. Thanks in advance Alan.

    Andy Szabo (2004-02-23 22:21:42)

    The Monitor 4 used four ESL panels per speaker, of two different sizes. The two outer panels are 9-inches wide, and the two inner panels are 8-inches wide. Other than the width, the two types of panels are of the same construction and performance. The purpose of the two different size panels was to distribute the low frequency resonant point. In later models, this was found to be unnecessary, and hence models like the 2+2 used all 9-inch panels.

    The Model 1+1 uses two 9-inch panels, stacked vertically.

    In converting the Monitor 4 into a Model 1+1, I would recommend using the two 9-inch panels. Since the 1+1 has barely enough panel area for adequate bass response, you\'ll want to employ as much panel area as possible.

    In converting the Monitor 4 into a Model 2+2, I would recommend using the two 9-inch panels stacked vertically in one column, and the two 8-inch panels stacked vertically next to them. For the other speaker, make the arrangement mirror image. It probably doesn\'t matter whether the narrow panels are on the inside edges or the outside edges, but I would probably put them on the inside edges. The two columns of panels should have an angle between them of about nine degrees.

    For the 1+1, you\'ll want to change the position of the Low Frequency Transformer Tap. (This is assuming you are using the MK-121 transformer interface, and not the Servocharge Amplifier.) The tap is normally set on the Yellow position for a four-panel system (minimum bass boost); you\'ll want to change to the Red position for a two-panel system (maximum bass boost).

    One real difference you\'ll notice in going from the 4-panel wide Monitor 4 to the one panel wide 1+1 is a dramatic improvement in stereo imaging, since the 1+1 more closely approximates a line source.

    Good Luck. This sounds like a fun project. Old Acoustats never die: they just take on new shapes!

  • Identification needed - Greg on 2004-02-23 22:21:42

    Is there a sure way to tell the difference between the 2200 and the 22 models electrostatics. Mine are completely wrapped in black cloth, the power supply number is MK2123. The owners manual says 2200.

    Andy Szabo (2004-02-23 22:21:42)

    The difference between the Spectra 22 and 2200 is purely cosmetic, and it is easy to tell the difference. The 2200 has wood strips with brass inlays along the sides and top of the panel frame. The 22 does not have this decorative trim.

    Otherwise, the Spectra 22 and 2200 are electrically and sonically identical. This same comparison also applies to the Spectra 33 vs. 3300; 44 vs. 4400; and 66 vs. 6600. This comparison does not apply to the Spectra 11 vs. 1100: there are many more differences between those two models.

  • Identification needed - Jim Toole on 2004-02-23 22:21:42

    I have a pair that would apear to be three\'s. They are 28” wide x 72” tall and have a MK-131 interface (can\'t find info on this model only the 121 and 141). The woofer is 8-1/2” in diameter.

    Please help me identify these. I am currently in the market for an amp to drive them. The pair were given to me as a gift. I have charished them but not feed them as they deserve. I have learned a great deal about the company and have always been thrilled with their performance.

    Any information on my model that you could give would be greatly appreciated. Amp suggestions and or upgrades to the speakers would also be great. Thanks very much for you very informative web page. Best regards, Jim Toole

    Andy Szabo (2004-02-23 22:21:42)

    From your description, you have an Acoustat Model 3MH. This model uses three electrostatic panels plus a built-in woofer, per speaker. It utilizes the MK-131 transformer interface, which is a limited frequency range unit designed for use with a woofer. It is very similar to the MK-141.

    The ”MH” of the model number stands for ”Modular Hybrid”. The speaker components are modular, having separate assemblies for the ESL panels, interface electronics, and woofer cabinet. It is a hybrid because it uses both ESL panels and a conventional woofer. A similar model was available without the woofer, known as the 3M, using the full-range MK-121 interface.

    An owner\'s manual is available on this site for the Models 2M, 2MH, 3M and 3MH. Unfortunately it does not include a schematic of the MK-131 interface. Does anyone have one they could share?

    There isn\'t much that can be done to upgrade the speaker, except possibly upgrading some capacitors. Without the schematic, I cannot give you specific values. There is a high-voltage audio coupling capacitor that could be replaced with polypropylene, if you can find a suitable replacement with sufficient voltage rating. The ESL/woofer crossover\'s capacitor is probably too large a value to be practical to replace with polypropylene, but you could parallel it with a 10-uF capacitor. Either of these changes would be worthwhile, but the improvement will be subtle. No changes to the bias supply are recommended.

    Incidentally, the owner\'s manual calls for a 3-amp slow-blow type fuse. If you have trouble blowing this fuse at moderate levels, you may safely increase that to a 5-amp fuse.

    These speakers, like all ESL\'s, are inefficient and hard to drive. To achieve the speaker\'s maximum potential, a good amplifier is required. There are many suitable choices. I would recommend at least 100 watts per channel (8-ohm rating), but you can use up to 250 watts safely. Since you are looking at a sizeable investment in a new amplifier, try to arrange a home audition with your speakers, to make sure the new combination lives up to your expectations.

  • Interfaces, MK-121-C, dead - Andy Szabo on 2004-02-24 15:16:27

    Whatever you do, don\'t throw it away! Even if you decide that the speaker cannot be fixed, or is too expensive to fix, your speaker is valuable to others as a source of parts to keep their Acoustats running. Someone will buy what you have, even if it is not functional.

    The model number MK-121C is the model number of the interface only (black box), so I cannot tell what model you have. If you supply me with the overall dimensions of the panel frame, I can determine what model number speaker you have. Acoustat never did put the model numbers on its speakers. The good news is that the ”C” version represents the latest-and-greatest version of the MK-121.

    But for now, the model number is probably not important. Are both speakers defective? It sounds like the panel is not receiving any bias voltage. Are you aware that the Acoustat speaker needs to be plugged into AC power for operation? Also make sure that the three wire connections from the panel to interface are intact (blue & white wires to the corresponding thumbscrews, and the red wires to the pin-plug).

    A lack of power to the bias power supply (or a defective supply) is the most likely cause of the problem. The panels themselves are extremely reliable, so it is unlikely that anything is wrong there. The audio step-up system could be defective, but you would probably be hearing more than you are, even if it sounded distorted.

    Be sure to check the fuses, too. There are two 1/4 -amp slow-blow fuses for the bias power supply (located inside the interface chassis), and a 5-amp slow-blow fuse for the audio (accessible from the outside of the interface). Make sure that the speaker is configured for your local mains voltage (110-120 volts, or 220-240 volts). If not, you will need to obtain a new bias transformer.

    If these checks reveal no solution, try contacting ”Sounds Like New” in Florida USA, at 516-736-0041. It would not be necessary to ship the whole speaker to them for repair: only the interfaces would need to be sent. They do not sell parts, but are capable of repairing almost anything for Acoustat (even the audio transformers).

    Alternately, feel free to write again if you discover more information that could lead to a solution.

    Andy Szabo (2004-02-24 15:16:27)

    David Hafler MK121 C. I need help figuring out why my MK121 c speaker is not working. I am getting no power out of the speaker but if I crank 400watts to it I can put my ear to it and barely hear sound coming out. Is there some place that I can go to find out what the problem may be? Can I buy parts for the black box... or a new black box...or should I just throw the whole speaker away?

    Wade Scott (2004-02-24 16:20:44)

    Hi Andy , Thanks for your response
    In answer to your questions: I only have the one speaker unit. Could this be my biggest problem? The speaker is 8\'9” tall x 11 1/2” wide x 3 1/2” deep. Unfinished wood frame with white plastic grills. I have plugged into 110 volts and all wires are connected and fuses are good. how do I check for speakers voltage configuration?
    I learned the hard (SHOCKING) way (with the unit unplugged) that there is definately a large amount of power being generated by the box but its just not getting to the speaker.
    If these answers to your questions give you any further insight as to what my problem may be please let me know. Thanks so much, Wade Scott.

    Andy Szabo (2004-02-24 16:35:07)

    You have an Acoustat Model 1+1, without its grille cloth. There are pictures on this website so you can see what your speaker should look like. There is also an owner\'s manual, with a wealth of information about the speaker\'s use and operation. The manual has a schematic of the MK-121B interface: a schematic of the ”C” version is shown under the Medallion Modification instructions.
    Having only one speaker of the pair certainly casts some doubt on the wisdom of trying to fix this speaker. Unless you have a use for a single speaker (like a center channel for a surround-sound system), then it may be best to sell the speaker for parts.
    Sorry to hear that you received an electrical shock, but that is actually good news. That indicates that the 5000-volt bias power supply is working. Even after the speaker has been unplugged, the capacitance of the electrostatic panel will hold a charge for some time. The owner\'s manual discusses how to safely discharge that residual voltage.
    This speaker has already experienced one traumatic event in its life. Electrostatic speakers mate for life, so when one of the pair is lost, the remaining one loses its will to play. Seriously though, I wonder if it may have been tampered with in some way. Do you know anything about its history? The fact that the bias supply is working, and the fuses are intact, but still no sound, suggests that the two audio transformers are both completely blown (possible, but unlikely), or that the electronics have been tampered with. The schematic is fairly simple, so you might try tracing out the wiring to see if your interface matches the schematic.
    Unless your speaker is labeled as ”220-240 VAC”, then it is most likely configured for 110-120 VAC. If you operated a 220-volt speaker at 110-volts, you would still hear some sound if all other systems were functioning properly.
    I\'m about out of ideas. If you still wish to repair this speaker, I\'m here to help. You\'ll need to do some detective work and provide me with more information for us to proceed.

    Wade Scott (2004-02-24 16:36:07)

    Hi Andy , Thanks for your response. I have the mk1212 black box on the 7\'9” tall by 3” deep by 11 1/2” wide speaker. I only have the one speaker. I have plugged it into 110 AC and all three wire connections from the panel to the box intact. The 2 1/4 slow blow fuses are fine and the external 1/16 amp fuse is good too. Still I get no more than a whisper of sound from the speaker. Do I have to have 2 speakers connected? Is the external 1/16 amp fuse not allowing enough power to pass? wouldn\'t it blow? How do I make sure the speaker is configured for 110 and not 220 volts.
    Thanks Wade Scott

    Andy Szabo (2010-07-02 11:09:08)

    It is not necessary to have two speakers. One will play just fine by itself, although it may feel a little sad without its mate.

    The bias transformer is the smallest of the three transformers inside the interface. If the bias transformer is marked XP117, it is for 110-120 volts AC. If it is marked XP240, it is for 220-240 volts AC. The 110/120 volt units use ¼-amp fuses, and the 220/240 volt units use 1/8-amp fuses.

    The external (audio) fuse should be rated at 3 to 5 amperes slow-blow. A 1/16-amp fuse will blow almost instantly, unless of course the interface is a complete open circuit and drawing no audio power. How are you determining that the fuses are good? Small value fuses are often very hard to check visually: they must be tested with an ohmmeter.

    If the 1/16-amp fuse is truly ok, and does not blow when you drive it hard with your amplifier, then something must be very wrong with the interface. I suspect missing parts, severed connections, and/or so much component damage that nothing works at all. Have you compared the contents of the interface with the schematic?

    Also check that the Low Frequency Tap is connected properly: the red tap is correct for the 1+1. (This is explained in the owner\'s manual.) Even if this tap is set for the wrong position (or even disconnected), you should still hear some sound from the speaker.

    You\'ve been silent on the subject of this speaker\'s history, or what you intend to do with only one speaker. None of my business of course, but I thought I\'d ask just the same.

    Roy Esposito (2010-07-02 11:09:08)

    I am very much alive. I am No-Where near retiring .... and over many years have come up with astounding improvements, variations and restorations for the Acoustat MK and Spectra Interfaces and even more so the Trans-Nova amplifiers (TNT-200 and TNT-120) and Trans-Nova Preamplifier (TNP). I also renew the earlier and more rare, Acoustat MRP and RP-2 preamps.

    To my chagrin ---- Folks don't realize I was many years younger than the other principals at Acoustat, back in 70's and 80's Fort Lauderdale. About half their age at that time. I am happy to continue lovingly working with Acoustat products. I do this with a fully functional laboratory and stockroom of original .........and improvement parts.

    But please realize that... in 2011.... this is part-time work.... in addition to my regular full-time engineering/consulting work. So it can take a few weeks in total, for me to work my Acoustat "magic"...... as my client's have often described the results.

    I hope the above will help explain why I don't provide a phone number, except to established clients, and I prefer email contact instead. I also prefer my work and "word-of-mouth" to speak for itself ....instead of having and spending time maintaining a website. There are others that offer work on Acoustat products. Fancy words .... Fancy websites. But NONE of them worked for the Company. And to correct the mess....Folks usually end up with me despite the glowing website tetimonials. That's just sad.

    I very much appreciate all of you, who continue to revere and enjoy the magnificent design works of Dr. Strickland, and our original Acoustat Engineering Team.

    May we all enjoy the Music

    Roy A. Esposito /

    sparky.d (2012-01-23 19:29:34)

    low sound coming out of speakers how much amps do i need going into speakers. thay are -mik -121-2a.i think thats the problem.but not sure.just got them. my church gave them to me.hooked them up to my sons sure theres not much amps coming out of i need more. thanks sparky.d

    Lisa vergara (2013-06-04 21:19:33)

    I recently bought a set of mk 121 c David hafler acoustat speakers in a storage auction..what's the value on them? They are tall about 7 or 8 feet tall and maybe 20 inches or so wide..ill go measure them in a minute..please help..

    AcoustatAnswerMan (2013-07-05 21:17:07)


    Based on the measurements you gave, what you have is probably a Model 2+2. Their value will depend on the condition, of course. I have seen plenty of auctions on eBay where the 2+2's go for anywhere between $500 to $1500 per pair. Much will depend on finding a local buyer, as shipping such a large speaker is difficult (or at least prohibitively expensive). The fact that the interfaces (black boxes) are marked MK-121C indicates that these are the 'latest and greatest' version of the interface, thereby increasing their potential value.

    Roy A. Esposito (2013-09-06 12:11:19)

    Hello Friends --

    This is just to let you know that my email contact
    has recently changed. It seems AT&T/Yahoo could no
    longer support my very old email address.
    For those of you requiring fantastic restorations
    and upgrading of Acoustat MK and Spectra Interfaces
    and Acoustat Power Amplifiers and Preamplifiers
    my new email address is

    (please notice the dots/periods between the words)

    Email is the preferred method for initial contact with me
    for Acoustat Service and questions.

    Thank you for your continued friendship, kind comments and reviews,
    and support of my work.

    All the Best,
    Roy A. Esposito

    CineDave (2014-10-30 05:52:59)

    Hey Andy
    Having some difficulty with a recently purchased set of model 3/MK121 Acoustats.
    One of the interfaces produces distorted lower end frequencies when pushed to moderate
    volume levels. At late night levels its barely noticeable, if at all. I

    I've performed the requisite interface swap as well as triple checking the fuses.
    Any idea as to the soure of the distortion and a possible remedy?

    AcoustatAnswerMan (2014-10-30 14:39:48)

    When you swapped interfaces, did the problem move with the interface?

    If so, my first suspicion would be a problem with the low frequency audio transformer. When these transformers go bad, it is usually a issue with the insulation breaking down at high voltage. That's why the speaker sounds okay at low levels. As you increase the volume, the voltage reaches a level where it starts to arc-over, causing distortion.

    This transformer cannot be repaired: it must be replaced. It will only get worse over time, and there is a possibility it could ultimately cause damage to your amplifier. If you want to make sure of this diagnosis, you could try swapping the LF transformers between interfaces, and see if the problem follows the transformer.

    For repairs contact Roy Esposito as mentioned in a previous post in this thread. Good Luck and write again if I can be of further assistance.

  • Amplifier in hibernation - Pang-Hsin Wang on 2004-02-25 22:14:30

    Dear Sir, I have a pair of the Acoustat X system with servo drive amps. Now one channel goes to hibernation state with the HV still on, while the other one goes to hibernation will shut off the HV. I tried to measure the brown wires to see whether there is AC 110 to the HV\'s primary, as soon as probes were on, the amp kick started as if there is audio signal on the input. Please let me know as to which of the state is by the original design. If I wish to have the HV on during hibernation, which relay switch that I need to make it into a manual switch? Respectfully yours, Pang-Hsin Wang

  • Request info - Hector G. Pesquera on 2004-04-26 07:32:47

    First of all, a big \"thank you\" to all of you for maintaining this forum and the wealth of information on Acoustat. They are incredible speakers. There is a gentleman that is selling a Model 1, MK-141-B Medallion interfaced set, but I have some reservations and questions to the group here: 1. The interaces had been rewired extensively by the previous owner for some reason, the wires leading to the panels (up to the very edge of the front and back were spliced, some with masking tape). The gentleman said that he would repair this, and when I asked him if he had the 10,000-volt-rated wire, he said he did, but that this was a misnomer b/c it was really 5,000 volts going each way, so the \"potential\" was 10Kv. He insists that his wiring is adequate and that he will cover the splices with heat-shrink tubes. Is heat-shrink tubing rated in the same manner, how would one know? 2. There appear to be two sets of fuses on the medallion interface, two on the inside of the metal backplane, which has two fuses exposed on their bracket, and one that faces outside the interface in a single cylindrical enclosure. The latter one has been disconnected/bypassed. My understanding from Andy\'s previous postings was that this is *not* a good practice, as it exposes the transformer unecessarily and replacement transformers are *very* hard to come by--I\'m going to guess harder even for the MK-141-B? There is also a clear insulator on a naked wire that comes out of the larger transformer (which looks like it has two cores? They are three overlapping shapes which I can show depict as \"[[][]]\" where brackets 1+3 and 4+6 represent the two windings overlapping in the chassis formed by brackets 2+5) and goes to the back of the unit which has deteriorated and parts of that wire are exposed. This looks like bad news, and not only does the wire look delicate, but it doesn\'t look like it can be unattached from either end to slip on another insulator of the same type (high-voltage?). In addition, the gentleman has said that a capacitor was missing, which he put in, which appears to bridge the two input terminals on the inside, if memory serves. Comments? 3. The wires that are supposed to go to the \"full bandwidth\" output for the sub module on both interfaces are not there. Would it be detrimental to run a powered subwoofer with these speakers by running things backwards (i.e., using line-level stereo output from the amplifier to the subwoofer, having it go through its crossover and *then* to the Acoustat left and right speaker)? I did not see this mentioned on other postings as a possibility... 4. Price: the asking price is $500.00, and the two references that I have checked on the internet list $275.00 and $450.00 as selling price (not wholesale); the way the item is listed appears to include the subwoofer, which the one for sale is missing, otherwise *sounds* fine and both speakers are in excellent cosmetic condition, both panels and socks are immaculate. Although this gentlemen is very adept with electronics, I would like to get a second opinion from the group on these issues. Thank you kindly for any input that you may contribute.

    Andy Szabo (2004-05-11 21:13:31)

    The easiest answer to all of your questions is that $500 is too much for only a remnant of the original speaker. Unless you have the technical expertise, or want to pay someone who does, I would say virtually any price would be too much for the speaker you describe. The panels themselves are probably fine, except that it sounds like the panel wires have been tampered with. There are enough used Acoustat panels available that you shouldn’t have to deal with that. Suitable high-voltage wire is available, and ordinary heat shrink tubing is ok if the splices are physically staggered. (Which might be difficult if the original wires were cut too close to the panel.) The interface has been modified, and without seeing it and testing it, I can offer no comment on whether it works, and if not, if it can be reasonably repaired. At the very least, I would recommend that the audio fuse be reinstated. Factory-original replacement audio transformers have recently appeared on the market. Yes, you could use a powered subwoofer with the Model One’s. In fact, it’s a good idea. Most of the foam surrounds on the original woofers have rotted, and so far I haven’t seen a good source for a replacement. Also, the woofer was the weakest performer of the 3-piece set, so you are likely to gain a better system. I’ve been watching Acoustat sales on e-Bay, and $500 is probably as high as you’d want to go for a pair of Model One’s that are in factory-original, immaculate condition. That may or may not include a properly functioning woofer, for the above-mentioned reason. Be prepared to mate them with a suitable amplifier – they are the least efficient of the Acoustats, and need lots of power to make them sing.

  • Fuses - Joan Pau on 2004-06-14 14:36:36

    I\'m a little surprised reading the fuses recommended here for the 2200\'s (5A, slow blow). I think that 2200 (without subwoofer) yet go beyond their capabilities furnished only with 2A T fuses (without blowing them !!!). This overdrive is noticeably heard specially on recordings having hard bass sections. So, why do you recommend 5A SLOW !!! fuses ?

    Andy Szabo (2004-06-19 17:27:40)

    Acoustat originally specified a 3-amp slow-blow fuse for its speakers. I don’t know for sure, but I suspect that Acoustat received customer complaints about “nuisance” fuse blowing, so the value was increased to a 5-amp slow-blow. This all occurred before I joined Acoustat, so I can only speculate on the history of this decision. A 5-amp slow-blow fuse offers only minimal protection for the speaker. Such a large fuse allows the use of very large amplifiers (up to 250-watts), without blowing the fuse on normal musical signals. A 5-amp fuse will blow only under the catastrophic condition of a failed amplifier or a shorted speaker. There is still no guarantee that one failed component won’t damage the other before the fuse blows. Keep in mind that the purpose of the fuse is to protect the interface electronics: i.e. the audio transformers and associated components. The Acoustat electrostatic panel cannot be overdriven, so there is no need to worry about protecting the panels themselves. The overdrive distortion you hear on very large bass notes probably indicates that the panel is reaching its excursion limit, but this should not be interpreted as a condition that will harm the panels. My personal recommendation is to use as small a value as possible that allows your loudest listening conditions without “nuisance” blowing of the fuse. Never use a value greater than 5-amps slow-blow. Values less than 2 or 3-amps will probably be too small for the amplifiers typically used with these speakers. I would recommend using a slow-blow type fuse: a fast-blow fuse will likely fail under normal musical conditions.

  • Woofers - Brian Wallen on 2005-05-19 19:28:33

    I can\'t seem to find any information on the SPW-1 woofer model that was added to the Spectra series. I\'ve never seen one in the flesh, but seem to remember that these had about 6-inch drivers.

    I have one Xerox copy of a brochure about the Spectras with the following information:

    \"Present day source material will tax the most capable of speakers, regardless of driving principle. Spectra 22 and particularly the 33 will handle all or most of the source material you care to listen to--as a full range electrostat. However, an electrostat\'s high intimacy of drive can occassionally lead to ionization of the air between its elements, on heavy, deep bass material, resulting in audible popping noices. The addition of Spectra Passive Woofer 1 (below 100 Hz) extends both panel performance and total system dynamics by 8db or more!

    Most important of all, listening reveals the SPW-1 to be the perfect Spectra companion....\"

    First, I assume that the drivers, or at least one of the drivers in the SPW-1 were electronically active, not just drones. Was the SPW-1 just a box with two drivers? Any crossover components, or are those built into the Spectra panels? Did this unit extend the range of the combination, in addition to increasing dynamic range?

    Andy Szabo has said in other places that the woofers for use with Acoustats should be low efficiency models. Does the use of small diameter drivers in the SPW-1 suggest that small cones will be quicker and come closer to matching the quickness of the electrostatic panels? What can we learn from looking at the SPW-1 design that may be helpful in constructing passive woofer units to use in place of the scarce SPW-1?

    I have a pair of KEF B-139 drivers--the oval ones with the flat diaphram--mounted in an approximately 70 litre sealed box. These are part of a KEF Constructor Series system that also includes a 110mm mid range and a dome tweeter. I built these so that the B-139s had their own dedicated box. KEF rates the characteristic sensitity level of these at 87dB spl at 1m on reference axis for pink noise input of 1W. I biamp these with an electronic crossover with a 100Hz crossover point, so there are no passive crossover components connected to the B-139s, although I used the standard KEF crossover for the MF/HF unit. Would the B-139s make suitable \"passive\" woofers for Spectra 22s?

    Andy Szabo (2005-09-11 19:33:00)

    The SPW-1 is a passive, vented system, consisting of four 6” drivers with high-level crossovers contained in the woofer box. It is a “stereo” woofer in that each channel drives a separate crossover and two of the side-firing woofers. Should there be any stereo information below 100 Hz, this arrangement will tend to preserve the image better than a single “mono-sum” woofer.

    The woofer output on the Spectra series interface is a full-range output: essentially just a pass-through from the input. This allows the use of a variety of woofer systems.

    Yes, the SPW-1 does extend the low frequency response somewhat, but it still does not provide extension to the lowest of notes, as is possible with more expensive systems.

    I can’t advise on the suitability of your KEF drivers in the described enclosure. Certainly, the use of an active electronic crossover has the potential for steeper crossover slopes and better matching between high-pass and low-pass curves. Active crossovers usually have level controls as well, so the relative efficiency of the woofer system becomes a moot point.

    The idea of “quickness” of small woofers vs. large is not really an issue below 100 Hz. However, due to the potential of better coupling between the voice coil and the smaller cone, small woofers can have lower distortion, if used well within their excursion limits. With so many other variables in woofer quality and system design, other factors may be more important. Larger woofers typically have a lower resonant point, and are therefore capable of better low frequency extension without electronic equalization.

    I have a Spectra 1100, which is a hybrid system consisting of a single electrostatic panel coupled with an 8” woofer. It has quite credible low frequency response, but is naturally limited in dynamic output due to the 8” woofer. I have added a woofer system made by Dayton Loudspeakers, available from Parts Express ( This is an active system, with a very robust 10” woofer, active crossover, and 250-watt amplifier. It is by no means a perfect system, but it is a very good value at only $350 in kit form. The kit was so easy to build I was disappointed it didn’t take longer – what can I say, I like building things! The Dayton system has been a positive addition to my system for about 2-1/2 years now, and has increased my enjoyment of music and video. They also make similar systems with 12” and 15” woofers.

    Like any woofer system without a computer-based room-equalization system (such as the Velodyne), it took quite a while to ‘dial-in’ the room placement, phase, crossover point, and relative level. To roll-off the main Spectra speakers, I inserted a capacitor in series with the main amplifier (working against the input impedance of the amp), to roll-off at 6 dB per octave.

  • ID model speakers - Eric Wadley on 2005-12-10 10:51:21

    I\'ve been considering buying another pair of Acoustats, I already own a pair of Spectra 22\'s that I love. I saw a pair recently locally advertised by someone who knew very little about then, and could only tell me they were Acoustats with the Mk-131 interface, and their dimensions are roughly 6 feet tall by 28 inches wide. Can anyone tell me which model this might be? Thanks.

    Andy Szabo (2005-12-10 11:02:25)

    Based on the width of the speaker (28”), it is a three panel system. Since it uses the MK-131 interface, it is a woofer-assisted model. Therefore, I would say the speaker in question is the Model 3-MH. The Model 3-MH uses three Acoustat ESL panels per speaker, and includes a 10-inch woofer mounted in an enclosure at the base of each speaker. The MK-131 is a limited frequency range transformer interface, and can be used only with models having a woofer system. Therefore, the woofer cannot be disconnected and the ESL operated full range.

  • Boards almost complete - Michael Grolle on 2006-01-21 14:45:09

    I used to work for Acoustat just before they were shut down. This weekend I was cleaning my garage and found about 10ea almost complete circuit boards from the Spectra 11 - 1100 speakers. They are missing the IC. I\'m guessing there is still a market for these and would hope someone could help me find an avenue to make them available to anyone who needs them. I can be reached at I have posted them on eBay and have four left at $60 + S/H. They are still missing the IC but have been calibrated. Thanks, Michael Grolle

  • Imaging and punch - Marc on 2006-02-01 21:02:42

    Hi - I own a pair of Acoustat Spectra speakers and I have some questions with regards to imaging and punch. What would be the best way to have more punch and increase or perfect the imaging of these speakers - shall I get two 10 inch active subwoofers and connect each subwoofer to one speaker????? I run an Audire Forte amplifier with them - is it enough power and high current Thx

  • A pair of back pegboards - HORACIO E CARVALHO on 2006-02-09 06:57:19

    I know its a long shot,but does anyone have a pair of back pegboards for the acoustat X?

    Thank you

    Andy Szabo (2006-03-24 22:26:03)

    I doubt anyone has the pegboard pieces pre-cut to the correct size for the Model X. They have, after all, been out of production for nearly thirty years. However, pegboard is a commonly available material (at least here in North America) and should be available in most home-improvement stores or lumber yards (usually in a four by eight foot sheet). If you are not up to the task of cutting them to size, any woodshop or home woodworker should be able to do it. Good luck! -Andy

  • Left/Right panel ID - Tom Burt on 2006-02-11 08:30:06

    I recently purchased a pair of Spectra 1100\'s, and according to the owners manual, the panels are dedicated left and right ( mirror image). My problem is that there are no longer any labels identifying which one is which. Is there any other way to tell ( physically etc) which is the left and which is the right? Sincerely, Tom Burt

    Andrew Holtum (2006-02-15 20:11:38)

    I know that the reason for the specific L and R speaker designation on my Spectra 4400s is because they are actually a two way system. If I remember correctly (I\'m not writing this from home, can\'t verify), the inner 2 panels were wired to the interfaces as full-range and the outer 2 bass only. If you carefully listen to a program source with lots of high frequency content at a low level (put your ear close to the inner and then the outer sides of a speaker), you should be able to tell which side is doing bass only vs full-range (bass + treble). I believe the speakers are to be placed such that the full-range panels are on the inside. Of course you could try either positioning and see which sounds better.

    Andy Szabo (2006-03-24 22:50:52)

    Mr Holtum\'s response is not entirely correct in how the panels are segmented (it\'s a bit more complicated than he indicates). Also, his method for determining left and right is correct, but only for the full-range Spectra models. For the Spectra 11 and 1100, the high frequencies should seem to be coming from the right side of the right speaker, and from the left side of the left speaker (when viewed from the front). By the way, only the panels themselves are right or left: the black-box interfaces and the woofer boxes are identical and interchangeable. You\'ll know you have it correct when you get a nice stable, concise sound stage. Operating them left/right backwards can yield some positively weird results.

  • Need electornics. Updated - Andy Szabo on 2006-04-28 21:10:43

    What you need is 2 pairs (four total) of the MK-121-6/8. This is a special version of the \'regular\' MK-121 used on the smaller models. What makes it special is a different low frequency transformer, which has a lower step-up ratio to compensate for considerable panel area of the Model Six or Model Eight. Then there is the issue of which chassis style you need. Early units used the \'2A\' style of chassis, which is rectangular in shape. Later versions used the \'B\' style of chassis, which is a cube shape. You can tell which one you need by looking at the mounting arrangment on the back of the speaker. In any case, finding the interfaces you need will not be easy. Not many of the Model Six or Model Eight were produced, so the chances of finding two pairs of interfaces (without the panels) are pretty slim. Good Luck, and write again if you have any further questions.

    stephen (2010-07-02 10:15:17)

    Need the electornics for model 6s that have newest modifications. Only have the speaker panels, but no electronics to run them on back of speakers. Used 2 sets per side. Advise.

  • Model 6\'s and Model 6600 - Jim Caton on 2004-02-23 22:21:42

    Andy, What can you tell me about the following speakers: Acoustat Electrostics, Model 6\'s & Model 6600\'s

    Andy Szabo (2004-02-23 22:21:42)

    Both the Model 6 and the 6600 use six electrostatic panels per speaker.

    The Model 6 was produced for many years, evolving through the various MK-121 interface variations. You might find a Model 6 built with the MK-121-2A, MK-121-B, or MK-121-C interfaces. Any of these may have been later upgraded to the Medallion Transformers.

    Each Model 6 speaker uses two interfaces, and therefore optimally requires a total of four amplifier channels to properly drive two speakers. This can get expensive. Paralleling each pair of interfaces is possible (at least as a temporary measure) but the impedance will be low: about 3 ohms. Many amplifiers won\'t like that.

    The Model 6 requires a large space for best performance: a room with dimensions of at least twenty feet or larger. Listening distance should be at least twelve to fifteen feet. Like all Acoustat models of its era, the Model 6 offered a rather narrow listening ”window”. On either side of that narrow area, high frequency response and imaging quality falls off rapidly.

    The Model 6600 is a Spectra Model, and is identical to the Spectra 66, except for improved cosmetics on the 6600. ”Spectra” stands for Symmetric Pair Electrically Curved Transducer. I won\'t go into the technical details of how this is accomplished, but compared to the Model 6, the result is far superior imaging, and a much wider listening ”window”.

    The Spectra 66/6600 also has the advantage of using only one interface per speaker, meaning that only two channels of amplification are required for a pair of speakers. The 66/6600 still requires a large room, but perhaps can be used in a room slightly smaller than the Model 6. This is due to its controlled imaging pattern.

    If you are considering the purchase of either of these models, you can\'t go wrong. Both are great speakers, with excellent bass response and high sound pressure levels. But the Spectra\'s do sound better in several aspects, and are much easier on the amplifier budget.

  • grill socks - adam on 2004-04-12 03:18:01

    does anyone know where to get new grill socks for acoustat speakers? i am pretty sure i have the model 6 but not certain. thanks

    Hans Zeeuwe (2004-04-21 19:44:56)

    Please check out the \'Available Parts\' section on the \'General information concerning Acoustat models\' page in the \'Models\' section. there you will find an address of the original supplier of the grille cloth.

  • Modifying 2+2\'s into 6\'s - Craig Schultz on 2005-12-10 04:13:09

    Hi - I have a pair of Acoustat 2+2\'s I bought new in the 80\'s, they have MK-121B interfaces. I have purchased 4 panels, and two additional MK-121B (with red medallion transformers) and they are coming. I want to build the correct frames for the model 6 in preparation for the panels so I have less down time. I have a few questions: 1. Does anyone have the dimensions of the MDF frames required for the panel mounting on the model 6 speakers? 2. Are the panels mounted flat or are they sligthly radial mounted like the 2+2 frames? I see posts here where folks have redone the 2+2 frames from original to make them flat vs convex. 3. I sent an email to the folks in Phoenix for the grille cloth. 4. How are the two interfaces connected to the 6 panels in the 3X3 interface to uppers and one to lowers? 5. Assuming I can\'t get my original interfaces converted to Medallion transformers, should the new ones with Medallions be connected to certain panels? Sorry for all the questions.........but I figured this was the place to ask!! Craig Schultz

    Craig Schultz (2005-12-10 04:28:32)

    I found Andy\'s post elsewhere in the transformer taps and colors in the 2+2 vs 6 and 8 models. It sounds like maybe by using two MK-121\'s I need to use the minimum bass boost settings or I may have too heavy a bass response......any help is appreciated to assit me in this conversion and wiring approach

    Andy Szabo (2006-03-29 21:54:08)

    The panels in an Acoustat Model 6 are mounted in a convex curve, just like the 2+2. However, if memory serves correctly, the angle is somewhat less, such that the depth of the arc is the same for both models. I can\'t recommend modifying these speakers into a flat configuration - that would tend to make them very beamy. Pre-Spectra Acoustats have a narrow enough \'sweet spot\' as it is! The original Model 6\'s were arranged as \'three up\' and \'three down\'. That is, each interface drives either the upper three panels, or the lower three panels. However, since you have mis-matched interfaces (one Medallion and one not) I might suggest a different arrangement so that you do not have a speaker with different characteristics top-to-bottom. You might try using the Medallion interface to drive the center column of two panels, with the non-Medallion interface driving the outer two columns of two panels each (four panels total). This puts the better interface in the center where it matters the most, and would eliminate and differences top-to-bottom. This arrangement might even provide a little more flexibility in setting the bass taps (since they no longer would have to be set the same). Have fun - sounds like a great project!

  • Request electronics - stephen Buchbinder on 2006-05-04 06:01:11

    The entire electronics for my model 6\'s acoustats were stolen. I need 4 electronic units to power them, like 4 pairs of 3\'s OR, if I could get 2 pairs of electronics to run them.

  • Modifying 2+2\'s into 6\'s - bear on 2006-09-05 01:08:12

    Keep in mind that there are *two* sizes (widths) of panels out there! My memory says 8\" and 9\". I think on the Model 4s the two center panels were smaller width and the two outer wider - on the Model 3 the center was smaller width and the outer larger... iirc. Anyhow, anyone rebuilding or building up a new frame for the Acoustats ought to consider a geometry and mounting scheme that will provide significantly greater stiffness and support to the frame. This can result in substantially improved sounding highs. A quick and easy approach is to make the base much larger (not just the interface box and the panels) and provide a non-resonant means of tranfering energy from the top and/or sides of the frame to the new and more stable base! The operative word is \"struts\". Ascii representation---> L\\ (albiet poor). Don\'t forget to upgrade those coupling caps in the interface to polypropylenes!! :-) _-_-bear

  • Model 6\'s and Model 6600 - Andre Sevigny ( MrAcoust on 2008-06-23 19:50:06

    These model 6 where modified by a guy named Jocelyn from Quebec Canada the frame is all steel covered with mahogany wood and they weigh 600 pounds each this fellow also made my 1+1s exacly the same but with a wood frame ( i live in a condo ) we have been Acoustat fans for over 25 years Dollar for Dollar nothing and i mean nothing even comes close to Acoustats and yes we are very very strong beleivers in Acoustats MrAcoustat

  • Answer to request - angelo on 2006-06-27 16:43:30

    dear Michael, I have just read your answer, and I am still looking for Transnova twin 200. I don\'t see your email. Do you live in Europe ? how much euro is your request ? This is my address: Raspante Angelo via Sac. A. Sammarco, 31 90011 Bagheria (PA) Italy. Telephon number 091-6562564 office (39)338.1882356 cell thank you Angelo

  • Electrostat? where to buy - harry trattner on 2006-07-10 03:44:55

    I loved the sound of the old speakers ,that I would listen to at Northridge audio ,in in 1980.The only speaker that comes close is the Magnapan.Are these speakers that are produced in China electrostat?and if so are we able to buy them in the states?and if so were can I buy them I am ready !!!

    MrAcoustat (2011-07-02 00:40:36)

    you sometimes find some on Audiogon

  • Interface modification - Rick Pettey on 2006-06-28 15:53:11

    Does anyone know of a modification to the Acoustat interfaces that improve their imaging to match the earlier series? I have a pair of model 33 with the \"newer\" interfaces. Their imaging does not match the earlier series (prior to the company being sold and moving to Arizona).

    Andy Szabo (2006-07-12 09:54:57)

    There is no practical way to convert a Spectra speaker into an ‘old-style’ model. The interfaces are fundamentally different, and the Spectra series accomplishes its dispersion pattern via electrical means, whereas the older models use a less precise mechanical means. Quite frankly, I do not know why you would want to do this. In my opinion (and everyone else I’ve ever talked to) the Spectra series offers a much more precise and stable stereo image that the previous models. In fact, the improved imaging is really the whole reason for the Spectra series being developed. It does occur to me that you might have your left and right speakers swapped. If that is the case, you will experience poor imaging at the least: sometimes the effects can be quite weird. And just for the record, the Spectra series was started in Florida, when the company was still a division of the David Hafler Co. The Spectra 2, 3, 22 and 33 were all developed in Florida. The Spectra 11, 1100, 44, 66, and SPW-1 Woofer were introduced from Arizona under Rockford Corp., as were the models 2200, 3300, etc., with improved cosmetics.

  • Subwoofer Replacement/Bi-Amping - Loren on 2006-02-17 16:33:29

    Good Morning Everyone, First, let me say that this site has been extremely informative, and that I have found some wonderful information here, great work! On to the questions... I have a pair of the 1+1S\'s. I recently lost my subwoofer due to foam rot. I replaced the driver with a Pioneer DVC. It had the best response numbers, lowest power requirements, and highest efficiency of the models that were available. After replacing the sub I noticed that the bottom end was a lot tighter, and the overall bass was better, however, I don\'t think the sub is getting enough power to fully push it. I am running a Marantz preamp (AV9000) and Marantz amp (MM9000). Both are THX Ultra rated, and I believe the amp is listed at 150 watts at 8 ohms. I have a second amp, a Carver M-500T that I wanted to use to drive the sub. I tried running the sub from the subwoofer output on the preamp, then through the Carver, but it barely put out any sound at all. I assume this is because of the frequency cutoff on the crossover. Does anyone have a suggestion on how to wire these up, without large scale modifications to the speakers? If I was to purchase an active crossover and biamp them that way, would that work? Is biamping them a waste of time? My other question is in regards to replacing the sub entirely. The original sub was passive, and its nearly impossible to find passive subs for home use anymore, if anyone has a suggestion, I\'d love to hear it. So, that being said, would you recommend buying a powered sub, with a built in adjustable crossover, and just set it to pick up where the panels drop off? I look forward to hearing some opinions, thanks!

    Andy Szabo (2006-07-15 12:20:38)

    Your set-up didn’t work because you used the subwoofer output on your preamp. More than likely, this output is low frequencies only, which then gets fed through the another crossover in the woofer, greatly diminishing its output. To make this set-up work, use the regular full range outputs of the preamp, both left and right, to feed the second amplifier (you may need to use Y-adaptors if your preamp doesn’t have dual outputs). Then feed the output of the second amplifier, both left and right, to the inputs on the woofer. You may have a level matching problem unless the second amplifier has level controls. I wouldn’t bother spending any money (for an active crossover, etc.) for use with the original woofer system. You’d get better performance by substituting the entire woofer system with a good-quality, self-powered woofer with a built-in crossover. You can use the dedicated subwoofer output from your preamp (in which case the woofer’s internal crossover would probably be bypassed), or you can use the full-range outputs from the preamp and use the woofer’s internal crossover. It all depends on the particular woofer you chose, and which set-up offers the best flexibility of control over frequency, phase, and level to match the woofer to the main speakers. Once you get the parameters dialed-in (and it may take a while!) you will certainly have a better system than the original. There are many woofer systems on the market, from about $400 to $5000 and above. You will pretty much get what you pay for, so it all depends on what you want to spend. If you are interested in a fairly economical solution, look at the woofer systems from Parts Express ( They have 10”, 12”, and 15” models. I am using their 10” system with my Spectra 4400, and I’m quite happy with it. This woofer may not be in quite the ‘same league’ as the 4400’s, but I’m using it only below 40 Hz (running the main speakers full range), and its addition to the system is definitely a positive change. Since you will likely be crossing-over at a higher frequency, the woofer’s relative contribution to the system’s sound will be greater.

  • Seperating woofer/panel - Marcel Teeuwen on 2006-05-06 01:43:03

    I want to split my woofer and panel of my Spectra 1100\'s which are connected by five color coded wires. I need to lengthen these by about 4 mtr. What type of wire should I use to do this: -shielded vs nonshielded? -diameter of core (in mm2) -maximum length I can lengthen? Regards Marcel Teeuwen Holland

    Andy Szabo (2006-07-15 12:23:03)

    Choosing a suitable wire is not all that critical. It should be high-voltage wire, with a rating of at least 10,000 volts (10 kV). Wire gauge can be very small: the original panel wires are only 24 gauge (AWG). Wire insulation type is not critical: the original wires are PVC, but other types are okay. Shielded wire is not necessary and not recommended. Wire like this is available from better electronics distributors (Newark, Allied, etc.), or possibly from your local TV repair shop. All connections should be soldered, with heat-shrink tubing protecting the splices. For maximum protection, keep a physical distance between the three groups of wires: red, white, and blue. Running the wires inside split-loom or PVC tubing is a good idea for both mechanical and electrical protection. Do keep in mind that the woofer in the 1100 operates up to about 150-200 Hz. Therefore, placing the woofers significantly away from the panels will likely introduce irregularities in the stereo imaging and frequency response. This is not the same situation as a separate subwoofer system, which may be operating only up to 80 Hz. In that case, room placement, and the effect on imaging, is not so significant. Strictly from an electrical aspect, I wouldn’t recommend a wire length of more than about 1 or 2 meters.

  • Distortion in panels - Rick Pettey on 2006-08-04 00:12:21

    I recently replaced my interconnects along with speaker cables. To expedite the break-in process I employed a cd for such a purpose. I noticed that in the midrange a very noticeable distortion. In previous listening sessions I had detected distortion in such cuts as Almost Blue by Kendra Shank on her Afterglow cd (Mapleshade). I had written it off to miking. Now I have to wonder. I have encounted popping from panels on other speakers before (from glue breaking off) and easily resolved it. But I have not experienced this previously. Any suggestions? What is confusing is that it occurs in both speakers. This makes me question whether it might be a panel issue or a problem in the interfaces.

    Andy Szabo (2006-08-04 00:13:13)

    I rather doubt your problem is in the ESL panels themselves. I am not aware of any failure mechanisms that would cause midrange-only distortion. On the other hand, there isn’t much that can go wrong in the interfaces that would affect midrange only, especially both speakers at once. Most electrical problems in the interface tend to cause problems in the bass only, treble only, or all frequencies equally. Does this problem occur at all volume levels, or only at high volumes? If it occurs only at high volumes, you may be clipping your amplifier, or there could be arcing in the audio step-up transformers (arcing is pretty rare in the Spectra models). My first suggestion would be to try another amplifier. If that doesn’t improve the situation, take a look inside the interfaces, and search for any obviously loose or overheated parts. (Don’t be alarmed by the black soot-like dust that may be found on the high voltage components – this is normal after a few years of operation.) If there are no visible problems, you may need to send the interfaces (only) for repair to Sounds Like New. If you can provide me with more information (volume levels, amplifier being used, etc) I might be able to provide more advice.

  • Where do hi's come from - patrick spiker on 2006-08-06 17:36:57

    have a pair need to know which side the hi\'s are to come from in room loaction. ? I.E. are the hi\'s to come from the outside of ther panel or from the insides??? thanks patrick

    Andy Szabo (2006-08-09 21:10:00)

    As with all of the full-range Spectra models (2, 22, 2200, 3, 33, 3300, 44, 4400, 66 and 6600) the high frequencies should seem to be radiating from near the inner edge of the panels, when the speakers are properly set-up left and right. For the Spectra 33, the sectors for the right speaker are as follows, from left to right as viewed from the front of the speaker. Note that one sector equals one-half of each ESL panel. Therefore, three panels in the Spectra 33 equals six sectors: 1 sector mids and lows only. 1 sector full-range (this is where the highs come from). 1 sector mids and lows only. 3 sectors low frequencies only. The left speaker is the mirror image of this pattern. A diagram of this arrangement (applicable to all Spectra models) can be viewed under my Technical Bulletin “Spectra Sectoring and Color Codes” on this website. The speakers were originally marked ‘left’ and ‘right’, by a variety of means: labels that say ‘left’ and ‘right’, located on the interface mounting brackets, and/or green (for left) and red (for right) labels, and/or a small hole in the top metal plate over the full-range sector. Unfortunately, these labels have a tendency to fall off, and if the grille cloth was ever changed, the top metal plate may have gotten reversed in position. So it’s a good thing you asked! Having the speakers left-right backwards can yield some pretty weird stereo imaging!

  • Buzzing - Paul Worrell on 2006-09-11 00:36:23

    My right channel 6600 has developed a buzz in the upper right side. It buzzes on low bass, no other problems, no apparent change in level. Doesn\'t sound like arcing. Any ideas what it could be??

    Andy Szabo (2006-09-30 16:07:19)

    The buzzing you describe is not an uncommon problem, and can usually be easily solved. There are two major causes of buzzing. One is that some component of the speaker itself has come loose, and is vibrating on certain bass notes. The other is that some sort of foreign material has become trapped in the area around the diaphragm. I would suggest you start by unplugging the speaker, and letting it de-energize for several hours. This will remove the electrostatic field that might be holding a foreign object in place. Then, with an open hand, bang on the front and rear surface of the speaker around the offending area. This may be enough to dislodge the object. Be patient, this process may take a few tries before it works. If that procedure doesn’t work, you will need to remove the grille sock. This is not a pleasant task, especially on the Spectra XX00 series that has the wood trim and brass inlay. See my discussion of this process under “Rehabilitation of a Spectra 4400” located in the 4400 section. The good news is that you will probably need to detach the cloth only at the top of the speaker, and you will be able to re-use the original cloth (or this might be a good opportunity to replace the cloth if it needs it). Once you gain access to the inside, first make sure that the mounting screws for the panel are tight. If one or more is loose, then the nylon bushing under the screw head can rattle. Also check all the cable clamps for tightness. Then thoroughly vacuum both front and rear sides of the panels (with the speaker de-energized). You may find a small plastic bit that has come loose from the panel. This is not normally a problem for the performance of the panel, but can cause extraneous noises if it gets caught in the ESL gap. If you have the grille cloth down, and you have eliminated the rattle, leave the cloth detached for a while to make sure the problem does not reappear. Sometimes the offending particle becomes dislodged, only to get caught in another spot later. Good luck, and congratulations on your ownership of what is arguably Acoustat’s finest loudspeaker. Andy

  • ES speakers - Mike Smeed on 2006-09-18 01:19:04

    I recently acquired a pair of Acoustat model X speakers with servo amps. They appear to have been sitting unused for quite some time. One of the amps definitely has damage. I can see burnt marks where one of the resistors was and underneath the circuit board. This one I plan on repairing. The other amp does not show any signs of failure, but I have not applied power to it yet. I would like to check and see if the panels are good and if it is worth repairing the amp. My plan is to use the amp that appears good to check the panels. I am somewhat familiar with tube amps and have an electronic background. Since I have no experience with ES speakers I have a few questions: 1. Can the ES panels be tested before power is applied? 2. Is there a life expectancy on the panel…how long are the panels expected to last? 3. Is the thin wiring to the panel susceptible to shorts? 4. How do you connect to the servo amps? Are they connected to a basic pre-amp out put through the RCA jack? 5. Any precautions before plugging these in?

    Andy Szabo (2006-11-03 14:19:12)

    1. Unless you have some sort of transformer interface/bias supply or servocharge amp to provide the stepped-up audio and high-voltage bias, there is no way to test the ESL panels. 2. Acoustat panels will last a very long time. Many of the original panels are still working after 30 some years, so true life expectancy is unknown. If the panels have been kept reasonably clean, and suffered no physical damage, they should still work fine. (Note this is almost certainly NOT true for other brands of ESL\'s when they get that old.) 3. The \'thin\' wire has special high voltage insulation rated at 10,000 volts. The gauge of the wire is very small due to the very low currents involved. 4. The servocharge amp has an RCA input jack that is intended to be connected directly to the output of the preamp. 5. Precautions before plugging them in? Yes, lots of them. If they have been sitting idle for some time, they likely require service. The arcing on the board is a common problem on these units due to the high voltages involved (5000 volt B+). Contact Mike Savuto for service and parts - he does work that both rejuvenates and improves the reliability of the circuit. (See contact info elsewhere on this site.)

  • Servo charge amp - Pang-Hsin Wang on 2006-10-26 00:18:52

    Could one remove the output capacitor (0.1 MFD 5000 volts) and make it direct coupled? Because the ESL\'s 3 panels are totally insulated. I may get half of the drive or it could work with music AC riding on 2600 volt DC bias? Would someone knows both AC and DC condition of the servo amp running \"OCL\" output capacitor less. Or I could have a 10 Meg 5 watt resistor to replace the output capacitor??? I am looking forward to hearing from the experts. Thanks,

    Andy Szabo (2006-11-03 14:32:42)

    DO NOT remove the output coupling capacitor in the servocharge amp! You must remember that the speaker operates on electrostatic forces, and applying a DC potential to the stators would seriously effect its operation. Furthermore, you would likely get current flow through the capacitance of the panel that could even cause damage to either the panels or (more likely) the amplifier. It is true that some people have replaced the original output capacitor with a better grade of part, but a capacitor must remain in the circuit.

  • Output one speaker - Eby Movahed on 2006-11-10 20:33:30

    Acoustat3, by Eby Movahed (November 9, 2006): Hi, I Owen a pair of Acoustat3 I had them restored by Sounds like new while back and they did an incredible job,and they worked fine since, but recently one speaker sounds much lower in volume than the other one , the fuses are all OK,and I have checked all conecting cables and everything else that I could think of on my owen ,does any one have any idea of what might be wrong, or know if Sound like new is still in business the phone# I have is out of service,any help is greatly appreciated. thanks

    Andy Szabo (2006-11-30 22:35:38)

    You can contact Sounds Like New, Roy A. Esposito at He will be able to help you. Before you contact Roy, have you tried swapping the amplifier channels, to verify that the problem is actually in the speaker? If you swap left and right amplifier channels, and the problem moves to the other speaker, then you will know the problem is not in the speakers. If you determine that the \'low volume\' problem is in the speaker, then you most likely have a problem in the bias supply circuit. Roy can certainly help with that relatively minor repair.

  • Speakers - Alyssa Siegel on 2006-09-23 16:10:36

    My father was a serious audiofile and I have had his Acoustat X speakers sitting in my living room untouched since around 1990. Time to re-arrange furniture and I need to decide whether to sell them or let my engineer husband delay looking at them another decade :-) . Without doing too much research (and my audio knowledge is limited), I remember that my father had driven out to Pennsylvania to someone who built some special kind of tube-Amp for them. Last I heard, one worked fine, one needed some sort of potentially simple repair. (Hence my husband\'s intent to check them out). Can anyone give me some idea as to the approximate value of this system were I to sell them? Thanks much, Alyssa.

    Andy Szabo (2006-11-03 17:13:54)

    Acoustat loudspeakers do retain their value quite well, even for units as old as the Model X. The main determining factor in this model\'s value is 1) their cosmetic condition, and (more importantly) 2) the condition of the servocharge amplifiers. I\'m not sure who in Pennsylvania might have worked on the amplifiers. Only a few individuals have the specialized knowledge and correct parts to properly repair this unusual amplifier. Alas, there have been a few individuals who have done repairs & modifications that were ill-advised (despite their assertions that they knew what they were doing!). I suggest you contact Mike Savuto (contact info elsewhere on this site) for repairs to the amplifiers. I suggest you have him check them out and repair as needed. Even if one of them was working okay when last used many years ago, it should still be checked, as high-voltage parts can age and fail just sitting there. For a properly working pair in reasonable cosmetic condition, you might fetch around $500, upwards to $1000. All of this depends on finding the right lunatic (smile) in the right place at the right time. The Model X enjoys a bit of a cult following. I monitor the Acoustat auctions on eBay, and see Model X\'s for sale a couple of times per year, so there is a market for them.

    Alyssa Siegel (2006-11-05 21:10:00)

    Thank you for the reply. I think I was mistaken, however. I checked the images on the \"Electrostatic Speakers\" page and my speakers match the image of \"Direct-Drive Vacuum-Tube Amplifier (Servocharge) Monitor 4\". Not Acoustat X as I previously thought. Same advice? Thanks.

    Andy Szabo (2006-12-08 13:51:55)

    Yes, my response is pretty much the same. Since the Model X has 3 electrostatic panels per speaker, and the Monitor 4 has four panels, it is actually a more desireable product. That might increase the selling price a bit. Both models use the same servocharge amplifier.

  • Biamp? - Robert on 2006-12-05 00:30:36

    Greetings folks, Does anybody know if the 33\'s can be configured/modified to be biamped.... Regards

    Andy Szabo (2006-12-11 22:31:36)

    Unlike the earlier MK-121 Series transformer interfaces, the Spectra MK-2123 interface does not have separate high and low frequency transformers (which, conceiveably, lends itself to bi-amping). The MK-2123 does have two audio transformers, but they are identical and are used to drive each phase of the push-pull system. All of the frequency-selective portions of the Spectra interface occur on the secondary, high voltage side of the transformers. So, there is nothing to split for the purposes of bi-amping and/or bi-wiring on the input side.

  • Amp fuse - Vince Cascone on 2007-01-19 02:20:22

    I have a pair of model ones that i love. Just the other day, one of them blew a fuse in my xl600 hafler. Traced it down to what appears to be a coil or choke in the subwoofer that was burnt. It is connected to the postive terminal in the subwoofer. It was letting midrange into the woofer and blowing my amp fuse. Is this part available. It has numers on it but no manufacturer infor.. Your input would greatly be appreciated. Thank you Vince

    Andy Szabo (2007-01-20 17:16:37)

    Let me say first that I doubt the fuse blew due to a failure of the crossover coil. Rather, due to very large amounts of power being applied, the coil got hot enough to burn, and then the fuse eventually blew. The fuses in the speaker should never be more than 5-amp slow-blow. At that value, very little protection if afforded, and personally, I recommend a lower value. If the coil is just a bit scorched, it may be still okay. If it is seriously burnt, then replacement is in order. For very early production Model One\'s, with only a coil and capacitor in the crossover, I do not have a record of that coil\'s value. If your crossover has a coil, two capacitors, and a resistor (per side), then you have a much improved crossover used in all but the earliest Model One\'s. That coil\'s value is 4.5mH and 4.3 ohms (air core). Most of the available ready-made crossover coils will have a much lower resistance value than that, but the difference can be compensated by adding the appropriate resistor in series with the coil. Try as a good source for crossover parts. If you have the early crossover, this would be a good time to update. The improved crossover has a 5-ohm, 25-watt resistor and two 220uF non-polar electrolytic capacitors in parallel with the voice coil. Then in series with that network and the audio input is the aforementioned coil. A schematic is shown in later versions of the Model 1/1+1/2+2/3 Owners Manual. (Available as a CD from our webmaster.) Of course, the crossover described above must be built twice, one for each half of the dual voice coil woofer.

  • Tuning and dimensions - Dave Stowers on 2007-01-17 18:35:59

    There seems to be current activity in the ESL portion of the Acoustat area, so sorry for the repost. I have obtained the crossovers, input panel, and drivers for an Acoustat SPW-1 system. I would like to construct a cabinet for this hardware, preserving the original design (volume, tuning), but have only a small ad photo from an old Speaker Builder issue to base the style on (oak top/bottom panels, sock around a very approx 26in wide x 22in high x 20in. deep cabinet with a single ~4\" port (no depth specified). I\'ve measured the drivers using WT2 and they all are fairly consistent parameter-wise, so I believe they are functioning as intended. Can provide T/S parameters if there\'s interest. Is there someone who can either provide or point me to less approximate information regarding SPW-1 tuning and dimensions? ... my dang Stereophile-pile has a gap that starts with Vol12, issue 10 (includes an SPW-1 review) :P Planning to use this with 1+1S system that came with no sub unit. Thanks and regards.

    Andy Szabo (2007-01-20 17:34:51)

    The external overall dimensions for the SPW-1 are 23\" wide, 17\" deep, and 18-1/4\" high. Since the wooden top and bottom plates hang over the edge a bit, I would subtract about 2\" from each dimension to yield the external size of the actual woofer box, that is 21\" W x 15\" D x 16\" H. The box was probably constructed from 3/4\" or 1\" material, so you can figure the internal volume from that. I have no dimensions for the port tube, but if you have measured the Thiele-Small parameters of the woofers, and know the box volume, a suitable port can be calculated. I am quite sure the system was tuned for maximally flat response, rather than having a \"bump\" to give initially impressive (but false) bass response. But this is your chance to make it whatever way you want. Yes, please do post the Thiele-Small Parameters of the drivers. Somebody is bound to want to know someday. Ask the webmaster to post under the \"SPW-1\". Was the SPW-1 reviewed by Stereophile? I don\'t remember any reviews - if it was, I sure wish I had a copy.

  • Woofer and tweaks - Andrzej Kruszewski on 2007-01-19 14:30:46

    Woofer crossover, building of 2 woofers for Model One, by Andrzej Kruszewski, Jan. 19, 2007. I just discovered the forum (great info. source), so I have few questions for Andy Szabo, or someone else with the knowledge of original design of One\'s woofer and tweaks. 1.) As a result of uncontrolled use of my system by my New Year\'s Eve Party guests, I discovered : audio fuse blown in one of the MK -141C , woofer dual-voice coils damaged and possible damage to Air core inductors (chokes?). When testing it, by direct connection of amp. outputs to the woofer, one chanel did not play at all, and other made scratchy noises. I examined interfaces carefully (but have no knowledge or tools to test it properly), and they look O.K. - no visible wire or component damage, no discoloration, and panels seem to play O.K. (but they are 20 or so years old). I have had coils of the woofer repaired by pro-technician. When testing woofer after repair, it started to play in full range. It looks as the crossovers are damaged. From the schematic of MK-141-C, I read (from left to right) crossover parts: L1 4.5 mH/4.3 ohm ; C5 330uF; R6 -10ohm/25w. Strangely, inside the woofer enclosure I have found two (one for each chanel)- what looks like -transformers w/o core, it must be Air Core Inductor (L1 4.5 mH / 4.3ohm) ???... Each of them is marked with numbers LA 002 and 2009128, and no other elements of crossover (C5 ,R6)... Am I missing some parts in my woofer cabinet???... I bought the One\'s \'second hand\" and don\'t know what woofer looked like originally inside. I would like to replace crossover with the original parts, or do you recommend upgrade to some different (newer and better)parts?... Where can I buy them???. I live in Poland, and shipping the woofer to Florida may be an overkill, so if i can get components, I can rebuild crossovers here. If I can not find suitable inductors, technician can rebuild them for me here in Poland, but he needs pertinent values: mH, ohm, wire or foil type and gauge. Please let me know what should be installed inside woofer cabinet - crossover parts ( is my info from the schematic correct???...). Where can I buy the parts?... and what parts (possibly upgrade?). In the future I am considering building of two separate woofers. As Andy Szabo explained, it may improve stereo imaging. If yes, what crossovers should I use (values and types). I have two 8\" woofer drivers that I got some time ago from Rockford. They were sent to me by mistake, as a replacement to my 10\" driver for One\'s woofer. They are \"new in the box\" and never used, so in the future I would like to build cabinets and put them to use. What size (in liters) do you recommend???... Another idea, is to build them in to lower section of the One,s frame and put the enclosure behind it.... ???. On the page for Acoustat 1, there are some pictures (2 and 3) and it looks as a good idea. Question to the person contributing this two pictures: are this Model One adapted to include woofer, or is it another model of Acoustat ?... Once again on crossovers - should I consider buying \"ready made\" crossovers, if yes what kind : a.) for 10\" single woofer - \"Parts Express\" has two types 4-ohm and 8-ohm, each 200 watt RMS, designed for dual voice coil subwoofer and 12dB per octave slope ( no other specs).b.) for two 8\" woofers with single coils - no info. or idea on brand or specs. Thanks for any help I can get out there, and please excuse my text book english. Kind regards, Andrzej Kruszewski.

    Andy Szabo (2007-01-20 18:08:59)

    It does sound like your woofer voice coil is damaged. Since high-quality, 10-inch, dual-voice coil woofers are hard to find, now may be a good time to build two cabinets, each with one conventional single-voice coil woofer. The difference you see between your woofer and the schematic may mean that your woofer is a very early production unit (or parts may have been removed). All but the earliest Model One\'s had an improved crossover as shown in your schematic. However, all schematics I have show the capacitance as two-220uF in parallel, with a 5-ohm resistor (coil value is the same). Perhaps both values were used in production at different times - that was a long time ago for me to remember those details. If I had to guess, I would say the double-220uF and 5-ohms was the final value. If you want to build another cabinet identical to the original, using a 10-inch woofer, then you can probably use the crossover as shown in the schematic. If you want to use the 8-inch woofers you already have, you could make woofer boxes for them, or create a hybrid system like the Spectra 11 or 1100, or the custom-modified units shown. This will be a bit more of a challenge, as you will need to experiment with crossover values, etc. The crossover shown in the Spectra 1100 Owner\'s Manual would be a good starting point. (the manual CD is available from our webmaster.) I would not recommend using a ready-made crossover. There are too many variables involved, not would I recommend 12 dB/octave for both slopes. All hybrid systems that Acoustat built used a 6 dB/octave on the ESL, and 12dB/octave for the woofer. Note that this requires the woofer to be wired out-of-phase. \'Parts Express\' is a good source for individual crossover components. Good luck with your project, and do write again if you have more questions (and your English is just fine!)

  • Output one speaker - Eby Movahed on 2006-11-09 00:44:52

    Hi, I Owen a pair of model 3`s I had them restored by Sounds like new while back and they did an incredible job,and they worked fine since, but recently one speaker sounds much lower in volume than the other one , the fuses are all OK ,does any one have any idea of what might be wrong, or know if Sound like new is still in business the phone# I have is out of service,any help is greatly appreciated. thanks

    Andy Szabo (2007-01-20 22:12:38)

    This email address is listed for Roy Esposito at Sounds Like New. This information comes from the Acoustat loudspeaker section of

    Roy A. Esposito (2011-07-17 20:08:08)

    July 17, 2011

    I am very much alive.

    I am No-Where near retiring .... and over many years have
    come up with astounding improvements, variations and restorations
    for the Acoustat MK and Spectra Interfaces
    and even more so the Trans-Nova amplifiers (TNT-200 and TNT-120)
    and Trans-Nova Preamplifier (TNP).
    I also renew the earlier and more rare, Acoustat MRP and RP-2 preamps.

    To my chagrin ----
    Folks don't realize I was many years younger than the
    other principals at Acoustat, back in 70's and 80's Fort Lauderdale.
    About half their age at that time.

    I am happy to continue lovingly working with Acoustat products.
    I do this with a fully functional laboratory and stockroom
    of original .........and improvement parts.

    But please realize that... in 2011....
    this is part-time work.... in addition
    to my regular full-time engineering/consulting work.

    So it can take a few weeks in total, for me to work my
    Acoustat "magic"...... as my client's have often
    described the results.

    I hope the above will help explain why I don't
    provide a phone number, except to established clients,
    and I prefer email contact instead. I also prefer my work
    and "word-of-mouth" to speak for itself
    ....instead of having and spending time maintaining a website.

    There are others that offer work on Acoustat products.
    Fancy words .... Fancy websites.
    But NONE of them worked for the Company.
    And to correct the mess.....
    Folks usually end up with me despite the glowing website tetimonials.
    That's just sad.

    I very much appreciate all of you, who continue to revere...
    and enjoy...
    the magnificent design works of Dr. Strickland,
    and our original Acoustat Engineering Team.

    May we all enjoy the Music,

    Roy A. Esposito /

  • Trans-Nova Twin-200 - Darryl Chagi on 2006-10-22 04:56:13

    I am looking for a transistor for my TNT 200. Toshiba is no longer making the 2SK146, the one I need. Does anyone have a few they could sell, or let me know where I could buy some. Or know of another FET that could takes its place. Thanks. Darryl

    Andy Szabo (2007-01-20 22:18:12)

    Try contacting Roy Esposito at \'Sounds Like New\' at SLN does good Acoustat repairs. Roy may have the parts you need, or may be able to suggest an available substitute.

    bob rolle (2011-06-23 20:10:19)

    Acoustat model 1 +1 and Trans nova twin 200 amp for sale with monster speaker cables. Will not ship. MA resident.

    Roy A. Esposito (2011-07-17 19:59:37)

    July 17, 2011

    I am very much alive.

    I am No-Where near retiring .... and over many years have
    come up with astounding improvements, variations and restorations
    for the Acoustat MK and Spectra Interfaces
    and even more so the Trans-Nova amplifiers (TNT-200 and TNT-120)
    and Trans-Nova Preamplifier (TNP).
    I also renew the earlier and more rare, Acoustat MRP and RP-2 preamps.

    To my chagrin ----
    Folks don't realize I was many years younger than the
    other principals at Acoustat, back in 70's and 80's Fort Lauderdale.
    About half their age at that time.

    I am happy to continue lovingly working with Acoustat products.
    I do this with a fully functional laboratory and stockroom
    of original .........and improvement parts.

    But please realize that... in 2011....
    this is part-time work.... in addition
    to my regular full-time engineering/consulting work.

    So it can take a few weeks in total, for me to work my
    Acoustat "magic"...... as my client's have often
    described the results.

    I hope the above will help explain why I don't
    provide a phone number, except to established clients,
    and I prefer email contact instead. I also prefer my work
    and "word-of-mouth" to speak for itself
    ....instead of having and spending time maintaining a website.

    There are others that offer work on Acoustat products.
    Fancy words .... Fancy websites.
    But NONE of them worked for the Company.
    And to correct the mess.....
    Folks usually end up with me despite the glowing website tetimonials.
    That's just sad.

    I very much appreciate all of you, who continue to revere...
    and enjoy...
    the magnificent design works of Dr. Strickland,
    and our original Acoustat Engineering Team.

    May we all enjoy the Music,

    Roy A. Esposito /

    Alfredo M. Claussen (2011-08-22 21:57:45)

    Since I live in Mexico City, I've only listened to Acoustat electrostatics twice: in a Showroom in Houston TX in 1982 and at a local dealer here in Mexico. I perfectly remember the truly amazing character of the soung from those old Acoustats: the most accurate and clear bass drum of all! My neighbor and me assembled and built many dynamic multiway speakers back in 1972 to 1985, and because he was an accomplished drummer, I was acustomed to the REAL sound of a drum set. I've never heard another speaker that reproduces the exact color and tonality, attack and the "membranaceous" quality of the bass drum like the Acoustats; even when the acoustats could never reach the true volume and intensity of the real bass drum of a recorded drum set. But anyway it was by far, the closest sound to the real one. amclaussen, Mexico City.

    P.D.: Mr. Esposito; could you please tell us what was the relationship of Acoustat with Mr. David Hafler, please?

    Andy Szabo, Acoustat Answer Man (2011-08-22 23:52:32)

    In regards to David Hafler's relationship with Acoustat: Acoustat suffered a bankruptcy in '84, and the company was subsequently purchased by the David Hafler Co of Pennsauken New Jersey. I was transferred from Hafler to Ft Lauderdale Florida to run the operation, with Jim Strickland continuing as Chief Engineer. In 87-88, Rockford Corp purchased both Hafler and Acoustat divisions, and eventually moved both to Tempe Arizona. Despite Rockford's good investments in both brands, Acoustat was sold to an Italian distributor in '91, then to China, but I'm not sure about the status of the trademark now. Hafler Home electronics were discontinued not long after Acoustat's sale,(along with my job!) and the seemingly successful line of Hafler Pro electronics followed a few years later. I believe the trademark is no longer in use. Please note the dates are approximate, subject to my fuzzy memory!

    Despite being out of production for 20+ years, Acoustat electrostatic elements have shown very few signs of degradation, and with a little attention to aging electronic components, the speaker systems continue to deliver their original performance. Check the used market - it's not too late for you to relive that experience from 1982! I'm still listening to my Acoustats and have no plans to change as long as I can keep them working (and you can bet I have a cache of spare parts!)

    Alfredo M. Claussen (2011-08-23 16:21:15)

    During my university years (Chemical Engineering), I paid part of my expenses by assembling, building and installing audio equipment, both home high quality and a few professional ones, like a couple of "Discotheques" and Auditoriums. Free trade then was non existent, and the import rules were outrageosly restrictive, so I had to use some components made in Mexico in my speaker design and in some cases (rich clients), I imported professional units from JBL and built the cabinets and crossovers in Mexico, better built ones BTW (hand selected caps and carefully measured inductances). At that time I worked for a couple of years for a Brazilian company called "Gradiente" that made good quality amplifiers with circuits adapted from JVC and some original ones. After some years, I discovered the DYNACO brand and started to import their Solid State and a few Tube amps, all in kit form (to be able to import them as "electronic components" instead of "HiFi components". Later on, the first Hafler DH-101 Preamp and DH-200 Mosfet amplifier appeared, and I rushed into assembling many of them to provide my customers with truly clear and powerful audio. After a couple of years I started modifying those designs slightly (to replace some cheap parts), still using my designs on speakers, now with Philips soft dome tweeters and midranges, and from time to time MB and Peerless, Seas and Vifa too. Then "The Audio Amateur" and Speaker "Builder" magazines brought many more mods and my sets were very well received, but I never went above the "artisan, hand-made level". With the advent of the personal computer, interest in Audio (High quality) almost vanished, and it stopped to be a business at all. I still have my Hafler DH-101 Preamp and XL-280 Amplifier much modified and sounding perfectly, after all these years (1979 the Preamp, 1989 the Power amp). We all owe the late David Hafler for his magnificent philosophy about honest, no frills, inexpensive but elegant designs; absolutely no non-sense approach. By the way, the slightly modified mosfet XL-280 can easily drive the Acoustats almost as well as the later Trans-Nova (TNT) designs. I remember a memorable session at the Hafler dealer in Mexico City in 1990, when we rigged the famous Hafler null-test, and made a well calibrated XL-280 sound even cleaner than a much over hyped amp which price was more than NINE times the modest cost of the Hafler, and the ultra expensive one was more prone to ultrasonic oscillation and cable sensitive!... the owner of the ultra expensive amp sold it and we sold him a triple set of Haflers in a Tri-Amped system that sounded much cleaner than his set. I only wish we could still find the Hitachi Mosfets to continue using them in the old Haflers.

    Andy Szabo (2011-08-23 18:38:52)

    I see the Hitachi MOSFETS occassionally on eBay, both in the original TO-3 metal cases and the later plastic flat-packs. Set-up an eBay email notification for "Hitachi MOSFET" and you might find some!

    Roy A. Esposito (2013-09-06 12:32:27)

    Hello Friends --

    This is just to let you know that my email contact
    has recently changed. It seems AT&T/Yahoo could no
    longer support my very old email address.
    For those of you requiring fantastic restorations
    and upgrading of Acoustat MK and Spectra Interfaces
    and Acoustat Power Amplifiers and Preamplifiers
    my new email address is

    (please notice the dots/periods between the words)

    Email is the preferred method for initial contact with me
    for Acoustat Service and questions.

    Thank you for your continued friendship, kind comments and reviews,
    and support of my work.

    All the Best,
    Roy A. Esposito

    Vince Maida (2014-01-20 15:40:39)

    There are a couple of potential reasons for the blown output FETS:
    1. Since the amplifier does not use a source resistor in series with the output FETS to circuit ground it is essential when replacing the FETS that you match the VGS of the FETS to within about 20 millivolts or less. The reason is, for devices in parallel, with unbalanced VGS, the device with the lowest VGS will be delivering the most current. In the extreme case you can have a condition where it is delivering almost all of the current to the load and eventually fail. The best way to do the matching is to purchase 2X as many FETS as you will need from the same date code (manufacturing lot)since the VGS spread in the same manufacturing lot will track quite closely or failing that add about 0.27 ohms in series with the source to ground for all of the FETS. I am currently trying the SEMELAB BUZ900 (N channel) and BUZ905 (P channel)FETS which I have been able to match VGS to within better than 10 millivolts at 700 ma. They are available in the US from MOUSER Electronics for $10.57 ea in 10 QTY and Farnell in Europe.
    I will post the results for these devices shortly.

    2. Amplifier instability i.e. High frequency oscillations. Mosfets have a tendency when connected in parallel to oscillate at RF frequencies. This can occur when the amplifier is driving some types of reactive loads.
    The fix is usually to add a lossy element (resistor) in series with the gate as was done in the TNT-200. The resistor fix does not always work by itself and the addition of a 47 pf silver mica capacitor from gate to drain for the P channel FETs and 22pf across the N channel FETS becomes necessary to avoid the mysterious oscillations/failures. Adding High permeability ferrite beads to the gate resistor leads will also help to discourage the oscillations.

    Vince Maida (2014-01-21 12:27:44)

    Mysterious Output Mosfet Failures
    There is another failure mode that I forgot to mention. When handing any MOS device always discharge your human body voltage to ground before handling them. The gate breakdown voltage of a Mosfet is on the order of 16-30 volts and electrostatic discharges can be in the thousands of volts which can cause an immediate failure of the Mosfet or a degradation of the gate insulation which will eventually result in a failure. When you buy the Mosfets make sure you receive them in ESD safe packaging and not in a standard plastic bag or else the damage will have already been done. Although the gates have significant capacitance on the order of 1000-2000 pf this still may not save them from ESD damage, so always use caution when handling the devices.

    Amclaussen (2014-01-23 02:02:30)

    You are absolutely right, Vince. Obviously, all the other cautions apply, like grounding oneself, using a static safe soldering iron, working on a static dissipative surface, avoiding synthetic fiber carpeting etc. Fortunately, my old "David Hafler XL-280" amplifier kit with the Hitachi Mosfets output stage arrived with the output trnasistors already connected ans therefore, there was much less risk; but a person handling the Mosfets by hand, your consideratiosn are a must.

    Roy A. Esposito (2014-04-08 12:52:45)

    I remain available for Restorations / Upgrades /Improvements
    of the Acoustat MK Series Interfaces with the optional "Air Mod"
    that I developed in 2008. Vast improvements of the Spectra Series Interfaces,
    the Trans-Nova Series of Power Amplifiers for which I offer the incredible
    switchable Monoblock and Balanced Input circuit Conversions
    and restoration of the three models of Acoustat Preamplifiers.
    I welcome your inquiries at
    (please notice the dots between the words)

  • New cloths for speakers - Michael on 2007-01-22 19:45:57

    Where can I get the new cloths socks for the speakers.

    Andy Szabo (2007-01-25 04:11:39)

    Original specification Grille Cloth Socks are still available from Acoustat\'s vendor. See the information posted under \"Refurbishment\" for contact info. I\'ve used their services myself - highly recommended.

  • MK141-C - Eric on 2007-02-18 20:40:47

    One of my speakers has started to crackle and not produce much sound. I have a subwoofer attached separately. It seems as though it started slowly and became worse. Now, hardly any sound emits, and the crackel is the louder of the two. Any suggestions on how to trouble shoot this?

    Andy Szabo (2007-02-24 15:31:20)

    Your problem is almost certianly in the transformer interface, and the not the ESL panels. If the volume has slowly decreased over time, I would suspect a problem in the high-voltage bias circuit. Working on this can be tricky unless you have the skills and equipment. If you do, parts are generally obtainable. Most likely one or more of the capacitors and/or diodes has failed in the voltage-multiplier. If you find no problems in the bias circuit, then you have a bad audio transformer. High-voltage breakdown in the transformer will cause a crackling noise, and it will get worse over time, but usually any changes in volume will be abrupt, not gradual. Finally, and least likely, one of the panel-connecting wires is pinched or damaged somewhere, and it has gradually broken down over time. If your troubleshooting skills are not up to it, I suggest you contact Sounds Like New (see under Refurbishing section).

  • Interface problem - Sylvo Schroeder on 2007-03-28 13:12:30

    Dear sir , i am a proud owner of a 1 plus 1 speakers. A short time ago (after 18 years )the one speaker called it a day. I took it to my trusted high end workshop to get it repaired - after connecting it again it seemed to work for a very short time - but then the same problem was there again . It is obviously a interface problem as the sound is audable if i put my ears to the speakers . I am here in india . Hope to hear from you soon . Regards , Sylvo

    Andy Szabo (2007-03-30 03:29:19)

    Do you have any idea of what your repair shop did in the way of repairs? If the sound stops suddenly, it is likely a problem with the +5000 volt bias supply, or something in the audio circuit with a loose connection. Check the external audio fuseholder - sometimes they suffer corrosion and don\'t make good contact. Also check the internal fuse clips for a tight grip on the fuse - these are for the bias circuit.

  • Popping noise - nathanso on 2007-01-11 21:38:45

    One of my Acoustat Model 2\'s makes a popping noise -- like a raindrop falling on a taught tarpaulin -- after it\'s been powered on for more than 8 or so hours. This happens with or without a music signal being sent to it, and pops about 1-3 times per minute. If I power them off for a night the popping stops, but it always returns after being powered on for a while. Per advice on this Web site I\'ve dropped the socks and thoroughly vacuumed and blew compressed air on both sides of the panels but it made no difference. Anyone have another idea on how to fix this problem?

    Andy Szabo (2007-01-20 13:17:54)

    Sorry to hear that the standard procedure for fixing a popping noise has not worked for you (yet). Have you tried this procedure several times? Sometimes the offending particle can be quite stubborn to remove - a hair or similar contaminent can get wrapped around one of the stator wires. Also, did you make sure the panel was throughly discharged before the procedure? I am not aware of any other solutions, other than removing the panels from the frame and washing them. This is obviously a major operation, and is not to be tried except as an act of final desperation. Even still, there is no guarantee that it will solve the problem any better than the other method. Your best course of action is to continue with the vacuuming and compressed air. There isn\'t much that can go wrong with an Acoustat panel, and it probably 95% certain that your problem is caused by some contaminent caught between stator and diaphragm.

    Nigel Addison (2007-04-02 04:34:36)

    it could be that the eht bias voltage on the diaphragm is too high, but if you have one such device for both panels, then both speakers will pop. Good luck.

  • Power amp parts needed - Bob Keller on 2007-03-30 20:33:30

    I\'m in need of two of the diodes used in the voltage doubler. They are labeled VG10. Does anyone have a clue as to what I can put in there place.

    Michael Savuto (2007-04-06 19:44:36)

    Alyssa, If you are still looking for this part, email me at I can provide you will the parts you need. Mike Savuto Analogue Associates, LLC

  • Amp repair - Bob Keller on 2007-03-30 20:27:45

    I\'m in need of two of the diodes used in the voltage doubler. They are labeled VG10. Does anyone have a clue as to what I can put in there place.

    Bob (2007-04-05 04:44:28)

    Are you sure the problem is with the diodes? On the schematic the diodes are marked as \"S3217\". It seems that any rectifier diode rated at least 3kV will do.

  • Selling working MK-121-C speakers - Jean Cimino on 2007-05-04 07:32:39

    I recently inherited a working pair of acoustat mk-121-c loudspeakers from a relative's estate. They are way too much speaker for me and would like to sell them to someone who would enjoy the The speakers work and sound great without any tracible distortion, etc. The frame paint has alot of chips, knicks, etc.a new paint job could take care of that. Add two new grill cloths/frames and you have yourself some really great speakers. They would also make a good 'refurbish' project or used for parts too. Here's the info.... Acoustat mk-121-c electrostatic loudspeakers-i think they are 1+1's, but not sure.powered by an Acoustat 'David Hefler' medallion transformer located at the base of the speaker. Height: 94" Width: 12" Depth: 3.5" Frame: steel painted with gray/black speckled paint. They both work and sound great despite missing the grill cloths. I live in Olympia, WA and don't have the means to ship or deliver them so the buyer would have to come pick them up. I have photos and would be happy to send them to you , etc. I'm stereo-challenged, so any input, suggestions on selling them would be greatly appreciated. I also would like to know how much did they cost new and how much should i sell them for in today's market. Thank you very much and I've learned a lot through this site. Great job, great site! Jean Cimino

    Andy Szabo (2007-05-06 23:31:39)

    From the dimensions given, I would say these are Acoustat Mopdel 1+1\'s. However, in describing the frame as \'painted steel\' it sounds as though the original frame has been replaced. The original frame was unpainted wood (medium density fiberboard or MDF, to be exact), covered in grille cloth. If these have been modified, it makes it harder to estimate their value. Some people may shy away from such customization, but if done neatly, it shouldn\'t really detract much from their resale value. eBay is a good place to sell Acoustats - at least several pairs appear each month, with many of them selling. Since they are difficult to ship, most sellers specify \'local pick-up only\'. I might suggest you start the bidding around $100 to intially attract buyers, but keep a reserve price at around $500 to make sure you get at least a fair price. For the right buyer, they could go as high as $1000. Good Luck with your sale!

    Jean Cimino (2007-05-09 16:25:58)

    I was wrong when stating that the speaker frames were steel. I checked them again and they are made of wood, which appears to have been repainted-underneath this paint there is a black finish. The base is made of heavy steel plate. What would be the fair market value be if I were to sell them? Also, what would be the fair market value be for the transformers if sold seperately (parted out)? Thank you, Jean Cimino

    Andy Szabo (2007-05-12 15:08:36)

    I\'ll stick with my original estimate of $500 -$1000 selling price. It all depends on finding the right motivated buyer in your area, at the right time. What doesn\'t meet your reserve this month may become a bidding war next month. Being a somewhat esoteric product, the buyers are few and far between, but I assure you they\'re out there. I would hate to see the panels and interfaces broken up as a set. Once broken up, the components become worth less than the whole system. But if that is the only way you can sell them, I would say only about 30% for either item, of the full set price. In other words, if the complete set is worth $1000, either the panels or interfaces are worth $300/pr.

    James Tiong (2007-05-30 17:45:08)

    Hi Jean, I\'m in the market for a pair of Acoustat MK-121C Medallion Transformer/interfaces. I like to know if it is still avaliable for I would like to purchase it from you. Thanks and hear from you soon. James Tiong

  • Driving with two ML-3's - RobertSabelis on 2007-07-13 00:41:08

    Is it possible with two bridged Levinson ML-3\'s (dual mono concept with big toroids and capacitance) two drive the Acoustat 2 + 2. I\'m still contemplating what would be the most efficient way to exploit a second amp into my system. Bridging the amps is technically possible but maybe even the load that a Acoustat presents at the high frequencies is to much for a bridged ML-3. Mono parallel configuration would be ideally but I do not now if that\'s wise/possible with this amp. Biamping could be the savest solution it leaves the amps as the are but there will be some hardware work on the interfaces and another speakerwire pair would be needed. Second, as for biampliifing, I measured and thought the most of the energy goes to the mid/high trafo while the impedence of the Acoustat goes down when the frequenz=cies risis. When I play Norah Jones with lots a bass and her voice I measure definitely the most current when she raises her voice. Should the fuse then not be situated at that region, I mean at the mid/high transformer connections? Thanks in advance

    Andy Szabo (2007-07-27 23:49:19)

    I\'m not a big fan of bridged-mono amplifiers, especially when driving a difficult load like an ESL. The problem is that each half of the bridged amp \'sees\' only half the load impedance. So, with the Acoustat, you may be loading each half of the bridged amp with as low as 1-ohm at certain frequencies. That said, the ML amps are probably better than most at tolerating low impedance loads. I\'d check with ML to see what they have to say. The circuit location of the audio fuse in the stock interface is sufficient to protect both audio transformers, as well as the amplifier. If you were to bi-amp, I would suggest a fuse be used in both high and low frequency circuits. When you say \"mono parallel configuration\", if you mean connecting two amplfier outputs in parallel across a single loudspeaker load, this is a very bad idea. This will present an effective short circuit on each amplifier, with resulting smoke and sparks (or at least fuse blowing). Don\'t even try this with somebody else\'s amplfier :).

    Robert Sabelis (2007-08-20 00:10:28)

    What I ment with mono-parallel configuration ia that the ML-3 stereo-amp will be setup as a no 20. or Threshold SA/1 or the older Stasis 1. So not inverting but paralleling the 40 outputtransistors together to get not more Voltage gain but increasing the currentcapability. The multichannel Jeff Rowland MC-6 can be converted by that way from a 6 to a stereo- or even monochannel amp. The safest option anyway would be the semi-biamplifing solution you mentioned before. I bought the speakers new in 1990 so I do have the original schematics supplied wit the Owner\'s manual which should help me out with the proposed option of biamplifying. Maybe there\'s a more detailed description possible from you i time to get it working. Thanks for your answer

  • Spectra Panels - Jim Lanier on 2007-08-21 08:28:19

    I have a question about the sectoring of the Spectra panels. What are the widths of the Spectra panels? Are they all the same size? It is my understanding that they are electrically sectored but not mechanically separated. Is this correct? (ie if the moving surface is 8\" wide the stators are electrically separated in the center(4\" from edge)..meaning that the high frequency drive from the full range side can mechanically propagate to the mid/low side of the diaphragm)

    Andy Szabo (2007-08-21 20:22:35)

    All of the panels used in Spectra models are Acoustat\'s standard 9-inch panel. They are electrically divided in half by making the wire stators in two sections (both front and back). Both electrical sections share a common diaphragm. I wouldn\'t worry too much about propogation from one section to the next. Electrostatic forces are very weak, and the effects of the stators on adjacent diaphragm areas will be negligible. I suppose there could be some mechanical propogation of the sound waves across the diaphragm, but it\'s not something that I\'m going to lose any sleep over. Nor should you.

    Jim Lanier (2007-08-21 23:07:40)

    Thanks for the answer. I was not debating the pitfalls. I just wanted to know if Acoustat built them that way. BTW, the mechanical propagation would be substantial, but this is not always bad. The speed of sound through the solid is much different than through air. I have been designing and building electrostats for about 30 years and some of mine have done just that. It is however a parameter to consider when modeling dispersion characteristics. The vector analysis is just a little more work :) Thanks again, Jim

  • With subwoofer - Teerawut on 2007-07-31 10:21:31

    I bought 1100 in 1990. It is still working good, but I would like to make it better. I plan to upgrade capacitor 100uF and 10 uF, new wiring for input ESL with new bidding post and seperate panel and its woofers. Then, I will use one active sub-woofer (300 W)cut-out at 100 Hz. The new active sub-woofer should give more deep bass around 25 Hz. Also, I will made base for ESL panel to lower height.. it should help for better sound image. Do anyone have any suggestion?

    Andy Szabo (2007-08-21 21:06:26)

    Adding a subwoofer to the Spectra 1100 is not a bad idea, but crossing over at 100 Hz is too low for the panels. I don\'t remember the exact panel crossover frequency, but it is closer to 150-175 Hz. If you cross over at 100 Hz, you will be losing some of the mid-bass information. If you raise the crossover to 150-175 Hz, and use a single subwoofer, then you may find the stereo image compromised at low frequencies. A better idea might be to retain the existing woofers, and cross over at 60-80 Hz for the subwoofer. I did a similar thing when I was using 1100\'s, with good results. Replacing the electrolytic capacitors with a better grade is always a good idea, presuming you can make them physically fit. Some film capacitors are huge when you get into the larger values. My suggestion to retain the existing woofers is in conflict with your desire to lower the panels. That will have to be your choice. The panel height was set to be optimum for a standard seated position, but if your seat is lower, you may have better results with lowered panels. I\'m not sure lowering the panels would improve the stereo imaging, but it could help with high frequency dispersion, since there is some fall-off in the vertical plane.

    Teerawut (2007-09-01 19:17:16)

    Thanks, Andy. I have just finished to upgrade capacitors. I still use existing woofers, but I found that my right panel had some problems. The sound on right was not bright and less volum than left panel. First, I thought that the problem should be on circuit. So, I changed the left circuit to right panel, but the problem was the same. I also tested my system with other speakers, and it was no problem. Do you have any suggestion how to slove this problem?

  • Voice distortion - Al.M on 2007-09-09 17:03:06

    Wondering how to fix slight voice or vocal track distortion in one of my speakers. Is this possibly an issue with the membrane or the interface circuitry? Thanks.

    Andy Szabo (2007-09-11 21:15:54)

    From your description, I will assume you have some sort of midrange resonance. This is a vague and hard-to-pinpoint problem, especially since it occurs at only specific frequencies. To quickly determine the location of the problem (panels or interface), try swapping the interfaces from one panel to the other. If the problem moves to the other panel, then the problem is in the interface. If the problem stays on the same panel, then the problem is in the panel. More than likely, you will find the problem is in the panel, caused by a bit of dirt caught in the gap on either side of the diaphragm. At certain frequencies, the offending particle vibrates and causes the resonance. You can try fully discharging the panel: often this will cause the particle to drop out of its offending position. Or, you may try vacuuming the panel in an attempt to remove it. Be patient - these problems are often hard to find, but I feel pretty confident that you do NOT have something fundamentally wrong with the speaker. Do write again if you have continued problems.

  • Amp plug in - Marc on 2007-09-13 05:25:27

    First: How did I plug these speakers to bi-amp them. (One amp per side or one amp for ESL and one for Woofer) Second: There is two connectors (+ -) on the left named ESL inputs; when I plug one channel of the amp there, with the switch at ``Single Amp``, the woofer works + the ESL. Is it OK ? If I plug it on the right, only the woofer works. If the switch is at ``Bi-Amp Bi-Wire`` each (ESL & Woofer) is independant, right ? Thanks Marc P

    Andy Szabo (2007-09-26 15:35:23)

    If your two amplifiers are not the same, you should use one to drive the ESL\'s, and the other to drive the woofers. If the amplifiers are identical, it hardly matters, and becomes more an issue of what is more convenient with the way you have your equipment physically arranged. When the switch is in the \'Single Amp\' position, the \'ESL Input\' powers both ESL and woofer. Incidently, since the switch\'s \'Single Amp\' position effectively connects the two inputs, connecting the amplifier to the \'Woofer Input\' will also power both ESL and woofer. When the switch is in the \'Bi-Amp/Bi-wire\' position, the \'ESL Input\' powers the ESL only, and the \'Woofer Input\' powers the woofer only. You should NEVER have two amplifier channels connected at once, when the switch is in the \'Single Amp\' position. As explained above, this will short the amplifiers together, possibly causing damage. A Spectra 1100 Owner\'s Manual is included on the Acoustat CD available from this site\'s webmaster. The wiring options are explained fully in the manual, with diagrams of several possible set-ups.

  • Upgrades for Interfaces - Darryl Peck on 2007-01-22 20:42:58

    Hello Acoustat Group I have contacted Mr. Roy A. Esposito about having my interfaces upgraded. He only answers to email, does not have a telephone or address. He accepts only items by appointment at a shipping only address, all prepaid. My question is: Is there anybody out there that can take our equipment and do business in a more professional and open manner? What if something were to happen to Mr. Esposito while he had your equipment? What recouse would you have in getting your equipment back in whatever condition it was in? There is no way to know where you equipment is,and since the company is out of business, it becomes harder to replace the equipment, and if not able to be replaced, it now renders your speakers useless. So, again does anybody else work on Acoustat Spectra interfaces? Thank you in advance Darryl Peck

    Andy Szabo (2007-01-25 04:29:18)

    I have heard nothing that would make me suspect Mr. Esposito of foul play, although he does seem to make himself difficult to deal with. I don\'t know what recourse you would have if something happened, and you had difficulty in getting your equipment back. That said, I note that you listed your question as \"Spectra 2200 Upgrades\". In my opinion there is nothing in the Spectra Series interface that needs upgrading. As the Spectra Series represents Acoustat\'s ultimate design achievement, it already includes all that was learned over the years, in the way of upgrades and improvements. So, if it\'s upgrades you\'re after, save your money and eliminate any worries you have about putting your interfaces in anyone else\'s hands. If your interface is broken and needs repairs, then I\'m afraid you have no choice but to use Mr. Esposito\'s services. I\'m not aware of anyone else who has the necessary repair parts unigue to Acoustat products. Fifteen years ago, had I had any inkling of Acoustat\'s enduring legacy and popularity so many years after production ceased, I might have tried to establish such a service myself. But now, I think it is too late start such an endeavor. So now, I just do my best to serve Acoustat customers by answering their questions.

    Michael Alazard (2007-03-22 04:21:27)

    I have had nothing but excellent service from Roy. He does top-notch work and is a dedicated specialist. I know that he is extremely busy and once in a while takes patient. I\'ve had him upgrade 2 sets of Acoustat Magnetic-kinetic interfaces. I cannot speak highly enough of his workmanship.

    Steve Ampokal (2007-07-21 20:08:49)

    3 years ago Roy Esposito repaired and updated a pair of Spectra 33 drive boxes for me. Two months ago I had my Acoustat TNT-200 amp restored by Roy. I could not be happier with the quality and service he provided for my components, he gave very good advice as well. I found him to be responsive by email, and also spoke to him by telephone while he was working on my interfaces (the guy even emailed me the tracking number when he shipped it back to me). Last year a friend of mine had his MK121 interfaces messed up by a stereo repair shop. Roy subsequently fixed those as well. Roy was highly reccommended to me and I would not hesitate to recommend him to others.

    Roy A. Esposito (2010-07-02 09:05:10)

    To Andy Szabo:

    Regarding your response to Mr. Darryl Peck\'s original question about his Acoustat Spectra 2200 speakers

    -----I heartily and respectfully disagree -----

    I quote your response to him here :

    \"\"\" That said, I note that you listed your question as \"Spectra 2200 Upgrades\". In my opinion there is nothing in the Spectra Series interface that needs upgrading. As the Spectra Series represents Acoustat\'s ultimate design achievement, it already includes all that was learned over the years, in the way of upgrades and improvements. So, if it\'s upgrades you\'re after, save your money and eliminate any worries you have about putting your interfaces in anyone else\'s hands.\"\"\"

    You are sadly mistaken about the MK2123 Rockford iterations being oh-so-perfect and not in need of corrections or service. The designed-in distortion is measurable. And curable. You have also been mistaken in the past praising Acoustat/Rockford\'s Ultrasonic Bias Supply, over the original Bias system used in many of the later interfaces. These are just a few examples of later day evolutions/builds of the original designs, that Dr\'s Strickland, Rieman ... and myself would never have approved of back in the early audio-purist days at Acoustat in Fort Lauderdale.

    There is too much selling and always has been, of snake-oil mods and cures in high-end audio. I stand behind only what I believe in. Improvements that one can actually hear and experience or that contribute to reliability.

    I hope you will accept my criticisms in the spirit of discussion and discourse. I have enjoyed our conversations and emails in the past, when you needed Acoustat historical data and technical advice to give out in your bulletins.

    I am always here to repair/restore/update and improve all Acoustat Interfaces, Amplifiers and preamplifiers for those who want the best possible performance from them, and then some.

    Despite the ridiculous and undeserved comments from Mr. Darryl Peck, a person who has never met me and has never experienced my services I am still here and plan to be for a very long time. I maintain a large stock of unique, original and obsolete/hard to find Acoustat parts.

    And if none of the other Acoustat \"experts\" on this forum want to speak up positively for me---then I will speak up for myself! I pride myself on my unfailing honesty and the 100% satisfaction of the Acoustat owners who have availed themselves of my meticulous workmanship over many years. I have piles of letters and emails that speak to the sonic improvements and integrity of my work.

    Roy A. Esposito /

    Roy A. Esposito (2010-07-02 09:05:10)

    I am very much alive. I am No-Where near retiring .... and over many years have come up with astounding improvements, variations and restorations for the Acoustat MK and Spectra Interfaces and even more so the Trans-Nova amplifiers (TNT-200 and TNT-120) and Trans-Nova Preamplifier (TNP). I also renew the earlier and more rare, Acoustat MRP and RP-2 preamps.

    To my chagrin ---- Folks don't realize I was many years younger than the other principals at Acoustat, back in 70's and 80's Fort Lauderdale. About half their age at that time. I am happy to continue lovingly working with Acoustat products. I do this with a fully functional laboratory and stockroom of original .........and improvement parts.

    But please realize that... in 2011.... this is part-time work.... in addition to my regular full-time engineering/consulting work. So it can take a few weeks in total, for me to work my Acoustat "magic"...... as my client's have often described the results.

    I hope the above will help explain why I don't provide a phone number, except to established clients, and I prefer email contact instead. I also prefer my work and "word-of-mouth" to speak for itself ....instead of having and spending time maintaining a website. There are others that offer work on Acoustat products. Fancy words .... Fancy websites. But NONE of them worked for the Company. And to correct the mess....Folks usually end up with me despite the glowing website tetimonials. That's just sad.

    I very much appreciate all of you, who continue to revere and enjoy the magnificent design works of Dr. Strickland, and our original Acoustat Engineering Team.

    May we all enjoy the Music

    Roy A. Esposito /

    Ralph P (2013-08-29 13:59:25)

    I just received my pair of Spectra 2200 interfaces back after they have been rebuilt and upgraded by Roy Esposito. He has done a truly marvelous job, the Spectras sound about 300% better then before. Mr. Esposito is - as an ex-member of the Acoustat crew - more then qualified to work on and upgrade these great speakers. He does not want to bother with tedious customs issues in case of items being sent from outside the US, so in my case I asked a contact in the USA to simply forward the shipment to Mr. Espositos address; what could be simpler then that? The upgraded speakers are now standing in Germany and sound fantastic.

    I recommend Roy Esposito highly for any work/upgrades/help/ regarding Acoustat speakers. He answers E-Mails quickly, communication is excellent, and most importantly he does great work! He doesn't want to be bothered with phone calls? Neither do I! That´s why they have E-Mail ....

    Roy A. Esposito (2013-09-06 12:04:15)

    Hello Friends --

    This is just to let you know that my email contact
    has recently changed. It seems AT&T/Yahoo could no
    longer support my very old email address.
    For those of you requiring fantastic restorations
    and upgrading of Acoustat MK and Spectra Interfaces
    and Acoustat Power Amplifiers and Preamplifiers
    my new email address is

    (please notice the dots/periods between the words)

    Email is the preferred method for initial contact with me
    for Acoustat Service and questions.

    Thank you for your continued friendship, kind comments and reviews,
    and support of my work.

    All the Best,
    Roy A. Esposito

    Roy A. Esposito (2014-04-08 12:48:24)

    Thank You my friends.... for your kind words and praise
    of my work. I remain available for Restorations / Upgrades /Improvements
    of the Acoustat MK Series Interfaces with the optional "Air Mod"
    that I developed in 2008. Vast improvements of the Spectra Series Interfaces,
    the Trans-Nova Series of Power Amplifiers for which I offer the incredible
    switchable Monoblock and Balanced Input circuit Conversions
    and restoration of the three models of Acoustat Preamplifiers.
    I welcome your inquiries at
    (please notice the dots between the words)

  • How to identify model - Igor Zenkov on 2007-10-04 01:45:25

    Hello I located locally Acoustat speakers. Owner is saying there is \'MK213\' stamp on the back of the speaker. I suspect it is related to the transformer model. Is there any way to identify the correct speaker model by the transformer model #? Thank you. Igor

    Igor Zenkov (2007-10-04 03:36:27)

    Clarification: The interface is MK2132, still curious if it is Spectra 2200?

    Andy Szabo (2007-10-07 23:24:36)

    The MK-2123 interface was common to Acoustat Models Spectra 22/2200, and 33/3300. An internal wiring difference changed the bass equalization for either the two-panel 22/2200, or the three-panel 33/3300. There should be a rubber-stamped number on the interface label indicating whether the interface is set-up for a 22/2200 or 33/3300. If for some reason that stamp is not visible, the speaker can be identified by its width: the cloth-covered portion of the 22/2200 frame will measure 21.5\" wide, and the 33/3300 will measure 31.75\" wide. The only difference between the 22/33 and the later 2200/3300 is the cosmetic wood and brass strips along the sides of the panel. The panels and interface electronics are identical.

  • Low output - Geoff Martin on 2007-11-25 02:43:36

    One of my Model 2\'s has developed a problem. It\'s output has dropped. The volume is lower & the bass output is also down. I have to turn the balance switch to 9 o\'clock to get the balance right. I have tested all other equipment & confirmed the problem is within the speaker. I\'m guessing the problem will be related to one or more of the transformers. Is there a replacement or service kit available for these loudspeakers? I am in Australia, so sending the units outside of the country is not practicle. I\'m using a Denon DAP-5500 preamp & Moon W3 power amp. Thanks Geoff

  • Acoustat's that hum - Gerald Mosley on 2005-09-08 19:22:55

    HELLO First of all this is a great! site. I have a pair of Acoustat\'s monitor 3 that are huming and I don\'t know if that is a sign of them going out or what.sos can anyone help

    Michael Savuto (2006-06-29 15:18:14)

    Hi George, There are two kinds of \"hum\" that Acoustat Servoamplifiers can make. The first is a mechanical hum from the high voltage transformers, the large transformer on top of the chassis. It is not heard through the speaker itself, but only in the vicinity of the amplifier. This is not uncommon and doesn\'t mean there are any problems. The second is a hum you you hear through the speakers along with any audio signal. This indicates that there is a problem with the amplifier. Usually, though, this second type of hum also causes another problem which you have not described, that the amplifier refuses to go into the standby mode from the full power mode. Hopefully this answers your question, but if not you may contact me at Mike

    Yann Zeeuwe (2007-12-09 21:29:41)

    Dear Mike, This is a test of our new mailing system. Whenever someone posts a question in model X. monitor 3 or monitor 4, you will receive an email. Friendly greetings, Yann Zeeuwe

  • Woofer repair - Marc Thompson on 2005-09-27 06:18:59

    Do you know of anyone that has a replacement woofer driver for the 3-m? The cone is intact the rubber suspension hs dry rotted...Please help

    Andy Szabo (2006-07-15 12:21:43)

    I don’t have a specific recommendation for a replacement woofer, but I would go to Parts Express to find a suitable part. They have a broader selection of drivers that I have seen elsewhere. They are at Generally speaking, I would go for the most expensive woofer that could care to pay for – and you’ll probably end up with a better woofer than the original. Do replace both woofers, as you certainly won’t be able to get an exact match to the original. Avoid woofers intended for musical instrument or auto sound applications. I don’t remember if the original woofer is 4 or 8 ohms. This is important so that the crossover will work properly with the new woofer. Disconnect the woofer from the crossover, and measure the DC resistance of the voice coil with an ohmmeter set on the R x 1 scale. A 4-ohm woofer will measure around 2.5 to 3 ohms, and an 8-ohm woofer will measure around 6 to 7 ohms. If you find a suitable replacement, please do post the information on this site. You’re not the only one with this problem.

    Alan Fels (2007-12-19 20:12:47)

    Miller Sound can rebuild your woofers. Contact Info 1.215.412.7700

  • Electronic unit failure - John MacPherson on 2010-05-14 17:55:43

    I have had these speakers since new. One of the panels stops working after being plugged in awhile. When it works, the sound is perfect. Can I get these electronic units, or get it fixed?
    Any suggestions.

    Thanks, John

    John MacPherson (2010-06-06 18:08:38)

    Or would anyone know what the problem might be?

  • Binding post - David Marshall on 2010-06-08 22:55:45

    I have a pair of Spectra 22 that have damaged 5 way binding post
    I would like to know which would be the best way to replace them?

    Andy Szabo (2010-06-09 06:12:53)

    You can get a variety of replacement binding posts, at quite a wide range of prices. One good source is Many of the ones available will even fit into the same size mounting hole in the chassis.

    You\'ll need to disassemble the interface box from the speaker, and unless you are familiar with electro-mechanical assembly and soldering, I suggest you take the interface box and your new binding posts to a repair shop and have them do the install.

  • One sided audio - Tim Johns on 2007-11-20 14:30:16

    I found a pair of spectra 1100\'s at a garage sale for $50 what a bargain!Been looking online for a year. Anyway,tanks to Soundvalves in Columbus, I got them up and running but sound only seems to be coming from one side of each speaker.Woofers work fine.I\'m not familiar with Acoustats sound so I wondered if tis was normal.

    Andy Szabo (2007-11-21 17:12:13)

    Congratulations on finding such a bargain! Acoustat speakers maintain their performance for many years, so finding a pair for only fifty bucks is great: they are worth many times that! Your observation of \"sound coming from only one side of the panel\" is a common misconception with Acoustat\'s Spectra Series. What you are hearing is the half of the panel that is producing highs and mids, with the other half producing mids only. Because you hear the highs coming from only half the speaker, it \'fools the ear\' into thinking that is the only area producing sound. If your speakers sound well balanced, frequency-wise, then you can rest assured that all of the panel area is operating as intended. The panels are arranged in a left-right mirror-image pair, so it is important that you have them on the correct side to preserve good stereo imaging. For the hybrid Spectra 11 and 1100, the highs should be coming from the outer edge of each speaker, when correctly arranged. That is, from the left side of the left speaker, and from the right side of the right speaker. (Note for the larger full range Spectra models, the opposite is true.)

  • crackling noise - Michele on 2010-03-03 14:01:06

    My 2 + 2 speakers make a popping noise. When you wash your panels do you
    wet the plastic membrane too or just the plastic inserts?

    I would like to keep these speakers but I need to eliminate this noise.

    Any suggestions would be helpful.

    Andy Szabo (2010-04-16 03:12:35)

    Before washing, I would suggest a complete discharging of the speaker, and then a good vacuuming of both sides of the panels (with the grille cloth off).

    If you decide to wash the panels, they must be removed from the wooden frame, and the felt blocks peeled away from the rear of the panels.

    The panel must be washed as a complete unit, as there is no way to disassemble the panel without destroying it. Use a very mild soap, only warm water of gentle spray, and rinse, rinse, and rinse again. Be sure the panel is completely dry before reattaching the felt blocks: use spray contact adhesive on the felt, not on the panel.

    Good luck, and write again if you need more help.

  • Acoustat 1100 - John MacPherson on 2010-05-14 17:49:00

    I have had these speakers since new and love them. The left speaker panel quits working after it has been plugged in awhile. When it works, it is perfect. All wires< etc. are tight. I believe the problem is in the electronic unit. Anyone know where to get it fixed?


  • Should I pick a set up for $300? - Bob Jones on 2010-04-26 09:39:10

    I have an opportunity to pick up a pair of 4\'s for $300.00. I have 1s, 2+2s and 3s and I would love to add this to my collection. Could you tell me what panels are in the 4\'s? I know the 2+2s share the same panels as the 1\'s and the threes with the exception of the center panels in the 3\'s. These speakers have not been used in years, they don\'t have covers (socks), thanks to you, and you told me where I could get those for my 2\'s, which I did. I have not seen the speakers but a friend of mine, who is a tech for one of the stereo stores in the local of where these speakers are at is going to take an amp and CD player over to the house and make sure they play, don\'t arc, pop etc. Is there anything else I should know about the 4\'s and again thank you in advance for your help...........Bob

    Andy Szabo (2010-04-26 15:33:03)

    The Model 4 uses the same basic panels as the other Acoustat models: the two outer panels are 9 inches wide, and the inner two panels are 8 inches wide. Essentially an expansion of the Model 3.

    The Model 4\'s are a fairly early model, so may not incorporate some of the later refinements, such as Medallion transformers, unless they have been upgraded. Otherwise, if they are in good condtion now, and haven\'t suffered any abuses, they should continue to work for a long time. I would say they are definitely worth 300 dollars. Due to their age and not being covered with socks, they panels may need a thorough cleaning. It may also take a while for the panels to \'quiet down\', that is, to stop minor snapping until the dust rearranges itself. I had the same experience when I bought a used pair of Spectra 4400\'s, which had unfortunately been stored under poor conditions.

    As far as sonic performance compared to your other models, they will have the bass strength of the 2+2\'s (having nearly the same panel area), but will not image quite as precisely due to their wider width.

    Thanks for supporting Acoustat with your impressive collection of models! Nice to hear from you.

    Andy Szabo (2010-04-26 18:40:10)

    The interface for the Model One is the MK-141 series, rather than the MK-121 series used on the full range models. The MK-141 uses a single, limited-frequency range transformer, whereas the MK-121 uses seperate low and high frequency audio transformers. Therefore you cannot swap parts from the Model One\'s into Model 3\'s.

    Bob Jones (2010-04-26 23:44:26)

    Darn, how about into the 2+2\'s, ti doesn\'t sound that would work either..... Oh well..............again thanks...........Bob

    Bob Jones (2010-04-26 23:47:18)

    Oopps, I mean 1+1\'s if that makes a difference with the interface.......Bob

    Andy Szabo (2010-04-27 02:48:54)

    Only hybrid (i.e. with woofer) Acoustat models such as the Model One, 2MH, and 3MH use the MK-141 (or MK-131) single-transformer interface. The 1+1, 2, 3, 4, and 2+2 use the MK-121 series interface. The various incarnations of the MK-121 may look different externally, but the innards are essentially the same, save for some minor component differences introduced over time.

    New-old-stock (NOS) Medallion transformers are still available, and appear from time to time on eBay. But be prepared to pay at least a couple hundred dollars for the set of two high frequency and two low frequency transformers.

    Bob Jones (2010-04-27 08:54:50)

    Andy thanks for your quick response, however, after asking questions from you in the past this comes as no surprise.

    I heard a pair of Sound Labs a couple years ago and that is what has gotten me on the Acoustat bandwagon if you will. The 4s I am hoping will give me that big sound stage that the Sound Labs seem to do so well. The pinpoint imaging, I have found, is not what gives me the goose bumps but the wave of music these panels seem to do so well at. I have had single ended amps driving very efficient speakers with that pinpoint image it was okay. But when I had the opportunity to attend a Christmas concert with a full piece orchestra several years ago I realized that there is no such thing as pinpoint imaging. I closed my eyes and I could not identify any single instrument, it was a wave of music with lots of air, again which the Acoustats seem to do real well at. What the Acoustat don't do well is the dynamics but I will give that up for all the things they do, do well, I guess that makes sense. I guess I also want to say, I have all the pure panel speakers they made in their day even if I don't listen to all of them all the time.

    I do find I listen to the 3s the most, the 1s the least and if I want to rock and roll on occasion I will listen to the 2+2s. I do listen with a sub only for the lowest of lows, not a big base guy. The one\'s I have, have the medalion transformers, can I swap them into the three\'s

    Andy again thank you for you information and the education I get from your web site!..Bob

    Steve Zeeuwe (2010-04-27 09:06:01)

    Dear Andy, Bob,

    There went something wrong with the forum section after I tried to change something, so unfortunately Bob\'s reply to Andy\'s first post has been moved. I will try and fix this soon, sorry for the troubles!

    Kind regards,

    Steve Zeeuwe
    The Audio Circuit

  • Price for broken Acosutat Spectra 11 - murkr on 2010-04-13 10:39:08


    I got an offer for a pair of Acoustat Spectra 11.
    They are about 10-15 years old.
    They dont work probaly due to faulty elektronics.
    They have new Canton-Bass-Chassis.

    So my question is: How much is an reasonable price?
    I dont know if I even get them repaired.
    How much should I pay for them?

    Thanks in advance


    Andy Szabo (2010-04-13 20:45:06)

    That is a tough question, since you have no idea what the problem is. It could be something very simple to repair (and often it is), or the speaker may have suffered a catestrophic failure. It sounds like the woofer portion has been modified, and perhaps the problem has something to do with the modification.

    By the way, any Acoustat speaker is at least 18 years old, since US production stopped in the early 90\'s.

    If you have no way of looking at the speakers, or can\'t listen to them, I would recommend against buying them. You just don\'t know what you may be getting, especially since they have been modified.

    On the other hand, Acoustats are extremely reliable and long-lived, so it could be a good investment if you can find out more about the problem. If you do, please write again and perhaps I can offer further guidance.

    murkr (2010-04-13 21:40:18)

    I do have pictures and the guy I want to buy them from couldnt tell me more than its probably the elektronics.
    How can I upload pictures?

    murkr (2010-04-13 21:41:31)

    Andy Szabo (2010-04-16 03:02:57)

    Based on the photos, my guess is that the modification project was never completed. Where does the metal interface chassis attach mechanically, and connect electrically? I cannot see where it would go. Some modifications have been done to the electronics. I can\'t tell exactly what has been changed, but it was not done with care.

    Also, it is strange that the ESL panel is mounted at the rear edge of the woofer cabinet, which could present problems with sound reflections off the top of the cabinet.

    Based on the information you have provided, I would say \'no thank you\' to these speakers, unless you have some electronics experience and a desire to do a lot of work. Even then, I wouldn\'t offer any more than $100 for the set.

  • Rattling panel-Diagnosis and replacement - DaveT on 2010-04-05 21:47:57

    The out-of-nowhere rattling of the bass panel on one of my Spectra 3300\'s has me quite concerned.
    I am a long time owner of various Acoustat models and diligently use the hairdryer mylar tightening procedure.I think we may be beyond such a simple concern. This sudden rattling isfar more severe then the yearly loosened mylar. When I tap the panel it sounds somewhat like a loose snare drum or a piece of paper flapping around; you can only imagine what a bass-heavy musical track sounds like.

    I tried the dryer trick-no go.

    Given this description am I to assume the panel is DOA?
    Can a panel in the described condition be repaired? If so, any suggestions as to who and where?
    In my Acoustat collection is a pair of Spectra 1100\'s. Can one of these panels be used as a replacement?

    Any and all feedback would be greatly appreciated

    Andy Szabo (2010-04-08 23:53:20)

    You might have some sort of foreign material trapped in there, which might require removal of the grille cloth to inspect the panel. This problem can probably be remedied with a thorough cleaning (be sure to check behind the felt damper block). If the mylar is punctured, or the panel has suffered some traumatic damage, it cannot be repaired.

    The panels in your 1100\'s are the same, and could be used as a replacement. All Spectra panels are the same, regardless of model. The only difference is how they are connected to the interface.

    Good Luck, and do write back if you need further assistance.

  • Stretched membrane ! - Anoop Nannra on 2010-04-04 05:54:55

    I have a pair of 2+2's. One is in good working order, the other however needs some help. The membranes have become stretched, don't ask how but needless to say they were over driven. Is there any way I can reshape the membranes on my own, or am I cooked ? I recall a few years back that one trick was to carefully go over each panel with a heat gun, and that several treatments might be required to re-shrink the membranes back to a useable shape.


  • Good amp to drive this speaker system - Chris Frie on 2010-03-12 22:10:12

    I am thinking about using a Threshold 400a amp to drive my 1+1s's. Does that seem like a good idea?

  • High-Volume Distortion from Trans. - Dave Woods on 2010-02-16 19:40:46

    After 25 years my 1+1s developed a high volume distortion problem in one speaker. The problem is a horrible distortion that occurs about 5-8 dB down from where the in-line speaker fuse (3 amp) would blow: fairly loud but not excessively so. I thought it was probably the panel, so I switched the transformers (entire black boxes) between the units, and he noise stayed with the transformer (R vs L). So I have several questions: has anyone else experienced this? What is the likely cause? Does anyone fix these things? Any further troubleshooting steps?

    I would be glas o send this somewhere to be fixed if I had confidence in where to send it.

    Andy Szabo (2010-02-17 01:29:43)

    You most likely have a bad low frequency transformer, and the problem will only get worse with time. It should be repaired soon before much further use. Try contacting Roy at Sounds Like New, listed under Refurbishing at the very top of the Acoustat section. Roy has the parts and know-how to fix your problem and get another 25 years from those speakers.

  • Dissembling speaker - Gary Hubbard on 2010-02-16 03:38:09

    For Andy Szabo: I may have a wiring short on the back of one of my Spectras - as evidenced by a suddenly appearing black smudge 6 inches up from the interface. If there is a short there it evidently (according to my local audio Dr.) took out the rail fuses in a B&K ST202. What I am wondering is the procedure for taking the speaker apart to find the short. Since I put it together (new) 19 years ago, I don\'t remember the sequence. Help, Andy!!

    Andy Szabo (2010-02-16 17:36:13)

    Is the black smudge on the grille cloth? If so, this might indicate a short in the high voltage wiring inside the panel frame. The black smudge could also be from smoke that curled up from the interface through the frame.

    First, get someone to help you disassemble the speaker. After allowing the speaker to discharge for at least several hours, remove the two screws on either side of the interface box. Be careful - the panel is now disconnected from the base. Gently pull the panel forward, being careful not to scratch the wood base. Disconnect the colored wires from the interface by pulling the pins straight out from the connectors. The panel is now free and can be set aside.

    If the speaker is a 2200 (with the decorative wood & brass strips along the sides), you\'ll need to pry off the wood from the sides of the speaker. Detach the grille cloth at the bottom of the speaker by removing the staples, and slide the cloth up until you can see the trouble area. If you see burnt wires, you can probably repair them by removing the burnt section and re-splicing, covering each splice with heat shrink tubing.

    I will say that wiring problems inside the panel are rare, so you should first look for signs of damage inside the interface before disassembling the panel. Unfortunately, removing the decorative strips tends to be a one-way proposition. You can re-attach the wood after removing the brass strips and nails underneath, but the brass strip will be damaged in the process. If you read my piece on rehabilitating my Spectra 4400\'s, you will see I had the same problem, and I have yet to find a suitable replacement for the brass trim.
    (And let the record reflect I had a big arguement with Marketing about those brass strips, knowing that they would interfere with repairs!)

    You may also need to replace the grille cloth after this, since it is usually very difficult to re-staple the old cloth back into place. New factory-spec cloth is available: see the parts section.

    Do write again if you have further questions, and please let me know what you find as the problem: I am curious to learn what caused your fuse-blowing and black smudge.

    Gary Hubbard (2010-02-28 21:57:12)

    Hello Andy: I am adding a picture of the alleged \"burn mark\" on the back of my left hand Spectra 22 (not 2200). It was the left side that did not want to play when I was having trouble with the pre-amp and amp.

    Andy Szabo (2010-04-16 02:41:53)

    Our webmaster sent you my address so I could look at the photo, but I haven\'t received it. Did you figure out your problem, or do you still need help?

  • Panel inop - John MacPherson on 2010-02-03 17:02:22

    I have owned my Spectra 11\'s since new (almost 20 years) and have had no problems. Recently the left panel quit working. The woofer works normally. I swapped out the wall transformer with no result. I checked the the wires and connections in the electronics box and where the wires are connected in the back of the woofer box. Still no result. I disconnected the power for about 12 hours and reconnected, then it worked, but only for a day, then it quit working again. When it does work the sound is still perfect. I suspect some problem in the electronics box. Are parts available, or the whole electronic unit available.

    Thank you,

    Andy Szabo (2010-02-04 19:27:07)

    Since the woofer is still working, we can rule out any problem of a poor connection to the amplifier, as well as some of the audio-input circuitry inside the interface box.

    If the problem was in the high-voltage audio section, I doubt you would get the intermittent behavior, unless you have a bad solder joint that goes bad when the unit warms up. Problems in the high voltage section usually go bad and stay that way, or will yield distorted sound.

    That leaves only the bias power supply, which provides the high voltage for the electrostat. Without the high voltage, the ESL portion will not play, but the woofer will still work. The problem could be as simple as a bad connection where the wall transformer plugs into the rear of the speaker. Those jacks can give trouble sometimes. You might try removing the input cup from the rear of the speaker to see if the jack\'s contacts have spread apart or are corroded.

    Beyond that, you probably have a problem in the bias supply itself. Unless you have some electronics knowledge, there isn\'t much you can do other than looking for bad solder joints, or possibly the IC is loose in its socket. Since you have an intermitent problem, you may get lucky and find that it is a bad connection.

    One other possibility - there was a change in the bias supply that improved its reliability. You can check to see what version you have by examining the air-core coil on the printed circuit board. Note the red wire coming out of that coil - if there is another wire heatshrinked to that red wire, then you have the updated version. (Note the extra wire is not electrically connected to the red wire - it acts as an antenna to provide feedback for the oscillator, so it is only wrapped around the red wire.) If you do not have that extra wire, then let me know and I can provide info on how to do the update: it\'s easy to do with commonly available parts.

    The fact that your speaker has operated without a problem for 20 years suggests to me that the bias supply update will not be your problem. But I mentioned it just in case - stranger things have happened!

    Do write again if you are still having trouble. I am dedicated to keeping those speakers running for another 20 years!

  • Foot or no feet - pkaram on 2010-01-30 23:50:18

    New owner of the Spectra 1100. Recently, bought a pair used without ever hearing the speaker before. Surprisingly, it is much better sounding than what others have wrote on the internet. My pair came without any feet or spikes. My question is what was originally supplied with the Spectra 1100? Will I gain much with the feet? Thanks in advance.

    Andy Szabo (2010-01-31 01:36:14)

    The spiked feet originally supplied with the Spectra 1100 were very simple - not much more than a screw with a sharpened point. FYI - the threaded receptacles on the bottom of the speaker are 1/4-20 size.

    Those feet (or any spiked feet, for that matter) are most effective at leveling the speaker if the floor is uneven, and/or for stabilizing the speaker on deep pile carpeting, by piercing through the carpet and resting on the solid floor below.

    You will find endless debates about the sonic merits of spiked feet. For example, some manufacturers claim the feet couple the speaker to the floor. Others claim the feet de-couple the speaker from the floor. You will even find some craftily worded ads that claim to do both!

    The perceived sonic effects of spiked feet, if any, will probably depend greatly on your room acoustics, and the construction of the floor. My personal view is that spiked feet, resting on a relatively unmovable surface such as concrete, might tend to reduce vibrations in the speaker\'s cabinet, which is a good thing. On the other hand, spikes resting on an springy wood floor may actually cause the floor to vibrate along with the speaker, making matters worse.

    Finally, there is the spousal acceptance factor, which may give you hell for making dents and scratches on that nice new hardwood floor. Good Luck!

  • Spectra series - Bill Armstrong on 2010-01-20 09:53:53

    Good day gentleman, Would you be good enough to furbish with the frequency range of the spectra series speakers:

    The Spectra 2200 Hz - Khz?
    The Spectra 3300 Hz - Khz?
    The Spectra 4400 Hz - Khz?
    The Spectra 6600 Hz - Khz?

    As well as the physical dimensions of each speaker?

    Thanks guys, Bill

  • Panel - Dave N on 2010-01-05 23:13:10

    I have a pair of Spectra 11 speakers, but one of the speakers was tipped and the panel was damaged. It still functions, but sometimes sounds like a giant bee was stuck in the panel. I do not think it can be repaired, but was wondering if anyone knows where I can get a replacement panel.


    Andy Szabo (2010-01-10 18:06:17)

    New replacement panels are not available, but they do appear frequently on the used market. Watch eBay and other sellers. Just be sure the panel you get is a Spectra panel, as the older non-Spectra panels are not compatible.

    Before giving up on the panel you have, remove the grille cloth and look for broken bits of plastic that may be caught in next to the diaphragm. If the Mylar diaphragm is torn, or if the wires have come loose from the plastic louver structure, then the panel is bad and cannot be repaired.

    Dave N (2010-01-17 00:04:27)

    Thanks Andy.

    The Mylar diaphragm is punctured, but I will try a little more cleanup on the loose plastic pieces to see if that helps.

    In reading the forum, I saw that issues were more common with the woofers and circuit board, but the panels were usually undamaged. If anyone has a extra panel sitting around, I would be interested.

    Andy Szabo (2010-01-17 15:25:07)

    Dave- if the Mylar is punctured, don\'t bother putting any work into that panel. It cannot be repaired.

    The panels are virtually indestructible in regards to overdriving them, and they do not seem to degrade over time. But of course, as in your unfortunate case, the panel can be damaged beyond repair by physical trauma.

  • will Medallion MK 141C work model 3 - Kim Bothwell on 2009-12-09 20:33:27

    will Acoustat Medallion MK 141C transformers work as an upgrade for a pair of 3\'s (which currently have a MK-121-2 trans?

    Andy Szabo (2009-12-10 01:32:48)

    The MK-141 series interface is designed for midbass to upper frequencies only, for Acoustat models that contain a woofer, such as the Model One. The same is true for the MK-131 series, used on models such as the MH Series.

    The MK-121 series is a full range interface, designed for larger Acoustat models that are pure electrostat, such as your Model 3\'s.

    So, the MK-141 would definitely NOT be an upgrade for you.

  • Sound volume difference - Timmy D on 2009-11-21 23:15:22

    Hi Andy my name is Timmy,just acquired a mint pair of Acoustat 3300,everything in original condition,get them home and find out that for some reason one speaker sounds much louder than the other,the owner told me that they\'ve been sitting in his garage for 4 yrs,when I listened to them with him in his garage(very bad testing condition,he have the speakers hook up to some lousy receiver and connect to the Ipod)they sound ok,I did not pay too much attention of how each individual speaker sounds.I wonder if anything can happen during transportation from his house to mine(I did protect them very good during transportation).What do you think of this problem?any suggestin would be greatly appreciated.

    Timmy D (2009-11-22 03:26:33)

    never mind Andy my bad,I found the problem,it just one of the 12 ac is plug into an outlet with no power,the speakers sound great now,really smooth,I\'m very impress with the bass,electrostatic is known to be lacking bass,not with these 3300.I think the speakers is in original condition,if there anything else I should do to update or to improve the sound,what do u suggest?great job you\'re doing here for acoustat owner.

  • Input Circuit - Andy Tomlinson on 2009-11-14 16:18:20

    Hi Andy
    Looking at the schematic for the 6600 I see that in series with the positive input there is a parallel network composed of two 10uF capacitors and a 1ohm resistor. What are these components doing?Are they contouring the input signal

    Andy Szabo (2009-11-15 13:00:16)

    The 1-ohm resistor in series with the audio transformers keeps the DC resistance of the speaker above 1-ohm. Otherwise, the DC resistance would be only a fraction of an ohm, which might cause problems with some amplifiers. This is a common feature of all Acoustat full-range models. It is NOT recommended that this resistor be removed, even if you think your amplifier might be stable under such conditions.

    The capacitors in parallel with the resistor simply bypass it at higher frequencies. Although the value of 20-uF is sufficient for this purpose, and the capacitor is a high quality polypropylene, you may, if you wish, increase its value and/or use a different type of capacitor dielectric.

  • Ohms < 4 - Randy Weiss on 2009-11-13 16:53:43


    I have a pair of Acoustat 2+2 which I have been driving with a Belles 400 amp for 20 plus years with no problems. Within the last 1.5 years my amp has blown twice. The tech said the amp blew because either the speaker cable wires were crossing each other or the speakers were broken. I checked my wires and they seem fine - no frayed wire and banana clips looked good. He also told me to check the impedance to ensure it was over 4 ohms. I checked and they are both reading approx. 1.7 ohms. Since they are both reading 1.7 ohms, I wanted to check here before I took them in. Could someone please tell me what reading they get from their 2+2\'s?

    Thanks, Randy

    Andy Szabo (2009-11-13 19:54:58)

    The 2+2 (and other speakers in the MK-121 series) are nominally rated at 4-ohms. However, the impedance does vary with frequency, dipping as low as 2-ohms at the high and low frequency extremes. At mid frequencies, it may rise to as much as 10-ohms. It is a difficult load, but most amplifiers rated to drive 4-ohms loads should be okay as long as they are operated within their limits.

    The 1.7-ohms you measured (presumably with an ohmeter) is the DC resistance, not to be confused with the rated AC impedance. A reading of 1.7-ohms DC resistance would be considered normal.

    Since your amp/speaker combination has been running fine for so long, I doubt it is a compatibility issue. It may be that your amp is just getting tired.

    Faults in the speaker can damage amplifiers, but you would probably know if you had such problems by hearing arcing noises or smelling a burning odor.

    Never use greater than a 5-amp slo-blo fuse in the speaker, and if you are concerned about harming either speaker or amplifier, try reducing the value to 3-amp slo-blo.

    Randy Weiss (2009-11-15 02:42:22)

    Thanks Andy, I guess you can tell I am not very knowledgeable about this. Yes, I used an ohmeter.

    The service tech said that the problem was not with the amp. I will check my speaker cable again, but it looked fine.

    I was afraid that 1.7 ohms is normal for the acoustat. Oh well, who said life was easy. I did check my brother\'s speakers and they were above 4 ohms, so I assumed I checked them properly. Is there a better way to check the speakers to ensure they are not the problem?

    Also, I saw in one post mention of changes that could be made to the 2+2\'s to make them sound better, but I could not find the modification info. Do you know where I could find it?

    Thanks again for your help,

  • Present market value? - Dino Ferrari on 2009-10-12 12:36:48

    I have been commissioned by a friend to sell a paiir of speakers that I think are the above model. They date back to around 1978. Does anybody have an idea of their present market value? Does anybody have their manual?

    Andy Szabo (2009-10-13 02:30:11)

    A manual for the Model X is included on the Acoustat Manual CD available from this website.

    The value of the speakers will depend highly on their condition, especially if they are equipped with the servocharge amplifiers. The servocharge amplifiers can be troublesome, but they are highly sought-after if they have been refurbished sometime in their life, and still work properly.

    If you find the right buyer (usually local due to their large size), a prime pair of Model X\'s could sell for over $1000/pair. Even if the amplifiers don\'t work, they can still be rebuilt by Mike Savuto. A less than perfect pair could still fetch at least several hundred dollars.

    Steve Marohn (2010-09-16 05:58:51)

    I looked to sell my pair of Acustat monitors a little while back but would only bring $2000 at the time. Where could you relplace these for that kind of price with the amps in good shape? Decided to keep them, the last time I heard a speaker this good it was $10,000 with no amps.

    Andy Szabo (2010-09-16 22:12:41)

    The fact of the matter is that you CAN'T replace the performance of your Acoustat speakers with brand new speakers for $2000. But because the speakers are 20+ years old, the resale price will necessarily be less than what they would cost to replace. The fact that your speakers have built-in amplifiers makes matters only worse.

    Which is why I always say that a pair of used Acoustats can't be beat for the price, if you can just convince someone to sell their old ones! Bad news for sellers but great news for buyers.

  • High Freq Balance Control - Chris on 2009-10-08 03:04:33

    I am not getting much base out of my sub-woofer. Can I increase the base output by adjusting the High - Frequency Balance Control?

    Andy Szabo (2009-10-11 02:17:17)

    No. Acoustat\'s High Frequency Balance control affects only the very top-octave of the audio spectrum, say above 10 kHz. It will have no effect whatsoever on the bass.

    If your subwoofer is self-powered (i.e. it has an amplifier inside) it should also have a control that will vary its volume. If your subwoofer is a different type, write again and tell me what you have. I might have further advice.

  • Hmmmmm sound - Chris on 2009-10-07 20:31:35

    Please help me find a solution if you can! I have a YAMAHA AVC-50 Stereo Amplifier setup as a control amplifier running a YAMAHA T-420 Stereo Tuner, and a YAMAHA CDC-91 Compact Disc Player. I also have a PARASOUND HCA-1200h High Current Power Amplifier powering my front pair of ACOUSTAT Electrostatic Speakers and a Sub-Woofer. I also have a YAMAHA M-45 Power Amplifier running my rear pair of Boston Acoustics speakers. This system as it stands is working great.

    The problem is when I try to hook up my Mitsubishi DLP High Def TV model WD-65733 to the YAMAHA AVC-50 control amp I get a loud hmmmm sound. I have double checked that my cable connections are good and the phasing is correct. The TV does automatically convert the digital incoming audio to an analog signal thru its analog output terminals which are the ones I am using to connect to the AVC-50. Do you have any advice to get rid of this loud hummm sound?

    Thank you,

    Chris (2009-10-08 03:09:02)

    I have isolated the humm noise to it only happening when I have the coaxel cabel hooked up. Someone has said that this means that I have a Ground Loop in the catv. Does this make since? and how do I fix this?

    Andy Szabo (2009-10-11 02:10:28)

    I agree with the previous answer. Ground loops with CATV systems are common. The problem comes from the fact that the ground potential of your local AC power line is not exactly the same as the ground potential of the CATV line, so small ground currents get generated in your system. Hence, the hum.

    The best and easiest way to eliminate this is to get an isolation balun for your CATV line. This small module installs in-line on the CATV line before it connects to your equipment. It is a 1:1 transformer that isolates the ground. They\'re cheap: probably less than 10 bucks.

    You can also use ground-eliminating adaptors on your 3-prong AC plugs, but that is less desirable as it removes the safety feature of having your equipment earth grounded. Since everything works great until you connect the CATV, I would recommend fixing the problem there.

    Hey wait a minute, that wasn\'t an Acoustat question!

  • Open SPW-1 - Joe Evans on 2009-10-06 05:21:38

    How do you open the SPW-1 woofer box? I have looked and there seems to be no obvious way. I want to check the surrounds on the woofers.

    Andy Szabo (2009-10-11 01:54:53)

    The wooden top and bottom panels are held on by press-fit pins. Gently pry upwards on the wood and it should lift off. Then remove 80,000 staples to remove the grille cloth and padding. Look at the woofer surrounds and I bet you will see that there is nothing wrong with them.

    Unless you are having a problem with the woofer, or it has been damaged by an external force, I wouldn\'t worry about the woofer surrounds. They are butyl rubber and should last a very long time. No foam-type surrounds here.

    Just trying to save you a lot of work!

    joseph lara (2011-03-02 19:48:43)

    Thank you in advance. I have an original spw-1 Acoustat speaker in the box. I purchased it back in the day, and it has been stored since. Just wanted an idea towards its valuation. The thing weighs a ton.~Joe

    Andy Szabo (2011-03-08 21:46:01)

    The Acoustat SPW-1 is an unpowered woofer system designed specifically for the Spectra 22/2200 and 33/3300. I don't recall its original sales price, but I would imagine a unit in good condition would fetch at least a few hundred dollars. The woofers (four 6" drivers) use butyl-rubber surrounds, so there shouldn't be any problems with degradation as commonly found with foam surrounds. Not many of the SPW-1's were produced, so you might find good demand for the system among Acoustat owners.

    joseph lara (2011-03-09 19:47:37)

    Thank you, Andy. I appreciate your being a gentleman.I really had no clue. I just might sit on them a couple of more years. I want you to know how much I learned from your website. Thank you for your quick reply. Stay the course and God Bless you.

  • Bias Rectifiers - Paul Del on 2009-10-02 23:54:41

    I can usually measure diodes with my Fluke in the diode mode but get nothing, open, with all of the rectifiers. Can they all be blown and if so is the type known and available?


    Andy Szabo (2009-10-11 01:44:23)

    The 25G10 diodes used in the Acoustat bias supply are called stacked diodes, meaning that each diode package actually contain several diodes in series to reach the high rating of 10,000 peak-inverse-volts (PIV). For that reason, these diodes defy the usual attempts to measure them with an ohmmeter. Most meters do not supply enough voltage to forward-bias the multiple diodes, so the diode will measure open, or infinite resistance, in both directions.

    These diodes are pretty reliable, but failures do happen. You probably won\'t encounter all five failing at the same time, unless the unit has been hit by a huge surge, like a lightning strike.

    Any diode with minimum ratings of 25 milliamperes (mA) at 10,000 volts (PIV) will work, as long as the package size fits the board. Go to the top of the Acoustat section, and scroll down to Available Parts. There you will find a source for these diodes.

  • Volume Problem - Edward Struchowski on 2009-09-22 02:52:32

    1. I had a problem a few years ago with the volume of one of my 2+2\'s and it ended up being one of the caps where leaky thus giving me 3.8k, I completely rebuild it and it was fine.
    2. A Couple of years later the other speaker seemed to be having the same problem. I bought enough parts to refurbish both and was waiting to to the other. I completely rebuilt the power supply but still have the same problem. I have replaced the (2) .01 uf caps also thinking it might be a drive problem. This weekend I am going to change interfaces to determine whether it is the interface of panels.
    3. The only thing I found quickly is that the voltage at the power to panels after the 500m ohm resistor is 2.3k on good one and 900 volts on bad one, leading me to believe either the panels are drawing too much current or the 500m ohm is bad. I don\'t have a meter that can measure resistance that high.

    what are your thoughts?


    Ed Struchowski

    Andy Szabo (2009-10-11 02:47:59)

    The different voltage measurements would certainly suggest a problem in the high voltage supply.

    It is unlikely the panels are drawing too much current and drawing-down one of the supplies. If that was the case, you would probably hear a buzzing or crackling from the speaker. But just to make sure, measure the voltages again, but with the panels disconnected (on both speakers). If one supply still measures low, then you know the fault is not in the panels.

    The 500-Mohm resistors don\'t fail very often, but it can happen. Unfortunately, they are impossible to measure with ordinary ohmmeters. The easiest way to check is to swap resistors between interfaces, and see if the problem follows the resistor.

    Check the AC voltage on the output of the bias transformer (smallest of the three transformers). They should measure the same unless you have a bad transformer.

    Otherwise, you probably have one or more bad diodes and/or capacitors in the voltage-multiplier. Troubleshooting individual components in the multiplier is a pain, so if you have eliminated all other possibilities, I would suggest replacing all the diodes and capacitors at once. If one is bad, they are probably all weak.

    Go to the top of the Acoustat section, and then scroll down to Available Parts. You\'ll find info there on where to find parts.

    Write again if you are still having troubles.

  • Transformers - Scott Olive on 2009-09-21 00:49:15

    Hello, I am looking for parts for my spectra 2 speakers. Needing interface parts. Love these speakers and would like to keep them going.

    Andy Szabo (2009-09-21 21:21:49)

    Hello Scott!

    Some parts for the Spectra series are still available from eBay sellers SoundValves and Dealsbyjason. Both of these sellers bought up Rockford\'s remaining inventory of Acoustat parts. Set up an eBay favorite search for Acoustat and have them email you whenever something appears.

    Schematics are available on the Acoustat CD available from this website. If you have specific questions on parts for you speakers, please write again.

  • Popping Pannel - BC on 2009-09-12 11:30:33

    The upper left panel of one of my 2+2\'s is making a light pop about every 30 seconds. I assume that is arcing.

    I have switched interface boxes and the popping did not move. I took the cloth off and cleaned the panel twice with vacuum and once with a can of compressed air. I also found a place were the grid wires were unglued from the grill. I glued them back with epoxy. None of this seemed to change the problem. The mylar itself looks to be in very good shape. No obvious signs of arcing in the conductive area or around the edges. It also seems quite clean now. The only thing I have not done is to remove the single panel and \"wash\" it.

    I have read that sometimes the insulation on the grid wires can break down and develop holes in the insulation. And that if that happens, there is no fix.

    Any comments?

    Andy Szabo (2009-09-15 22:49:36)

    Sorry to hear of your popping panel problem. This is a somewhat common problem, especially for the older panels with the lower-resistance coating on the Mylar. The newer coating (identified by a red spiral stripe on the bias wire) is much less susceptible to popping.

    It may take several attempts with the vacuum and/or compressed air to dislodge the bit of dirt that is most likely causing your problem. Be sure that the speaker is fully discharged (unplugged overnight) before attempting to clean the panel. Otherwise,the electrostatic force may hold the dirt in place.
    You may also have some success with lightly banging the panel with your open hand to dislodge the offending particle. Rarely, if ever, is washing required, but it is possible using a very mild detergent and a thorough rinsing.

    The felt pads on the rear of the panel may be interfering with removal of the offending particle. The pads can be easily peeled off, and then reapplied with 3M brand 77 spray adhesive. Spray a generous coating of the glue on the felt, wait for it to tack-up, and then press the felt back into place. If you elect to wash the panel, the felt pads should be removed first.

    In my 23+ years of experience with Acoustat, involving speakers up to 30 years old, I have never heard of the insulation failing on the grid wires. Comments you may have read probably referred to another brand, or may refer to an isolated case with an original manufacturing defect in the wire. That said, nothing lasts forever, and someday the thousands of Acoustats out there will begin to fail, but so far I have yet to hear of any widespread degradation over time. And even when that does eventually happen, I would expect to hear first about problems with models much older than yours.

    Do know that the popping sound is not causing any further damage to your speakers. The arc you hear is a very minor, localized discharge that does not have enough energy to do any damage. It is just annoying.

    Do write again if you have further questions. And do keep up the faith - it\'s not time to give up on your Acoustats just yet!

    BC (2009-09-17 09:33:44)

    Andy, Thank for the reply and the assurance that there is probably not an insulation breakdown. I\'ll give the panels another cleaning or two. I will let it discharge a bit more first. I will admit to being impatient and only powering off for a couple of hours before my prior cleanings.

    Is there a safe way to discharge the panels, like connecting a resistor across the poles?

    Andy Szabo (2009-09-17 20:53:26)

    There is an easy way to quickly discharge the panel. After disconnecting power, pull-out the center red plug (holding it by the insulated portion) on the interface\'s printed circuit board, and touch the metal end of the plug to either the white or blue thumscrew. You will see a spark and hear a tick from the panel. Repeat this several times over a few minutes. This will remove the majority of charge from the panel. As a precaution, make sure that no other part of your body is touching any metal or other components of the interface chassis while doing this. The shock hazard is not dangerous, but it will make you mad at me for suggesting the procedure!

    However, I would still recommend you wait at least several hours before cleaning the panel. You do want to make sure that all electrostatic force is removed from the panel so that your cleaning efforts are most effective.

    BC (2009-09-23 20:41:16)

    It was a dark and foggy night... Perfect for arcing electrostats! And so it was last night. But that is getting a bit ahead of things.

    Last weekend, I pulled the sock half way down, exposing my popping panel and gave it a very thorough cleaning front and back with two cans of compressed air. A couple of interesting things:

    1) About 3 or 4 small pieces of stator \"glue\" came off with the compressed air. I made sure that I got those pieces out. It did not affect the stability of the stator wires, which are solid everywhere.

    2) When shining a light through the panel, the top 4\" of the conductive area seems to be breaking up, with light shining through many very tiny cracks - similar to the way old paint cracks up.

    After the cleaning, I plugged them back in, and... same thing. The popping is the same as before. Since in all the cleanings, the popping has not changed, I am beginning to suspect something other than contamination. I also tried switching the interface boxes and that did not change things.

    So, then last night was very foggy (high humidity) and dark. I stayed up to listen and watch for arcing.

    To my surprise, I heard multiple panels arcing. It seemed to be at least two panels on one side and probably two panels on the other side. Overall it was about equal left and right. The original suspect panel popped the loudest by a few db, but was less than 50% of the pops. The humidity may have brought out other arcs.

    I could see some of the arcs as very dim flashes of light. The arc flashing on the original suspect panel was in various places on the panel, Often in the left third and in the middle third vertically. It did not appear to be at the edge.

    There is also a faint 60hz or 120hz hum from both speakers when not connected to and input source. It is audible from within 3 feet, but not from 10 feet away. This hum goes away when an input source is connected. I assum that this is just leakage from the A/C line source into the floating audio circuit.

    I am now wondering if I might have a bias voltage that is a touch too high given the normal humidity of my environment (San Diego). Is this likely? Could it be caused by age? The circuity looks to be in good shape visually, with only the high freq variable resistor showing some oxidation on exposed wire turns. Could the reduced conductive area caused by the small amount of cracking up cause a concentration of higher charge on the rest of the panel?

    Is there a way to test these theories? Can I measure the bias voltage? I have a DVM, but it is only rated to 1KV. Can I adjust the bias, perhaps by changing the 500MOhm resistor?

    BTW, I have a pair of old SoundLab R1\'s that used to arc. This was easily solved with their externally variable bias voltage. (Yes, I love the sound of electrostatics!)

    Thanks Andy for reading this and for any advise you can provide. I would be pleased to exchange direct email or talk on the phone if that would be more convenient for you.

    Cheers. -Brad

    Andy Szabo (2009-09-24 00:01:14)

    It is not entirely unheard of for small flakes of plastic or glue to be loose inside the panel. Your use of compressed air is a good idea, but I would also strongly recommend vacuuming the panel. Since these particles are non-conductive, they are probably not the source of your trouble. Such particles can cause extraneous rattles that correspond to certain musical signals, but that is a mechanical problem, not an electrical one.

    There can be voids in the conductive coating that may look like pinholes, streaks, or even cracks. The coating was applied by brush, so it not uncommon to see some voids. So far, I have heard no reports of failure of the conductive coating. If somehow your coating has degraded to the point of actually disconnecting certain areas from the power supply, it could possibly cause a charge concentration that would increase the likelhood of arcing. But I think that is highly unlikely.

    Certainly, conditions of high humidity will increase any likelihood of arcing. Generally speaking, Acoustats are pretty humidity-resistant (remember, they were developed in south Florida). But if you have an arcing problem, it is normal for it to get worse in high humidity.

    Your speakers do not feature an adjustable bias voltage (only Acoustat\'s Spectra series featured adjustable bias). Changing the value of the 500-mohm resistor would not change the bias voltage. It is unlikley that a failure of the power supply could cause a higher than normal bias voltage. But, if you want to check the bias voltage, several methods exist for checking the voltage, including using a normal DVM. See my Technical Bulletin on the ultrasonic bias supplies. Although the bulletin is aimed at the adjustable-bias models, the methods for measuring bias voltage is the same.

    The only way to reduce the bias voltage would be to hook up the AC power to a variable source. The bias voltage is proportional to the AC input voltage. Don\'t use a regular light dimmer: you\'ll need a variable auto-transformer (aka Variac) Keep in mind that reducing the bias voltage will also reduce the efficiency of the speaker.

    The hum you hear from the speaker with no input is a new one on me. But, your theory sounds plausible that the audio transformers could be picking up a hum field from the bias transformer. Connecting the amplifier effectively shorts-out the generated field, and the speaker goes quiet.

    I do realize I\'m not helping much with your actual problem, despite the lengthy discussion (which I don\'t mind at all). Is there a heavy smoker in your home, or frequent use of a fireplace, oil lamps, or candles? There has been evidence that smoke or soot can deposit a residue on the panel, which could compromise the insulation. It is possible to wash the panels in mild soap and water, but obviously that is a last-resort measure, since it involves removing the panels from the frame, and the felt from the panels.

    At this point my best recommendation if to pull the grille sock down to the bottom, and thoroughly vacuum both sides of each panel.

    Keep writing - I am dedicated to keeping as many Acoustats producing music for as long as possible!

  • Grill covers - Michele on 2009-08-09 16:00:11

    I would like to purchase new grill covers. Any idea where I can purchase them?

    Andy Szabo (2009-08-09 20:21:13)

    Info copied from Acoustat section Refurbishing and them for genuine factory spec grille cloth:

    We manufacture the Acoustat Replacement Grill Socks. We formerly made them for Rockford Fosgate Corp. and were featured on their site. We are still making them for the previous Rockford customers.

    The Upholstery Company Inc. (Ren and Shirley Jenson)
    418 N. Hunt St. Mesa, Arizona 85203, USA
    +1 (888)994-8273
    +1 (480) 898-9546

  • Additional restoration questions - Tom Montgomery on 2009-07-05 01:24:47

    Andy, thanks for your insight into my wiring problems. Using your guidance, I’ve managed to trace the speaker leads back to the panels and undo the “modifications” of previous owner; I also found another useful nugget of your knowledge here on TAC that I used to order and install new pin connectors on the boards.

    Unfortunately, I have a bit more work to do to bring these spectra 22s back to spec:
    Once I had the socks off and was giving the panels a little dusting with compressed air and a heat gun treatment I discovered the source of a “rattle” that’s grown worse over time at certain frequencies of playback. One of the Mylar panels has become completely separated, torn all the way around the “tab” where the bias wire attaches to the membrane. Although the tear seems to be complete around the 1 inch square area where the coating adheres to the bias wire …somehow that panel seems to be functional except at just that one frequency where it rattles.

    My guess is that I’ll need a new 5 wire panel. In that case, what would be your suggestion for connecting the “new” replacement panel …how do I connect the new leads to the old wiring if, for instance, I’m able to source a used panel from a spectra 11 and the leads aren’t long enough to reach the Spectra 22 transformer? Any advice in effecting this repair would be greatly appreciated.

    I guess that\'s your \"AJS\" I see on the transformers inside my speakers?
    Yours, Tom

    Andy Szabo (2009-08-04 22:16:35)

    Sorry for the delay in responding. I\'ve never heard of a panel failing in that manner, but I suppose there is a first time for everything! If indeed the panel is damaged (probably due to some physical trauma), it is essentially unrepairable. If the bias tab is seperated, the panel might still operate if there is enough high-voltage leakage across the gap.

    You can use any Spectra panel to replace the one you have. To avoid any confusion, remove any traces of old color coding on the replacement panel before attempting the transplant. If you document the wire colors and their positions before removing the old panel, you can easily transfer the color coding to the new wires.

    If the wires on the replacement panel are not long enough, cut the wires off the old panel, flush with the panel. They can be spliced (with solder, please)onto the wires of the replacement panel. Stagger the splices to they are not next to each other, and insulate each splice with heat shrink tubing.

    Yes, those would be my initials \'AJS\' on the transformer. I didn\'t do the testing on a regular basis, but I certainly did quite a few when needed. So does that make your speakers a \"Collectors Edition\"? Signed by the master, hah hah.

    Keep those questions coming - we\'ll get those speakers up to factory spec!

  • More general information please - Raul on 2009-06-21 16:51:52

    Does anyone know where I can get some further information about the Acoustat 1+1?

    Andy Szabo (2009-06-21 17:24:56)

    What kind of information are you looking for? The owners manual for the 1+1 is included in the Acoustat Manual CD available from this website. If your question is not answered there, please post specific questions here and I will answer as best possible.

    Robert (2009-07-13 20:27:16)

    If you want a set, I have one to sell. You can contact me at rjpaulsen1@ g mail (dot) com.

    France Pelletier (2010-02-08 23:22:19)

    I am looking for the following product: A loudspeaker original 10 inches X3761 number or serial number 10 668 802 acoustat model one.

    If you do note have this product, could you help me in my research.

    Excuse my english is very bad.

    Thank you

  • Listening results after repairing - Al.M on 2009-06-08 18:38:04

    Well, from below post I finally got these speakers going about 6 months ago after seeing a professional valve amp repairer who rebuilt the tube amp circuit sockets to help heat dissipation, new valves and capacitors and resistors.

    The resulting listening tests are very impressive for an electrostat with all the usual good ESL sound, good bass, strong voice, imaging, good treble and very powerful impact all round. The sound is not thin at all, just very lush and fullrange. The room I have is not so large for them so anyone interested to buy them, especially in Australia can contact me.

  • Crossover question - David Taber on 2009-05-06 01:43:00

    HI all. Just bought a pair of Acoustats, and looked at the circuit diagram for the xover. Given what sounds to me very thin high end performance, I have a question:

    Across the primary of the step-up transformer for the panels is a big fat (40w) 10-ohm resistor. This is sure to swallow a lot of power, and lower the impedance of the high-end speaker quite a bit. So...what\'s the problem with removing this resistor, or replacing it with a 20 ohm?

    The woofers in my pair were replaced with oddballs that are way too efficient, so I\'ve got the choice of lowering their output or increasing the output of the electrostats. I can imagine totally removing the 10-ohm resistor could cause some impedance-matching issues or maybe even some ringing of the xformer.

    Enlighten me, please...thanks!

    David Taber (2009-05-06 01:43:00)

    Ryan - Assuming that your bandpass filter will adequately protect the audio transformer from low frequencies, then all crossover components on the low-voltage, primary side of the transformer may be removed. All components on the high-voltage, secondary side of the transformer must be kept intact for proper operation of the speaker.

    You did not say if you intend to use a passive or active bandpass filter. If active, I would recommend installing a 0.5 to 1-ohm resistor in series between amplifier and transformer. This will protect the amplifier from the very low impedance at low frequencies. This can be a problem for some amplifiers, even if you are not driving low frequencies. If the filter is passive, located between the amplifier and the audio transformer, then you probably don’t need the resistor.

    Andy Szabo (2009-05-06 19:36:12)

    The 10-ohm resistor is part of a resistor-capacitor network that forms the high-pass crossover for the ESL portion. This is a vital component for the speaker\'s operation, and I do not recommend its removal. Removing it will not significantly increase the volume of the ESL, but it will adversely affect the frequency response.

    Until the woofer is properly matched to the rest of the speaker, you cannot properly judge the overall performance. Many woofers are more efficient than the original ones used in the Spectra 11, so you will probably need to reduce their level to match the electrostatic portion. It is not possible to increase the efficiency of the ESL (otherwise Acoustat would have already done so). The woofer must be matched to it.

    There have been some other posts to this website regarding replacing the woofers in the Spectra 11. Look around, you will probably find information on replacmeent woofers that may work better than the ones you have.

    Ryan Benitez (2012-12-24 04:17:04)

    My plan is to replace the crossover network with a band pass filter crossing over at 15 to 16 kHZ to a tweeter at about 7.5 to 8 ohm at the given crossover point. I also plan to crossover to the woofer at about 250 Hz. What I would like to know is what parts I can remove from the current crossover and what is vital to the panel operation and go be left in place or replaced with a higher quality part. The goal of added tweeters is to flatten then high frequency while increasing the seen impedance my the amplifier. Any help would be greatly appreciated.


    Ryan Benitez (2012-12-29 19:44:03)

    Thanks David, I still do not fully understand the 1 ohm and 10 ohm resistors. I suspect the capacitive value of the panel may be what I am missing. Also unless the impedance is much different than I am thinking (4 ohm) the 100 uF cap should be 6db at about 390 Hz. This is not close to what I was expecting. I am using passive filtering but may go active to the woofer in the future.


    Acoustat Answer Man (2012-12-29 21:33:27)

    Ryan â Iâm not sure why that response was attributed to David â I wrote it. Anyway, on to your questions.

    The purpose of the 10-ohm resistor is to equalize (to a certain extent) the impedance that the capacitor is working against for the high-pass filter, since the impedance of the transformer by itself varies widely with frequency. Calculations of crossover frequencies based on â4-ohmâ or â8-ohmâ will only get you so far, because no speaker has a constant impedance across the audio band. Thereâs always a good chance that a speakerâs impedance at the crossover point is not the same as its nominal specification. Final tweaking of crossover component values should always be done by measurement and/or by listening.

    The 1-ohm resistor is in there to keep the high-frequency impedance above a certain value. Itâs probably a good idea to leave it in there, especially if your amplifier is uncomfortable with impedances below 4-ohms.

    Ryan Benitez (2012-12-29 23:44:56)

    Thank you acoustat answer man. I based my impedance guess on the impedance chart of the spectra 1100. It makes sense that a real measurement at the given point in the circuit should be taken. I think I will leave the 10 ohm resistor in place and take measurements both with and without the 1 ohm. I am ok with dipping a little below 4 ohms but under 2 ohms is uncomfortable.


    Acoustat Answer Man (2012-12-30 00:25:50)

    Now that I think about it, leaving the 10-ohm in place makes sense if you are using a passive crossover.

  • Stacked Spectra 3s - David Whittaker on 2009-04-22 03:21:02

    I was thinking of taking the panels from two sets of Spectra 3s and either stacking them vertically or horizontally making one new set of speakers. I would keep two interfaces per channel and run both full range. A new frame for the panels and boxes for the interfaces would need to be built. I would take care to keep the high frequency portion of the panels together either as a tall line source or in the centre if arranged horizontally. Any thoughts? Thanks.

    Andy Szabo (2009-04-22 21:04:54)

    I\'d recommend the vertical arrangement, if you have the required ceiling height.

    The fundamental difference between the 2/3-panel Spectras and the 4/6-panel Spectras is the audio transformer. Although similar, the 4/6 transformer is designed to drive a larger panel area, and hence has less bass boost.

    Ideally, you should use the 4/6 transformer, p/n TTA-246. These might still be available on the surplus market. If you use the 2/3 transformer, you\'ll want to use the minimum bass tap, and you might still have a little too much bass.

    You can use two interfaces per speaker, but this arrangement would require a separate amplfier channel per interface (four total for the stereo pair). You don\'t want to parallel the two interfaces on one amplifier channel due to the difficult load.

    I don\'t see any reason why you can\'t drive all the panels of one speaker with one interface. This would reduce the number of required amplifier channels, and greatly simplify any modifications to the interface enclosure. In essence, you would parallel the top panels\' connections with those of the bottom panels, connected to one interface. This is the way it is done in Acoustat\'s Spectra 44/4400 and 66/6600.

    If you don\'t have the ceiling height required for a vertical stack, I would suggest at most 2 panels added to the outer edge of each speaker, driven at low frequencies only.

    Sounds like a fun project. Do write again if you have further questions.

  • replacement panels - Bob Jones on 2009-04-14 17:04:33

    Are the panels in the 1100 the same that are in the 2+2\'s........again need to replace a 2+2 panel, thanks Andy............

    Andy Szabo (2009-04-15 22:04:17)

    The panels in the 1100 (or any Spectra model) are not the same, but they are compatible as replacements for the panels in your 2+2\'s.

    First, all Spectra panels have a split stator, which allows each half of the panel to be driven with a different signal. But you can hook them up the same as your 2+2 panels, where the two halves of the panel will be driven by the same signal. The speaker will never know the difference. If your speakers are so old that they use 3-wire panels, you can still use the 1100 panels, but write again so I can guide you through their hook-up.

    Second, later panels (and all Spectra\'s) used an improved conductive coating, which allows higher dynamics and is also less susceptible to popping noises (good news for you!). Unless your 2+2\'s are very late production, they will have the earlier coating, but you can use the newer-coating panels with no ill-effect.

    So, if you are eyeing a pair of 1100\'s as a potential source of replacement panels, I say go for it!

    FYI - I have seen on eBay some \'Italian-made\' Acoustat panels. They look very different, and I don\'t know if they are even the same size. I cannot comment on their compatibility.

  • Panel - Bob Jones on 2009-04-14 15:42:36

    Andy, thanks for the reply yesterday regarding the popping I was getting out of one of my panels. Well I totally destroyed that panel, to much heat. My question is, do I buy another set of speakers and than have a ready supply of panels (7) or do I move on to an electrostatic that has a readily available part supply. I have had these speakers for 3 weeks and I won\'t go back to a conventional box speaker. Put your Acoustat prejudice’s aside for just a minute (LOL) and guide me in the right direction.............again thanks........Bob

    Andy Szabo (2009-04-15 21:49:50)

    Replacement Acoustat panels do appear occassionally on eBay, so don\'t give up hope just yet in finding a replacement. Or, you may be able to find a smokin\' deal on a pair of speakers that you could use as a parts source - just about any Acoustat model could be used.

    Setting aside my Acoustat prejudice (which admittedly is pretty strong), one does run the risk of not being able to get replacement parts for a brand that is no longer in business. However, some genuine parts are still available from surplus dealers who bought up Acoustat\'s remaining parts inventory (again, see eBay). Also, among ESL brands, Acoustats are definitely the most rugged and long-lived, so your need for replacement parts will be (statistically speaking) rather low.

    Admittedly, some currently-produced ESL\'s might provide a certain performance improvement over at least some of the Acoustat models. But in terms of value (i.e. purchase price) I doubt you can find a better sonic value than a pair of used Acoustats.

    OK, that might not sound like I put aside my Acoustat prejudice, but I truly believe in what I say. I no longer work for the company or have any financial stake in the brand. I answer questions for Acoustat owners because I believe in the product, and want to see them enjoyed for as many years as possible. I have owned various Acoustat models for over 22 years now, and they still thrill me on a daily basis.

    Bob Jones (2009-04-16 05:58:41)

    Again thanks for the reply..... I went and found and bought a pair of 1+1s for a donor as well as a pair of 3\'s that I will leave alone. Are the 3\'s panels as follows; two 9\" panels and one 8\" panel? The 1+1s have the medallion transformer, can I use that in the 2+2s that I have? And one last question, can I use these speakers on a daily basis with the reliability you so much talk about or because of the age of these speakers they should be used sparingly?

    Buying the 1+1 as a donor set will give me the flexibility to have extra\'s to use or to sell to someone that gets in the same situation as find myself in.

    Again thanks for sharing the knowledge. My 2+2s are only 3 weeks old to me and I find them to be the most realistic speaker I have had in my system, which is going on for well over 35 years. I have had Magnepan’s, Quad’s and Martin Logan within that period of time and they did not have the bigness that the 2+2’s have, I can’t wait to get them back up and running.

    Andy Szabo (2009-04-17 03:24:22)

    You are correct: the center panel on the Model 3 (and the two center panels on Model 4\'s) are only 8 inches wide, whereas all other standard Acoustat panels are 9 inches wide. These 8 inch panels are the only ones you can\'t use in your 2+2\'s.

    Yes, you can use the Medallion transformers from the 1+1\'s in your 2+2\'s. Both use the same MK-121 series interface. The upgrade is definitely worth it. The only difference is the adjustment of the bass-tap on the low-frequency transformer. Red tap for the Model 1+1\'s, yellow tap for the 2+2\'s.

    If the interface chassis is the same style on both models, it is a simple matter of swapping out the interfaces. If your 2+2\'s use the older oblong box, then you\'ll have to transfer components from one box to the other.

    By no means should you \'use the speakers sparingly\'. They are meant to be played and enjoyed, and will probably sound even better if played frequently. And don\'t be afraid to turn it up when the mood strikes: the 2+2\'s are capable of fairly high SPL. I have found no evidence of any significant degradation of the panels with age, even for panels from Acoustat\'s earliest models from the 70\'s. As long as they are cared for and kept reasonably clean, they should provide many more years (or even decades)of excellent performance.

    This extremely long lifespan is certainly not the case with most ESL\'s, and even some dynamic speakers fall apart after 10-20 years (think rotten woofer surrounds!). This is yet another reason I help Acoustat owners: I get to monitor the speakers\' long term performance, and if I can help to \'cheat death\' for a few speakers with my repair and restoration advice, all the better!

  • Popping...........again - Bob Jones on 2009-04-13 17:29:24

    I have read all there is to read on these phenomena as well as other forums regarding this popping or snap noise. I have owned these speakers for 3 weeks and the left speakers left lower panel has developed a soft pop or snap in the middle. I took the sock off and left the speaker over night, I vacuumed, used compressed air, tapped with the palm of my hand to see if I couldn\'t knock a small piece of dirt or lint from the panel, to no avail. About every 30 seconds the pop again pops...... This is not audible when playing music, the panel seems to have the same db as the others. Is there anything that I haven’t done to remedy this. Also there are two very small pinholes in that same panel, they are in the up 25% of the speaker, not where the pop seems to originate from however.

    Andy Szabo (2009-04-13 22:42:18)

    Sorry to hear that you have not been successful in eliminating your speaker\'s popping noise. This can be a pesky procedure, and it often takes several attempts before you are successful. When you say you \'left the speaker overnight\' I am assuming that means you disconnected the AC power and let it discharge. If that is not the case, you\'ll want to repeat what you did with the speaker fully discharged. Any electrostatic forces remaining in the speaker will tend to make any foreign matter that much harder to dislodge.

    What you see as \'pin holes\' are probably not holes in the mylar diaphragm itself, but small voids in the conductive coating. This is not entirely uncommon, as the conductive coating was applied by brush in a liquid form, and sometimes small voids or even streaks are visible. I don\'t see this as a problem, and it is not likely related to your popping sound.

    My only advice going forward is to keep trying. When I bought a pair of used Spectra 4400\'s a few years ago, they were very dirty and hadn\'t been used in many years. They exhibited a similar popping sound, and a thorough cleaning helped, but it did not entirely eliminate the problem. However, the problem went away on its own after a while. Don\'t give up hope yet!

  • Wiring question - Tom Montgomery on 2009-03-13 02:22:26

    I took delivery on a pair of Acoustat 22s and trying to assemble them ran into this problem: the transformers each have seven inputs (labeled and color coded in descending order WHITE-YELLOW-BLACK-RED-BLACK-YELLOW-BLUE). Each speaker has only five connectors (BLUE_YELLOW, RED and BLUE/BLACK for one, for the other BLUE_YELLOW, RED and YELLOW BLACK).

    So, what goes where ...and why?

    Thanks for any input in advance, Tom

    Andy Szabo (2009-03-26 19:41:28)

    The seven outputs from the transformer interface are as follows:

    blue-black: rear stator, lows only
    blue-yellow: rear stator, mids and lows only
    blue: rear stator, full range
    red: diaphragm, +5000 volts
    white: front stator, full range
    white-yellow: front stator, mids and lows only
    white-black: front stator, lows only

    As to why your Spectra 22s have less than seven groups of wires per panel, I am stumped. My guess is that someone has modified the speaker, although from the remaining colors on your speaker, I am not sure what they were trying to accomplish.

    Unless you can contact whoever modified these speakers, (to find out what they did), you will probably need to remove the grille cloth and (hopefully) find the missing wires. For each Spectra 22, you should find these wires (10 total):

    blue-black: 1 wire
    blue-yellow: 2 wires
    blue: 1 wire
    red: 2 wires
    white: 1 wire
    white-yellow: 2 wires
    white-black: 1 wire

    Unless the missing wires have been cutoff flush with the internal panels, you should be able to reconstruct the speaker. If you can\'t fix it, you should ask for your money back. If you can find all ten wires, but you\'re not sure how to reconnect them, I can help with that.

    I know this is not the definitive answer you were looking for. Do write again if you need more help. I\'ll do everything I can to help you get your speakers working properly. Good Luck!

    Tom Montgomery (2009-05-21 19:32:58)

    Thanks for the info Andy; this has clarified what I need to do. I can see now that all ten leads from the panel array are present and that the previous owner seems to have pulled the leads off the \"bass only, black\" connectors on the board and combined them with the \"full-range, white\" connectors effect, making two full-range sectors ( at least I can see through the sock that there\'s ten leads going into the panels). I haven\'t yet removed the sock and followed all the leads to the panels but I have bought twenty new plugs and jacks from Mauser (using your valuable info here on TAC). My next task is to rewire the speakers, planning to use 16ga vampire wire. I should mention that I have very little experience in attempting this work and have questions:

    It looks like from your factory tour photos here at TAC that the bias wires are taped onto the frame and otherwise attached how? I could\'nt see the how the other, stator wires are attached to the panels, but I assume when I get the sock off that I\'ll see how they\'re attached and merely follow your instructions here as to which wire (front and back) goes to which sector. I\'m somewhat confused by your reference to the original color coding, since my transformer jacks are only one color each(white, yellow etc.), as are the pins from the arrays. As I could buy only red pin connectors, the color coding is irrelevant to me now and I\'ll find another way to ID the leads for future hookup. Although the connectors have been obviously resoldered and rearranged, the board itself, resistors underneath and so on I remeber as having been untouched I\'m hoping the board itself is untouched. Any advise for me on attachment at the array end or other considerations for which I should be looking out?
    Thanks, Tom

    Andy Szabo (2009-05-21 22:41:58)

    I recommend against replacing the internal panel wires with anything different than original. The original wire is custom-made, with a special oxygen-free copper conductor, and a 10,000-volt rating on the insulation. The gauge of the wire is small, but the current flow is very low. Almost any \'audiophile\' wire will not have sufficient voltage rating and may arc-through.

    Furthermore, the wires are not connected to the panel with any sort of detachable terminal. The wires continue uninteruppted inside the panel and form the stators. The bias wire is also permanently connected to the diaphragm.

    The bundled wires are secured to the wooden frame by nylon cable-clamps, not tape.

    When referring to the different colors on the interface board, the single red bias jack is in the middle. The \'blue group\' is on one side, and the \'white group\' is on the opposite side.

    It looks like the previous owner tried to \'un-Spectra\' the speaker. That doesn\'t really work, since the transformers and RC networks were designed to drive a split-sector system. If you don\'t have the owners manual, I recommend you get the Acoustat Manual CD available from this website. It shows the schematic and a diagram of the interface board, which should help you understand the connections. Keep writing with your questions until we get these speakers back to factory-original configuration. It\'ll be worth the effort!

  • Different sound levels ( left > right ) - Roy on 2009-03-09 09:40:15

    I have recently purchased a pair of Acoustat 2+2. The left speaker seems louder than the right one. I can centre the imaging by positioning the speakers assymetrically which is not the proper solution.
    If positioned symmetrically i.e. both in the same position on both sides of the room and toed in the same, the image is way to the left so I get only half a soundstage with the the whole performance from the middle of the stage to the extreme left and nothing on the right. There is output from the right speaker and, listening from close up, it is not obviously down in volume.
    I believe the Spectra 66 volages can be adjusted. Is this possible with the 2+2 and, if so, how? This unit has the MK121-2A power supply/crossover with Medalion transformers.

    Andy Szabo (2009-03-09 20:42:48)

    The bias voltage cannot be adjusted on the Model 2+2, as can be done on Spectra models with the Ultrasonic Bias Power Supply. The bias supply on the MK-121 series is fixed and unregulated.

    But you are correct in suspecting that you may have a problem with low bias voltage. Elsewhere on this site, check out my Technical Bulletin that discusses measuring the bias voltage. You may have a bad diode or capacitor in the voltage multiplier that is causing a low bias voltage.

    You might also check the blue and white wire connections to the panels\' stators. If one of the stators is not energized, it will definitely cause the speaker to play at reduced volume. If the hook terminals at the end of the wires are covered with heatshrink tubing, the wires may be broken inside the tubing even though it looks securely attached from the outside.

    Since you didn\'t mention that the reduced volume is frequency dependent, you can probably rule out a problem with the audio transformers (good news!)

    I suggest you measure the bias voltage on each speaker to see if they are very different from each other. If so, measure the voltage with the speaker connected, and then again with the speaker disconnected. If the bad speaker measures low under either condition, then you have a problem with the bias supply. If it measures low only when the speaker is connected, there is something in the panel that is drawing down the voltage (this is a pretty rare circumstance). This can also be verified by swapping the interfaces from one speaker to the other.

    Do write again if you can\'t solve the problem. We WILL get your speakers working properly!

    Roy (2009-03-10 20:46:03)

    Thanks for the advice. Actually, I thought the hook connectors were broken rings so I replaced them with rings crimped and soldered.

    Roy A. Esposito (2011-07-17 20:01:17)

    July 17, 2011

    I am very much alive.

    I am No-Where near retiring .... and over many years have
    come up with astounding improvements, variations and restorations
    for the Acoustat MK and Spectra Interfaces
    and even more so the Trans-Nova amplifiers (TNT-200 and TNT-120)
    and Trans-Nova Preamplifier (TNP).
    I also renew the earlier and more rare, Acoustat MRP and RP-2 preamps.

    To my chagrin ----
    Folks don't realize I was many years younger than the
    other principals at Acoustat, back in 70's and 80's Fort Lauderdale.
    About half their age at that time.

    I am happy to continue lovingly working with Acoustat products.
    I do this with a fully functional laboratory and stockroom
    of original .........and improvement parts.

    But please realize that... in 2011....
    this is part-time work.... in addition
    to my regular full-time engineering/consulting work.

    So it can take a few weeks in total, for me to work my
    Acoustat "magic"...... as my client's have often
    described the results.

    I hope the above will help explain why I don't
    provide a phone number, except to established clients,
    and I prefer email contact instead. I also prefer my work
    and "word-of-mouth" to speak for itself
    ....instead of having and spending time maintaining a website.

    There are others that offer work on Acoustat products.
    Fancy words .... Fancy websites.
    But NONE of them worked for the Company.
    And to correct the mess.....
    Folks usually end up with me despite the glowing website tetimonials.
    That's just sad.

    I very much appreciate all of you, who continue to revere...
    and enjoy...
    the magnificent design works of Dr. Strickland,
    and our original Acoustat Engineering Team.

    May we all enjoy the Music,

    Roy A. Esposito /

  • IC chip replacement - rex hookens on 2009-01-17 11:00:24

    Hello Andy Szabo,thankyou for the reply,regarding both my speakers not powering up,i take on board your comments, i had a technician take a look at these boards,he found the problem to be the LM13080 chip has gone down on one board,the other board was a small cap,which has been repaired,the problem is this IC chip is no longer in production,do know where i can get one or is there an equivilent?thankyou for any help.
    kind regards Rex(in France)

  • Buzz (Round Three) - N. Tony Fasola on 2008-12-27 00:15:17

    Andy: First let me thank you again for your previous and prompt responses. I am sorry to report that after four attempts with my heat gun I have not been able to solve my panel buzzing/vibrating. In fact, after today's attempt, the panel (upper left on the left speaker) has become totally unlistenable. It now vibrates very loudly on virtually every musical passage with any bass notes. Another thing that I noticed, was at this time powering up the speaker, the panel began emiting crackling that seems to not have abated after the initial charging. I was very careful and conservative with my heat source and I can't imagine that I damaged the mylar but I also can't imagine what is going on and why it is so much worse now. (It almost sounds like the wires are vibrating off of the mylar) I'm kind of at wits end and sounds as if I might be in the market for a replacement panel. Do you have any more advice to what I am experinceing and possible solutions before I begin my panel hunt? Also, if indeed the panel is bad and I remove the one panel, would it be safe, or prudent, to drive the speaker with one panel missing? Will it effect the interface? Thanks, as always, for your support. Kindest regards, Tony

    Andy Szabo (2009-01-01 16:31:56)

    Sorry to hear that your problem continues to get worse. You might have one of the very few Acoustat panels that has permanently failed - maybe. Once you remove the panel, you might be able to see the problem. Don\'t give up on that panel until you know what the problem is! You might have a foreign object caught in the gap. Be sure to remove the felt blocks on the rear to inspect the area underneath. A loose wire is pretty bad, but maybe could be fixed (at that point you would have nothing to lose by trying). If you have a tear in the mylar, the panel is trash.

    It is ok to operate the speaker with a panel missing. You can compensate somewhat for the loss of bass response by temporarily moving the tap on the low frequency transformer from yellow to orange. The interface will think it is driving a Model Three, albeit with an odd shape. Your system balance control may also be used to re-balance the speakers.

    Good Luck, and keep writing if need be: I\'ll hang in there with you until we get the problem solved.

  • Looking for Spectra 66/6600 to buy - Gary Smith on 2008-12-23 06:23:39

    Are there any posters that may have a pair of either the Spectra 66's or 6600's to sell as I have been searching for a decade without success, will arrange to either have myself personally pick them up or to be have a freight company pack them and transport?? Thank you Gary

    Andy Szabo (2008-12-23 19:05:01)

    I understand your frustration in trying to find a pair of these speakers. Very few of the 66 or 6600 were produced. I would guess fewer than 100 pairs, perhaps much less. Add to that the fact that such speakers usually represent an ulimate lifetime purchase, and it is easy to see why they rarely appear on the used market. I\'ll assume you\'ve been monitoring eBay. Acoustat models appear frequently, although I don\'t recall a pair of 66 or 6600 ever being offered for sale. Keep up the search: you won\'t be disappointed when you find them!

    Gary Smith (2009-08-11 23:30:32)

    Andy, I fianlly fulfilled my dreams..I got a pair of 6600\'s, infact drove half way across the country to pick them up..and they were definitely worth it..great midrange and bass, truly the best speakers that I have heard, so natural and melt right into the room. Definitely worth the wait in all respects, ashame that didn\'t make more as I think they\'d be hard to keep in stock.

    Andy Szabo (2009-08-12 19:37:49)

    Congratulations on finding a pair of 6600\'s! I\'m so happy for you! Not too many of the Spectra 66\'s or 6600\'s were produced, and most owners hang on to them for a long time, so you were lucky to find a pair.

    My 4400\'s still thrill me on a daily basis, but if I were to change, it would only be for a pair of 6600\'s, which I\'m not even sure would fit in my room.

    Happy Listening!

  • Acoustat transformers - Dan Todd on 2008-12-13 03:13:13

    Andy, I had owned a pair of 2+2s that I bought from Read Brothers back in 86\'. I know (the hard way) that the problem with these speakers is the low frequency transformer (TT-121L) is prone to arcing in the secondary if driven hard. (All transformers can be overdriven.) The most common problem is where the secondary wires are \"dressed\" and secured. The yellow wire tends to arc to opposite polarity (blue) outer windings due to the high voltages and close proximity. Anyway I do notice that the TTA-246B transformers utilized in the Spectra 44/4400 greatly reduce this by using separate cores for each polarity, but I also noticed a 10M ohm resistor in line between the two transformers common return and ground. I think this also helps to prevent arcing to the core, since the old TT-121L single core has a center tap that is connected with the ground of the bias power supply. I know that the 44/4400 and the 2+2 are different and have read all the postings over the years. It is possible to convert the 2+2 to spectra with the mod (cutting of the stators at mid point of each panel), purchasing the TTA-246B transformers which I have and then incorporating the necessary resistors of the spectra interface. All in all, not easy but for me not to bad. The only thing I dread is the frame change to bring the panels back to a straight plane. My questions are concerning the 10M ohm resistor and also the input 10uf caps on the primary of the TTA-246B. Are these caps used to prevent some sort of ringing (resonant frequency)? I think the 1ohm resistor is as described with the TT-121L, am I right?

    Andy Szabo (2009-01-01 17:06:36)

    The MK-121 low frequency transformer does have a tendancy to arc when driven very hard. The Medallion version of the transformer addressed this problem somewhat, but did not cure it. The basic problem still exists: both plus and minus voltage swings are on the same transformer. The full range Spectra models avoided this problem by using two transformers, one for each phase, thereby reducing the maximum voltage difference inside the transformer by a factor of two. I don\'t recall ever seeing an arced-over full-range Spectra transformer.

    The 1-ohm resistor in series with the transformer primary has the same purpose in both MK-121 and Spectra: to make sure that the impedance at extreme low frequencies is above 1-ohm. The difference in the Spectra is that the resistor is paralled with capacitance, essentially bypassing the resistor at higher frequencies.

    The 10-Mohm resistor in the Spectra transformer\'s secondary ground connection is there for shock protection. If you were to accidently connect your body across circuit ground and a high voltage audio point, the fault current would be limited by the 10-Mohm in series. This component is recommended for safety reasons, but is not required for audio reasons or for arc-protection.

    It seems as though you have correctly identified the various challenges to convert a 2+2 into a Spectra 44. Not a project for the timid - good luck if you decide to embark on this project.

    Dan Todd (2009-01-01 19:34:01)

    Thanks Andy. You have been a GREAT asset to the enduring fans of Acoustat! I remember talking to you when Acoustat was still in Florida. I have went back to my old 2+2 speakers after trying the low watt, single-ended, direct heated triode realm of audio. If only it were possible to drive electrostatics with a 45 tube triode amp...oh well.

    Yes, I know about the arc problems with the TT-121L transformers, and have talked to Ken at Galaxy transformers about getting a larger core with more mylar insulation. He\'s a great guy to deal with. The problems are still existing today even with their improved models, if you drive the transformers hard. Well it\'s going to be a mute point when I change over to the TTA-246 Spectra interface. I was fortunate to acquire a set of four to change over to Spectra 44. The 680K resistors and 75K resistors should ideally be high voltage (5KV) types but it doesn\'t appear that way when acoustat produced them. The .022uf poly cap will be substituted with a .02uf, 15KV high quality polypropylene from and ebay source. I\'m sure even the original acoustat type wasn\'t that close in tolerance. As I said before, I don\'t look forward to modifying the frame and may build a new one.

    I\'ll post the results after the change. I too have a set of HSU/Dayton subs to crossover on the very low end. Thanks again...Andy. God bless Jim Strickland.

    Andy Szabo (2009-01-02 01:49:27)

    The 680K and 75K-ohm sector resistors are indeed high-voltage types, rated at 5-kV. The .022-uF was likely 5% tolerance, but .02-uF would probably be fine. I believe the bare high voltage board is still available as surplus on eBay, which would sure make construction easier. I have even seen fully stuffed boards for sale (with component values for the 44/66) but they may be gone by now. Contact sellers \"dealsbyjason\" and \"soundvalves\" and let them know what you are looking for.

    The Acoustat CD available from our webmaster has frame drawings, and I believe the Spectra 44 is amoung them. I\'m not sure that modifying a 2+2 frame will work, as there may not be enough space within the frame rails for two panels laid flat. I think it would be easier to build new fgrames from scratch.

  • Buzz (Revisited) - N. Tony Fasola on 2008-12-12 22:07:46

    Well the gentle pounding on the grill didn\'t seem to turn the trick. Because I knew the \"buzz\' issue was at the top left,I shimmied the grill cloth from the top down (Acoustat employess must have been paid per staple!!) Imagine my surprise to fine everything in order. No loose screws, and nothing apparent to be damaged or such. I charged the speakers back up sans grill and the buzz is quite a bit worse. (go figure) I guess it\'s time for the hair dryer. Excuse my ignorance but should I work from the front or the back of the speaker to shrink the mylar or does it even matter? I\'ll let you know what transpires.

    Andy Szabo (2008-12-13 03:57:18)

    It doesn\'t really matter which side of the speaker you apply the heat to, although you will have better access on the front. The rear surface is partially blocked by the felt. Just remember to keep the source of heat moving at all times, so as to avoid overheating a small area.

  • Extra resistor in parallel with driver? - Liam on 2008-12-06 04:32:29

    Andy in comparing the circuit diagram supplied on the CD obtained from this site with my interfaces I note that I have a high wattage 6 ohm resistor in parallel with my 8 inch driver. Andy do you know if this was a later factory mod or was this just mistakenly left out of the schematic?

    Andy Szabo (2008-12-07 01:05:03)

    I answered this question (as best I could) under your previous question \"Interchanging 11 drivers with 1100\'s\".

  • Acoustat 2 versus New Quad els2905 - Andrew Mack on 2008-12-05 19:07:46

    I have owned these speakers for 20 years and they still delight me every time the stylus hits the groove. We have recently auditioned the Quad ELS 2905\\\'s and although the Quads are excellent they certainly do not wipe the floor with our faithful old Acoustats, a design nearly three decades old. The Acoustats image incredibly well creating a depth of field which is simply breath-taking. Amplifing anomalies prevented a full and fair assessment of the Quads, which I hope to have back for a further audition sometime soon. I use DNM pre and power amps (see Stereophile Dec 2008) which are average watts but high current. The results are stunning. Can you please advise what maintenance or renewal of components i can do to bring them back up to scratch? I am told that some components will be tired by now. great to see there are other enthusiasts out there. many thanks Andrew Mack I look forward to your reply

  • Power handling - francesco Izzo on 2008-11-26 16:53:09

    Hello again Andy, time ago, listening to my friend\'s Martin Logan CLS I wondered how my spectra 11 ESL would sound WITHOUT any crossover. That\'s because I use to listen at night at low levels and I supposed that @ low signals no damage could occour. So, I arranged a large wooden baffle to mount ESL like a dipole, bypassed the crossover in the interface and disconnected the woofer... Surprise ! Driven in full range the sound of the ESL was excellent! There were low frequencies enough to enjoy all kind of music, at levels that could wake up my wife with ease! For sure it can\'t handle hundreds of watts, I think it should follow the same law of normal speakers (excursion increases as the frequency gets down), but now I would like to know what is the real max excursion of the panel vs frequency (at rated distorsion, say, 1 %)? In other words, what is the maximum level I could apply to the interface without slamming the membrane to the stators? It would be a great work to me to check it by myself (I should have at least a frequency meter, a signal generator, an oscilloscope...), maybe there is any documentation out there? Thank you in advance for your reply and for helping us dream with Acoustat. Francesco izzo

    Andy Szabo (2008-11-26 17:35:40)

    There are no hard numbers available to answer your question. But, I can offer some comments that should put your mind at ease. The system will let you know when the diaphragm reaches its mechanical excursion limit. It will emit a crackling or snapping sound. This will do no damage to the panel - unlike some ESL\'s, it\'s almost impossible to damage an Acoustat panel from over-driving. This is true of any Acoustat model, whether it was designed to operate full range, or operate over a limited range as in the Spectra 11. And, unlike conventional magnetic drivers, the behavior of a push-pull ESL will remain nearly the same all the way up to the limit of the diaphragm excursion. In other words, there is no steady increase in distortion as volume increases. However, with a single panel operating full range, the dynamic output will be limited, especially at bass frequencies, due to the limited panel area. It is possible that you may over-saturate the audio step-up transformer in the 11, since it is not designed to operate full range. Note that the transformers in the full range Spectras are much larger due to their ability to handle bass frequencies. I\'m not so much concerned that you would damge the transformers, since the panels will probably reach their excursion limit before the transformers could be damaged. But, you may suffer some low frequency distortion in the transformer before you reach the panel\'s limit. So, there is nothing wrong with what you have done, as long as you are happy with the results. Adding baffles to the panel will increase bass response somewhat, although that may interfere with the open, airy sound, and hence imaging.

  • Woofer enclosure dimensions anyone? - Liam on 2008-11-20 01:03:07

    Can any one run a tape measure over their speakers and provide either the outer or inner H x W x D dimensions of the SPectra 1100 woofer enclosure? Many thanks in advance. Liam

  • Interchanging 11 drivers with 1100 \'s? - Liam on 2008-11-17 04:54:39

    Does anyone know if it feasible to use the 8 inch drivers from the spectra 1100 in the Spectra 11 speakers? Note, I am only thinking of changing over the drivers (won\'t be using crossover on the cups in the 1100\'s). I am interested in this as an upgrade. I imagine since the panels are identical in both models that it is likely that the crossovers in the spectra 11 interface will work with the spectra 1100 8 inch drivers with no need to change any values. Many thanks in advance for any comments or suggestions.

    Andy Szabo (2008-11-18 00:49:38)

    You can probably use the 1100 woofer in the 11, assuming the hole is the same size (I\'m not sure that it is). They are both nominal 8\" drivers, but the different baskets may have slightly different mounting holes. If the driver does fit, you will not instantly have an 1100. Although both models roll-off to the panels at the same frequency, the crossover component values are not the same. This is due to the different cabinet volumes and very different woofers. So, you will probably notice an improvement, but not necessarily so, despite the much better woofer.

    Liam (2008-11-18 06:54:52)

    Many thanks for your help with this poject Andy. I am stunned at the fantastic support you are still providing to the Acoustat faithful! Many thanks! I had wondered if the enclosures were different sizes as I have begun to suspect my woofers are over damped. I am going to stick a brick in the cabinets with the current 11 woofers as a quick experiment to see what I learn Andy you may be interested in this very interesting article I found written on replacement woofers for the Spectra 11\'s writen in March 1990. I am going to do some calculations to see what I think the ideal characteristics of a new woofer might be based around a QT of somewhere between 0.7 and 1 and the current volume of about 1.6 cu feet and the existing cross over and then see if I can find a driver that works better than standard. It\'s been many many years since I attempted this stuff!! Keen to share info with anyone who has been down the same pathway. I\'ll post what I learn and discover. Once again Andy many thanks for your help so far.

    Liam (2008-11-18 10:39:36)

    I think I have come up a reasonable option. Can\'t say yet whether it will sound better than original. The Peerless SLS 830667 8\' 8 ohm driver (assume original is 8 ohms but will check tomorrow) Pretty good fit for existing hole @ 178mm or 7 inches. Qts = 0.54 Vas = 33.1 litre (1.169 cubic feet) FS = 36.5 Hz Using the calculator at I calculate with a Qtc of .707 (Flattest truest response) the following: Volume of box 1.637 (very close to current cabinet size) F3 (lower 3dB cut off point) 47.8 Hz It has a reasonably low Fs resonant frequency of 36.5 Hz. Read elsewhere originl is 70 Hz The magnet seems fairly big 870 grams (30.7 ounces). should have lower Q than original - which should smooth resonances. I read elsewhere original magnet is about 7 ounces. So unless anyone can recommend anything of higher quality I am going to try these. they are available from for $52.75 The one thing I am not sure of is will there be a need to alter the cross over circuit?

    Andy Szabo (2008-11-18 18:56:20)

    You will almost certainly have to alter the crossover for optimum performance. You\'ll just have to try it and go from there. I can\'t give you any advice in advance. Parts Express is another good source for audio parts (woofers and crossover parts included). They are at They currently have a very nice Morel 8\" woofer on clearance sale.

    Liam (2008-11-18 23:44:11)

    Big surprise! I just measure my existing 8 in drivers speakers DC resistance. It measures 3.5 ohms suggesting it is actually a 4 ohm impedance speaker.(not an 8 ohm as indicated in the audio basics article I mentioned earlier in this thread). The Peerless mentioned earlier in this thread is 8 So it\'s back to the drawing board in search of a replacement. ohm. Mine are later model Acoustat 11 speakers. I\'ve owned them from new. I guess it is possible that Rockford ran out of 8 ohm Spectra 11 drivers and put a 4 ohm driver from the Spectra 1100 into my speakers - in which case they would have needed to change the crossover values and my box volume 1.6 litres would be wrong for the spectra 1100 speakers. I\'ve checked and I don\'t have any crossover components on the back of the cub in the driver cablinet - so they would have had to do this on the main board - so it\'s a bit of a mystery. Ror interest part numbers for existing driver are: P6318 on the paper cone 791105 on the magnet 24126 on the metal base (same number as the photo for Dave Ayer\'s 1100\'s here

    Liam (2008-11-19 11:48:07)

    Andy I am coming to the suspicion that Rockford fitted the 100 drives into my spectra 11\'s. They certainly look identical to the photo that Dave Ayers posted for his 1100 drivers. Not sure how I can confirm this unless the part numbers I quoted above match someones spectra 1100\'s or if someone has a photo of the spectra 11 drivers In which case the volume of my box and the crossover values could be wrong. Firstly I want to check the box volume: Could you do me a big big favour and give me the either the outside or inside dimensions of your woofer box? My boxes inside dimensions are 13.5W X 16.5H x 12.5 D = 2784 sq inches = 1.611 cubic feet. Of course the volume of the driver inserted in the box reduces this slightly.

    Liam (2008-11-19 21:23:03)

    Thanks to fantastic support from Rockford I I have incredibly obtained from Rockford Acoustic Designs, the drawings and full specifications including thiel paramaters (dated oct 3rd 1996) for the 4 ohm driver used in the Spectra 11 (and I think the 8 ohm ) driver used in the Spectra 1100 speakers! Can some one advise how I can post this PDF to to this web site or if you want me to email you a copy just let me know.

    Liam (2008-11-20 00:52:41)

    Ok now I have had a bit of chance to play and here are my findings. Andy and many of the original reviewers are correct, the woofer in the Spectra 11 is it\'s Achilles heal. I think it\'s a waste of money upgrading to esoteric capacitors, etc until you have dealt with the major problem. The Spectra 11 has a beautiful midrange and fantastic stereo presentation, but the base is an uncontrolled mess. The driver specifications obtained from Rockford confirm the driver is wildly underdamped in the 1.611 enclosure. In theory and practice this driver is much better suited to a significantly smaller enclosure. As an experiment I stacked 6 inches of Vanity Fair magazines in the bottom of each speaker (being careful to keep the editions with Jennifer Aniston and Angelina Jolie on the covers in different speakers - to avoid inter-issue interference) As expected damping the driver in this manner tightened up the base considerably. And although I haven\'t measured it I suspect I have also lowered the frequency of the 3dB cut off. Both good achievements. OK so why did the very clever engineers at Acoustat/Rockford put this driver in a cabinet that was clearly to large to control the driver at lower frequencies and that also raised the frequency of the lower 3dB cut off point? Efficiency! Putting the driver in a smaller enclosure greatly increases the efficiency of the driver and as I have discovered by inserting Angelina and Jennifer into my speakers the woofer drivers now over power the top end and bringing the middle to upper midrange to forward (loud) and consequently ruining the beautiful natural smooth vocals of the Spectra 11 - but by god does it improve the quality and tightness of base drums! Clearly Jennifer and Angelina are not the right match for me (sorry for any offence I might cause the two ladies). I don\'t think the quality of the driver is the main issue. Although there have probably been improvements in driver linearity and it may be possible to extend the lower range of the speakers with a better suited replacement driver. The right solution could be to make the enclosure smaller and make some revisions to the cross over circuitry to cut some power to the driver. Or alternatively find a lower efficiency driver better suited to the current volume of the enclosure. So why wasn\'t this addressed initially? The Spectra 11 was a budget version of the Spectra 1100. Contrary to other comments I suspect that both speakers may have used very similar drivers (if not the same drivers). the drive in my Spectra 11\'s looks identical to the photo of David Ayers Spectra 1100 driver - shown eleswhere on this site) It\'s been reported that the Spectra 1100 had a smaller cabinet size (1.3 cubic feet -without driver inserted - I am currently trying to get L x H x w measurements to confirm volume.) and it definitely had a different cross over configuration that may have addressed the efficiency issue.

    Andy Szabo (2008-11-20 17:09:14)

    I can assure you that the woofers used in the Spectra 11 and 1100 were definitely different drivers. They are visually quite different, from both the front and the rear. The 1100 woofer has a larger magnet and was much more expensive. I cannot confirm your comment that Rockford might have substituted the 1100 woofer in some 11\'s. This seems unlikely, but not impossible. If any one had asked my advice on the issue, I would have said don\'t do it. If you have seen photos of a Spectra 11 with what appears to be 1100 woofers, it may be that the pair was upgraded with different woofers. Just so you know, both woofers were specifically designed to operate in their respective cabinet volumes. How well that was accomplished is certainly open to debate. The smaller cabinet volume of the 1100 was dictated by the marketing dept\'s desire to make the cabinet more pleasing to the eye and to lower the panel height slightly. I have a pair of Spectra 1100\'s and will measure the cabinet for you. I also have an extra pair of woofers (sorry, they are not for sale) and I will get the p/n from them, as well as verifying whether they are 4 or 8 ohm. Congratulations on getting the spec\'s from RAD - that is incredible. Contact the webmaster about posting the information: it can be added to the Acoustat Manual CD available from this site. By the way, you should try stuffing the speakers with \'National Geographic\' or \'Smithsonian\' magazines rather than \'Vanity Fair\'. I think you will find the sound to be less snooty and more refined and er...educational. Seriously, that was a clever idea for temporarily reducing the cabinet volume - an interesting variation on the old brick-in-the-toilet-tank trick to save water.

    Liam (2008-11-20 21:23:38)

    Andy unfortunately the specifications for the drivers I got from Rockford don\'t seem right to me The tech claims they came out of the Spectra 11 book. If you calculate Vb (box volume) from these numbers you get silly size cabinets. Here are the most pertinent figures from the sheet. Part # RFS -1408 8\" 4 ohm DC resistance 3.6 ohm fs 44 Hz Qts 0.37 Vas 0.6711 100W RMS Magnet: weight 18oz diameter 4\" Part # RFS -1808 8\" 8 ohm DC resistance 7.1 ohm fs 46 Hz Qts 0.38 Vas 0.6711 100W RMs Magnet: weight 18oz diameter 4\" My reading of these figures is that these drivers were designed for a ported enclosure or possibly even a very small sealed box speaker. I have also asked for the specifications for the Spectra 1100 drivers - but so far no response. I bought my speakers new and have never altered them. But my best guess at this stage is that they put the 1100 drivers in them -as they are certainly over damped in my enclosures - and they look identical to the photo of Dave Ayers driver.

    Andy Szabo (2008-11-21 17:29:21)

    I discovered that I have both 11 and 1100 woofers on-hand, so I can provide some info on both. The 11 woofer has these two numbers on it: 24126 and 791042. It\'s voice coil DC resistance is 3.5 ohms, so it is presumably a 4-ohm driver. The magnet is un-shielded, the dustcap is smaller than the 1100\'s, and it\'s depth is 3-5/8\" from flange to back of magnet. The 1100 woofer has these two numbers on it: 24857 and 719043. It\'s voice coil DC resistance is 4.5 ohms, so it is more likely an 8-ohm driver. The magnet is shielded, the dust cap is larger than the 11\'s, and it\'s depth is almost 4\" from flange to back of magnet. I should mention that the spare 1100 woofers I have are versions that were used in later production. During the life of the product, one of the woofer\'s components was discontinued, so the design was reconfigured with one or more different components. It was our opinion that this new woofer was indistinguishable from the original, and its use was approved. (In fact, the woofers I have are the very ones used in that approval process - that\'s why I have them!) What I cannot tell you is whether this new woofer was assigned a different part number, or when this changed occurred. So, the number referenced above may be different from other 1100 woofers. The 1100 woofer cabinet\'s inside dimensions are approximately 14.5\" x 14.5\" x 11.5\". As I mentioned in a previous post, the 1100 is shorter overall compared to the 11. According to literature I have, the 11 is 72\" tall, whereas the 1100 is 67.5\" tall. The panel height is the same for both models, so the difference is all in the woofer cabinet. The 1100 woofer enclosure is shorter, deeper and slightly wider than the 11. The \'slightly wider\' is due to the decorative trim on the panels making the 1100 slightly wider overall. By the way, you should know that the woofer systems were not optimized for maximum efficiency, as is the case in many designs. This is because the ESL is rather inefficient, and so it can actualy be a challenge to get the woofer\'s efficiency low enough to match the ESL.

    Andy Szabo (2008-11-21 17:38:04)

    I just looked at the woofer photo shown in the 1100 section of this site, and it is not an 1100 woofer - it is an 11 woofer, both by part number and appearance. I have noticed a few photos labelled (or filed)incorrectly on this site, so do proceed with caution when looking at them. Our dear webmasters are not Acoustat experts (being more in the Quad camp), so we must forgive them. They do a great job as it is!

    Liam (2008-11-28 00:56:18)

    Andy I just began reworking my woofers. I will publish results when I have something I am happy with. But one surprise I got is that my speakers have a large 6 ohm resistor across the woofer driver. This is not shown in the schematics on the TAC disc. It would seem that placing this in parallel with the driver reduces the impedance seen by the amplifier and also causes a drop in the voltage seen across the driver and an increase in voltage seen across the series inductor. I can only assume that this was done to reduce the efficiency of the woofer. As mentioned before I bought these new and haven\'t modified them in the past so I can only assume this resistor is factory original.

    Andy Szabo (2008-11-29 05:32:41)

    Liam- You really have me stumped now. I have no recollection of a 6-ohm resistor being added to the woofer. Adding a 6-ohm resistor in parallel with an 8-ohm Spectra 1100 woofer would make it (sort of) act more like a 4-ohm Spectra 11 woofer as seen from the crossover. My first thought was that this could add support to your theory that Rockford used 1100 woofers in some 11\'s. But in going back through your posts, I see that the number on your woofer matches the Spectra 11 woofer I have. I think you have gotten from me just about all I have to offer on this subject. I certainly tried to know everything that went on at Acoustat product-wise (because that was my job and my passion) but clearly some things either eluded me at the time, or have been subsequently erased from my memory.

  • Only one speaker working. - Liam on 2008-11-13 23:43:15

    Recently I noticed an electrical frying smell (Ozone?_) coming from both of my Spectra 11 speakers are a long spell of playing them at high volume. Both speaker were still playing OK and sounding as brilliant as normal. I turned them off and had a look in side both interfaces. Nothing appears to be burnt off the circuit board, etc. However on turning them back on only one speaker is now operating. No sound is coming out of the flat panel on one speaker (the Bass speaker is still working). Also the 12 v power pack is gets hot on the faulty speaker. I love these speakers and I am keen to repair them. Long in the distant past I studied electronics and now definitely suffer from a little knowledge is dangerous/embarrassing. Can anyone suggest the most likely cause of the problem and a fault analyses procedure?

    Liam (2008-11-14 00:29:42)

    Hmmm...To isolate the problem I swapped over the interfaces...and guess what now both speakers are working and neither power supply is getting hot. I guess that I may have something like an intermittent soldering joint. Anyway I will leave well enough alone for the moment on the theory of if it isn\'t broke don\'t fix it

    Andy Szabo (2008-11-16 14:57:55)

    My guess would be that the plug for your wall transformer was not fully inserted into the jack. This could cause a short circuit, causing the transformer to get hot, and preventing the ESL portion from working. Read my story \"Ted Nugent vs Spectra 1100\" in the 1100 section. Although you have the Spectra 11\'s, they are similar enough when driven a bit too hard!

    Liam (2008-11-16 20:01:17)

    Thank you very much Andy. I traced the problem to a faulty power supply plug. Interesting story. The original jacks on my power supply/speakers started causing problems in the first couple of weeks of ownership way back in the early 90\'s. The local dealer swapped out the original 15V power packs for new 12V power packs ( I checked the good on and they were 12 volts with no load) he sourced locally with different two prongs pin where they insert into the speaker. (I don\'t have a clue what these plugs are called). When he soldered the new plugs on he stripped back too much insulation inside the plug and I discovered this had shorted inside the plug and yesterday afternoon this shorted enough to blow the power pack. I checked I have the 470 ohm resistor and I have changed out both power packs with 15V units. Interestingly this has significantly lifted the volume coming from the panels and improved the tonal balance of the speakers as a result. (I\'ve been missing this for 18 years!) The burning smell was from the circuit board getting fried under the 10 ohm 25 watt high pass resistors. I have temporarily spaced these 1bout 15 mm off the board until I can get some metal bodied replacements to do your recommended mod. Reading this site has got me inspired to try and source a better 8 inch driver and build replacement bottom cabinets out of MDF.

  • Buzz - N. Tony Fasola on 2008-11-12 20:38:29

    Since my last post, I did add a pristine pair of 2+2\'s to my system. (11/07) The speakers were bought from the original owner in Austin and shipped here to Atlanta. I had Roy do the upgrades on both interfaces. In the past month or so I am hearing a buzz on low frequency sections of certain music. Electronic music (Radiohead) seems to be most apparent. Not all bass notes (music) will reproduce the buzz but I think it is appearing to get worse. The location of the noise is approx. 2/3 up from the bottom. Like I mentioned, I can listen to 90% of my music without a problem but that other 10% is starting to bug me. So, do I need to remove the cloth (please remind me how) and check for debris (or worse) or something else that can account for the noise. Thanks! Tony

    Andy Szabo (2008-11-20 16:28:58)

    You probably have some foreign material trapped in the space between stator and diaphragm, or possibly one of the diaphragms has lost tension. I suggest you consult my Technical Bulletin \"Popping Panels\" and if necessary \"Removal of Grille Cloth\". These are located under \"Refurbishing\" at the top of the Acoustat section. This problem can almost certainly be fixed.

  • Acoustic 3 Non-Medallion - Rocky on 2008-11-12 17:34:46

    1) In the HV supply can I replace the diodes (25G10 rated at 10-kV at 25-mA) with M100FF3 (rated 10KV at 20ma)? The M100FF3 diodes are soft-recovery type with Trr = 30ns. 2) I bought my Acoustat 3\'s in the early 1980\'s. Sometime later, a friend of mine modified the speakers (the C-mod with the 47uf +10uf+.01uf caps). don\'t have the medallion transformers though. Recently I noticed that the low frequency audio transformer is connected to its Red (2-panels) lead rather than the Orange (3-panels) lead. I know I have an Acoustat 3, I can see the three panels. Is the wiring incorrect or was this part of the C-mod? Rocky

  • Spectra 3 modifications to a Spectra 66 - Gary Smith on 2008-11-11 23:27:53

    Andy Is it possible to make a Spectra 66 based on an existing Spectra 3 model other than adding the other panels and wiring to the interface providing that the existing interfaces for the spectra 3 can be wired to handle the extra panels? I have advertised in most audio publications looking for a pr of Spectra 66 or 6600\'s but after a year, none have become available, thought that this modification to a spectra 66 from a spectra 3 maybe the next best way.

    Andy Szabo (2008-11-12 13:13:58)

    See the 6600 model section for an answer to this question.

  • Spectra 3 mods to become a 66 - Gary Smith on 2008-11-11 23:25:26

    Andy Is it possible to make a Spectra 66 based on an existing Spectra 3 model other than adding the other panels and wiring to the interface providing that the existing interfaces for the spectra 3 can be wired to handle the extra panels? I have advertised in most audio publications looking for a pr of Spectra 66 or 6600\'s but after a year, none have become available, thought that this modification to a spectra 66 from a spectra 3 maybe the next best way.

    Andy Szabo (2008-11-12 13:10:57)

    Making a 6-panel Spectra from a 3-panel Spectra is not as simple as adding additional panels. The audio step-up transformers are different for the 4 and 6-panel Spectra\'s. These transformers provide less bass boost due to the larger panel area. Using transformers designed for 2 and 3-panel Spectras would result in too much bass in a 6-panel speaker. There are also some component values that change on the high voltage board for the larger models. But don\'t give up hope yet: the Spectra 44/66 transformers appear frequently on eBay: these are genuine surplus parts sold to a liquidator when Rockford Corp sold the Acoustat division. The part number is TTA-246 and you will need four of them for a pair of speakers. The different component values for the high voltage boards can also be sourced. I\'m not surprised that you are having trouble finding a pair of Spectra 66 or 6600 on the used market. Not many of them were made (definitely less than 100 pairs) and it\'s not the kind of speaker that one gets tired of after a few years. I suspect most of them are still with their original owners. Good Luck!

  • MK-121 units upgrade - Phil Griffin on 2008-11-11 22:04:11

    Is there a way you can tell if the Mk-121 unit has received the medallion upgrade by looking at its serial number? Please advise. Thank you. -Phil

    Andy Szabo (2008-11-12 12:56:27)

    Sorry, but the serial number is no indication. When the Medallion Transformers were introduced, a very popular upgrade program was offered, so speakers of a wide range of manufacturing dates were ultimately upgraded. The serial numbers did not change when upgraded. There should be a label on the interface box indicating Medallion Transformers if so equipped. If the lettering on the label is BLUE, then you have the medallion transformers, but not the later \'C-mod\'. If the lettering is RED, then you have both the transformers and the C-Mod. The C-mod is faily easy to perform using commonly available parts (instructions can be found elsewhere on this site).

    Peter Cade (2010-10-14 00:40:35)

    Andy - I have a pair of Mk121-2's with the medallion transformers, but not apparently the "C-mod" (blue label). You mention that instructions for doing the mod can be found elsewhere on the site, but I can't find 'em....... duh. Could you tell me where they are, please ?

    Thanx Pete.

    Andy Szabo (2010-10-26 02:26:14)

    Much of the information that used to be on this site is no longer available, such as the document you are looking for. (So don't feel bad that you couldn't find it!) I am working with the webmaster to correct that situation, as having that technical info makes answering questions much easier. In the meantime, I will prepare a pdf version of that document, and perhaps the webmaster can forward it to you.

    FYI - if your interfaces have Medallion transformers, they should have a blue Medallion label. Units with the later C-mod should have the same label in red.

    Glenn Harned (2014-04-22 18:47:33)

    Andy, could you please forward a copy of the instructions in pdf for doing the mod to me.
    Thank you very much!

    Glenn Harned

    AcoustatAnswerMan (2014-05-28 20:12:09)


    I would be pleased to forward the C-Mod instructions to you if you provide me with your email address. Not sure how else I might transmit it to you.

    Glenn Harned (2014-05-28 22:29:56)

    Hello Acoustatanswerman. Please find my email address as you requested.

    Than you in advance!

    Glenn Harned (2014-05-28 22:31:09)

    Hmm seems I have to input it directly.

  • Low supply voltage - fitzroy wellington on 2008-11-04 19:09:16

    hello Andy thank you for your response to my query regarding a very unusual problem with my speakers. i am in the process of removing and inspecting the panels since the interface checks out ok.I will be checking each panel individually,if theere is no physical fault in either one or in the wiring then please let me know what resistance or capacitance I should expect from each. i greatly appreciate your advice and assistance since i know of no other reference in the caribbean where i live; i agree with you, a better speaker is yet to be built. with thanks, fitzroy wellington trinidad

    Andy Szabo (2008-11-04 20:29:48)

    Before you do any measurements of the panels, please make sure they are completely discharged. Otherwise, you may damage you meter, or at least get an erroneous reading. For an individual panel, you should measure infinite resistance (i.e. no conductivity)between the red wire (diaphragm) and either of the blue or white wires (stators). You should also measure infinite resistance between the white and blue wires. Be sure to use the highest ohms-range on your meter. Any finite resistance (i.e. some conductivity) measured between these wires would indicate some sort of conductive path inside the panel, most likely caused by foreign matter lodged between the stator and the diaphragm. If you have the ability to measure capacitance, the capacitance between the blue and white wires should measure about 200 picofarads (pF). However, resistance measurements will be more telling of a problem, so I don\'t think a capacitance measurement will be much of a troubleshooting tool. You should also inspect the wires leading up to the panels. Look for any signs of arcing (black marks are a tell-tale sign)or for pinched wires. It is possible, though not likely, that a defect in the original assembly of the speaker took all these years to manifest itself. So far we have been looking for a short circuit that could be pulling down the bias voltage. This is the most likely scenario since the entire set of panels connected to that interface is not playing loud enough. One bad panel (or bad wire) with a short circuit would affect the whole set of four panels. The other possibility is an open circuit that is not letting the bias voltage get to a panel. However, this would affect only that panel, so unless you have four bad panels in one set, this would not be the case. Just in case, I will tell you how to check the bias feed to the panel. The red wire is connected to a small metal-foil tab, that is laid on top of an extension of the diaphragm\'s conductive coating. Measure the resistance between the red wire and the conductive coating near where it connects to the foil tab. Be careful not to puncture the diaphragm with the meter probe (probably best to use a blunt tip), and make sure you are measuring on the side of the diaphragm with the conductive coating. I can\'t give you an exact reading to look for, but if you get infinite resistance, then you have a problem. A normal measurement would probably be in the range of a few thousand or ten-thousand ohms. The measurement will depend on how far from the tab you are measuring (closer will yield a lower resistance). Fixing a bad bias tab is nearly impossible, as the panels are permanently glued together. I don\'t think I\'ve ever run into that problem, and I have no experience in trying to fix one. So let\'s hope that\'s not the problem. If all else fails, you can send me a plane ticket and I will come and fix them for you. I could use a vacation in the Caribbean! Just kidding of course, but do write again if you need further help. We need to keep those Model Eights running for a long time!

    fitzroy wellington (2010-09-29 20:59:27)

    hello andy
    it's been a long time since i contacted you last, but i finally took my speaker apart and found that some of the wires were corroded and broken. i did a repair job but the solder joints all seem to corrode again and cause the same problem; i do not know if this is a problem consistent with the tropics. can you advise me as to how to join these high voltage wires so that they do not go green and separate. also can you recommend alternate diodes that i can use in the power supply since i cannot find the originals.

    Andy Szabo (2010-10-26 02:17:17)

    The original diodes have been discontinued for some time. Replacement diodes are avilable from: Search for part number G10FS, which is rated at 25 milliamps and 10,000 volts. You should be able to buy directly from them, but there may be a minimum order.

    Corrosion could certainly be a significant factor in your humid salty air, and is probably made worse by the high-voltage attraction of salt particles. First, make sure you are using a high grade solder intended for electronic connections. Never use an acid flux solder like you would use for plumbing. Clean all the corrosion off the connections with emery cloth or a fiberglas bristle brush, and then coat the troublesome areas with Glyptol, which is a thick, dull red enamel designed for protecting electrical connections. It should be available from any well stocked electronics supplier. The down side is that it makes later repairs more difficult, as the coating has to be scraped or dissolved off prior to re-soldering. The same Glyptol can be used to coat the first inch or two of the wires, in an effort to prevent further 'greening', or oxidation of the copper conductor.

    Good luck, and do write again if I can help further. The offer still stands for that plane ticket...

    fitzroy wellington (2010-12-28 01:20:18)

    Hi Andy
    Again I must thank you for your very useful advice. I certainly have benefited, since I have the eights running at close to 'full steam' now. I got the G10FS diodes and upgraded the power supplies but those high voltage capacitors are hard to find, even in the US.I would appreciate any advice on this since efforts on my part through suppliers recommended by other contributors on the website proved unsuccessful. Apart from the diodes and capacitors (.0033/1500V are all I can find, bias voltage slightly low 4.5kv supply volts 2.8kv) in the voltage multiplier, everything else is original equipment and needs upgrading so I guess what we have so far is a work in progress, sweet however.
    I extend fond wishes to you for the new year. As a professional pilot myself, who knows, maybe I will fly up to the US and bring you to Trinidad... think I"ll need an airplane though.
    PS: what is the minimum supply voltage to the panels for proper operation?

  • Disassembly - Ed Kleemola on 2008-10-15 23:31:06

    I have removed the arrays from their bases on several occasions, and have usually gotten \"zapped\". After reading through your information regarding the MK-2123 bases, it turns out that one of mine appears to be wired for the Spectra 2200 series (22 on the back left). Since I\'m going to have to remove the array again to check the low end wiring, I was wondering if you had any advice on how to properly discharge the unit other than through my body. Also, I have the subwoofer, but there\'s no finished wood top or bottom on it. Do you know where I might find these? Why do I have this strange set of 3300\'s with the missing subwoofer wood and the mixed up bases? I bought the set from a guy that did some video work for Rockford Fosgate in the early \'90s. They gave him the set as a bonus of sorts. He got sick of lugging them around, so he sold the set to me for a grand total of $250.00!!! He even threw in a Carver M-500 amp! Sorry, I just had to brag a little... Thanks for your help! Ed Kleemola

    Andy Szabo (2008-10-17 23:20:32)

    Congratulations on finding these speakers at such a reasonable price. Always nice to hear good-luck stories like that. The panels and power supply can be discharged in two ways. If you power-down the speakers and wait several hours before disassembly, the residual charge should be bled off by then. But who wants to wait? If you carefully pull out the red wire from the jack (being careful to handle it by the insulated portion)and touch the tip of the plug to any of the other colored connections, you will get a spark. That will discharge the majority of the charge on the panel. Repeatedly replacing the red plug, and removing it again and touching another connection, will bleed the charge from the power supply. Doing that 2 or 3 times should be sufficient. This procedure should remove enough of the residual charge to safely remove the rest of the pin-plugs and proceed with disassembly. Even still, there could be some residual charge in the power supply, so it\'s best to wait a while before getting into any disassembly of the interface itself. If one of your interfaces is wired for a 2-panel speaker, I do recommend correcting that. Otherwise the bass response will be bumped-up on that speaker. I doubt anyone has any of the wood tops or bottoms for the subwoofer. If memory serves correctly they are the same size as the Spectra 2200 or Spectra 3300 base. They are definitely the same style of construction: veneered plywood or medium-density-fiberboard (MDF), with solid wood trim around the edges. Someone with only moderate woodworking skills should be able to duplicate them. I don\'t remember for sure, but I think the Acoustat Manual CD available from this website has drawings for the Sepctra bases.

  • No power - rex hookens on 2008-10-05 19:08:30

    Hallo ,can you please help,after listening for a while,i decided to review a pair of Apogee Divas,so i rolled my 22 to the otherside of the room while i auditioned the Apogees,after a few months,i have moved the 22 back for play,but both will not charge up,i have checked the fuses,none blowen,plug in the wall transformers are showing 15v supply,but the LED,does not light-up,any ideas why? reards Rex

    Andy Szabo (2008-10-29 21:03:46)

    Neither speaker will play? Wow: that\'s pretty unusual to experience the same problem in both speakers at the same time. But obviously it does happen! Maybe your speakers are mad at you for putting the Apogees in their place: speakers have feelings too, you know. OK, so you\'ve already verified that the wall transformers are putting out the correct voltage, but the LED\'s do not light up. I would check first that the wall transformer plugs are making proper contact. For some wall transformer plugs, the hole in the interface metal is too small, and will not allow the plug to fully insert into the jack. I had that problem on my Spectra 4400\'s when I tried to use non-original plugs. I enlarged the hole in the metal to remedy that. You may also have an older design of the ultrasonic bias power supply, which can suddenly stop working for no apparent reason. If memory serves correctly, that problem was already corrected by the time the 2200 was introduced, but maybe not. The easiest way to identify the \'new and improved\' design is to look at the squarish air-core transformer on the small bias power supply board. Note the red wire exiting the top of this transformer - if this red wire has another wire wrapped around it (and secured by heatshrink tubing) then you have the newer design and should have no problems with the bias supply. Note the wire wrapped around the red wire doesn\'t actually make electrical contact with the red wire - it acts as a close-coupled \'antenna\' to provide feedback for the oscillator. If the red wire has no wire wrapped around it, then the supply should be modified to the new design. That procedure is fairly easy using commonly available parts, and is outlined in my Technical Bulletin on the Ultrasonic Bias Power Supply, found elsewhere on this site. That\'s about all I can think of for now. Since the LED\'s are not lighting, it is clear that your problem is either not getting power to the supply, or a problem with the supply itself. That pretty much rules out any problems with the audio step-up system. By the way, the fuse on the rear panel is in the audio circuit, and has nothing to do with the bias supply. Good Luck, and do write again if you need further help.

  • Review my tinkering - Jim Roller on 2008-09-17 18:20:39

    Andy, Thanks for answering my previous questions on the Spectra 3\'s. I would like your thoughts on some of the tinkering that I have been doing to them. I took the woofer out of the box. The panels sound cleaner when the interface is not being vibrated and there is no big magnet near by. The grill cloth and felt dampening are off. I don\'t play the panels full range so I don\'t have any mylar slapping problems. I have replaced the 1 and 10 ohm resistors on the panel crossover with Mills audiophile crossover resistors.(paralleled two 2ohms and two 20 ohms for better power handling) I have replaced the 20uf cap with a 30uf Clarity Cap. This tweak in particular has added more body to male voices and instruments whose fundamentals are in the upper bass and lower midrange. I use two outboard 12\" stereo subs with sub amps with low pass set a 50hz, 12db/oct. slope. My next tweak might be to take the panels off of their woofer/interface box and build some dedicated stands that will place the panels closer to the floor with the hope that it would fesh out the mid and upper bass even further. Have I done anything that you don\'t like or might you have some further recommendations? Thanks. Jim R.

    Andy Szabo (2008-09-17 19:14:09)

    Since you asked, I\'m not crazy about the idea of removing the felt dampening strips on the rear of the panels. They are there to dampen resonances, and are generally considered \'necessary\' for optimum performance. However, if you like the results, then that is all that matters. I doubt the felt\'s removal will cause any harm to the speaker, especially if you are not operating the panels at bass frequencies. There is nothing inherently wrong with re-mounting the panels on a stand that would place them closer to the floor. However, due to limited vertical dispersion of the panels, you should try to keep the vertical center of the panels close to the same height as your ears in the listening position. I\'m not sure if lowering the panels will help, but the idea should be easy enough to try temporarily. If you like the results, you can build something permanent. Since you are using a -12 dB/oct filter on your subwoofers, the phase will be inverted on the woofers. If you had not previously considered this, you should try reversing the phase of your woofers and see if you like the result. Although you are crossing over at a rather low 50-Hz, this could still have some effect on the mid-bass. If you are using the ESL\'s internal high-pass crossover, keep in mind that it is set for 100 Hz. This could lead to a lack of output between 50 and 100 Hz. If so, you might try raising the frequency of the subwoofer crossover.

    Pramod (2008-10-26 19:54:02)

    Dear Sir, I want to buy Acoustat Speaker. Can you help me in this regard? Best regards, Pramod

    Andy Szabo (2008-10-27 18:56:01)

    Acoustat speakers are no longer manufactured in the USA by the original company. The company was sold to an Italian firm for a few years: they produced a few models in limited quantities, but I\'m not sure how wide-spread their distribution was. They may not have been exported outside Italy. The company is now owned by a Chinese firm, and they appear to have quite a few models available, but the extent of their distribution outside China is unknown. Most of the discussions on this website involve the USA-built models that are still available on the used market. There are a number of websites and local stores dealing in used equipment - eBay is another good source. New auctions appear there almost weekly. Despite their increasing age, Acousta speakers are quite reliable, and can represent a very good value for the money.

    thomas paul (2009-03-06 23:12:37)

    I have a pair of spectra 3 speaker that i would like to sell they are in very good shape and sound great. What would be a fair price. I live in baltimore,md and will not ship because of size.Thanks Thomas.

    brad cary (2009-05-30 18:05:53)

    I have a pair of spectra 22s and the factory SW-1 woofer that I have owned since new. recently added a pair of custom subwoofers with 2 NHT 1259s in a sealed enclosure per side, externally crossed over at 60hz to create a three way system using the internal crossover to the SW-1. power the panels and the SW-1 with a single Aragon 4004 and the NHTs with 2 Adcom 555s in mono.

    I ran the acoustat only system from two Audio Research D-51s in mono for 20 years and was content with the sound but 4 12in drivers for the low end has more that offset the loss from switching to solid state amps for my 50 something hearing.

    Thomas, if you still have those spectra 3s I\'d be interested in taking them off your hands. I have started on a home theater system the is crying out for a pair of electrostats.

    Brad Cary

    boatbeat (2009-11-04 03:37:53)

    Brad: if you are still looking for a pair of spectra 3?

  • How much power for Acoustat Model III\'s? - David Shaw on 2008-09-17 05:19:38

    What is the optimum for both solid state and tube? How about the minimum? Thanks in advance, guys!

    Andy Szabo (2008-09-17 18:53:17)

    How much power you need will depend, of course, on how loud you like to listen, and how large a listening area you have. That could range from a low of 50 watts per channel, up to 250-watts per channel (8-ohm rating). Regardless of power rating, the amplifier should be able to deliver high current and be stable for difficult loads. Personally, I would want at least 100 wpc in a solid state amplfier. Some people do use tube amplfiers with Acoustats (with good results), but the selection process is further complicated by the fact that tube amps tend to have a higher output impedance that varies with frequency. This means that the interaction between the speaker\'s impedance and the amplifier\'s output impedance will have a much greater effect on the sound (primarily frequency response).

  • low supply voltage - fitzroy wellington on 2008-09-16 19:54:23

    I own a pair of acoustat 8s that i acquired from a friend. the left half of one of the speakers does not play very loudly simply because the supply to the panels from the 500megohm resistor drops down to 800 or 900v once the panel wires (HV supply and audio), are connected. please note that on its own the interface produces a robust 4.8kv; CAN YOU HELP? Thanks.

    Andy Szabo (2008-09-16 23:44:33)

    That\'s a fairly unusual problem! Since you have a total of four interfaces with your Model 8\'s, I would suggest you try one of the other interfaces on that panel set (they are interchangeable). If it works ok with another interface, then you know the problem is with the original interface. If the problem exists no matter which interface you use, then the problem is in the panels. If you determine the problem is in the interface, and since it produces proper voltage unloaded, my first suspicion would be the 500-megohm resistor. It may have failed to a much higher value, or opened entirely. I\'ve seen these same resistors for sale on eBay, so finding a replacement should not be too difficult. Although less likely, you could have a failed capacitor in the voltage multiplier. If the problem is in the panels, I have much less advice to offer, since that would be a virtually unheard-of problem. But, there is a first time for everything! My first suspicion would be a break or a short circuit in the connecting wires. This can only be determined by removing the grille sock and doing a physical inspection of the wires. I can\'t really imagine a scenario of how the panel itself could pull-down the bias voltage, unless some physical, conductive object was lodged in between the diaphragm and the stator grids, and was actually cutting through the wire insulation of the grid. Pretty unlikely! So, my best guess would be a problem with the interface. Please do write again if you need further advice. And congratulations on owning a very rare, top-of-the-line Acoustat Model Eight. I have no idea how many Model 8\'s were produced, but my guess would be in the range of only 25 pairs, maybe even less!

  • Adding Panels - wanchai on 2008-09-11 09:21:07

    Hi Andy,I\'d like to bother you again. I am myself the Acoustat freak because I love their nuance and smooth sound. I have own 2+2,1-s mk141c, DIY 3+3 connected to Soundlab m3 interface and a bunch of 8\" & 9\" panels. But the life is not easy whenever I compare Acoustats to my Apogee DIVA ,they still lack the high freq. transient and macrodynamic even they have better quiet noise floor and microdynamic. When I listen to 1-s which has the high pass filter and low pass to the subwoofer ,they have better transparency to 2+2. So I guess that the low freq. may interfere to the high freq. when they are driven full range to the same panel.Now my question is I want to add 1-8\"+1-9\" with new frame to my 2+2 by connecting to the high audio transformer (after the capaitor) and let 2+2 connected to the low audio transformer only. Is there any problem such as audio transfomer saturation ,etc? And will it help ?

    Andy Szabo (2008-09-25 22:26:13)

    Your observation that the Model 1 with woofer is \'more transparent\" than the 2+2 may be correct, but I don\'t think it is due to the low frequencies being absent from the transformer or panel. Rather, I think it is because the wider area of the 2+2, operating full range, does tend to \'smear\' the sound somewhat, compared to the narrow, single-panel \'line source\' speakers like the Model 1 and 1+1. This is a compromise inherent in all of the older Acoustat speakers. That is, the smaller, narrower models tend to have superior imaging and transparency, with the larger, wider models having better bass and dynamics. This is the reason that the Spectra series was developed: to avoid that compromise. All Spectra models have the same, narrow-width panel area producing the high frequencies. This way, all the models have very similar imaging and transparency, with the larger models simply offering more of the same great sound, with deeper bass and greater dynamics. The Spectra models no longer force listeners to accept that compromise between different models - the choice of which model to buy becomes more a matter of economics and room size. That said, I doubt you can accomplish your stated goals by adding more panels. You must remember that there is considerable overlap between the high and low frequency transformers, and they cannot be thought of as \'woofer\' and \'tweeter\' transformers. They operate together over a considerable span of the midrange. As long as your are attempting to use the older (pre-Spectra) models, you will be forever frustrated by their inherent compromise - no single model has everything that you are looking for. Since you do like so much about the \'Acoustat Sound\' (and there is a lot to like) I suggest you look into one of the Spectra models. They appear frequently on eBay, sometimes for very reasonable cost. Another option might be to add a line source ribbon tweeter, which could certainly extend the top-octave response. However, just like adding a subwoofer to a system, it can be difficult to find a component that has a similar sound chararteristic, and getting the phase, amplitude and crossover point \'dialed-in\' can take quite a bit of experimentation. And in case you are wondering, (and I know you are!) no, it is not possible to create a Spectra model using the MK121 transformers. The Spectra transformers are radically different than the MK121 transformers, and it\'s just not possible to get the required equalization from the old-style transformers.

  • Pin connector for high voltage to panels - Alan Kelly on 2008-08-25 02:04:19

    Does anybody know where to get the pin and socket connector for the high voltage to the panels from the circuit board in the Acoustat MK-121 interface? Even what is called might be helpful. Regards, Alan Kelly

    Andy Szabo (2008-08-29 14:53:37)

    The tip plug and jack are made by Johnson. You can get them from Digikey ( or Mouser ( Neither distribitor lists the exact same style of plug, but they do have a compatible solderless type, available in a variety of colors. Tip Plug: Johnson #105-0302-001 (red, other colors available) Tip Jack: Johnson #105-0752-001 (red, other colors available)

  • Tube drive ESL - Martin on 2008-08-22 21:41:54

    Dear Andy, Thankfully to your help I have acquired proper transformer for my acoustat 1100 and make panel operational, and I bought a pair of acoustat 11, which I have repaired. The speakers sounds really good with one problem they need a lots of power, my tube amps restored HK-A700 with 7591 PP tubes puts about 35w per channel, and it is enough for quiet listening.. furthermore as a tube amps gets more distortion with higher volume now I can hear distorted sound when I drive it to the max.. (on solid state mosfets both sounds better, but amp is over 200w) So counting on your kindness and professional expertises I am wondering if you know which tubes will be good to build an push pull AB output stage, for electrostatic panels I mean OTL, with bias voltage only, do you have any links or ideas about the power strage schematics made with modern tubes ? the other question is about bias supply voltgae, I have bought a 110 ac to 7.5 kv dc module used in ion generators (like in air purifiers) there are also same modules with 15 and 18 kv.. do you think it would make any sonic difference to supply higher bias to electrostatic panels, I know the humidity makes a difference in performance so my idea was that higher B will make more dynamic sound (of course I remember about safety and 500M 5W resistor like those in acoustat interfaces..) many thanks for all help ! MArtin

    Andy Szabo (2008-11-16 14:47:06)

    I agree that 35-wpc is not enough for Acoustat speakers. All ESL\'s are inefficient, and require lots of power. With care, you can safely use 250-wpc with these speakers. \'Care\' meaning avoiding signs of distortion from the speaker, and not allowing your teenage son to play his music when you\'re not home! The only OTL schematic I can recommend is Acoustat\'s original servocharge amplifier, available from this site. It uses tubes designed for the horiz. output stage of B&W televisions. Personally, I think the idea of building your own OTL amp to drive ESL\'s is a waste of time, and it could also kill you (the HV power supply is nothing like the wimpy panel bias supply). In all fairness, there are plenty of folks who would disagree with that statement, but no one has yet to show me a working example. I would not recommend deviating from Acoustat\'s original 5K-VDC bias supply. That value, along with the stator spacings of the panel, was determined after significant research to find the best compromise between efficiency and humidity-resistance and longevity for the Acoustat panel. 7.5K-VDC would increase efficiency, but at the risk of arcing the panel, depending on your climate. Voltages as high as 15K or 18K-VDC would cause the panel to arc instantly and fail. At those spacings and voltages, the air itself would break down and conduct electricity (think lightening).

  • Acoustat MK-121-B - Chad on 2008-08-15 04:42:02

    Hello, I recently came across a pair of tower speakers with the Acoustat MK-121-B as the type on the back of the plate. I would like some info on what these would sell for, or if this is a desirable model. I hooked them up to my Toshiba receiver and they sounded quite nice, although I think an amplifier would help the sound. Any info would be appreciated! Chad

    Andy Szabo (2008-09-15 23:46:50)

    Unfortunately, Acoustat usually didn\'t identify the model number on the speaker. The MK-121 designation refers only to the \'black box\' transformer interface and power supply on the rear of the speaker. This box was common to several models. If you can provide the overall dimensions of the speaker, I can probably identify the model number. Yes, Acoustat speakers are still highly sought after, despite having been out of production for over 15 years. They are very reliable, and have shown little tendency to degrade with time. They can represent a fantastic bargain for buyers interested in the used market. Compared to more conventional speakers, they are rather inefficient and difficult to drive, so a large separate amplfier is recommended to get the maximum performance. Even without knowing the model number, I can say that they are probably worth at least $500 for the pair.

  • Panel impedance - Jim Roller on 2008-08-12 15:40:06

    What is the impedance of the panel portion of the Spectra 3? I am not using the woofer portion. I am trying to decide whether to use the 4 or 8 ohm taps on a tube amp I just picked up. thanks.

    Andy Szabo (2008-08-12 23:43:16)

    The nominal impedance of the Spectra 3 ESL system (i.e. transformer interface and panels) is 4 ohms. However, the impedance varies quite a bit over the audio band, running from about 2 ohms to around 10 or more ohms. Therefore, there is no correct answer to your question. The typical tube amplifier\'s output impedance also varies quite a bit with frequency, so the effect on frequency response can be quite dramatic. Each brand or model of tube amplfier will be different in this respect. My advice is to try each tap and see which one you like best - more than likely each will involve compromises, and you\'ll need to decide which combination yields the best results for your taste. The important thing to remember is that there is no wrong answer - no harm will be done to either the speaker or the amplifier from the use of the 4 or 8-ohm tap. (In fact, if the amp has a 16-ohm tap, it could be worth your time to try that, too!) One last comment - most tube amps make it easy to experiment with the output impedance, merely by choosing a different output terminal. However, I am aware that some designs require an internal wiring change, making experimenting with impedance much more cumbersome. If that is the case with your amp, and you feel it necessary to choose a tap without first experimenting, then I suggest the 4-ohm tap. But there is no guarantee that that is the best one for your taste.

  • Undo modifications - Don West on 2008-07-26 09:12:45

    I\'m lucky enough to own a pair of these wonderful speakers but years ago I made the mistake of having them modified by a now defunct company called \"Wescott\". A man named Jim Ott, in Oregon I believe, modified the interfaces of my speakers and they\'ve never sounded as good again as they did originally. Big mistake. My question is, can the modified interfaces be restored to the original or updated correctly, and, if so, whose available that can do the job right? Many thanks for keeping Acoustat alive.

    Andy Szabo (2008-08-05 23:09:54)

    I don’t remember what modifications Jim Ott performed (although I do remember his name), so I can’t be of much help here. My recollection is that we didn’t hear much about aftermarket modifications by the time Spectra was introduced, so I am actually surprised to see a model as late as the Spectra 22 being modified. Generally speaking, Acoustat recommended against most modifications. Granted, upgrades such as better wiring, binding posts, film capacitors instead of electrolytic, etc, were fairly benign, as they didn’t change the fundamental circuit. They merely improved the quality of parts that couldn’t be done in the original design due to cost constraints. But I will say that Acoustat was against all modifications to the circuit itself, because in all cases that we encountered, the modifier displayed a lack of understanding of the circuit’s fundamental design principals, and violated one or more of them in the process. Modifications to the bias supply were quite popular, including bypassing of the 500-megohm resistor (violating the constant charge principal); adding a large capacitor on the supply’s output (both unnecessary and dangerous); or changing the diodes and/or capacitors in the voltage multiplier (again, both unnecessary and dangerous). There were other modifications, too, which time has erased from my memory. Who knows what might have been done to the circuitry that is unique to the Spectra models. It is unfortunate that a few well-intentioned, but misguided folks convinced Acoustat owners to allow their speakers to be modified (at great expense, no doubt). At best, these modifications did little or nothing to improve performance, and in some cases, as you have found, actually degraded the sound. More than likely, your speakers can be returned to the original form. Perhaps, if you can send me some detailed photos of the inside of the interface, I can determine what has been changed. (I am assuming the panels themselves were not modified.) It might be that only some of the modifications need to be reversed. Some of the changes may be of the benign variety that I mentioned above) I will ask the webmaster to send you my email address, if you want to send photos. I am rather curious to see what has been done!

  • Contact Andy. - James Tanner on 2008-07-19 16:17:02

    Hi, James tanner here from Bryston in Canada. Trying to get in touch with Andy Szabo. thanks, James Tanner V/P Bryston Ltd.

  • Roy Esposito Contact Info - Gordon Nesbitt on 2008-07-15 16:51:44

    Please provide contact info for Roy Esposito at Sounds Like New. Can\'t seem to find it elsewhere.

    Andy Szabo (2008-07-18 23:18:51)

    I\'ve had reports that Roy can be difficult to get a hold of. The only contact info I have is his email address, which is

    Roy A. Esposito (2011-07-17 20:00:10)

    July 17, 2011

    I am very much alive.

    I am No-Where near retiring .... and over many years have
    come up with astounding improvements, variations and restorations
    for the Acoustat MK and Spectra Interfaces
    and even more so the Trans-Nova amplifiers (TNT-200 and TNT-120)
    and Trans-Nova Preamplifier (TNP).
    I also renew the earlier and more rare, Acoustat MRP and RP-2 preamps.

    To my chagrin ----
    Folks don't realize I was many years younger than the
    other principals at Acoustat, back in 70's and 80's Fort Lauderdale.
    About half their age at that time.

    I am happy to continue lovingly working with Acoustat products.
    I do this with a fully functional laboratory and stockroom
    of original .........and improvement parts.

    But please realize that... in 2011....
    this is part-time work.... in addition
    to my regular full-time engineering/consulting work.

    So it can take a few weeks in total, for me to work my
    Acoustat "magic"...... as my client's have often
    described the results.

    I hope the above will help explain why I don't
    provide a phone number, except to established clients,
    and I prefer email contact instead. I also prefer my work
    and "word-of-mouth" to speak for itself
    ....instead of having and spending time maintaining a website.

    There are others that offer work on Acoustat products.
    Fancy words .... Fancy websites.
    But NONE of them worked for the Company.
    And to correct the mess.....
    Folks usually end up with me despite the glowing website tetimonials.
    That's just sad.

    I very much appreciate all of you, who continue to revere...
    and enjoy...
    the magnificent design works of Dr. Strickland,
    and our original Acoustat Engineering Team.

    May we all enjoy the Music,

    Roy A. Esposito /

    Rick Pettey (2011-11-15 21:19:05)

    Please allow me to recommend Roy anyone and everyone. I worked with Roy at Acoustat back in the early 80s. Though I am no longer in the audio industry (I left Acoustat to attend college and then the seminary to become a Lutheran pastor), audio equipment/music is still a major passion. Roy has performed the most amazing modifications on my 3300 (replacing the electronic biasing circuit with transformers, like the stats of old) as well as servicing my TNT-200 and TNP. HE IS WELL WORTH THE WAIT as he is honest and performs the services that he promises.

    richard (2012-01-25 01:52:07)

    Roy is THE MAN. He has performed incredible amplifier and acoustat speaker mods for me over the years that I doubt anyone else could have done. Certainly don't trust your Acoustats to anyone else.

    Roy A. Esposito (2013-09-06 12:18:13)

    Hello Friends --

    This is just to let you know that my email contact
    has recently changed. It seems AT&T/Yahoo could no
    longer support my very old email address.
    For those of you requiring fantastic restorations
    and upgrading of Acoustat MK and Spectra Interfaces
    and Acoustat Power Amplifiers and Preamplifiers
    my new email address is

    (please notice the dots/periods between the words)

    Email is the preferred method for initial contact with me
    for Acoustat Service and questions.

    Thank you for your continued friendship, kind comments and reviews,
    and support of my work.

    All the Best,
    Roy A. Esposito

    Roy A. Esposito (2014-04-08 12:47:24)

    Thank You my friends.... for your kind words and praise
    of my work. I remain available for Restorations / Upgrades /Improvements
    of the Acoustat MK Series Interfaces with the optional "Air Mod"
    that I developed in 2008. Vast improvements of the Spectra Series Interfaces,
    the Trans-Nova Series of Power Amplifiers for which I offer the incredible
    switchable Monoblock and Balanced Input circuit Conversions
    and restoration of the three models of Acoustat Preamplifiers.
    I welcome your inquiries at
    (please notice the dots between the words)

    Richard Lucas (2017-01-21 03:58:33)

    Dear Sir,

    I recently bought and paid premium for a Acoustic Trans-Nova 200 and hear static in the right channel and even less power than a much less cost NAD 2600. The bay seller has me for 750.00$ ! Advertised 9.5 almost perfect condition and says it sat on a shelf for some 25 years. I hear this is not good either. I cannot afford to lose this much money it appears no one can fix or properly diagnose. You see e-bay REQUIRES me to have a professional produce paper it's defective! OMG I bought it only because I was given a pair of 2 + 2"s in really nice condition and they play beautiful with the Nad 2600 but always will go into protection mode if turned up much at all. ?? Can you help. The so called Geek squad won't touch it and says parts are non existent. ? Can you please call me and advice me. I've verified with the 2 + 2' Acoustics and my still very dependable old style DCMs speakers. My Nad 2600 plays powerful and clear with the DCM's but far less power is there on the 2 + 2's. Clear but no way much volume. They sound fuzzy and yes I have correct 350$ 4 strand wire ... using a Audio Research preamp. The Amp has Issues and all I need is someone like you to verify to eBay in writing I suppose is what they are looking for ... Much spooked hear I'm POOR! Will you can you help?

    Richard 772-335-5555 772-221-8114

    Richard Lucas (2017-01-21 04:02:33)

    Mr. Esposito,

    I'm feed up at this point and would like to dump these speakers as well! Great shape I might add!
    I see your last writings here were 2014, ieee I hope all is well up and running.
    I have 15 days left to resolve with eBay and get a full refund. PLEASE help.
    May God Bless.



    AcoustatAnswerMan (2017-01-21 13:02:20)

    I doubt that Mr. Esposito monitors this forum, but I do, so I will tell you that he can now be reached directly via email at

    Sorry to hear of your difficulties with the amplifier. I feel confident that Roy can fix it. And don't give up on the speakers: even if the amp is a goner, there are many amps out there that will make them sing!

  • Cross Over Modification - Wanchai on 2008-07-12 07:20:32

    Hi Andy,After my Crossing the Species Project,I notice that the Low Audio Transformer in Soundlab m3 has the coil series 5 mH,10 mH and 20 mH infront which I made some modification to reduce to about 1.5 mH to raise the dip in mid freq. My question is why Acoustat 2+2 has only resistor series to the Low Audio Transformer instead of providing coil infront series to let lowpass filter to the Transformer as Soundlab. Now I am going to put 1 mH series to my Acoustat 2+2 to minimize the interference from the Low to High Audio Transformer which I hope to solve the weakness of high freq. in Acoustat 2+2. Your comment and explanation will be appreciated.

    Andy Szabo (2008-07-13 14:20:28)

    In Acoustat\'s MK-121-series interface, the high and low frequency transformers overlap considerably in their range of operation. No crossover is necessary to roll-off the highs going to the LF transformer - its own natural roll-off is sufficient. Think of it this way: the LF transformer is the \'main\' transformer, covering as much of the audio spectrum as it can. The HF transformer merely picks up where the LF transformer begins to roll-off. The HF transformer uses a high-pass crossover to prevent low frequencies from saturating its smaller core. The purpose the the 1-ohm resistor in series with the LF transformer is to make sure the DC resistance of the interface is not less than 1-ohm (otherwise, the DC resistance of the transformer itself is only a small fraction of an ohm). In cases of a slight DC offset from your amplifier, this prevents excessive current flow. I recommend that this resistor remain in circuit, although some advantage may be gained by replacing it with a better quality part.

  • Report of crossing the species - Wanchai on 2008-06-30 12:17:52

    Hi Andy ,This is my report after getting your last time answer for using Acoustat panels with Soundlab interfaces: 1.I use steel frame with two steel pipes as column with compacted glass wool in the pipe for 6 panels of 9\" and spikes at the bottom pipe support. (they look like Soundlab U1 but higher) The panels are angled 6 degree to each adjacent panels as your recommend.I provide 2 mm. rubber sheet between panels and steel frame. 2.I put the stepdown to 24 Vac transformer before the Soundlab bias transformer to get the proper supply voltage for the Acoustat panels. These are the results: 1.The audio transformers of the Soundlab M3 can handle the 6 panels capacitance load without problem. 2.The Acoustat panels are the most durable stat panel in the world. Older than 20 years still work well and reparable. 3.The Acoustat panels are the most intelligent stat panel in the world.I use them for the substition for the original panels of Soundlab M3 and Final 0.4 without any side effect. 4.The sound quality of 3+3 on the steel frame with the Soundlab interfaces is superb .Bass reaches 20 Hz at -3 DB (set at -3 dB for the bass at the Soundlab interface to the best tonal balance in my room ). High is second to my Apogee DIVA only but I can add ribbon super tweeter of Townshend which can add the highest harmonic range. Mid is the best as the electrostatic trade mark. 5. The image and soundstage are improved by the steel frame with spikes.The size of image is not magnified to larger than the real life.(big Soundlab may have this problem) The singer stands on the floor not the ceiling even the panels are nearly 8 feet high.The piano is not large as the room but exists at the recording position. I hope this report would be useful for the Acoustat Lovers and Owners.

    Andy Szabo (2008-06-30 23:23:10)

    Thanks for the report on your project - it sounds like it was fun to build, and the results well worth the effort. Yes, the Acoustat ESL panel is very rugged and long-lived, and can be expected to operate as originally intended for many years. Quite a few of Acoustat\'s original speakers (in original form or otherwise re-configured) are still providing enjoyment, often to second, third, or even fourth owners. One only needs to watch the auctions on eBay to see that the speakers are still quite popular and retain their value well, despite being out of production anywhere from 18 to 30 years ago! It is interesting to observe that the eight-foot models tend not to produce a \'larger-than-life\' image, despite their immense height. And yet, on some recordings, I have noted a distinct vertical positioning of certain instuments or voices. How that works has always been a mystery to me, given the speaker\'s equal production of all frequencies from top-to-bottom!

  • Looking for a pair! - Kenneth Dawkins on 2008-06-03 16:27:41

    I owned a pair of Acoustat Spectra 66 7 years ago and sold them when I bought my (Apogee / The Apogee) Now I have been searching for the last 4 years trying to find those speakers again: I now know that I made a big mistake in selling those speakers and want to purchase the 66 again! Can anyone help me? I am looking the 66\'s made in the USA, in any condition, I just want those speakers Thanks, Ken

    Andy Szabo (2008-06-03 19:28:03)

    Oh Ken! That was a mistake. There weren\'t many made of that model, so finding a pair on the used market will not be easy (as you already know!). I suggest you establish an eBay account, and set up a Favorite Search for \"Acoustat\" and have them email you whenever a new item is listed. There are other web-based sellers of used audio equipment: look around, I\'m sure you will find a few. Some of them may even have similar automatic notification systems. Keep in mind that very few sellers are willing to ship such a huge speaker (for good reason), so local pick-up is almost always required. Be sure to remove the bases and interfaces before moving the speaker, to avoid twisting and possibly damaging the frame. Also look for the Acoustat Spectra 6600, which is the same as a Spectra 66 but with added oak and brass trim. All Spectra models built in the USA will say so on the interface label. I rather doubt any of the Italian 6600\'s were exported, if indeed any were ever built. Good Luck with your search - I feel your pain!

  • Problems: blue sparks coming from circuit - Al.M on 2008-06-03 16:21:11

    I have model 4 panels with model X servo amps but the amps are not working well. There are blue electric charges coming from the circuit board capacitor ends where they meet the board near the tubes and a sizzling type sound. Panel sound is very weak as well when music is played. Any possble ideas on what might be obvious solutions? Thanks

    Ken Ealey (2008-11-08 04:58:10)

    Al, I\'m surprised nobody has answered given your post time, so I\'ll try helping. I assume you know that the blue sparking is the high voltage seeking a conductive path, and that when you see arcing, you\'re actually looking at current - just like a spark plug. For the path on the board to be conductive, it\'s safe to say that it is not clean. Rather, contamination is present, such as oil that has leaked from the oil-filled .1uf output cap. Oil itself is a great insulator of sorts (and is why oil caps have it), but oil draws air-borne contaminants, which in turn attract moisture. This mixture can be a good conductor and if enough accumulates, then we have the sparking that you\'re seeing. So, a possible solution would be to clean the board with something like denatured alcohol (mostly ethyl alcohol), and also inspect all high voltage parts, in particular the oil caps themselves for pinhole leaks. Just normal handling can tell you alot since anything will likely get on your hands. Also, the cap might have a sizeable air bubble inside that indicates some oil has escaped - although some perfectly good caps can have these as well. The last pair of servos I rebuilt were for a customer that had an oil leakage problem develop out of his main HV p.s. caps and pretty much took out the supply by the means mentioned above. It all could have been avoided had the amps been properly maintained, as they had been serviced prior to my looking at it but with no action taken. I would advise taking care of the problem first before continuing to operate them, even though music does come out. The weak level is probably due to this problem, or may be a separate one altogether. You mention both amps are not working well, which I find interesting that both chose to have problems at the same time. Perhaps you meant just one amp was having trouble. Also, just make sure you have good tubes and a clean mounting for them, with no carbon (burnt) buildup. Hope this belated answer helps. It\'s all I can think of given what you mention. Ken Ealey

  • Amp problem - Al.M on 2008-05-31 15:18:14

    Hi All I just bought a Model 4 like the one pictured here (servo amp label says Model X). One of the amps is sparking up when turned on and continues so. Sparking as in the circuit board individual components (long black and orange striped capacitors) making a fizzing and electrical charge sound and visible blue electrical charge at numerous points where they connect to the circuit board. Some smell comes with this as well. Any suggestions please on what to do initially. Thanks

    Mike Savuto (2008-06-10 03:48:14)

    Hi Al, All of the servoamplifiers have the same model designation (Model X) on them, no matter what array of panels they were sold with. You appear to have the original 4 panel versions with the separate stand marketed as \"Acoustat Monitors\". The sparking could be any number of things but is most often indicative of high voltages jumping where they don\'t belong. One good thing is that the amplifier is not blowing any fuses, so the problem is not life theatening (to the amplifier). It could be as simple a tube failure, but might also be a part in the high voltage circuit (around the tubes)has failed. What ever you do, don\'t leave them powered up for very long until the problem is resolved. I would first replace the tubes with a new set (or the set from the other amplifier if it is not experiencing any problems) and see if the problem persists. If it does than you are going to need some repair work done to get the amplifier to settle down. Often this problem can be due to the aging of the circuit board due to heating from the tubes. If your amplifiers do not have brown or tan tube stand offs, but the tubes plug directly into small brass sockets soldered to the circuit board, the problem is very likely carbonization of the circuit board at the base of the tube due to overheating. This needs some remedial clean up to alleviate, but is something that should be done with great care because it involves grinding away some of the circuit board between the tube pins and the leads underneath the board to fix and installing the tube standoffs. These amplifiers are remarkable durable considering what they have to do, which is a testament to a great design. After replacing the tubes, let me know what happens and we can go from there. Best Wishes, Michael Savuto Analogue Associates, LLC

  • Transformer substitute - martin on 2008-05-31 03:13:55

    Dear Andy Thanks for detailed and honest answer, which at some point overwhelmed me, with technical approach, (Feedback correction with woofer). Since I am not familiar with spectra interface, I just saw briefly the schematic of MK 121... Because recently I have acquired the brand new (old stock) spectra 1100 panel with the bias transformer (750v) which I can make a voltage multiplier to 5k or more and choke it to stabilize ripples, as seen in MK 121 mods. Essentially I am missing step-up transformer, I know the person who have a old stock of acoustic step-up transformers (hi and low freq) , could you please advise me which transformers model## from Acoustat stock I can use to substitute those from original spectra 1100 interface? Or which one use to build an interface which will drive the panel alone.. ( I am planning to use it as a center channel in THX setup with 180hz crossover point not that much dynamic I long for rather natural transparent dialogues)

    Andy Szabo (2008-06-01 03:37:28)

    You could use the MK-121\'s high and low frequency transformers together for your single panel, but it is not necessary since you will be operating only above 180 Hz. The MK-121 transformer set is intended to drive from 2 to 4 panels over the full audio range, and would be overkill for your application. Your best bet would be to get an Acoustat transformer designed for a single panel operating at non-bass frequencies only. These transformers include the Spectra 11/1100\'s TTA-70K, the MK-131\'s TTA-131, or the MK-141\'s TTA -141. My first choice would be the Spectra model. I have seen all of these transformers on eBay, from sellers \'dealsbyjason\' and \'soundvalves\'. You could try contacting these sellers through eBay to see if you could arrange a sale. Tell \'em I sent you, as I have helped both of them indentify their Acoustat parts. I also highly recommend you get the Acoustat CD available from this site\'s webmaster. It contains schematics for all of these units, which you will need to properly connect the transformers. Since you already have the Acoustat bias transformer, I suggest you follow the MK-121 bias supply as closely as possible. You might have trouble finding the 500-megohm resistor, but you can use as low as 100-megohm. Don\'t omit this resistor (as some have incorrectly recommended): it is an essential part of the speaker\'s constant charge operation. I would also recommend against most of the \'modifications\' suggested for the Acoustat bias supply. Most of them offer little or no sonic improvement, and some are even dangerous to both you and the speaker.

  • woofer design passive or active - mike goering on 2008-05-24 22:41:14

    for my 22s? any way to get the original design specs on the sub add on Acoustat sold for the 22s and 33s? i had 33s and sold them, what a fool! then i miraculously located 22s and bought them immediately. they are my rear channels believe it or not!! so i want to add qty 4 eight inch drivers in sealed boxes. but 2 drivers per mini floor tower not all in a common box like the factory did. but i would like to see their design - what was the product model no.?

    Andy Szabo (2008-05-25 18:31:03)

    The accessory woofer for the Spectra series is known as the model SPW-1, sometimes referred to as merely the SPW (because there was only one such woofer system). It is a passive system, consisting of two 6\" woofers per channel (four total) contained in a single ported enclosure. I don\'t have any information on its design details, as the unit was primarily designed and completely manufactured at Acoustat\'s sister division Rockford Carbonneau (now known as RAD, or Rockford Acoustic Design, in Grand Rapids MI). The woofers themselves are Carbonneau\'s own design. Probably the easiest solution to adding woofers is using a powered subwoofer (or two) crossing over at 80-100 Hz. With my Spectra 4400\'s, I am using a single 10\" powered subwoofer available from By no means a top-of-the line system, it neverthless provides a welcome stength to the bottom end, and offers enough flexibility (crossover frequency, phase, amplitude and either low or high-level inputs) to be easy to integrate into the system. A few years ago, I paid slightly over $300 for it (in an easy-to-build kit form), and I consider it a good investment and my system is better for it (not perfect, but improved). If you are more interested in a do-it-yourself passive (or even active) design, the particulars of the enclosure and crossover design will depend heavily on the woofer(s) chosen. Again, Parts Express has a wide variety of woofers, crossover components, amplifier modules, speaker design books, etc. available for the do-it-yourself enthusiast. Please note I have no ties to Parts Express - I simply have found them to have a lot of neat stuff and an easy to use website. There are no doubt other good sources available (some of them advertised on this site). Good Luck! (And shame on you for selling your Spectra 33\'s - but I will forgive that one lapse of sanity!) Acoustat speakers and repair parts do appear quite frequently on eBay.

  • kinky interface - martin on 2008-05-21 06:14:59

    my question is about the spectra 1100 interface, I found that some other ESL uses simple xover, with step up transformer and bias supply.. spectra 1100 have some more advanced electronics, where the transformer alone have many windings and is being connected oddly to the pannels.. my understanding of ESL is simple as the membrames being pushed by the charges... why spectra 1100 have all those extra IC ? does it adjust bias voltage depending on the material played ? what if I try to run the pannels alone on a simple step up transformer with bias ?

    Andy Szabo (2008-05-22 02:34:53)

    It is true, that the electronics for an ESL (in its simplest form) consist of crossover, audio step-up transformer, and bias supply. However, to extract the best musical performance, refinements are both possible and desirable in all three areas. Spectra’s bias supply is a high-frequency oscillator-type power supply. This allows the supply to be both adjustable and voltage-regulated, meaning that the constant charge on the diaphragm can be set for the optimum level, and then maintained over a wide variety of operating conditions. The speaker’s performance is therefore predictable and stable. Spectra 1100’s crossover is fairly simple, but does have some additional components to smooth the transition between woofer and ESL, and to provide the different settings of the High Frequency Balance Switch. Spectra’s audio step-up system and method of connection to the panels is what really improves the performance over a simpler approach. The 1100’s transformer may appear to have a lot of wires, but this is because the two phases are wound on separate sides of the transformer. The two primaries are driven in parallel, but out-of-phase. The two secondaries feed the front and rear stators of the panel. Part of the transformer’s output is fed directly to one vertical half of the panel, delivering frequencies from the woofer’s crossover point to the top-of-range. The other part of the output is fed through a resistor to the other half of the panel. The action of the resistor working against the capacitance of the panel rolls off the high end, delivering low frequencies only to that sector. The overall effect is that the speaker operates over the full area for lower frequencies, becomes effectively narrower at high frequencies, and in fact, acts like a curved surface! This significantly improves the dispersion of the speaker, making for a wider listening area. Furthermore, each speaker’s two sectors are arranged mirror-image from the other, greatly improving stereo imaging. For a detailed explanation of Acoustat’s Spectra technology, I recommend the White Paper on this subject, available elsewhere on this site. Regarding your last question, you certainly could drive an Acoustat panel with a simple bias supply and step-up transformer. However, compared to the refinements offered by the Acoustat design, I think the results would be very disappointing. You will find that most, if not all, commercially-successful ESL’s incorporate many refinements over the basic concept. Each manufacturer has their own favorite approach, and of course I am partial to Acoustat’s methods, but all have found it necessary to go beyond the basic concept in order to make a widely accepted product.

  • Wall transformer replacements? - Ralph Edwards on 2008-04-22 00:33:38

    Does anyone know where I can get replacements for Acoustat 1100 wall transformers? Somewhere between Connecticut and California they came up missing. Why didn\'t I pack them with the speakers? A very good question that I can\'t answer without incriminating myself. My wife is smiling at my discomfort, and rightly so. Thanks! Ralph

    Liam (2008-11-17 08:39:49)

    You should be able to buy replacements at most electronic stores. Your originals will either be 12Vac or 15Vac unregulated. They need to be rated at 150 mA or greater. (Don\'t worry if they are rated higher than 150 mA - mine are 800 mA.) Acoustat used both at different times. Make sure your new one are the same voltage as the old ones You may need to change the jacks to suit the jacks on your speakers. if your existing jacks are OK you should be able to re-terminate these on the new power supplies you get.

    Andy Szabo (2008-11-18 00:56:05)

    You can also try searching on eBay for Acoustat. Genuine NOS (new-old-stock) wall transformers are frequenctly offered by a seller called Soundvalves. These were sold as surplus when Rockford Corp got rid of all their Acoustat inventory. Soundvalves has lots of valuable Acoustat and Hafler items: I\'ve helped him identify some of them.

  • Mis configured speakers - Bruce Domenella on 2008-03-31 00:46:32

    I suspect that my Spectra3s are mis-configured. The HF panel is on the right edge of both speakers. I can tell this by the dust accumulation. If I\'m correct, is it ligitimate to turn one of the panels around (the RH one) so that the HF panel is on the inside making the speakers mirror images? In that case would I have to reverse the audio cables to correct the phase?

    Andy Szabo (2008-04-01 17:42:19)

    It is true that the Spectra panels should be left-right mirror-image. That is, the highs should sound as though they are coming from near the inner edge of each speaker. However, even though the dust accumulation may be an indication, I would not rely on it to positively identify the correctness of the panel. This must be done by scanning your ear at close range across the width of the panel, and listening for where the highs come from. If you determine that you indeed have two identical panels (instead of a mirror-image pair), reversing the panel (with or without an electrical phase reversal)would not be suitable, for a number of technical reasons. The only way to fix this is to rewire the panels. This would involve disassembling the current pin-plugs (except the red set), identifying the individual wires from the front and rear stators of each sector, re-wiring them to the opposite configuration, and reassembling the pin plugs and applying new color coding. A tricky job, but certainly not impossible. A diagram of the sectors and their color codes is available on this site. At the top of the Acoustat section, go to \'Refurbishing\', then scroll down to my Technical Bulletin titled \'Spectra Sectoring and Color Codes\'. By the way, if your speakers have been playing incorrectly, you\'ll be amazed at how much better they will sound when configured as a mirror-image pair. After all, the \'SP\' in Spectra stands for \"Symmetric Pair\".

  • Adjusting til Ultrasonic Bias - Jan Jepsen on 2008-03-21 19:15:05

    This is kind of a question....and a \"what-happend-here-????\" expirience. I\'ve written before about the Spectra 11. Ever since I got them, they\'ve been a puzzle. They have the ability to remove a backwall in a room. Suddenly you can hear the depth in a recording. I was reading another question about the bias voltage. And that the panel wouldn\'t be damaged from over voltage. I did the \"lets-see-what-happens\" way. Grabbed a screwdriver after removing the power, and turned the pot from 9 o\'clock to 3 o\'clock, and put it all back together. Ladies and gentlemen.....the side walls went away !!! I\'ve never heard anything changing so dramatically !! I\'ve been going through different music the whole day because I just couldn\'t belive what happend. So Andy...can I continue using the speakers without damaging anything ? I haven\'t got a clue about the bias voltage now. But the speakers sounds so much better than before. And don\'t we all like a free upgrade !! Best Regards Jan Jepsen

    Andy Szabo (2008-03-21 19:53:06)

    Increasing the bias voltage (within the limits produced by the ultrasonic supply)should not harm the speaker. The nominal bias voltage of +5000 volts DC is used for the Acoustat as the best compromise between efficiency and performance over a wide variety of climatic conditions (humidity, temperature and altitude). Increasing the bias voltage will increase the ESL\'s efficiency somewhat, at the possible cost of producing extraneous \'crackling noises\' when the humidity is high. This may or may not be a problem in your area. In any case, the noises do no harm to the speaker - they are just annoying. What you are hearing is the air itself breaking down, and causing minor discharges from the diaphragm (kind of like a bug-zapper). The Spectra 11 is a hybrid model (having a conventional woofer), and the bias voltage has no effect on the woofer. Therefore, changing the bias voltage has the effect of changing the tonal balance between woofer and ESL. If you like the results better, then that is all that matters. I should note that turning the bias adjustments \"full on\" will probably NOT produce equal bias voltages in each speaker. If you are lucky, the difference may be small, but if you notice a channel imbalance, you may need to turn-down the speaker that is playing \'hotter\'. Ultimately, it is best to use a high voltage probe and meter to adjust each speaker, to ensure that the bias voltages are equal. A procedure for measuring and adjusting the bias voltage is described in one of my \'Technical Bulletins\' located on this site.

    Jan Jepsen (2008-03-22 10:55:16)

    Hi Andy Thank you for the quick answer. I don\'t have any of the mentioned crack noises. And I will put on a meter and do it the right way. As you mentioned, full throttle on the bias is a bad idea. Therefore I didn\'t do that. But by now I have a much better balance between the panel and the woofer. I have from the very beginning, had a feeling that the speaker had a very \"dark\" sound. That is all gone ; it\'s an awesome speaker. Thank you. Best Regards Jan Jepsen PS: I took a lot of time locating the BIAS adjusting service bulletin.

  • Woofers - Gary Smith on 2008-03-07 05:42:12

    Andy I have just bought a pair of Spectra 3\'s but notice the woofer in the base has a small hole in the surround. Is there any information as to what name or characteristics of the speaker that I need to be aware of to replace this speaker. Do getting the surrounds redone work..if not is there a certain replacement speaker that would maintain the intial sound characteristics?

    Andy Szabo (2008-03-07 17:38:49)

    The woofers in the Spectra 2 and 3 were custom made by Carbonneau in Michigan. Oddly enough, the relationship between Acoustat and Carbonneau started years before Rockford Corp. acquired either Acoustat or Carbonneau (which is now known by another name, but still a part of Rockford). That said, it will be virtually impossible to get an exact match for the original woofer. But that is not all bad news. Although the woofer is a good one, there are better ones available. I suggest you check out They have the widest variaty I\'ve seen, at many price points. Spend as much as your willing to, and you will likely end up with a better woofer. I do suggest you stay away from woofers intended for musical instrument and autosound applications. Of course, you\'ll want to replace both woofers so that they match. Replacing the surround is possible, and that may yield the closest match to the original. But that process is quite expensive, and you might not pay that much more for new woofers. If the hole in the surround is small enough, and was caused by a puncture, you might be able to patch it with a small dab of silicone glue. If, however, the hole is due to a general failure of the rubber (i.e. it is dried out and rotten)then your only recourse is the replace the surround or the entire woofer. If you do find a good replacement woofer, please post the information under \"Available Parts\" so that other may share your good news.

  • Sounds Like New - David on 2008-03-05 02:21:22

    I have what I believe to be Model 3 with Medallion upgrades. (72\"x28\"). They work and sound great but I thought I would have Roy at Sounds Like New rebuild/recap the interfaces before he retires. I may have waited too long. It appears he has closed. Do you know if he is still in the business? If not is there anyone else in the SE that can do it (I really don\'t want to ship these things). I don\'t think I want to try it myself. Thanks.

    Andy Szabo (2008-03-06 18:11:21)

    For years I have heard comments that Roy can be difficult to contact. I have no idea if \'Sounds Like New\' is still a going concern or not. Keep trying! In my opinion, if the speakers are working okay, I would leave them alone.

    randall worrell (2008-03-29 16:05:35)

    Hi David, I just had the pleasure of meeting Roy whilst I was in Florida this week(March 22 2008) and spoke with him again yesterday.He can be reached at and he still does rebuilds of interfaces and also conversions of the TNT 200 amp to monoblocs.He is extremely knowledgeable about the Acoustat line and does great work.Hope that you reach him if not please let me know. Regards Randall.

    Roy A. Esposito (2011-07-17 19:54:20)

    July 17, 2011

    I am very much alive.

    I am No-Where near retiring .... and over many years have
    come up with astounding improvements, variations and restorations
    for the Acoustat MK and Spectra Interfaces
    and even more so the Trans-Nova amplifiers (TNT-200 and TNT-120)
    and Trans-Nova Preamplifier (TNP).
    I also renew the earlier and more rare, Acoustat MRP and RP-2 preamps.

    To my chagrin ----
    Folks don't realize I was many years younger than the
    other principals at Acoustat, back in 70's and 80's Fort Lauderdale.
    About half their age at that time.

    I am happy to continue lovingly working with Acoustat products.
    I do this with a fully functional laboratory and stockroom
    of original .........and improvement parts.

    But please realize that... in 2011....
    this is part-time work.... in addition
    to my regular full-time engineering/consulting work.

    So it can take a few weeks in total, for me to work my
    Acoustat "magic"...... as my client's have often
    described the results.

    I hope the above will help explain why I don't
    provide a phone number, except to established clients,
    and I prefer email contact instead. I also prefer my work
    and "word-of-mouth" to speak for itself
    ....instead of having and spending time maintaining a website.

    There are others that offer work on Acoustat products.
    Fancy words .... Fancy websites.
    But NONE of them worked for the Company.
    And to correct the mess.....
    Folks usually end up with me despite the glowing website tetimonials.
    That's just sad.

    I very much appreciate all of you, who continue to revere...
    and enjoy...
    the magnificent design works of Dr. Strickland,
    and our original Acoustat Engineering Team.

    May we all enjoy the Music,

    Roy A. Esposito /

    Andy Tomlinson (2012-04-10 17:40:40)

    Just so you all know Sounds Like New will now only accept shipments that originate and can be delivered in the USA. They will not accept shipments that originate anywhere else in the world. A move designed to "HELP " their customers I was told.Most unhelpful/ unreasonable company I have ever dealt with.

    Roy A. Esposito (2012-04-11 01:44:39)

    I am responding to this posting.

    I happened to have a spare Spectra U-Bias power supply board
    that this gentleman needed when he contacted me.
    He was advised CLEARLY and... up front.... that
    I no longer ship TO or accept shipments FROM
    addresses outside of the USA-48 states. I explained to him that
    this was due to problems that happened every time I made an exception
    in the past for international folks. So, I asked him to provide a USA
    shipping address of a friend or associate.

    I also explained that I am not a "company" .... per se...
    and I do not normally offer any PARTS for sale but that it was
    my aim to help out folks needing assistance with Acoustat products
    in any way I possibly could.
    And that I am merely an individual ex-Acoustat Engineering Team member
    and former humbled assistant to
    the Esteemed and Brilliant Dr. James Strickland PHD.
    The Chief Designer of all things Acoustat.

    I have made myself available to the Acoustat loving community for many years now....
    as a very competant source for repairs, mods and improvements to the already
    amazing products. I tried to work with this guy, but he insisted on me
    shipping to Canada directly, insulted me repeatedly and then threatened me
    with smearing my name on every forum he subscribes to.

    This is the first I see of his threatened attacks
    and I shall respond to each. I also have no doubt that
    Acoustat owners I have helped to repair, restore. and upgrade
    beyond their wildest hopes might respond with something to say in my defense.

    All this guy had to do was apologize.....
    for insulting me and
    "Americans" in general, and I would have gladly helped him
    under the original terms I outlined.

    As Always...... I remain at your service for
    amazing Acoustat repairs and updating into 2012 and beyond.
    --- MK Series Interfaces featuring the optional AIR MOD since 2008
    ----Spectra Series Interfaces featuring distortion reducing
    and performance enhancing upgrades
    ---- Trans-Nova Series 120 and 200 Amplifiers and Preamplifiers
    featuring Mono-Block and Balanced Input Conversions

    I have 100% satisfaction for my work and countless
    letters and emails that prove it.
    Just ask anyone who has seen and heard the results.

    I invite anyone who is serious about having their
    Acoustat products made the best they can be
    contact me.

    Most Sincerely,
    Roy A. Esposito

    Randall Worrell (2012-04-11 03:08:16)

    I must say that I have had the pleasure of dealing with Roy Esposito and I can vouch for his excellent work and his high principles.I certainly am not from the USA and I live in BARBADOS which is NOT an address within the USA .Roy was extremely helpful and worked with me in order for me to get a pair of TNT 200 monoblocs.He also rebuilt another TNT 200 amp for me and also a pair of Acoustat interfaces all with the Air mod .My point is that it certainly was not as easy as dealing with products going to or coming from CANADA but Roy was exceedingly Helpful and I followed his advice and everything went as planned and directed by him.The end result was that I received my amplifiers and speaker interfaces all well rebuilt and excellent sounding units.He is the consummate professional and a highly talented engineer.I would have him do any mods or repairs for me again and hope that he continues his excellent work.

    Randall Worrell

    Andrei Tudoran (2012-04-11 04:08:22)

    My Acoustat #8 speakers live in Thailand.

    Roy is alive and well and very helpful.
    While tinkering, I damaged one speaker.

    Via Email, I contacted Roy; he immediately offered technical advice without compensation.
    Later on, when I was confident the panels have a solution; I decided to upgrade the medallion transformers (number 8 = 4 transformers)
    From Thailand, its quite a challenge.
    Roy does this work mostly as a hobby and at very modest charges.

    I had my freight forwarder deliver the medallions at Roy's place, than pick up upon completion.
    With a little patience, they were delivered back to my house in mint condition, sounding amazing!

    I would not hesitate to contact Roy for any sound related issues.
    His work is impeccable.

    Louis Nicolia (2012-04-11 04:51:57)

    It's been my pleasure to know and be a client of Roy Esposito the past 15 years. He has rebuilt and upgraded all of my Acoustat equipment including a preamp,two mono blocks and Model 3 speakers.Aside from his stellar workmanship and expertise ,Roy has always gone out of his way to help when needed. Listening to music on this system is a joy.I wouldn't hesitate to call Roy.Thanks Louis

    BOB NACE (2012-04-11 11:03:23)


    Andy Tomlinson (2012-04-11 13:20:39)

    I'm just stating what you told me Roy. I offered to comply with your terms but then you refused to respond to any of my emails.Here is the content of my last email to you

    " I'm sorry if I offended you with that ,but from my point of view as a guy who trades across the border every day I can't get my head around Americans who will not deal with people in Canada.Its just not that difficult. I can see your point of view and I appreciate that you are selling this unit to me but, there has to be some way so that you don't get burned and I don't have to drive to the US twice . Thats a 100 mile round trip,twice, not to mention the border wait times .This is not like we are shipping back and forth large interfaces or amplifiers, its just a circuit card and a small transformer. In my case the transformer fits in a small package that would easily go by Canada Post. I could send you the transformer and money order ( adjusted to cover any additional mail cost to Canada) by mail and you can send the HVPS by mail . I still need the U-bias supply and will still meet your terms but it is not the way I would like to go."

    I did not make any comments about Americans I just said I don't see how YOU can be so narrow minded about shipping , in this case to Canada. I even offered an alternative, suggesting that the item I wanted was a small circuit board worth less than $50.00 and could easily go by mail.I said I can understand your policy but that I don't have to like it. Instead of trying to resolve this even when I said I would comply with your terms you did the adult thing and refused to reply to my email. I'll let the facts speak themselves, you were unhelpful/unreasonable

    Alan Chandler (2012-04-11 13:29:41)

    I reside in Toronto, Canada and I have owned Acoustat Speakers since the early 80's. Many years later I was able to track Roy down in order to seek out some advice. From that conversation I was on the look out for a Acoustat MRP-1 and after locating one I sent it to Roy for per his instructions...which required my driving the unit across the border and shipping it to Florida via FedEx 'Ground'.

    The unit was shipped back to the FedEx Office in Buffalo where I retrieved it and brought it back into Canada.

    The work performed was nothing short of a miracle...and since that time I have had Roy service my MK - 131 Interfaces, 'monoblock' 2 TNT-120 Amplifiers and 'upgrade' a TNT-200 Amplifier.

    Roy explained in great detail the reasons for his no longer wanting to deal with 'International Shipping' and taking a moment to put myself in his position I had no problem in understanding his decision.

    I believe that there is no person better qualified to work on Acoustat gear than Roy...and therefore it is worth the extra effort on my part to adjust to his request.

    Roy has always proven to be a man of integrity and honesty and as a dedicated owner of Acoustat equipment I feel truly blessed that I am able to avail myself of his services.

    Rick Pettey (2012-04-11 13:54:45)

    Please allow me to echo several of the comments previously offered. Roy is without qualification a man of ethical integrity and will provide his customer with the highest quality work and more than fair prices. As one who worked with Roy at Acoustat in the early 80s, I know him to be great to work with and easy to get along with. I say this because as I was in sales and often asked of him and his group to accomodate some wild demands from the field, he would also do all within his power to support our end customers.

    Because he cannot afford to do this work full time (simply won't pay the bills) he takes care of his customers during his "off-time." It is for that reason that you cannot call him during typical work hours for a chat. However, do not let that dissuade you from using his services. Although he is not doing this full-time, the slight amount of wait (and I do mean slight) to have him schedule your work is MORE than compensated by his quality and value of work. As I am no longer in the audio industry (am a Lutheran pastor), I do not have a great deal of disposable income to splurge on my system. The work Roy has done on my amp, pre-amp and ESPECIALLY on my Spectra 300 (he replaced the electronic circuit with transformers, like the old Acoustat thereby eliminating many components and increasing the quality of sonic presentation in every way) has been of the highest caliber.

    I am inserting my email address if anyone would like to contact me directly if they have any further questions as to Roy's credentials. (If this web-site will allow me to do so.) It is

    Andy Tomlinson (2012-04-11 14:05:51)

    I don't like to air my dirty laundry in public. Roy would not reply to my emails even after I said I would comply with his terms, even if I didn't like his terms.I even apologized if I offended him. But he chose to ignore me. No where on this page did it say he wouldn't deal with international shipping I chose to make people aware of that policy.

    Rick Pettey (2012-04-11 14:28:27)

    Andy, I do not know you nor you me. I am also not aware of the actual circumstances of your dealings with Roy. What I do know is that there are ALWAYS two sides to a story. As one who has dealt with the public in the retail audio field and then from the manufacturing end and especially now as a pastor, I have found that how one person perceives an event can often be quite different from another. For that reason I cannot address your specific issue. Having said that, there is no doubt in my mind that there is more here going on than you indicate. I say this not to impugn your character but to suggest that what you express is simply from your point of view (Naturally, of course).

    I have dealt with Roy under too many circumstances not to believe that there is some reason he is not accomodating you (if such is the case). Having tried to resolve numerous complaints from customers over the years it was always amazing how the custormer's view of the situation was so radically different from that of the store where they bought my product (Acoustat). You would think you somehow dropped in on the wrong conversation.

    All this is offered not to call your integrity into question. I simply do not know all the facts. I DO know Roy well enough (both as co-worker and now as client) to state without qualification his high standards of ethics as well as his desire to support the joy of owning/using the equipment that he has invested so much of himself in over the years. He is too committed to this endeavor not to do all within his power to serve others with the same love as his. While you try to please everyone I know from experience that there are times when there is simply no way to do so. Perhaps this is one of those times.

    Ivan Bendl (2012-04-11 15:57:38)

    I thought it was a miracle that I found Roy. He repaired 1 Acoustat for me, and upgraded both without asking. He wanted me to have the best he knew how, and he certainly does. Then he gave me advice how to set them up and where to send a speaker for repairs. When I found another pair (I run 4 channels) he also upgraded those. I now have the latest and they all work perfectly.

    Roy was always friendly and a pleasure to deal with. How can anyone complain about him is beyond me. As for receiving and sending things to other countries, it is not easy and takes a lot of time. His work for us is in his spare-time so time is precious, and I for one, treasure his policy to help us with our Acoustats. Ivan

    Charly Brewster (2012-04-12 02:17:10)

    Have known Roy Esposito close to ten years. In that time Roy has worked on a pair of Acoustat Spectra 44 speaker interfaces, once to update interfaces which were approximately 30 years old, and once to convert the same interfaces to 120v instead of the original wall bricks Acoustat used on the Spectra 44 speakers. The sonic differences were FANTASTIC.
    Both experiences with Roy were nothing but professional, and friendly. Communication was by E Mail most of the time. Roy prefers E Mail. From a business point of view this works very, very good.
    There is less chance of a miss understanding, and a documented account of what was really said between both parties. Personally I like doing business this way. Roy s Phone number was made available to me after he worked on the first interfaces. When there is need to talk directly to Roy, he has always been friendly and helpful.

    Roy has also done "Full Restoration Factory Updates" on three of my Acoustat TNT 200 Power Amplifiers. Two of these amplifiers having gone on to be converted to Mono Blocks with Balanced inputs.

    If you have a pair of Acoustat TNT 200 Power Amplifiers. You will not believe the Magic that happens when they are given Full Restoration Factory Updates and converted to Mono Blocks.
    I personally believe they can drive ANY Speaker system on the market. Past or Present.
    Another thing. The power output for each amplifier is close to 1 KW.

    Roy s work is [ALWAYS PERFECT] mechanically and electrically. Never has there been one single problem with anything Row has worked on. The work is scheduled, sent to Roy, and returned to me on a timely as agreed to schedule. Roy s pricing and shipping is fair and reasonable. Return shipping is included in the original quoted price.

    Having dealt with shipping things to Canada or other places. I am with Roy 100 per cent.
    Nothing personal. It has become a lot of work to get things in and out of foreign countries, yes I know Canada is not that far. However, the difference between shipping a pair of speaker to Canada as far as paper work is involved. Five pages of paperwork to Canada versus one to ship here in the USA.

    As Bob Nace said, "WHY DEAL WITH THE REST WHEN ROY IS THE BEST." Could not agree more.

    Roy Esposito: a true credit to Acoustat and Acoustat Full Restoration, Factory Updates.
    Very, Very honored to know and do business with Roy.

    You may also contact me at if further information is needed.

    Charly Brewster

    Dan Burkett (2012-04-12 03:22:01)

    On the recommendation of Charly Brewster, I contacted Roy about upgrading my 2+2 interfaces. I followed Roy's procedure for sending in the interfaces. He did exactly what he said he would do and in the amount of time he said it would take and his price was very reasonable.
    Having an engineering background myself, I was very curious to examine the work he did. The quality of his work and the components he used were absolutely outstanding.

    Additionally, Roy has helped me isolate a system problem by answering questions and providing suggestions, all without taking a cent for his work above and beyond what I had contracted him to do. He really does want to help people enjoy the music.

    In my dealings with Roy, He has been honest, courteous, professional, and straight forward with me. I can recommend Roy without any reservations whatsoever. He is just that good at what he does.

    Chuck Rieman (2012-04-12 12:11:11)

    I have known Roy Esposito since 1979 when we worked together at Acoustat in Fort Lauderdale. Roy helped develop all Acoustat products. The TNT-120 was his idea. Besides Jim Strickland, he is the foremost expert in the world on the technology, repair and enhancement of all Acoustat equipment. He is a world-class electronics diagnostician with incredible intuition. Out of this intuition and diagnostic skill come his modifications which make vast improvements to the sonic quality of the already legendary Acoustat sound.

    His workmanship is peerless both in appearance and quality. He has taken on several incredibly challenging modifications for my Acoustat equipment and performed flawlessly.

    Mr. Tomlinson’s complaints seem to be about shipping to and from Canada and Roy’s communication. I don’t know what happened between them and maybe Mr. Tomlinson can fault Roy for his shipping policies. I do know that Mr. Tomlinson cannot fault Roy for his work.

    Roy is a true credit to the Acoustat community; we are lucky to have him.

    Chuck Rieman

    Andrei Tudoran (2012-04-13 03:15:34)

    It is amazing, after so many years Acoustat is still in may peoples living rooms performing better than most things on the market.

    Thanks to Roy, my system is one of them.

    David L Hardin (2012-04-13 16:54:34)

    I for one am very proud to call Roy Esposito one of my friends. I have known Roy since the late seventies when he was at Acoustat. He has always been there to help me with any problem I may have, and the results are always excellent. Roy has updated many Acoustat products for family and friends and they are all very please with his work. My brothers Model Three Acoustat's have never sounded so good. Ata boy Roy. !Aside from all this about his tech background, he is first and foremost a gentleman and we always look forward to spending time with him. Hey Roy lest get together for Dinner real soon !!!!!

    David L Hardin

    My personal email

    Rick Pettey (2012-04-13 20:44:01)

    This thread has really brought something home to me. It is incredible how many people are still using Acoustat speakers and electronics. Perhaps we should put together something by which we can share our experiences with the products. It would be fascinating to me to get some idea of the places where they are used. Although I was only with the company for approx. two years I know that during that time we shipped a lot of speakers to Asia and I personally assisted in securing a TNT-200 for a gentleman in Sweden (I have a small collection of Opus records as a token of his appreciation from that endeavor). Roy would undoubtedly find it even more fascinating due to his substantial contribution to the design and development of the TNT-200 as well as other products. If any of you would be interested in pursuing this please email me at:

    btw- for geographical purposes I am located in a small town 1 & 1/2 southwest of St. Louis, MO.

    Randy Hart (2012-04-17 14:25:04)

    Hi all
    I have a pair of Acoustat 2+2's which Roy Esposito has done his magic on. I have been reading this forum. To recap, I have seen posts that say: "Roy is hard to reach" \\ "Roy is about to retire"\\ "Roy is hard to deal with"\\ and things about Roy's work.
    I want the group to hear my experiences with Roy. He was referred by another former Acoustat employee-- David Hardin, whom I have known for 35 years!

    I emailed Roy at the email address here on the forum and asked him for information on the interface mod. I received a response within 24 hours with an explanation of what was involved, prices and some possible modifications. I elected to do the whole thing included his "air" mod. He told me that if I got the "air" mod I would probably want to cut it out for classical music and he would provide me a switch for that operation.

    Well, I sent the interfaces to him and within 2 weeks they were returned with a plastic bag full of parts he pulled out and replaced. He sent a very nice note with some instructions and a phone number (which I am not going to share on the forum) in case I should need him. I hooked the interfaces up withour realizing that I had a bad speaker cable. I could not make one of the interfaces work and called him on a Saturday. We spent all weekend on the phone working through all possible interations. He asked me to send them back, which I did. While they were gone, I pulled out my amplifier to audition a new set of speaker cables with another speaker. Roy went completely through the interfaces for a week and could find nothing. I asked him to send them back to me and hooked them back up with the new speaker cable and guess what.. They worked.

    The speakers picked up a new life that I had never heard in the 20 or so years I have owned these speakers (yes I am the original owner). I put the old cables back in the system to see the cable difference and low and behold found where the problem was. It was the cables. I have now had the interfaces for Several months and must say that they have improved my system more than any money I have spent less than $2000 in my system. The speakers have a better top end, more controlled bass and much more stable image. The image is also deeper and wider and the tonal balance is just unbelievable. All of the things I like about electostats are here and I must say that I no longer use my subwoofler. Roy has continued to stay in touch with me to make sure the interfaces are fine and he has been a good resource for incremental, low cost improvements as well.

    The story does not end there. I bought a TNT 200 for my son's system. I had intended all along to send it to Roy to look at. I put it in my system to listen to and after a couple of days it blew up. No smoke but the mosfets went while I was listening. I called Roy and told him what had happened and wanted to know if it would still be a candidate for his restoration service. He told me to send it and he would rebuild it for the restoration price.

    He got the amplifier and found that it was worse than he had expected. He replaced everything and I do mean everything except the output transformer. He called me with in a couple of weeks and told me it was ready to ship but that he wanted to listen to it for a while if it was alright due to the level of work he had to do. The output transformer began to hum while he had it. He tore that thing apart and got it fixed as well. He did not charge me an extra dime for the work and once it was suitable in his system, he sent it to my son. My son tells me that it is quite as can be and sounds wonderful. Roy and my son talked a couple of times and Roy gave him some hints as to hook up and configuration.

    Roy has been nothing but a great person to work with. He is friendly, timely and knows the Acoustat product line as well as anyone I have ever met. his work is first rate. The interfaces he sent me has just pristine work. The work is meticulous.

    I CAN NOT SAY ENOUGH GOOD THINGS ABOUT ROY! He is a fine engineer, a wonderful craftsman and more customer friendly than I deserved. If any of you out there have an Acoustat product that you feel could use a refresh, could benefit from updating or modification, I would suggest, no URGE you to send Roy an email. He will respond promptly unless he is in the Hospital as he once was during some of our conversations. I am confident that you will be pleased with your dealings with him and your Acoustats will be new and better sounding.

    Randy Hart

    If you want to call me, just call 770-503-7724

    Andy Tomlinson (2012-04-17 16:48:53)

    You guys do all know that this board is based in Denmark.Most of the replies here are from people in the USA.For you,the shipping policies for Sounds Like New are not a problem, for the rest of the world it is and now they are aware of it.I've moved on, I can build HV power supplies for my MK2123 so I don't need anything from Roy.I'm sure he is a nice guy and a great engineer but his shipping policies are not helpful for anyone outside the USA.

    Philip S. Griffin (2012-04-20 18:28:05)

    My experience with Roy Esposito and Sounds Like New, mirrors that of the many other happy customers above. Roy has mono-blocked by TNT-200's, and twice modified the interfaces on my Model 2+2's. Roy is uniquely experienced (from his work at Acoustat and with its founder Jim Strickland) and is a consummate craftsman. Everything he has done for me has always been returned in pristine cometic condition and with peerless sound quality. Roy has never told me anything about his services or his modifications that has not been true. I feel lucky to have found him because I know my system would have never made it to its current level without his involvement.

    Keep in mind that he is not a 24/7 hi-fi repair shop. He is a singular engineer working in his lab. Sometimes this work can take time . . . but remember: "Good things come to those who wait."

    David (2012-04-20 23:04:21)

    Andy, your sense of entitlement is disappointing but not a surprise. The freedom we American's enjoy allows us to set company policy as we see fit. If you don't like it, you're free to shop elsewhere. To trash a guy because he chooses not to expose himself to the risk of international shipping is irresponsible.

    Against my better judgement, I shipped an amp to Europe and it arrived it 3 pieces. The buyer demanded his money back and of course, I paid. I never received restitution from the shipper because the buyer didn't document the damage in the fine detail demanded.

    Roy's decision is not unwarranted.

    Don Strouzas (2012-04-29 06:57:28)

    I have been a customer of Sounds Like New for over 15 years. In that time Roy Esposito has serviced numerous Acoustat items for me. These items include the interfaces for several 2 + 2’s, model 6’s, Spectra 66 and a pair of model 8’s. Roy was actually able to have new medallion transformers manufactured to upgrade the interfaces to my model 6 speakers. He has also serviced several TNP preamps, and custom modified one TNP for a special project. Roy has serviced all 22 of my TNT power amps and also mono blocked most of them.

    It goes without saying that I have been extremely happy with the work performed by Roy Esposito. Over the years, I have found Roy to be very professional and a pleasure to work with. Roy’s level of service and insight to all Acoustat products has exceeded my expectations, and goes beyond what is typically available when servicing audio equipment.

    Sounds Like New is highly recommended to service all of your Acoustat needs.

    Eby Movahed (2012-05-15 21:54:42)

    I`ve known Roy probably longer than 10 years. In the past he has always done an incredible job on repairing, upgrading, and modifying my model 3 Acoustat interfaces. I`ve been exceedingly happy with the results time and again. In fact I`ve told Roy he should change the name of his company to "Sounds Better than New". I`m just so grateful to know him.

    MrAcoustat (2012-05-18 16:26:47)

    QUOTE: Andrei Tudoran2012-04-13 03:15

    It is amazing, after so many years Acoustat is still in may peoples living rooms performing better than most things on the market.

    Thanks to Roy, my system is one of them.

    Yes Andrei it is amazing that speakers almost 30 years old are still performing and bettering many more expensive NEW speakers i have been with Acoustat since 1984 i have owned Spectra 22s - 33s - 2+2s - and what i have now my third pair of 1+1s i live in a condo so for the room that I have this is the model for ME i belong in a group of Acoustat proud owners and would like to thank guys like Roy Esposito in the U.S.A. and Jocelyn Jeanson in Quebec Canada for keeping the best bargain in audio ALIVE if you wish you may see the making of Acoustat 1+1 all steel version the small speaker that weighs 200 pounds here. pages 6 - 7

    Ivan Bendl (2012-05-18 23:14:39)

    As I know that Roy will always try to help, answer emails and talk advice, even tell repair is not needed (as to me), may I recommend that a bit of a remuneration is nice and creates good fellowship. PayPal is happy to send it.

    MrAcoustat (2012-05-18 23:25:24)

    You are absolutely right, nobody should work for free, even for FRIENDS nobody.

    Matt L. (2012-07-19 17:46:42)

    I have a pair of Acoustat 2+2 interfaces and a TNT 200 amplifier that Mr. Esposito at Sounds Like New performed his Service and Upgrade packages on. I am pleased to report that all units work fabulously, I was wowed. Turnaround time and price was very reasonable.

    With Roy, I was met with enthusiastic Professionalism and Dedication to Acoustat products and his customers. I have no doubt that any issues that may have arisen during our exchange, would have been handled effectively and efficiently, to our both satisfaction. I had several questions that I felt were too complicated for e-mail, that he was happy to help me with him over the phone.

    In fact, I am so happy with the results, that I look forward to having Roy service and upgrade my Spectra 22 and Spectra 44 interfaces. This month, yes!! Thanks Roy!

    Randy Hart (2013-05-18 15:54:16)

    I have a pair of 2+2's that I have owned since new. I have had various Magnapan products, a pair of Koss electrostats ( model 1a) among the products I have owned over the years. The Acoustats have always been a good listen. On recommendation of one of my friends who is a professional in the audio industry, I sent my interfaces to Roy. Long story short. They came back much better laid out physically than he got them. His work was fastidious in its execution. Now to the sound.
    The oft noted narrow sweet spot grew a little. The "air" made them work really well on rock. Try money on Dark Side of the Moon to see what I mean. With "air" disengaged Pearlman performing Beethove's Violin Concerto is just unbelievable in its warmth, definition and clarity. My friends will tell you that my listening session run into the hours at a time as it relaxes me. I have never had a speaker in my system that made that so easy. They just disappear. The sound stage is so large that it goes well past the left edge of the left speaker and well right of the right speaker while being seamless aal the way to center stage. The image is a mile deep.
    In all the time I have had these Thayer have never sounded this good. They have always held their own with some of the best made but these are better than the Maggie 3.7's I have been listening to recently. They are better than all the Martin Logan's I have listened to just to name a couple.
    Way to go Roy.

    Randy Hart (2013-05-18 16:02:05)

    Oh, I forgot
    That experience covers just over a year of listening since Roy performed his magic. The sound is better than ever. They like tubes a lot as well.

    Peter W. (2013-05-29 21:26:36)

    I have now had some time to listen to Roy Esposito updated interfaces for my circa 1986 1+1s and the first impressions are truly fantastic. Everything is working fine and the improvement is breathtaking. Though I think they had been gradually getting "tired" for years, I'm quite sure they sound better than they did when they were new. The soundstaging specifity and solidity is shockingly better than it has been for years, and the extension at the frequency extremes is startling. These speakers are so underrated! Thanks for your terrific service Roy!

    Roy A. Esposito (2013-08-21 12:53:35)

    Hello Friends --

    This is just to let you know that my email contact
    has recently changed. It seems AT&T/Yahoo could no
    longer support my very old email address.
    For those of you requiring fantastic restorations
    and upgrading of Acoustat MK and Spectra Interfaces
    and Acoustat Power Amplifiers and Preamplifiers
    my new email address is

    (please notice the dots/periods between the words)

    Thank you for your continued friendship, kind comments and reviews,
    and support of my work.

    All the Best,
    Roy A. Esposito

    MrAcoustat (2013-08-21 13:40:07)

    One more time,i have been an Acoustat owner since 1984 dollar for dollar NOTHING even come's close to the sound of these speakers i was at T.A.V.E.S. 2012 and heard the Audio Exklusiv P3.1 electrostatic speakers they where the closest thing to my Acoustat modified 1+1s yes i did say closest but not quite as good and those speakers cost 16k my all steel framed 1+1s cost me about 3k yes i understand that this is DIY but still my moto as always been ( BEST BANG FOR THE BUCK ) and with Acoustat that's what you get.

    AcoustatAnswerMan (2013-08-22 16:40:06)


    Thanks for the updated contact information - and THANK YOU for your continued support of Acoustat products. Many of us ex-Acoustat employees, and audiophiles alike, feel a strong sense of loss over Acoustat's demise, but between my advice and your repairs, let's hope we can help Acoustat products live the long life they were designed to serve! I continue to be amazed at the sustained interest in the product, often in the hands of a third or fourth owner. It gives me great personal satisfaction to participate in that legacy!

    Joe Pacaccio (2013-10-18 03:41:23)


    I have installed the interfaces on my 2 + 2's, and did some listening............and as they say, âThe proof is in the puddingâ...................... ROY, it is like I am hearing these speakers for the first time!! I have heard many speaker systems in my years, but nothing that compares to Dr. Stricklandâs design, and, of course, your wonderful mods. I love the Air mod.... such transparency !!
    Thank you so much for performing your magic with these speakers!! I remember, back in the 80âs, Acoustat said these speakers were bullet proof, and would literally last a lifetime. They spoke the truth.

    Keep up your great work !!

    Joe Pacaccio

    MrAcoustat (2013-10-18 04:07:38)

    Very true,Acoustat owner since 1984 Spectra 22s - Spectra 33s - 2+2s - and three pairs of 1+1s the last pair being a very special all steel frame with highly modified interfaces, photos can be seen in my Flickr galery - - - again dollar for dollar NOTHING even come's close to Acoustat electrostatic speakers and i do mean NOTHING.

    Acoustat Heaven On Earth.

    Andre MrAcoustat Sevigny - - - Quebec - Canada.

    Mark Svien (2013-11-21 10:38:44)

    I just want to add my name to the list of satisfied Sounds Like New customers. My entire experience with Roy was outstanding. He was professional, prompt and courteous throughout the process. The magic he worked on my interfaces is astounding, and I consider myself lucky to own a product of his efforts. I even located a TNT-200 amp on his recommendation, and will send it to him for service as soon as the listening season ends.

    If you have an old set of Acoustats and wonder what can be done to improve them, look no further than Sounds Like New! Feel free to email me at mx5 if you want further reassurances before you plunk down your hard earned cash. Otherwise, go for it, you won't be sorry!


    Robert Ochi (2014-02-11 20:35:09)

    I've owned my Acoustat model 2's since 1985 when one interface went bad. I searched online and came across this forum. I first figured I would recap the bad interface, to no avail (I am reasonably facile with a soldering iron, but have no electronic diagnostic skills or equipment). It was worth a short, but I needed professional help at this point. Enter Roy Esposito.

    Roy was very conscientious throughout the whole process. He laid out the expected cost from the get-go, and provided updates along the way. In the end, I received fully refurbished interfaces that sound fantastic! The 'Air mod' is great addition to these already capable devices.

    I am extremely happy with the results, and recommend Roy Esposito's service/restoration/engineering expertise without reservation.

    mathieu (2014-04-07 22:10:09)

    Good day,

    I received a message error from
    is the adress always correct ?


    MrAcoustat (2014-04-07 22:19:23)

    This is the last address i have for Roy A. Esposito

    Roy A. Esposito /

    MrAcoustat (2014-04-07 22:28:50)

    ( Living without Acoustat is possible BUT senseless. )

    Ivan Bendl (2014-04-07 23:49:03)

    Roy's address is now

    MrAcoustat (2014-04-08 01:20:03)

    Thank You Ivan, for everyone that need's his help.

    MrAcoustat (2014-04-08 01:20:04)

    Thank You Ivan, for everyone that need's his help.

    Roy A. Esposito (2014-04-08 12:44:46)

    Thank You my friends.... for your kind words and praise
    of my work. I remain available for Restorations / Upgrades /Improvements
    of the Acoustat MK Series Interfaces with the optional "Air Mod"
    that I developed in 2008. Vast improvements of the Spectra Series Interfaces,
    the Trans-Nova Series of Power Amplifiers for which I offer the incredible
    switchable Monoblock and Balanced Input circuit Conversions
    and restoration of the three models of Acoustat Preamplifiers.
    I welcome your inquiries at
    (please notice the dots between the words)

    mathieu (2014-04-11 04:02:19)

    OK thanks


    I forward to you by email the file about the setting and measuremenjt of the 1+1 in a spectra version... Let say the '1+1s' ...

    The listening results are different from the original 1+1 -in a positive way-
    - The sounding in smoother, pehraps a bit less dynamic (the treeble is reproduced by a half pannel only)
    - The big improvement is the stereo image which is more focused, stable, and far deeper !
    The 'sweet point' is larger and the auditor can move without the usual loss of focus thet occurs with the original panels.


    Alan B. (2015-03-28 03:37:05)

    It's been almost a year since the last post on this thread - so let me assure you that Roy is definitely still in business, having just completed the upgrade and Air Mod on the interfaces for my Acoustat Model 3's (Medallion).

    I have owned my Acoustats since 1983 - they were an early model but with the Medallion factory upgrade completed in 1992. I have always enjoyed them and considered them to be an excellent speaker, especially if one likes the electrostatic concept. I have listened to many high end speakers over the years, and honestly have never heard any speaker that I thought was significantly better for less than $20K - but that's just me. But they were getting long in the tooth and I had heard good things about Roy's interface upgrade (and Roy had previously repaired and upgraded both my TNT120 and TNT200 Acoustat amps - with excellent results - sonically, the bass was tighter and deeper - it seemed to me).

    So, when I cranked them up after allowing the panels to charge for an hour or so (it takes two weeks for them to fully charge and achieve maximum results), I wondered if I would hear much of a difference. I was literally draw-dropping stunned at the improvement over what were already excellent speakers. Imaging and sound stage were dramatically better. Overall clarity, transparency, and resolution were markedly improved as well - music was decidedly more natural. Bass and mid-bass were especially improved. With the Air Mod, highs were improved as well. "Roy's Acoustat Magic" that I had read about here and elsewhere certainly came true for my interfaces. I must really recommend this interface upgrade if you have Acoustat speakers - you will not be disappointed. You will have to email Roy for an appointment if you decide to use his service - he seems to be booked several weeks in advance.

    I was fortunate enough to be able to purchase a second TNT200 Acoustat Amp and have already scheduled the monoblock conversion with Roy - very much looking forward to the results.

    Good Listening to All,


    ELian Levy (2015-08-24 16:17:12)

    Roy is an outstanding person, both personally and professionally. He had modifies my acoustat 2+2 interfece and I canât express my happiness with the upgrade. The speakers sound better in every aspect : cleaner sound, better bass, and better image. Add to this mix Royâs complete and total devotion and care â and you get the picture. I had some problems with one speaker interface that had nothing to do with the upgrade (a loose wire connection ), and Roy went way and beyond anything imaginable, with countless emails, to try to resolve the issue. ( of which he did, sending me the correct part). So thank you again Roy for being such a gentleman. Iâm planning to send Roy either one or two Acoustat TNT 200 amplifiers soon for his upgrade!!! His work is untouchable!!

    Mark Svien (2015-08-25 09:08:45)

    Some sad news for those of you who were not aware: André Sévigny who had the nickname Mr. Acoustat passed away recently. You would recognize him as the guy standing next to his HUGE pair of custom Acoustats which were built for him by his friend. He was a passionate audiophile who loved his Acoustats and audio in general. Rest in Peace Mr. Acoustat!

    Roy A. Esposito (2015-08-25 12:36:05)

    So Sorry to hear of the Passing of Andre S.
    ----known to us as Mr. Acoustat ---
    I know he was a devoted fan of the Acoustat
    technology and always very involved in the relevant forums.
    Roy A. Esposito --

    Alan Braswell (2015-08-25 18:31:07)

    Mark, thank you for letting us know, even though the news is sad. Although I did not correspond with him directly, I have read many of his posts on the forums and found them very helpful. I'm sure his contributions were appreciated by the whole Acoustat community and will be for many years to come. Good listening in the next realm, Mr. Acoustat!

    mathieu (2015-08-27 08:43:53)

    Andre welcomed my father and I last year nearby Montreal, for a listening session of his system. We went from France to the Montreal hifi show, and he proposed to invite us at home. He was so proud and happy of his music.
    Since he left in april, I'm often thinking at him and the large black T-shirt with the white slogan "Acoustat heaven on earth" marked on it that he wore.
    This gives an idea of how much he was passionated... He was always enthusiastic and motivated about everything linked to the Hifi world.
    Passionate people have something more than others, a strength which makes them communicate with a total conviction, and share their passion without any limit. Lets call this the generosity.
    He was one of these, I wonder who will carry the torch of our beautiful electrostatics now...

    Thanks Andre, rest in peace.

    Alan Braswell (2015-09-11 21:56:38)

    A few months back, I posted my preliminary impressions of Roy Esposito's upgrade of my Acoustat Model 3 - Medallion Transformers. First, reading back over that review, please excuse the typo - that obviously should have been "jaw dropping" not "draw dropping" - it was getting late.

    A few months of listening to the upgraded transformers has only confirmed my initial impressions. Primarily, Roy's upgrade seemed to enhance what electrostatic speakers are already known for - transparency, speed, resolution, imaging, sound stage - as if his upgrades had unlocked more of the Acoustat's potential. Performance in these key areas, already very good in the Acoustats, definitely moved up a level. As many others have reported in reviewing Roy's work, imaging and sound stage are just remarkable - the image is both well defined and rock solid stable - the sound stage is both wide and deep. I have had the opportunity to hear the top of the line Wilson speakers recently ($200K+) as well as the top of the line Linn speakers. Both were extraordinarily good speakers with excellent respective strengths - but neither, to my ears, imaged as well as my Acoustats do (when sitting in the "sweet spot").

    Very deep bass reproduction is always a challenge with electrostatic speakers because of the physics involved, and full range electrostatic speakers (such as my Model 3 - Medallions) simply cannot achieve subwoofer depth - or produce a large "quantity" of bass. However, the bass reproduction that is achieved (the published low frequency spec for the 3's is 30 Hz) is generally considered to be tighter, faster, and more accurate in a good full range electrostatic speaker than in a dynamic speaker system. I had found this to be true with my Acoustats over the years. After Roy's upgrade to the transformers, however, there was a noticeable improvement in the bass reproduction - frequency response seem to go a little lower and accurate bass resolution, already quite good, improved even further.

    My impressions of Roy's transformer upgrades were made listening on my Acoustat Model 3's (Medallion - Full Range), driven by an Acoustat TNT 200 Amp - which had also been previously upgraded by Roy. The preamp is my aging, but still very respectable, Adcom 565. Primary sources included my Linn LP12 - Lingo (with Cirkus/Trampolinn upgrades), Ittok arm, and Grado Platinum Reference cartridge. On the digital side, my Arcam Alpha 9 cd player is serving as a transport for the Musical Fidelity V90 DAC (also with a USB input from a dedicated laptop serving as a music server for streaming and digital file playback).

    Before moving on to my impressions of the monoblock conversion listening experience, I will take a moment just to comment on the physical quality of Roy's work - which, in itself, is just plain excellent. For example, my transformers - it turned out - were from a very early production run, and after too many moves with them over the 30+ years that I have owned them, they were just physically beat up. Now, I was not expecting this to be addressed at all - I was only expecting the electronics to be refurbished and upgraded. However, the transformer cases were returned to me with the bents in the case having been straightened out and the cases freshly painted inside and out. Since my "official Medallion transformer" stickers were missing - apparently overlooked in the Medallion upgrade in 1992 - Roy even created a replacement sticker for the back of the case as well as documenting and dating his work on the inside of the case. The transformers came back to me as close to "like new" as reasonably possible.

    Also, during the monoblock conversion, we discovered that one of the amps was also from a very early production run, and while functioning just fine in stereo mode, it was not meeting expected output in mono mode. Roy caught this before sending it back, and spent a significant amount of time tracking down the problem to a couple of parts that had been upgraded in the later production runs. He then had to track down a place to order the parts from - before finally getting the amp up to his standard - all of which he did at no extra charge above the agreed contract price. So, be assured that Roy will not return your equipment to you before it has been bench tested and listening tested and is meeting standards - he has both a meticulous attention to detail and high degree of integrity regarding his work. However, also be prepared to be patient as this level of quality can sometimes take a bit longer - especially considering that much of the brand is 30 years old and more. Also, Roy does have a full time job in addition to his part time business of refurbishing Acoustat equipment, so reservations for work are required, as well as patience in allowing Roy the time he needs to work his "Acoustat Magic".

    After the transformer upgrade, I managed to acquire a second TNT 200, and then took turns sending each of the two amps to Roy for upgrading and monoblock conversion. I now have them both back and in my system powering my Acoustat 3's. Each amp, in monoblock mode, delivers approximately 1000 watts into the nominal Acoustat 4 ohm load - so with the two monoblocks hooked up to their respective speakers, the power output is approximately an impressive one kilowatt per channel.

    The listening results are impressive, perhaps even more impressive than the transformer upgrade. The first impression I had is that the Acoustats are now completely unrestrained, and able to function at any volume with ease and no sense of strain - as if they had access to unlimited power. While the transformer upgrade "locked down" the imaging and soundstage, the monoblocks add "authority" to the image - making it more "solid and palpable", if you will. Combined with an even further increased sense of resolution - instruments seem to be more focused and defined, the result was a musical presentation that is almost uncannily natural. The Sheffield Labs direct to disk recording of Thelma Houston and the Pressure Cooker has been my reference recording for over 30 years - I know it well. I have never heard Thelma sound more in the room with me - just remarkably real.

    The improvement in the bass reproduction was also remarkably impressive. Frequency response was definitely lower - while remaining tight and accurate. Additionally, the "power" of the bass reproduction was unlike anything I've heard on an electrostatic speaker - I was actually getting "bass slam" when playing the Sheffield Labs Track and Drum CD (recommended for component evaluation and testing) - approaching that of some of the best dynamic speaker systems that I've heard - leaving me a bit befuddled and confused (open mouthed and shaking my head).

    Another reviewer on a different forum had a very interesting review of the same scenario - using two of Roy's converted TNT 200 monoblocks to drive his Acoustat Model 3 - Medallions. The reviewer, an owner of Audio Research electronics, compared the Audio Research monoblocks with the Acoustat monoblocks. For use with the Acoustats, he preferred the Acoustat monoblocks over the Audio Research monoblocks. His review can be found here:
    Scroll down the thread and you will find his review - his first name is Charlie.

    In summary, the cumulative result of Roy's upgrade to my Acoustat Model 3 Medallion transformers and the conversion to two (Roy Esposito modified) TNT-200 monoblocks has resulted in a major upgrade to my Acoustat system. While I will not claim that it is superior to the very high end systems that one finds at the best audio salons, I personally believe that it would be at home in that league.

    If you have aging Acoustats, you owe it to yourself to have Roy do the transformer upgrades - if for no other reason than the aging of the electronics requires some refurbishment for best results. If you have the patience to locate and purchase a couple of the Acoustat amps, and have Roy do the conversions, I suspect that you will not be disappointed. Even one TNT 200 without the monoblock conversion will likely power your Acoustats better than almost any other amp out there, having been built for the primary purpose of powering Acoustat speakers - but I still suggest you have Roy do the basic upgrade and refurbish, just due to the age of the amps.

    Roy A. Esposito (2015-12-17 14:00:45)

    My Dear Friends -
    What I have observed over many years now causes me to make the following prudent recommendation.
    I would like to encourage everyone with Type MK-121 Interfaces (check serial number label)
    to replace the single Audio Fuse with a 4 ampere or 5 ampere FAST BLOW fuse.
    If these blow too often, then try 3 ampere or 4 ampere SLOW BLOW. Use the smallest
    ampere rating that will hold. 125 volt or 250 volt rating--does not matter.
    I suggest Bussman or Littelfuse brands (Home Depot, Lowes)
    because cheap fuses can roll off high frequencies.
    Reason for this change--back in the 1980's when we designed the interfaces
    the factory-specified 5 ampere Slow Blow audio fuse was sufficient protection.
    But with today's digital source devices and "faster" amplifier and pre-amplifier
    designs, using the originally specified fuse can risk damage to the costly and
    scarce Low-Frequency transformer in the MK-121 interface.
    I am always interested in buying low frequency transformers of the part
    numbers 2008733, 2009064 , or TT121L for use in my service/restoration/upgrade work
    for those relatively rare cases where I find a damaged transformer.
    Please contact me at
    if you have these transformers or even complete MK-121 interfaces to sell,
    whether Medallion or Non-Medallion types.
    All the Best, Roy

  • Wall transformer - Chris Anzelmo on 2008-02-25 18:51:30

    To Andy or whom it may concern: I have learned a lot from this website! I remember reading somewhere that you can upgrade the wall transformers to 15VAC 400mA if you changed out a resistor. Could someone provide me with more details as to which one to change and a photo on where it is located? Thanks very much! I wish to extend the life of my Spectra 11\'s!

    Andy Szabo (2008-03-02 14:29:01)

    The 15-volt wall transformer is not an upgrade over the 12-volt model. This was merely a change made during the life of the product, mainly due to available vendor supplies. There is no advantage in changing your wall transformers as long as the originals are working ok.

    Chris Anzelmo (2008-03-19 03:47:18)

    My appologies, Andy. I failed to mention that one of my wall transformers quit working. Can I use the 15VAC\'s without harming my electronics? Thanks VERY much!

    Andy Szabo (2008-03-21 20:13:01)

    You can change to 15-volt AC transformer with no other modifications. I do recommend that you replace both transformers at the same time to keep everything matched. Technically, you should also change a resistor in the circuit, but that also involves measuring and re-adjusting the bias voltage. If you don\'t have the necessary equipment or don\'t want to mess with that, you can leave it alone. The existing resistor may run a little hot, and could possibly fail someday, but it won\'t affect the sound for now. The resistor in question is a 100-ohm 1/4-watt(color code brown-black-brown, about 1/2\" long). This value is used for the 12 volt transformer. For the 15 volt transformer, this resistor should ideally be a 470-ohm 1/4-watt(color code yellow-violet-brown). The resistor is located on the printed circuit board, grouped along with the other smaller components on the board. Measuring and adjusting the bias voltage is described in one of my \'Technical Bulletins\' located on this site.

    Chris Anzelmo (2008-04-01 04:58:09)

    You are a savior, Andy! Thanks so much for the help! After cutting off the plug on the new transformers and soldering on the new 1/8\" (info found on this site) plug, I plugged them in and they are back! I have forgotten how 3-dimensional and fantastic they sound. I don\'t drive them too hard but now I know what to do when or if the resistor does go out. Thanks again!

  • subwoofing the Acoustat 3300 - Greg Bergin on 2008-02-24 03:39:35

    Hi, I\'ve owned a pair of Acoustat 3300\'s for about 15 years. I am interested in purchasing a subwoofer now. Do you have any recommendations, concerns, suggestions, and/or warnings about this? Local shops carry the Velodyne DD series and the J L Audio Fathom f113, which I have read a bit about. Thanks, Greg

    Andy Szabo (2008-02-27 20:04:17)

    Adding a subwoofer is a fine idea, not only to extend bass response, but also to increase dynamic capacity of the system (provided that you roll-off the lows to the ESL). There is probably no subwoofer on the market that will match the quality of the ESL\'s bass, so you\'ll want to cross-over as low as possible. I suggest a crossover frequency in the range of 40 to 80 Hz, with a 2nd or 3rd-order slope (12 or 18 dB per octave). If you go much higher than 80 Hz, you will begin to hear the subwoofer too much in the upper ranges. Although I have not experienced either the Velodyne or JL Audio woofers paired with Acoustats, both have good reputations and should work well. I have always been impressed with Velodyne\'s room-equalizing software, and note that quite a few magazine reviews utilize the Velodyne software to measure other brands of subwoofers! I use a Parts Express/Dayton 10\" powered subwoofer with my Spectra 4400\'s. Although this is an inexpensive unit (around $300) I am quite happy with it, as I use it only to extend the very bottom end. I\'m sure I would be happier still with a more expensive unit, but it is a good cost-effective solution. I\'m using the woofer\'s built-in 12dB/octave crossover set at 40 Hz, and then I\'m rolling off the ESL\'s at 6dB/octave using a capacitor in series with the main amplifier\'s input. Expect to do quite a bit of experimentation to get the crossover frequency, phase, level, and room placement correct. This process took me several months of fiddling, although I\'m sure the process would be much quicker with something like Velodyne\'s software.

    BIG AL (2008-11-28 02:38:41)

    Greg: You dont\' know what you have been missing. I have a pair of Spectra 33\'s with the Acoustat sub since 1989. The sub smooths out the whole sound,opens up your amp\'s bottom, provides excellent sound stage, and respectable weight on the bottom. The Vocals have much better depth and image. More bottom end authority will be based on the type of amp or amp\'s you are using. I would look for the Acoustat sub, as your panels have the built in cross over. Just flick the switch, and run another set of speaker cables from the panels. It is kind of big, but after all you purhased a big pair of panels. It sounds best in the center of the panels. Find one and go for it!!!! Keep Checking ebay or local hi fi shops on line. Enjoy em. Big AL

  • Bypassing crossover - Dave Thorngren on 2008-02-19 06:23:29

    Hey Andy,As a proud owner of a variety of planar-type speakers I must admit that curiosity has been known to get the best of me. Armned with a passive crossover and suitable amplification, I have mixed and matched numerous Magnepans, Janzens and Acoustats with interesting results. Here\'s my current dilema: I have recently acquired a set of 2+2\'s which suffer from poor high frequency reproduction. I took your advice of applying contact cleaner and sand paper to the minor corrosion on the HF pot I did indeed find, yet the problem remained. My uneducated guess is a bad cap in the crossover. In the interim, I used a set of my modified and seperated Tympani 1D tweeter panels to replace the missing frequencies. The result: a wide open soundstage, larger sweetspot and less beamy presentation. What do you imagine the result would be if I removed the 2+2 crossover completely and dedicated all 4 esl panels to mid and low-end reproduction similar to the 1D configuration and used an external crossover? My current passive XO (which I find works well with many differant speakers and would most likely be using in this application)has its\' low pass set at 1KHz. Thanks for all your inforative work. Dave

    Andy Szabo (2008-02-20 19:41:14)

    I don\'t have any experience with trying to make the MK-121 operate at lows and mids only, so I can only guess at the results if you disconnect the high frequency portion of the interface. The simplest way to try this would be to disconnect the RC-network that feeds the high frequency transformer\'s primary, and see how you like the results. Since there is considerable overlap between the low and high frequency transformers, I\'m not sure what the effective crossover point should be for your tweeter system. Different results might be had if you take it a step further and also disconnect both phases of the high frequency transformer\'s secondary. If only the high frequency transformer\'s primary is disconnected (as above)leaving the secondary components in-circuit may have some interaction, so you might want to try it both ways. At best, this will require some experimentation to get the transition correct between the ESL panels and the tweeters. Ultimately, you may find it best to allow the ESL\'s to play full range, and just roll-in the tweeters at the frequency where you find the Acoustats lacking.

  • acoustat servo amps - John Hovard on 2008-02-10 20:33:10

    It appears that the issue giving these amps the most problems are the frequent failures of the HV power transformers. What can modifications can be done to correct this? Is too much being asked of the transformer? Perhaps some of it\'s load demand should be pulled from it and driven by an additional transformer. Any thoughts on this?

    Mike Savuto (2008-06-10 04:13:18)

    Hi John, I wouldn\'t say the high voltage transformers fail frequently, but in the long run they can fail. Actually the HV transformers do a heck of a job and we find the 150vt circuit often gives us trouble before the transformers do. I have seen some 20+yrs old that are still fine and some fail in a few years. It is not the \"load\" of the circuit so much as they do one heck of a lot of voltage step up the output is about 1800vts, pretty high. The most common proximate cause of HV transformer failure is that over time moisture builds up inside of the transformer (particularly if left unplugged for long periods of time in high humidity areas) which makes an easier path for the high voltages in the secondaries to jump across the internal insulation between the secondary coils. Once that happens the problem will only get worse and ultimately (sometimes very quickly) cause a short in the secondary wiring of the transformer and the transformer will fail. That is why Acoustat had the idle circuit which keeps the tube filaments at half voltage when the amplifiers were not being used. It keeps the amplifier warm driving away moisture. \"Damp Chaser\" is how it was described to me. The company building replacement transformers for the servoamps now, Galaxy Transformers, has continued to refine the construction and materials used in these transformers and are a real asset to Servoamplifier community. We have begun using a circuit from George Kaye which involves two HV transformers instead of one. This makes a dramatic effect on the sound of the amplifiers, but also makes them considerably heavier! Interestingly the current drawn by the new circuit is actually less than the original single transformer design, so if load reduction is what you want, this accomplishes that goal. Best Wishes, Michael Savuto Analogue Associates, LLC

  • No volume or volume 20 dB down. - Robert Sabelis on 2008-02-08 23:00:00

    Recently I observe a new behaviour with my Acoustats. When I power up one of my amps for listening one side or the other is 20 dB down in level or completely mute. Checked all the preceding electronics but with AB testing I can single one of the MK-121C medaillon Interfaces out as the \"offender\". My friend who has exactly the same interfaces at his 1 + 1 experienced the same problems with his Acoustats. Whe I pull the interface off and measure some of the parts inside I get no errors. Always when I put it back the unit operates good again. This evening when a switcht my ML-3 on there was no sound from one channel (it happens also with the ML-2\'s with changing positions for the mono\'s). Not wanted to loose the Interface from his base I muted the channel and pulled of the speakercable from the interface and reconnected it. Turned up the volume and the sound was back again but 20 dB down. Then I disconnected the bias (pulled out the AC) put it back again and the sound was okay. I got this problem now for the twentieth time this year and it happens more often lately. Is the biascircuit of both units degrading due to age or something. Should specific parts in the circuit be replaced. Any suggestions or ideas? Thanks in advance, Robert

    Andy Szabo (2008-02-20 19:55:56)

    Hello again Robert - sorry to hear of your problem. Intermittent problems like this are unusual for Acoustats - they usually work or they don\'t. Due to the intermittent nature of your problem, I suspect you have a mechanical problem (i.e. bad connection), rather than a failing electrical component. My first suspicion would be to check the audio fuseholder: it might be corroded inside and making poor contact. Those contacts are hard to get at for cleaning, so you might want to try temporarily bypassing the fuse with a jumper (inside the interface) to see if the problem goes away. Also check the condition of the wires that connect the panels to the interface. The RED pin plug, or its mating connector, may have some corrosion which is making poor contact. It is also possible that the fine-gauge wires are broken inside the heatshrink tubing that covers the wire\'s connection to the pin plug and BLUE and WHITE terminals. Finally, check the soldered connections on the PC board for any bad connections. Do write again if you can\'t solve the problem by these methods.

  • Biamplifiying the MK-121C - Robert Sabelis on 2008-01-29 21:59:15

    Dear Andy, This weekend I get my refurbished/repaired Class A Levinson ML-2\'s back. New large cans etc... When I drove my 2 + 2 with them the 15 Volts max output of these amp is rather quickly attained. I also have a ML-3 Class AB2 amp then can blow out the audio inputfuses on the MK121C medaillon quite easily without clipping. I prefer the sound of the ML-2 over the ML-3 except for the higher soundpressure levels of course. I read in this thread your comment on biamplifiying the interface but I\'m not quite sure about the connections and the merist of it. 1. I bought my set 2 + 2\'s new so I have the Owners manual with the schematics. Can you explain me a little bit deeper how to make the proper connections for this biamplifiying scheme? 2. Approx. at which frequency does the interface \"cross\" from low to mid/high. In other words how much of the load burden will be taken by the natural supplier of the low end, the ML-3 amp for giving the ML-2\'s some more dynamic headroom. I\'ll intend to keep these three amps so there\'s no efficiency question involved. I can drive the three amps with my ML-7a pre because It has two sets of output connectors. Any suggestions? Thanks in advance, Robert

    Andy Szabo (2008-01-30 22:53:34)

    Other owners of the MK-121 series speakers have successfully bi-amped the interface, so you may find some helpful comments among the other Q&A sections. Doing it is relatively simple. Note that the low frequency (LF) transformer is directly connected to the audio input through a 1-ohm resistor and the fuse. I suggest you use the original input jacks for the LF input, maintaining the fuse and resistor in-circuit. The high frequency (HF) transformer is connected to the fuse through a resistor-capacitor network. I suggest you disconnect that circuit at the fuse, and connect it to a second set of input jacks, preferrably through another fuse for maximum safety. The advantages of bi-amping are questionable. Most who have done it seem to be happy, but that may be a case a \"wishful hearing\" after doing all that work. There is no exact crossover point between the LF and HF sections: rather, there is considerable overlap between the two sections. If your aim is to increase dynamic output, you will probably gain some, but not nearly as much as the sum of the two amplifiers\' wattages. In other words, you would gain more by using a higher-wattage amplifier in single-amp mode. But, I can understand your desire to retain the use of the ML amplifiers. If nothing else, they sure will make a neat display of equipment, and keep your room warm year \'round!

  • Lacking level - Jan Jepsen on 2008-01-21 15:46:50

    I\'ve just bought a pair of Spectra 11\'s. When you sit down in front of them, they sound pretty much the same. Nice !! The wierd thing that happens as you get up to stand in front of them, the left panel seems to drop in level. The woofer is the same no matter what box I listen to. I\'ve tried listening to each panel on it\'s own and it seems as if the top third of one of them is down to half the level of the other panel. As I have no clue to how the panel works, I\'m lost. Any advice from someone who knows about this wierd problem ? Best Regards Jan Jepsen

    Andy Szabo (2008-01-21 21:29:26)

    There is no mechanism (that I am aware of) that could cause an abnormal change in level as one moves the listening position up and down. It is true that the speakers have limited vertical dispersion, so it is normal to hear a difference as you move up and down (more so at high frequencies). But, that change in level should be the same for each speaker. Spectra panels are segmented in the horizontal plane: in the case of the Spectra 11, you have two side-by-side segments. However, each of those segments are driven equally from top-to-bottom, so they either work or they don\'t. I think what you are hearing is caused by room acoustics. Due to differences in reflectivity of adjacent surfaces, you might perceive a difference in the two speaker\'s vertical dispersion. I suggest you listen to each speaker (separately) in the exact same position and then determine if you still hear a difference. Ultimately, any of the Acoustat models that are only one panel high are intended to be listened to from the seated \'chair\' position. They won\'t sound the same if you are standing up, or if you are sitting on the floor. The two panel high systems, of course, don\'t have this problem since they have panel area stretching from floor to ceiling. If, after more careful listening, you still perceive the problem, do write again. Just because I\'ve never heard of this problem, and can\'t think of a reason for it, doesn\'t mean it couldn\'t happen. I\'m not adverse to learning something new, especially when it comes to my favorite brand of loudspeaker!

    Jan Jepsen (2008-01-21 22:17:11)

    Thank you for the quick answer. Well,you seems to be as puzzled as I am. The listening on the panels, that I have done is with my ear all the way in to the grill. Like 1 cm. away from the panel. I\'ve been reading in the Spectra 1100 group as well. There was a posting mentioning the different binding post in the \"crossover\". I therefore opened up to see how it looked. Next to the red binding post, the board is all black and I cand tell what kind of flat component is sitting there. Perhaps some kind of a capacitor ? Is this some how connected to both panels in the panel ? Is there a way to send a photo of it ? A picture tells a lot more. I will go and listen again. Best Regards Jan Jepsen No other components looks wierd.

    Jan Jepsen (2008-01-22 21:06:03)

    The story continues..... Listening a bit more I decided to have a look at the \"right\" panel crossover. And that was a look. Just as described somewhere else : TOAST !! The inner of the two resistors side by side had been replaced with a 25W metal resistor of 4R7 ; must translate into 4,7 ohm. The capacitor after has also been changed. The outer resistor look as if it would like be replaced. The resitor next to the coil is in a bad shape visually. The coil had been replaced with a \"no number no name\". Apart from that it loooks as if the black binding post does not connect propely to the lead , as the lead pin has been resoldered. But this is the good sounding speaker !! As mentioned before ,I took a picture of the \"bad\" crossover. I uploaded my picture and it appears as picture number 14. Comparing it with picture 12 ,it seems as if some of the components are different. Meaning that the resistor near the edge on my crossover is a capacitor in the new crossover. Am I confused ? Oh yes ! What are the proper values for the resitors and capacitors and the coil, as I think I will replace all crossover components, just to make a clean start. And where should they sit on the board ? Best regards Jan Jepsen Sorry for the long story but I need help.

    Jan Jepsen (2008-01-23 18:50:54)

    Case closed !!!! I found the culprit. The tip on the jack from one of the wall transformers were loose. So occasionally it was ok. That was when I thought the sound was wrong and tried to switch transformers. A couple of times it changed nothing, but suddenly the error was consistent. Bingo. But then again....I had to refresh how to build a crossover. And changing the capacitor that acts as high pass to the panels should, in theory, improve the the sound of the panels. And maybe doing a rebuild of the whole crossover with the components that was ment to be used, no offence Andy (½), proper metal housed resistors and audio caps, putting it in a seperate enclosure with good quality speaker cables going to the woofer and into the tranformer for the panel... But that\'s another story. So far ,thank you for a brilliant speaker and soory for wasting your time. Best Regards Jan Jepsen (½) Yes, I read the Ted Nugent story. Like it !!

  • Identifying mk-2123 - Dave Thorngren on 2008-01-16 04:23:07

    Hey Andy, I\'ve been searching your woderful sight hoping to identify exactly what model Acoustats would utilize the MK-2123 transformer. The only other information mentions the speakers dimensions as being 65X32. Assuming that these are un-modified, which model could this description be referncing? Thanks Again

    Andy Szabo (2008-01-17 20:15:09)

    The MK-2123 interface is used on the 2-panel Spectra 22/2200, and the 3-panel Spectra 33/3300. The only difference in the interface between the 2 and 3 panel versions is the wiring of the low frequency winding of the audio transformers: the 2-panel version has more bass boost to compensate for the smaller panel area. The interfaces should have a rubber stamp (22 or 33) on the label indicating which version they are wired for. If the speaker in question is 32 inches wide, it is either a Spectra 33 or 3300. The only difference between those two models is cosmetic: the 3300 has a wood trim strip with brass inlay running up the sides of the speaker. Performance-wise, they are identical.

  • Acoustat MK121 2a ? identification - Marc P on 2007-12-23 17:22:01

    I\'m not sure wich MK121 I own... There are 3 panels in the box. Is it 2a ? or 3 ? The label is MK121 2a. I drive them with Audio Research pre and amp with good results. Are they 8 or 4 ohms ? Thanks a lot.

    Andy Szabo (2007-12-26 03:32:50)

    If your speakers have three ESL panels per speaker, then you have a Model Three. The MK-121-2A is the model designation for the transformer interface, which was common to several different models. Unfortunately, Acoustat did not mark their speakers with the model number, so this is often a point of confusion. The speakers are nominally rated at 4-ohms.

  • How to remove cloth? - Rick Pettey on 2007-12-17 17:14:05

    How do I remove the cloth from these speakers? With my old 2 + 2 it was quite simple. By removing the top plate I could remove the staples holding the cloth. With the framing of the 3300 I do not see an easy way to do it. As I lost my owner\'s manual I cannot refer to it for assistance. I need to remove the cloth to determine if a rattling from the left panel in the left speaker is due to a panel malfunction or has somehow become loose and needs to be tightened. I noticed the problem when extreme low frequency exposed the problem. It is not due to pieces of glue trapped in the field. I have discharged the speakers and pounded in the appropriate area to dislodge any such particles. No difference. If it is a panel, how would I go about purchasing one?

    Andy Szabo (2007-12-18 03:17:52)

    Read my piece entitled \"Rehabilitation of a Spectra 4400\" in the 4400 section: I went through all of this myself. Removal of the brass and wood trim strips is a pain, but it can be done. I\'m still searching for a replacement for my brass strips. I\'ve looked at in-laid wood or metal strips in woodworking catalogs, but haven\'t found the correct width yet. It is unlikely you\'ll need to replace the panel. If the Mylar diaphragm has lost its tension, the old hair-drier trick usually works. Replacement panels are only available on the used market now: be sure you get one from a Spectra (not too common, since most Spectras are still surviving intact). Be sure to vacuum the panels (front and back) to make sure you get any debris in there. Be expecting to need new grille coth: it\'s virtually impossible re-install it, especially on the Spectra XX00 series.

  • Looking for a pair - Silvan Karrer on 2007-11-26 12:12:11

    Hi, I am looking for a pair Spectra 2200. Living in Europe. Sellers can contact me: Cheers, Silvan

  • Two Left panels - steve on 2007-11-20 23:18:59

    I have a pair of Spectra 1100\'s and both have left-side top panels. Does anyone know a way I can convert one to work like a right-side panel? Thanks. Steve @

    Andy Szabo (2007-11-21 17:26:49)

    Before attempting to modify the panels, make sure that you really have two left panels, as opposed to panels that are merely marked as \'left\'. If the grille socks were replaced at some time, the identifying marks may have been mixed up, or they may have been originally marked wrong at the factory. To determine by listening, a \'right\' panel should have the highs coming from the right side, and a \'left\' panel should have highs coming from the left side. If you determine that you indeed have two \'left\' panels, it is possible to re-wire and re-color-code one panel into a \'right\' speaker. How to do this is much easier to explain with a few sketches, rather than trying to explain it in writing. So, if you need to modify one panel, please write again and I can send you the necessary info to your private email address.

  • Replacement MOSFET's - Jim Kenney on 2007-10-26 21:56:21

    I noticed a gentleman selling NOS Hitachi 2SK134/2SJ49 pairs on ebay and indicating they would be a replacement for Hafler and Acoustat amps. It was my understanding the TNT-200 used the 2SK135/2SJ50 pair. Would the 2SK134/2SJ49 pair be appropriate for replacments? I would like to have a couple of them around as they are hard to come by. Thanks..Jim

    Andy Szabo (2007-10-26 23:04:04)

    The K135/J50 combo used in the Acoustat TNT-200 (and others) has a higher voltage rating than the K134/J49 combo, as used in the TNT-120. They might work okay for a while, but it would be risky using the lower voltage parts in the higher powered amps.

  • Problem on ESL Panel - Teerawut on 2007-10-08 10:02:07

    My right panel has some trouble - its sound is not as lound and clear as left panel. First, I think that it is from circuit inside. I changed circuit from left to right, but the problem is still occured. Then, I change left panel with right panel, it is still occured. Do anyone have any recommendation how to solve this problem? Is it possible that some wires inside panel broken or loosen? Is it possible to open the panel?

    Andy Szabo (2007-10-26 23:24:57)

    If I understand correctly, you exchanged interfaces from one speaker to the other, and the problem is still in the right speaker. The problem is not in the interface. Then you exchanged panels from one speaker to the other, and the problem is still in the right speaker. The problem is not in the panel. (Don\'t forget to change the panels back to their original positions to keep the left/right mirror-image pair correct.) That leaves the woofer box and the wall transformer. Since the crossover is in the woofer box (mounted on the back of the input cup), your problem could be there. You may also have a bad wall transformer. Check its voltage output to make sure it is the same on both wall transformers. If I have misunderstood your situation, or you need more help, please post another question.

    Teerawut (2007-11-05 08:01:52)

    Hi Andy, Sorry about my writting, I\'ve already modified the input for ESL. Input is direct for ESL only, and I used bi-wiring. So, I did not think that the prblem was from low-pass network in woofer box. Also, I switched the wall transformer from L to R as your recommend, but the problem was still on the R. Is it possible to check the ESL pannel by using any equipment? I think that my pannle is lossing some sound in midrange. Could you give me some recommendation. Teerawut

    Andy Szabo (2007-11-21 17:52:16)

    It is not possible to check the panel with any equipment, other than using some sort of microphone-driven test signal and/or a spectrum analyzer. At best, that would only serve to confirm what you already hear. It is possible to remove the grille cloth to inspect the panel and internal wiring, although it\'s a messy job and should only be done as a last resort. There isn\'t much that can go wrong in there: the panel itself is extremely reliable (and cannot be repaired anyway), and the wires exiting the speaker are part of the panel itself (there are no internal connections to come loose). You might want to check where the wires are soldered to the metal pins that connect to the interface. Since these connections are covered in colored heatshrink tubing, it is possible that you have a bad connection hidden underneath the heatshrink tubing. Since you have already gone through the usual swapping of interfaces, panels, and wall transformers, I am at a loss to explain where the problem might be. Are you certain that swapping panels did not cause the problem to move with the panel? Your room acoustics may be a factor. If you have very different reflective qualities on the walls behind and near each speaker, that could have a significant effect on the perceived frequency balance between speakers. If, for example, you have curtains behind one speaker, and a bare wall behind the other, that could cause the problem you describe. Remember that Acoustats radiate from both front and rear, so room surfaces can have more effect than with conventional front-firing-only speakers. Good luck, and keep writing until we get this problem fixed! I can usually diagnose problems better than I have done for you, but I feel confident we\'ll get the speakers running to your satisfaction.

  • Diaphragm Spacer Thickness - Jim Lanier on 2007-10-07 16:33:46

    Does anyone know the thickness of the diaphragm spacers in the Acoustat panel? Did they change the thickness in later models? (BTW, I am not asking for diaphragm to wire spacing, but the actual thickness of the shim) Jim

    Andy Szabo (2007-10-07 22:40:19)

    If memory serves correctly (and it might be a little dusty) the shim stock used used as spacers in the Acoustat panel is .150\" thick. If you have a panel at hand, it is easy enough to see from the edge of the panel. I am not aware that Acoustat changed the shim stock anytime during the manufacture of their panels. The only panel changes were 1) going from a three-wire to a five-wire connection to the interface; 2) increasing the resistance of the conductive coating (identified by a yellow w/red stripe bias wire); and finally, 3) Spectra panels, which were built using the same materials, the only difference being the split stator grids.

  • Diaphragm Spacer Material Thickness - Jim Lanier on 2007-10-07 09:02:15

    Does anyone know the thickness of the spacers (shims) used on the acoustat panels? (I am referring to the material that is used to space the diaphragm from the stator wires). Did they change the spacing on later models? Jim

    Andy Szabo (2008-11-26 17:47:12)

    If memory serves correctly (and I won\'t guarantee that it does) the spacers used in the Acoustat panels were 0.125\" thick on each side of the diaphragm. I have no knowledge that this spacing was ever changed during the life of the product.

  • Acoustat Choices - N. Tony Fasola on 2007-10-03 15:18:07

    I realize that this is a very broad question but I would truly appreciate input from the listers. I am an original Acoustat owner from the early 80\'s (Model 3) who has been without for almost 20 years. I am currently getting back into \"audio\" and building a dedicated room for such. (15 X 17) My question is: which model, Spectra 22/2200 or the 2 + 2\'s should I choose? Sonics are tantamount but reliabilty and others are also important. I just wanted to hear from owners and those experienced with both models. Thanks in advance, N. Tony Fasola

    Andy Szabo (2007-10-07 23:00:10)

    Thanks for your interest in returning to the Acoustat culture! Despite their age, Acoustat speakers remain a viable solution for audiophiles seeking excellence at a reasonable price. In terms of reliability, I wouldn\'t have a strong preference for either model, as all models have enjoyed an excellent reputation for reliability and long life. Clearly, any 2+2 will be older than any Spectra 22/2200, since the models did not overlap in production. In terms of stereo imaging, I would definitely prefer the Spectra series, with their controlled dispersion pattern. In terms of bass response and dynamic capacity, the 2+2 would be preferred. It simply has twice the panel area. Also consider that the 2+2 was manufactured for a very long time, and had several minor and major improvements during its life. Most important is the Medallion Transformers, which significantly improved the clarity of the sound. Many older models were upgraded with the newer transformers, so the age of the speaker is no indication as to whether it has the Medallions. All units with Medallion transformers have a label on the back of the interface. Ultimately, if you are trying to choose between the 2+2 and the 22/2200, my suggestion would be to seek out a pair of 44/4400\'s. This model would give you all of the advantages cited above in one speaker (i.e. no compromises). Granted, the 44/4400 wasn\'t made in great numbers, so finding one might not be easy. But if you have a large (and tall) enough room for the double-height Acoustats, the 44/4400 would be way to go.

  • Matching sub? - paul messmer on 2007-09-21 05:37:25

    i have a set of what i believe is acoustat 3300\'s and a matching sub. first question is what sort of amp do i need to drive these things,and how much is it going to cost me for one. next question, i hear that these speakers have a lifetime warranty, is this true? i ask this because the sub out on the left speaker is not puting out anything. please help this is my first electostatic speakers,and i am in love with them. i currently have them hooked up to my pioneer surround sound reciever, when i heard just the small amount of sound they were able to produce with just my little underpowered reciever, i went and sold my bose the next day. any help would be greatly appriciated.

    Andy Szabo (2007-09-27 22:49:49)

    Congratulations on your purchase of an Acoustat loudspeaker. Upgrading from Bose speakers is quite an improvement, and you will have fun re-exploring your music collection. There are many choices in amplifiers, at many different price points. I would recommend an amp of at least 100 watts-per-channel (8-ohm rating). With care, you can use up to 250-watts per channel. If you are inclined to buy a used amplifier, you might look for a Hafler or Acoustat amplfier. These work very well, but there are many more choices as well. Acoustat did offer a Lifetime Warranty, but with the company now out-of-business, there is no longer any warranty. Fortunately, the speakers are extremely reliable, so that shouldn\'t be of great concern. Many factory-original parts are still available, as well. If there is no signal on the \'woofer output\' on one speaker, I would suspect a loose connection on the binding posts inside the interface (black metal box). These binding posts are connected by screws to a printed circuit board, and they may have loosened over time. Of course, do make sure the switch is in the appropriate position (\'Above 100-Hz\' for woofer operation).

  • Power to use - Marc on 2007-09-16 00:32:20

    I just buy a pair of these (Spectra 1100) and I want to know how much power is best to drive them. Better valves or solid state ? Is it enough to use only one amp. I have 2 Rotel RB980BX (120 X2) and 2 Hafler DH200 (100-120 X2). Pre-amp: Hafler Model 100. Wich combination is best ? The Rotels can be bridged mono at 360 Watts, but I use them on Acoustat MK121-2a and fuses blow often. Thanks. Marc

    Andy Szabo (2007-09-26 15:53:45)

    I\'m not familiar with the Rotel amplifiers, but I am very familiar the the Hafler DH-200, and it would be an excellent choice, either as a single amp, or in a biamp configuration (since you have two). The Spectra 1100 can handle more power than that, but 100 wpc is sufficient unless you like it very loud in a large room. When I was using 1100\'s, I drove them with a Hafler 9500 (250wpc) with very good results. Some care is required, though, not to over-do it. See my piece \"Ted Nugent vs Spectra 1100\". I\'ll leave the debate of tubes vs solid state for someone else. Since you already have four solid state amps, try those first! And certainly, any tube amp capable of driving ESL\'s to a reasonable level won\'t be cheap! I\'m not fond of bridged amps, especially when driving difficult loads like an ESL. The reason is that each half of the bridged amp \'sees\' only half the load impedance. Therefore, a 4-ohm speaker suddenly becomes a 2-ohm speaker to each half of the bridged amp. This is probably why you had fuse-blowing problems when you bridged your Rotels.

  • Spectra1100 (power to use with) - Marc on 2007-09-15 21:28:03

    I just buy a pair of these (Spectra1100) and I want to know how much power is best to drive them. Better valves or solid state ? And do I need a crossover to bi-amp them, or it\'s enough to use only one amp. I have 2 Rotel RB980BX and 2 Hafler DH200. Pre-amp: Hafler Model 100. Wich combination is best ? Thanks. Marc

  • MK121 2a - Marc on 2007-09-15 21:15:16

    How much power is right to drive them ? I use a pair of Rotel bridged mono360 watts and they keep blowing fuses on amps and speakers. Was-it too much ? I tried on amp not bridged and they blow half volume open. Pre amp: Hafler 100. Thanks Marc

  • Thanks, Andy - Robin McConnell on 2007-09-12 18:31:24

    Andy, thank you so much for the info on how to bi-amp the 66\'s. I have completed this successfully and the results are well worth the effort. For future reference there is a circuit of 2 caps and a large 1ohm resistor in line in the positive input circuit. It was necessary to duplicate this for each stator input. I used silver cable throughout and Eichmann binding posts. I also bypassed the fuse completely. Thanks again, Robin

    Andy Szabo (2007-09-26 15:07:07)

    Thanks for the update, Robin. You are correct, of course, about the resistor and capacitor needing to be duplicated for bi-amplifying. I hadn\'t thought of that when I wrote my original response.

  • Dead biascircuit? - Robert Sabelis on 2007-09-01 00:31:11

    Dear Sir, I have a MK-121C interface that does not transfer any signal to the electrostatic elements. When I turn the pot on me preamp almost fully clockwise I hear only a very soft sound coming from the planar. I think it\'s the biassupply that\'s dead but I\'m not sure. How can I measure it with a standard DMM and what could be the possible cause/failing component. I bought the acoustat new so I have the Schematic and component value list in my owners manual. I checked both the 1/4 A fuses of course but thers\'s the biastransformer it self, a couple of high voltage diodes and 3300 Picofarad ceramic discs and at the and a carbon 500 MOhm resistor. I measured 721 Volts at the secondary\'s of the biastransformer so that\'s working. Can\'t measure the 5 KV over the 500 Ohm resistor because my DMM goes not further then 1000 Volts AC. When I try to measure it anyway I only get 5 Volts but that\'s maybe a errorreading. If I put the positive end of the DMM near one of the leads of the 500Mohm resistor blue sparks start to develop so there must be some charge. I\'m really in limbo what\'s the cause but I do not know were to start. Hope you can help me out.

    Andy Szabo (2007-09-11 21:32:03)

    First, check the condition of the audio fuse with an ohmmeter - sometimes slow-blow fuses are hard to check visually. It is also possible that the fuse holder is broken or fouled with corrosion. I\'ve definitely seen cases of that before. Also double check the red-white-blue wire connections to the panels. You should also try swapping the interfaces from one speaker to another. If the problem follows the interface, the problem is in the interface. If it stays on the same panel, then the problem is in the panel itself. The output of the bias transformer is about 750 volts, so it sounds like that is okay. It is preferable to use a high-voltage probe for measuring the +5kV, but it is also possible to use a good-quality digital voltmeter, as long as you measure AFTER the 500-Mohm resistor. You won\'t measure anywhere near 5000-volts, due to the voltage-divider action of the 500-Mohm resistor working against the input impedance of the meter (usually 10-Mohm for better quality meters). In that case you will measure more like 90-volts. Regardless of the meter measurements, if you are seeing blue arcs when you contact the high-voltage points, then high voltage IS present, and you should get at least SOME sound from the speaker. Therefore, I suspect the problem is audio-related, and not in the bias power supply.

  • Acoustat Links - Andrew Tomlinson on 2007-08-24 21:17:54

    I don\'t know where else to post this but a number of links \"Rehabilitation of a Spectra 4400\"as an example are not working Thanks Andrew

    Andy Szabo (2007-09-07 23:47:21)

    Thanks for the notification, Andrew. I had already noticed this problem, and have notified the webmaster. He has promised to fix the problem.

  • Bi-amping Spectra series - Robin McConnell on 2007-08-23 10:25:03

    I have been fortunate to fulfil a very longtime ambition to own a pair of Spectra 66 Acoustats. I currently have 2+2\'s which I love and have modified to allow them to be driven by 4 valve monoblocks. Is it as simple to modify the audio inputs of the Spectra series and are there any other mods which I should carry out at the same time which will improve the speakers? The speakers I have purchased are 110V models and our supply is 240V 50Hz. Do the speakers have different supply voltage taps or will I have to use a T/x on the input? Thanks in advance, Robin

    Andy Szabo (2007-08-24 20:14:45)

    The Spectra series does not lend itself to simple biamplification, but it can be done. The Spectra uses two identical audio transformers, rather than a high and low frequency transformer as on the earlier models. I suppose one could separate the primary feeds to the two transformers, and drive each one with a separate amplifier channel. Be sure to drive one of the transformers out-of-phase, since one drives the front stator, and the other drives the rear stator. You would need to completely disassemble the interfaces to gain access to the transformer\'s primary connections. That sounds like a lot of work to me, and I\'m not sure of the sonic benefits, but if you already have the amplifiers, I can see the attraction of the idea. Since your Spectra 66 has a 110V input, I am assuming it is an earlier model without the Ultrasonic bias supply. There are no taps to change inside the interface, but you can solve this problem in one of two ways. Since the power consumption of the bias supply is so low, you could use a 240-to-110 step-down transformer to obtain the required 110 volts. Or, you could change the bias transformer to part number TTA-240V, which is the 240-volt version. I have seen these recently for sale on eBay, from the seller \'dealsbyjason\'. I can\'t think of any modifications to do on the Spectra 66, since the circuit is so simple. There is only one capacitor in the audio path, and it is already polypropylene. You could increase it\'s value somewhat if you like. See my piece \"Rehabilitation of the Spectra 4400\" in the 4400 section. Good luck, and congratulations on obtaining the finest speaker Acoustat ever made! I have the Spectra 4400\'s, and I am very happy with them.

  • Speakers cause amplifier clipping - Alan Hoffman on 2007-08-08 22:09:41

    I am the original owner of a pair of Acoustat 2 + 2\'s with MK-121 Medallion Transformers. I am presently using Bryston monobloc amplifiers model 7B-ST rated at 500 wpc. Even with this power available, I still experience momentary clipping of the amplifiers when the music is played at “live concert level” (probably 100-105 db on peaks). I listen mostly to classical orchestral music. The Acoustats are rolled off at 80 Hz (6 db/octave) with the lower frequencies channeled to a Velodyne HGS-18 subwoofer. The Bryston amplifiers can be run in series (higher voltage for 3-8 ohm loads) or parallel modes (higher current for 1-3 ohm loads). Specific tests of my amplifiers yielded at clipping 630 watts in series mode and 615 watts in parallel mode (8 ohms at 2 KHz). This should be more than sufficient to drive the Acoustats to 115 db levels, especially since they are rolled off at 80 Hz. I ran the amplifiers in both modes and there was no improvement in the parallel mode over the series mode. In fact, clipping occurred at lower volume levels in the parallel mode. The amplifiers are connected to the crossover in the subwoofer via unbalanced Monster cable RCA connectors that are 20 feet long due to space limitations. The speaker cables are also Monster cable and are 12 feet in length. I would appreciate your comments as to why this problem is occurring and how to solve it. Thank you in advance for your reply. Alan Hoffman

    Andy Szabo (2007-08-10 23:58:26)

    You certainly have enough watts to drive the 2+2 to its maximum output, and therein may lie the problem. You may be clipping the amp occassionally, but what you are probably hearing is minor \'crackling\' of the speaker, indicating it has reached its maximum output. This causes no damage to the panels themselves (unlike some ESL\'s). You may also have a problem in the step-up transformers. They can develop problems at high-voltage levels, causing an arc inside the transformer. This does damage the transformer, and will get worse (and eventually fail)over time if you continue to play at high levels. If your problem has developed recently, this may be the case. Most people find the 2+2 capable of producing acceptable SPL levels, so you may be asking too much of the speaker, especially if you are in a very large room. Crossing-over at 80 Hz will certainly increase the speaker\'s effective dynamic range, but the speaker still has its limits. You might try using a steeper slope than 6 dB/octave - at the present crossover slope you are still getting quite a bit of low frequency energy into the speaker: the signal is only 6 dB \'down\' at 40 Hz. I would suggest a 12 dB or 18 dB/ocatve slope, and/or possibly raising the crossover frequency somewhat.

  • resistor 500 Mohm for MK-141C - Andreas Blum on 2007-07-20 11:08:34

    After searching this site i came across the adress of with its german contact Farnell. They provide 500 Mohm resistors.Here is my Question: will the 500 MOhm, 5W, 20000V thick film resistor suite as refitting for the damaged 500 Mohm resistor in the MK-141c. Any help is welcome. Sincerely, Andreas Blum

    Andy Szabo (2007-07-27 23:19:16)

    The resistor you describe should be fine as long as it physically fits - some high voltage resistors are huge. Just make sure it has plenty of room around it, without touching any of the other parts on the board. The resistor does not get hot in operation, but should have plenty of space to prevent any possibility of high voltage arcing to other components. The exact value of this resistor is not critical: 500 M-ohm is optimum, but it could be as low as a few hundred M-ohms. Both speakers in a pair should have the same value.

  • Help with MK-141c in germany - Andreas Blum on 2007-07-14 13:39:34

    Hello, i just came across this site. Hopefully someone can help me with my damaged acoustat speakers. I bought these speakers including subwoofer about 15 years ago from my brother (he has an hifi shop and imported them via JAMO). A few weeks ago i recognized that one panel has only 5% output. I brought the panel for fixing to my brother\'s. The technition doesn\'t speak english so i try to translate. After screening he found out that some parts are damaged e.g the 500 MEG Ohm resistor(Wiederstand). His problem is to find someone in germany delivering these Parts and the schematics. It would be very kind if someone can help me getting these parts so that my speakers can be fixed. Sincerely, Andreas Blum

    Andy Szabo (2007-08-03 23:17:49)

    Try Newark Electronics ( as a source for the 500-Mohm resistor. It does not have to be that exact value. 500-Mohms is optimum, but you can use anywhere from 100-Mohms to about 700-Mohms. The wattage rating does not need to be more than 2 watts (the existing part is rated at 5 watts). Alternately, you may be able to find a suitable part through a local distributor who specializes in television repair parts. Unless you find an exact replacement, I would suggest you replace the resistor is both speakers so that they match. Schematics for the interface are included on the Acoustat Manual CD, available for sale on this website.

  • scratchy sound - matt herko on 2007-07-10 00:13:09

    I have a pair of Spectra 11\'s,one of which recently started making the music sound garbled & scratchy when playing. I open up the circuit panel portion, and found that the resistor nearest the 2 ballast resistors is burnt. The one next to it looks like it might be starting to cook too. (this is on the right of the burnt resistor, the smallest one on the board) The circuit panel itself is a bit browned where the burnt resistor is as well. Any ideas what went wrong, and if so where/how to replace it?

    Andy Szabo (2007-08-01 23:50:43)

    It is not uncommon for the resistors in the Spectra 11 interface to get very hot, sometimes to the extent of getting quite \'toasted\'. If you play a lot of loud music, you can expect this to happen. These resistors are easliy replaced, and if you use better-quality, metal-bodied resistors, they can be mounted on the metal chassis (to act as a heatsink) and connected to the board with short lengths of wire. However, I\'m not sure the burnt resistors are causing the \'garbled and scratchy\' sound. Resistors don\'t usually fail in that manner. You may have some high-voltage arcing on the board or in the transformer. Go ahead and replace the resistors first, and see if that solves your problem. See my piece called \"Ted Nugent vs Spectra 1100\" located under \"Spectra 1100, Refurbishing\" to see how I did a similar modification to the Spectra 1100. Look for any signs of arcing (i.e. black marks) on the components and wiring to see if you have a greater problem. Check too, for any loose connections at the speaker wire, wall-transformer plug, woofer box to interface, and panel-to-interface connections. Write again if you still have the problem or need further advice.

  • Acoustat Model One Woofer - David S on 2007-07-07 21:59:05

    Hi. Total neophyte here. Purchased Model 1\'s (141b)yesterday; picking them up tomorrow. Very excited! 3 questions: 1) I have an Adcom GFA-535 Amplifier. Will this be sufficient for use in a small room at modest volumes? 2) Do the speakers stay plugged in and turned on 24 hours a day, or do I power them up only when listening? 3) I have a powered subwoofer plugged into my preamp\'s subwoofer output. Can I use this instead of the Acoustat woofer and simply attach the speakers directly to the amp? Or is the Acoustat woofer necessary to maintain proper speaker operation? Thanks muchly

    Andy Szabo (2007-08-03 23:29:58)

    Congratulations on joining the Acoustat family! The Adcom amplifier is probably sufficient to drive these speakers, especially if you are in a small room and are looking only for modest volume. With care, you can use up to 250 watts per channel (8-ohm rating). The speakers should remain plugged-in and powered at all times. Their power consumption is minimal, and leaving them energized will ensure that they are always performing their best. If you expect not to be using the speakers for some time (more than a week) it\'s okay to unplug them, but it may take a few hours after re-energizing for them to reach optimum performance. The Model Ones do not require the woofer to be connected for the ESL panels to operate. Using your powered subwoofer as you describe is fine, and it is probably a better solution than the Model One\'s woofer. The only difficulty might be matching the crossover point, slope, and volume levels on the woofer to work well with the ESL\'s. The ease of doing this will depend on the flexibility of the controls on your powered subwoofer.

  • interface 121-c playing about 6db lower - Gary Smith on 2007-07-05 08:30:27

    Hi Andy I have a pair of 1+1\'s with the red medallion interface. One side is playing 6db than the other. As there aren\'t any repair places in my area that have even heard of Acoustat let alone repaired one it\'s been a challenge to get this repaired. I tried sounds like new without any response and after reading some of your answers it may seem that possibly a transformer has gone or is it possible some capacitor or resistor has. Not sure who to ask. I see the parts on ebay listed by sound valves and am thining of bidding on the bias transformer or high frequency..or what would an educated guess be to look at? I have checked all the fuses..put another 121c on the fine with that from a pair of threes I have but would like to get this one working if I can so I don\'t have have 1/2 a pair not working. Any suggestions?? Gary

    Andy Szabo (2007-07-27 23:30:03)

    If one speaker is playing lower in volume than the other, but otherwise sounds ok (no distortion or break-up) then I would suspect a problem in the bias power supply. It could be the bias transformer, but I doubt it. Those usually fail completely, rather than operating at a reduced level. I would concentrate on the 5 diodes and 5 capacitors in the bias multiplier. If one or more of those components is bad, it will reduce the bias voltage, and hence reduce the volume. There are some technical briefs on the bias power supply on this website, with instructions on measuring the bias supply. Your first step should be to determine if the bias voltage is low. Under \"available parts\", a source is listed for the diodes, and the capacitors are not generally too difficult to find (try Good Luck, and write again if you need further help. This problem can be fixed!

  • Improving dispersion - Gary Clausen on 2007-06-22 03:34:51

    Ok, finally I have several B&G (Carver)ribbons and thinking about building some new frames as I\'ve got to replace some ripped pannels anyway. Thinkning about placing them between panels and wondering if that 11 degree angle should still be used and good x-over freq and slope? I see some others have supplemented their Electrostats with ribbons.

    Andy Szabo (2007-07-06 20:18:43)

    I don\'t have any direct experience adding ribbons to Acoustats, so I can give you only general advice. You didn\'t say what model Acoustat you have. If it\'s a two-panel wide speaker, (i.e. Model 2 or 2+2, it is probably best to place the ribbon between the two panels. If it\'s a three panel wide speaker, I would put the ribbon between the inner and center panel (thus yielding mirror image speakers). The recommended crossover and slope would be best recommended by the manufacturer of the ribbons. If your aim is to extend the very top-end response, then crossing over rather high (maybe above 5 kHz?) would be sufficient. But it really depends most on the ribbon. Any one else have experience in this area?

    Gary Clausen (2007-07-26 21:28:11)

    Hi Andy, The Carvers are normally used around 150-175Hz with a rather steep 18dB slope in their design. I do have a pair of Model Two\'s and 2 pairs of Two+Two\'s. I was also thinking that another way I could improve dispersion would be to use the inermost panels (facing listener) full range with the resistors from the bass x-former summing with the caps from the high x-former and then add another pair of 50K 50W ohmites to just the output of the bass trannies and feed the outermost pair form just the bass side. I would then put the ribbons on the inermost side of each pair (to get the mirror images)crossing at much higher freq with gentler slope. I imagine the I would probably want some low pass filter on the output side of the resistors feeding the bass only panels to help keep the higher freqs from causing two wide surface to be used to reproduce highs.

  • Interface Problem - Greg Wiesner on 2007-06-13 14:58:41

    I have a set of Acoustst 2+2 Electrostatic Speakers with a Mk-121-C interface. My left speaker started sparking the other day at the interface. I read that it could be the 50,000 ohm, 50 watt resistors breaking down. There is bad distortion and hi and low peaks on the volume for that speaker. I saw that David Hafler suggest a repai tech in Florida, Sounds Like New. Called the number and got a disconnection notice. Does anyone know who repairs these interfaces? Please Help! Greg

    Andy Szabo (2007-06-15 02:53:44)

    Try contacting Roy by email at: I have heard that Roy is difficult to contact, keep trying.

    Andy Szabo (2007-07-27 23:35:39)

    The 50,000 ohm resistors appear frequently on eBay, from a seller called \'Soundvalves\". These are genuine Acoustat \"new-old stock\". However, these resistors are pretty reliable, and although they can fail, I would first suspect a problem in one of the audio transformers. Since you have one interface that is operating properly, you could track down the problem by swapping one part at a time from the good interface into the defective one. This is assuming, of course, that you are handy with a soldering iron, etc. I\'m not sure, but Soundvalves may have some audio transformers, too.

  • Bass transformer resistor MK-121 - Gary Clausen on 2007-06-06 00:08:44

    I\'ve heard of replacing the 1 ohm wirewound resistor in series with the large bass transformer with 1 ohm 25Watt Dale in the heatsink case and have a set with that mod for in a MK-121 C mod. pair. I was think of doing similar for my other pairs (surround setup), but have 1.5 ohm and 2 ohm 50 watters.(2 of each) What would the effect be of using this higher value?

    Andy Szabo (2007-06-09 14:58:35)

    I would not recommend using more than 1-ohm in this application. The DC resistance of the low-frequency (LF) transformer is extremely low, and if your amplifier had any residual DC output, it could cause excessive DC current flow. The 1-ohm resistor (in series with the LF transformer\'s primary)raises the DC resistance to a safe level to prevent this from happening. Some people have suggested removing this resistor entirely, but that is bad idea for the reason mentioned above. The sonic improvement in replacing this resistor will be minimal at best. If you can\'t replace it with a value in the 0.75 to 1.0-ohm range, I would suggest you leave it alone.

  • Bias supply smoothing caps - Gary Clausen on 2007-06-04 17:41:14

    I\'ve come across a lot of Vitamin Q P52477 caps rated .1uF 7500Vdc. Does anybody know the dielectric used in these and whether they would be suitable as bias supply filters as I have read about in various mods for the Acoustats? They are rectangular cans approx. 3.75in. W X 3.25in. L X 1.375in. D with some ceramic insulating post that are about 2.25in. L adding to the 3.25in for total of 5.5in. L I have enough that I can do my complete surround setup plus some left to sell if any interest.

    Andy Szabo (2007-06-09 15:08:18)

    Please disregard anything you\'ve read about modifying the Acoustat bias power supply. All the \'suggested improvements\' I\'ve seen range from merely silly (offering no improvement) to stupid (actually degrading performace)to down-right dangerous (shock hazard, possibly lethal). The factory-original bias supply is quite adequate for the job, and I strongly suggest (and beg) for you to DO NOTHING.

  • MK121-A - BOB NACE on 2007-05-26 19:15:51

    Wanting to upgrade to medallion transformers will 141 interfaces interchange with MK-121-A model 3 speakers ??

    Andy Szabo (2007-05-27 23:42:13)

    Sorry, no. The MK-141 is designed for limited range speakers only, where a conventional woofer carries the bottom end. The MK-121 series is for full range speakers that cover the entire audio range with ESL\'s.

  • Any differences in TNT 200's? - Dan Chrisman on 2007-05-25 06:07:44

    I notice there are some TNT 200s with silk screened fronts and some with a molded nameplate........Andy or anyone know if there is a difference in the two? Dan

    Andy Szabo (2007-05-27 23:46:25)

    Acoustat amplifiers with the cast logo plate on the front are early units. Later units (and most of those produced) used the silkscreened front panel. I am not aware of any major changes in circuitry during the life of the amplifier, although later production units generally had better quality capacitors.

    Vince Maida (2009-01-19 23:11:08)

    The input differential devices were changed at some point from the dual 2SK146 JFET to two single MOSFETs type VN01. The JFET is a better choice due to improved linearity and a much lower (>10dB) noise floor.

    Andy Szabo (2009-01-22 20:59:01)

    I think you may have your chronology wrong. If I remember correctly, the input differential used the MOSFETs initially, but later (and most) production used the dual JFETs. I agree the JFETs were a better choice.

  • Mk141C transformer - Nick Gouras on 2007-05-21 04:40:51

    Hi all. Does someone know if it\'s possible to replace a Mk 131 interface transformer (non medallion), as used in the Model 3MH, with a Mk141C transformer (medallion I think)? I don\'t know which model speaker the Mk 141C interface was used with, but suspect it might be possible? If so, would it be advantageous to also replace any other values in the MK 131 interface? Thanks in advance, Cheers, Nick

    Andy Szabo (2007-05-22 06:10:50)

    I don\'t see a problem with substituting an MK-141 transformer for an MK-131, but I\'m not sure there would be a huge improvement, unless it was to take advantage of the improved Medallion technology. Normally, I wouldn\'t suggest you go out of your way to make such a change, unless there was something wrong with your MK-131, and parts for an MK-141 is all that you could find.

    Nick Gouras (2007-05-23 04:11:42)

    Thanks very much Andy. I was thinking of doing this purely from the point of view as a sonic upgrade. My previous experience with the 2+2 versus 2+2 with Medallion and C upgrade made me realise the improvement was worthwhile, but I don\'t know if there is much difference between the MK141C improved transformer and the original Mk131 transformer. I do have a schematic for all of these interfaces and there are some other component differences too from memory. My intention is to use the 3MH panels/interface and use a really good upper bass/bass section which should improve on the original woofer box, so I\'d like to get as much as I can out of the panels sonically. Must admit they do sound very musical as is though. I did notice the 2+2 with Medallion upgrade did sound more neutral and less warm than the original, but has slightly better resolution and dynamic contrasts, IMO. Cheers, Nick

  • Plus a Subwoofer? - Silvan Karrer on 2007-05-10 19:29:27

    Hi, I am pretty happy with my 1+1 ELS. I am now thinking of adding an active subwoofer (Velodyne type) to them. Is there a possibly to roll of the low frequency at about 80Hz internally i.e. in the interface? I ask because an activ freq crossover is costly and I dont want any more units in my system. cheers, Silvan, Switzerland

    Mathieu (2007-05-10 22:25:18)

    Hallo Silvan, YES it works ! I\'m using Acoustat since years, and the best solution I found is to cut the low end simply with a single condensator 0.033 - 0.067mF placed before the amplifier (between the pre-amp and the amp). You have to choose a good capacitor, and make tests. The greatthing is that the power handling is increased in a HUGE maneer : you can hear live musc at almost true levels without any stress for the speakers. Other solution is to use a Behringher digital filter. Costs 200-300 Euros now, works well, but not so good for my taste on lyrics. For the low end frequencies, I use à 46cm JBL speaker charged with 100 liter Jensen volume, a CARVER amplifier, connected to an active filter (Behringer digital) with 18 db/oct at 50 Hz. So the Acoustat are filtered with a passive 6db/oct system and the bass are fltered with the active filter. It is simple and flexible. Your idea of a Velodyne sub is very good, but don\'t forget to choose a model which matches to the acoustat : big and quick. On my side I ve got also aquestion : I\'m looking for a good amplifier for the Acoustats, but until today i could not find the perfect atch. I would like to avoid Audio Research, Jeww Rowland stuff and so, because of budget... Can you advise me ? Thanks, Mathieu

    Silvan Karrer (2007-05-11 08:29:17)

    Hi Mathieu, thanks for your answer. Will check this technical solution. As I use KR Audio Amps (Kronzilla DM) for the Acoustats, I have heard also the VA350 on the Acoustats - Priced about 7000 Euro. So if you look for budget priced amps, I just have heard the SPHINX hybrid amps on Acoustats, which also sounded good. SPHINX Amps are not in production anymore but sometimes you find them used. If you want to know more, just write me an e mail to: Cheers, Silvan

    Andy Szabo (2007-05-12 14:53:58)

    I agree that using a capacitor in series between preamp and amplifier is the best low-cost way to roll-off the bottom end. If you use a good capacitor (polypropylene or polystyrene) it introduces negligible distortion. If you know the rated input impedance of your amplifier, then you can calculate the required capacitor value for a desired roll-off frequency. Use f= 1/(2piRC), where f is frequency in hertz, pi = 3.14, R is resistance in ohms, and C is capacitance in farads (not microfarads). Good luck with your project - adding a subwoofer to the 1+1\'s will make a huge difference!

  • MK-141-C - frank carpenter on 2007-05-04 18:01:05

    Is there a difference between the 141-c and 141-s. If so, what? On the speakers I have, the transformer wires have been cut. How do I connect the these 4 wires and in what configuration?

    Andy Szabo (2007-05-07 00:07:31)

    The MK-141 series interface is a single audio transformer system operating above approximately 150 Hz. It is used mostly on the single-panel Model One with subwoofer, and also on the somewhat rare Model 1+1S, which differs from the normal 1+1 (which uses the full range MK-121 interface) in that it uses the MK-141 interface and a subwoofer. The MK-141 \"C\" is that latest version of the series, using the Medallion transformer and an improved crossover network. I am not familiar with the \"S\" designation: perhaps it was used on the 1+1S. That model was discontinued before I joined the company, and little or no documentation exists. It is possible that version uses different values in the high-voltage resistor-capacitor network, since it is used with two panels (and hence twice the load capacitance). I\'m really not sure. What model are you intending to use with the MK-141? As far as electrical connections are concerned, I suggest you buy a copy of the Acoustat CD from this website. It has a schematic of the MK-141, showing the transformer connections. Good luck, and do write again if you need more help in getting your speakers operating. It is my goal that all existing Acoustats are working and being enjoyed as they should be, \'cause they sure can make a lot of joy.

  • Acustat one plus one - Sylvo Schroeder on 2007-05-04 06:01:36

    Dear Andy , Thanks for your advice - they checked everything as you have said but no result .The second one also gave up -both dead - I have seen how they test the parts here but I am not confident! The Standard of High End Audio Repairs still have a long way to go in India. .My suggestion would be to pack the two and send them to you for a check up and repair under your guidance - the cost is of no impotance since these two products have given me lots of good music and joy - I would hate to wtite them off. Believe me I have in the mean time tried many other very good speakers. Both Acustats are from the last year of manufacturing.( serial No.18028006- with Medallion transformer ) Any suggestions? Regards, Sylvo Schroeder

    Andy Szabo (2007-05-04 22:06:08)

    I don\'t do repairs myself, so I suggest you contact Roy Esposito at Sounds Like New. He is an ex-Acoustat employee who is quite qualified in repairs and has (or can get)the necessary repair parts. See the section under \"General\" and then \"Refurbishing\" for how to contact Roy. Good Luck!

    Roy A. Esposito (2011-07-17 20:02:14)

    July 17, 2011

    I am very much alive.

    I am No-Where near retiring .... and over many years have
    come up with astounding improvements, variations and restorations
    for the Acoustat MK and Spectra Interfaces
    and even more so the Trans-Nova amplifiers (TNT-200 and TNT-120)
    and Trans-Nova Preamplifier (TNP).
    I also renew the earlier and more rare, Acoustat MRP and RP-2 preamps.

    To my chagrin ----
    Folks don't realize I was many years younger than the
    other principals at Acoustat, back in 70's and 80's Fort Lauderdale.
    About half their age at that time.

    I am happy to continue lovingly working with Acoustat products.
    I do this with a fully functional laboratory and stockroom
    of original .........and improvement parts.

    But please realize that... in 2011....
    this is part-time work.... in addition
    to my regular full-time engineering/consulting work.

    So it can take a few weeks in total, for me to work my
    Acoustat "magic"...... as my client's have often
    described the results.

    I hope the above will help explain why I don't
    provide a phone number, except to established clients,
    and I prefer email contact instead. I also prefer my work
    and "word-of-mouth" to speak for itself
    ....instead of having and spending time maintaining a website.

    There are others that offer work on Acoustat products.
    Fancy words .... Fancy websites.
    But NONE of them worked for the Company.
    And to correct the mess.....
    Folks usually end up with me despite the glowing website tetimonials.
    That's just sad.

    I very much appreciate all of you, who continue to revere...
    and enjoy...
    the magnificent design works of Dr. Strickland,
    and our original Acoustat Engineering Team.

    May we all enjoy the Music,

    Roy A. Esposito /

    MrAcoustat (2011-11-01 01:56:53)

    Mr.Roy A.Esposito i am happy that you are still improving on the original Acoustat's for audiophiles that still believe in that product i for one have been with Acoustat's since 1984 and will probably leave this world before my modified 1+1s that can be seen in my Flickr photo galery here ( ) these where modified by Mr.Jocelyn Jeanson from Kingsbury Quebec Canada Jocelyn is in regular contact with some of your old buddy's from Acoustat USA and others across the world he own's a pair of modified Spectra 6600s that can also be seen in my photo galery all steel frame covered in wood mine weigh 200 pounds each and his 600 pounds each as of today october 31st 2011 i have not heard ANYTHING better at even three times the price than these panels i am 66 years old and have been attending shows for 25 years i'm not saying that they are the best speakers in the world i'm saying that they are the best that I have heard and i have heard many very expensive speakers in over 40 years plus dollar for dollar Acoustat electrostatics even in stock form are very good BUT modified they can be EXCEPTIONAL please keep up the good work in the U.S.A. and Jocelyn will keep up the good work in Canada it's all for the enjoyment of audiophiles everywhere.

  • Drastic loss of gain - Trevor Monroe on 2007-04-30 05:02:28

    I have a 2+2 speaker that losses about 20 db of gain, and is \"brought back to life\" by directing a space heater at the transformer box. This fix can last for hours or days; however, the speaker will inevitably loss gain once again. It appears that the temperature of the box is not the issue; however, humidity is. If the humidity is below, say, 50 percent, as far as I can tell the problem is alleviated. If the humidity is above 90 percent, both speakers suffer. When the humidity is between 50 and 90 percent, the space heater solution works. I\'ve had the speakers since the mid 80s, and this problem began to occur about 2 years ago. Do have any idea which part or parts has/have become sensitive to humidity, and how do I go about isolating the offending part? Thanks a lot, Trevor Monroe

    Andy Szabo (2007-05-03 17:46:46)

    This is a new one on me! In the early stages of developing the Acoustat panel, great effort was made to make sure the speaker operated properly in all conditions of high and low altitude, and in conditions of high and low humidity. There have been no reports (that I am aware of) of any subsequent failures of the panels due to the effects of humidity. So I am inclined to think your problem is not in the panels, but in the interfaces. And since the problem exists in both speakers, I suspect an externally-induced environmental problem, rather than a component failure (although that is not impossible). Even still, I am not aware of any reports of humidity-related component problems in the interface, so I am just guessing here! My suspicion is that you have a build-up of dust in the interface, which becomes partially conductive under conditions of high humidity, causing the high-voltage bias to leak-off. High-voltage circuits do have the habit of attracting air-borne particles, and after many years, a layer of black soot-like stuff will form on the high voltage components. I would suggest you use a damp rag to clean off as much of the soot as you can from the high-voltage components, printed circuit board, and wires. This type of dirt is generally somewhat sticky or greasy, so using compressed air usually doesn’t work. Do make sure the interface is completely dry before re-energizing it. That’s about all I can think of for now. When you open up the interfaces, you may see the problem right away. You may find spider webs, insect parts, or some weird corrosion (salt air environment?), that could be causing the problem. There is still a chance that you could have a problem in the panels, but again, I suspect dirt as the culprit rather than a component failure. If you are a heavy smoker, and/or the speakers have been used or stored in a particularly dusty environment, there may be sufficient deposits on the panels to cause humidity-induced high-voltage leakage. But I would concentrate on the interfaces, especially since blowing a heater there seems to temporarily solve the problem. Please do write again and let us know what you find. I am anxious to know what is causing this very unusual problem!

  • moving to europe - Stephen Casmier on 2007-04-28 17:20:08

    my father gave me a pair of acoustats that he bought maybe 20 years ago. they\'ve been in storage. are they worth my bringing to europe with me for a year. what do i need to do to make sure they are in working order?

    Andy Szabo (2007-04-29 16:55:12)

    The simple answer is to hook them up and try them! No sense lugging a pair on non-working speakers across the ocean. Acoustats are quite reliable and long-lived, so there is a very good chance they\'ll be fine. Once you become accustomed to their sound quality, it\'ll be hard to live with anything else. Since an electrostatic speaker like the Acoustat needs to be plugged in to a source of AC power, you\'ll need a step-down transformer so you can operate the 120-volt speakers on Europe\'s 220/240 system. But no doubt you\'ve already considered that since I\'m sure you will be taking other electrical devices with you. The AC power requirements of the speakers are minimal - no more than 20-watts for the pair.

  • increasing HF - Fancesco Izzo on 2007-04-26 21:56:17

    Hello, I own a pair of Spectra 11 and they sound very well to me but sometimes when listening to various musical programs I would like to obtain a bit more treble in the upper end of the frequencies, I guess if there is a way to do that (I don\'t have tone controls on my amps...), maybe any mods in the values of the components (capacitors, resistors) would do the job? Thank you very much. Francesco Izzo Italy

    Andy Szabo (2007-04-27 01:30:38)

    Yes, there is a simple mod you can do. There is a large 1-ohm resistor on the pc board inside the interface. Don\'t confuse it with the similar looking 10-ohm resistor. This resistor may be reduced in value, all the way down to zero ohms if you desire. This will reduce HF roll-off, although don\'t be expecting a big change. The penalty of doing this(and the reason that resistor is there) is that you will reduce the speaker\'s impedance by the same amount at high frequencies. If your amplifier is okay with that, then you should have no problems. The HF Balance switch on the upgrade-version Spectra 1100 gives three possible values of that same resistor: HI is zero ohms, MED is 0.4-ohms, and LO is 1-ohm. Also keep in mind, that if your amplifier has low damping factor at high frequencies (i.e. high output impedance), that will combine with the low HF impedance of the speaker to create significant HF roll-off.

  • single panel w/sub - Doug on 2007-04-21 18:19:59

    Hello, I have 1+1\'s with all the latest updates but with trashed panels (rips near frame). I have located two 8\" replacement panels. I have mated 1+1\'s with a Mirage BP 150 sub crossed at 80Hz with good results. Can I use the 1+1 interfaces on only a single panel? How much bass will I likely lose/what sub crossover frequency will likely be required? Thanks PS I know I will need to fabricate some kind of frame but that should probably be the subject of another post. PPS These are only surround speakers so maybe some parameters are slightly less critical.

    Andy Szabo (2007-04-27 01:42:06)

    You will lose a lot of bass. You are reducing the panel area by more than 50%, since you are changing from two-9\" panels to one-8\" panel. You\'ll probably want to increase your crossover frequency to about 150 Hz. That\'s the approximate value used in Acoustat\'s single-panel Model One. Unfortunately, at that high a frequency, bass becomes directional, and with only a single sub, LF imaging will suffer (perhaps not an issue for your surround system). I don\'t see any reason why you can\'t drive only one panel with the MK-121 interface. To keep from over-driving the panel at low frequencies, it may be advisable to add a high pass crossover there. Needless to say, you\'ll need to experiment to get everything adjusted correctly. But I see no reason why your ideas couldn\'t be made to work. Write again if you have any more questions - sounds like an interesting project!

  • Purchasing 150K 5W Resistor for MK-2123 - Bob on 2007-03-09 08:26:02

    Hello, where can I purchase the 150k 5W resistor for the MK-2123 interface? There two of them, one between the blue and yellow wires and one between white and yellow wires. Thanks.

  • Acoustat Spectra 22 / Monitor 4 - Peter Kloos on 2007-03-08 10:40:06

    Hello Mike Savuto, I have a pair Spectra 22 and I´m looking for a better amp to drive it. Have tryed Luxman MQ75, Fisher SA-100, Heathkit/Acrosound W3 (very nice sound), ARC D-115 (the best,so far). Do you have a better idea what amp (tube or SS)plays whith the Spectra 22 ? On the other hand, would it be a good improvement to use a Monitor 4 whith servoamp instead of Spectra 22 ? Thank you, Peter

    Mike Savuto (2008-06-10 04:30:31)

    Hi Peter, First question concerning what amplifiers to use with Spectra\'s. I have had limited experience with the Spectra series, but in the MK series, which really isn\'t that different, we found high current capable solid state amplifiers worked best. We found that tube amps we tried (ARC among them) tended to sound somewhat dead driving the interfaces. The speaker just didn\'t seem to respond well. A good SS amp can make them jump. This from a guy who just loves the warm glow of tubes, but in this case, they just aren\'t a good fit. Second question concerning what I would choose. Yes I do prefer the sound of the servamplifiers driving the panels directly. I will say however that when I heard the Spectra\'s at CES many years ago, it was the first time I liked what I heard from Acoustat ESL\'s driven through an interface. There are a lot of reasons why I think Acoustat discontinued the servoamplifiers but sonics is not one of them. I personally feel that the Monitor 4 style Acoustat was the best panel configuration, particularly when driven by the servoamplifiers. It provides the warmest sound with the best bass you can get from an ESL. You can buy the speakers/amplifier combinations fairly inexpensively (around $1200 will buy you a pretty good condition pair) and you/we can update them to any level you want at your convience (shameless plug). Best Wishes, Michael Savuto Analogue Associates, LLC

  • 5 wire panel with total of eight wires - JAMES JOHNSON on 2007-03-04 15:47:38

    Hi, my question is how do I wire these so called 5 wire panels down to 3? There is a group of 3 wires on both ends of the panels, 1 red and 2 white for each end, then in the middle there are 2 white wires. This looks a lot like 3 -2- 3. I don’t really know what to do with all these wires, it does seem like only the red wires are attached to the Mylar on both ends. I can’t figure out why there are two additional white wires coming from both ends of the panels. Can we use any device to check out these wires and really find their purpose? Thanks to anyone who can provide me with answers to these questions.

    Andy Szabo (2007-03-06 02:38:53)

    Wow. I have never seen an Acoustat with wires exiting from both ends of the panel. I\'ve seen thousands, and they all had wires coming from one end only, whether they were 3-wire, 5-wire, or Spectra panels. Just when you think you\'ve seen everything! Your description has confused me - just how many individual wires come out of these panel? It sounds like six, but that makes no sense to me. As before, there should be only one red wire, and that connects the diaphragm to the bias voltage. The white wires will exit the panel slightly forward of the centerline of the panel: these are for the front stator. The blue wires will exit the panel slightly behind the centerline: these are for the rear stator (felt block side). All white wires should actually be the same piece of wire, so they can be verified with an ohmeter or continuity testor. Same thing for the blue wires. There should be NO conduction between any two different colors.

    Andy Szabo (2007-03-06 02:41:53)

    Ooops - let me clarify a point. The white and blue wires should all exit from one end of the panel. The red wire actually exits from the side of the panel, about 1/4 of the way from the end with the other wires. Still only five wires.

  • 5 wire panels - JAMES JOHNSON on 2007-03-01 22:27:30

    Hi My question is how can I replaces my new panels that came with 5 wire for my present panels that only have 3 wires. I see one white,gray and one red only from my old panels; I also can see mange-kinetic interface Mk 121-2a on the black box at the bottom of my speaker. I have purchased two upper panels and two bottom panels, because I hope replacement of all 4 drivers top and bottom, is just like replacing one full speaker, to use the new panels with 5 wires should I all so purchase the newer interfaces is there a way to use these new panels as my left speaker and keep a perfectly working 3 wire panel as my right speaker or will I need to replaces those 4 with new panels all so because of a differences in efficiency or what ever. Your response above was very alarming because I will never give up trying to get a perfectly working pair of 2+2 The repair was looked at with fear and trepidation but now I can see my way through to the end of this tough repair. Thanks in advances for your answer. James Johnson

    Andy Szabo (2007-03-03 01:41:49)

    I\'m happy to hear you\'ve found replacement panels so quickly. You can use the 5-wire panels with no problems. In a 3-wire panel, the white wire is the audio connected to one end of the front stator grid; the blue wire is the audio connected to one end of the rear stator grid; and the red wire is the bias to the diaphram. In a 5-wire panel, there is only one red wire, and its function is the same. The two white wires and two blue wires are simply connected to both ends of their respective grids. Therefore, when connecting to your interface, simply connect all the blue wires to the blue terminal, all the white wires to the white (or unmarked) terminal, and all the red wires to the red pin-jack. Your interface is completely compatible with these 5-wire panels. What you see as gray wires are actually the blue wires: they must have faded and discolored over time. The change from 3-wire to 5-wire panels was an early change at Acoustat - way before my time. Supposedly there is a subtle sonic improvement using a connection to both ends of the stator grid, but I am at a loss to explain why. I doubt you will experience any change in efficiency. I suggest you wait and see if you notice a difference between your apeakers. Be sure to give it some time to give the panels time to \'settle in\'. Good Luck! It sounds as though your speakers are on the road to recovery. Long Live Acoustat!

  • Mylar type? - JAMES JOHNSON on 2007-02-21 00:58:42

    I have two upper panels on my left speaker where the Mylar has been torn it has a whole in it. I need to know where to buy the Mylar to replaces these two panels and what type of Mylar to use to replaces the membrane all so where to purchase the honey comb white plastic that has been melted by a very hot hair blower or worse.

    Andy Szabo (2007-02-21 13:59:10)

    Acoustat panels are extremely reliable, but when the Mylar breaks, they are junk. They cannot be dis-assembled and repaired. Used, replacement Acoustat panels do appear occassionally on eBay. New replacements are, of course, no longer available.

  • Acoustat Madallion Transformer - Hank on 2007-02-20 05:01:59

    1. What are the signs of a failed low frequency transformer? 2. Do they fail completely, or can they still function to a certain volume level? 3. Did anyone experience a failed medallion transformer, as a result of the A/C plug disconnecting from the wall? What are the symptoms? Thanks, Hank.

    Andy Szabo (2007-02-21 13:24:20)

    Sorry to hear you asking these questions, as I can only assume you are having a problem. LF transformers can fail in several ways, but the most common is high-voltage breakdown at higher volume levels. So, yes, they can play ok up to a certain level. Breakdown is a high-voltage arc jumping from one winding to another: it sounds horrible and can blow fuses. If it breaks down repeatedly, it will eventually occur at lower and lower levels until the transformer fails completely. Leaving the AC unplugged on an Acoustat will not damage the audio transformers per se, AC power means little or no bias voltage, so there is the tendency to \'turn up the volume\' trying to make it play. This can over-drive the audio transformers, leading to the start of high voltage breakdown. Unfortunately, the transformer cannot be repaired: it must be replaced. Medallion transformers have much better breakdown resistance than their predecessors, but still have their limits.

  • Another problem - Brad M. on 2007-02-19 16:32:06

    Thanks for addressing my last question but the problem still persists to some extent. We finally measured the value of the bias directly with a high voltage probe. The voltage was reading only 3800 volts. On one speaker we were able to turn the voltage right up to 5000 no problem and the other was maxed out at 3800. BTW this relates to DC voltage at the red connector (where the bias wires plug in) of 75 V (for 3800) and 92.7 V (for 5080 volts). So, I took an ultrasonic power supply out of my pair of 2200s (after checking to make sure it could generate at least 95 V at the red friend took his HV probe back with him at this time) and installed it into the 4400. However; it STILL won\'t deliver 92.7 V at the bias connector. It would only give to 86 V. THis seems strange because in the 2200 the supply could give much more output. My friend suggested that perhaps one of the HV diodes is no longer functioning properly. Do you think I should replace the HV diodes on the board? In the meantime I have taken the other speaker down from 92.7 to 86 so that they match at least but I would prefer the extra 2 db or so that I get at the higher voltage (just a guess because when set this way the soundstage shifts to the speaker with the higher voltage audibly). One other comment, the higher voltage settings do seem to have more High frequency content (not verified yet with a measurement). The speakers STILL sound as if there is less HF energy than the 2200. Is there any reason at all you can think of for this? As to the height, well I also have 1+1s and have not noticed anything amiss with them (they actually measure quite flat to around 12Khz then a gentle rolloff.) I am getting pretty frustrated because I know how good the Acoustats sound and the great sound of the 2200 is what motivated my to get the 4400 when it became available. One final thing. Was there any difference in the sock material over the lifespan of these speakers? It seems that the material of the 2200 is a bit thinner and optically more transparent than the fabric on the 4400. Could this account for a significant difference? Thanks

    Andy Szabo (2007-02-21 13:52:43)

    Don\'t expect to measure anywhere near 5000 volts at the red connector. Due to loading of the bias supply, and the voltage divider action of the 500-megohm resistor and the resistance of the HV-probe, you will measure considerably less. Depending on the probe, you may only measure only 2500-3500 volts. Even if you measure at the +5KV point on the board, you still have loading effects that will reduce the measurement. This does present a problem for setting the bias voltage, because any attempt to measure it will also alter it (The Heisenberg Uncertainty Principle at work again!). The most important thing is that both speakers in a pair are set the same. I doubt you have a bad high-voltage diode. The measured differences would be much greater if that was the case. It is not unusual for the ultrasonic power supplies to have a fairly wide variation in maximum output on a unit-to-unit basis. I do have a recollection (now that you\'ve reminded me), that in the final years Acoustat switched from a double-knit fabric to a single-knit, which is both acoustically and optically more transparent. It is quite possible that the difference you hear between the 2200 and the 4400 may be due to the difference in grille cloth. I am fairly certain that the fabric currently being sold by The Upholstery Company Inc. is the newer single-knit.

  • Integrated (or power) amps for Acoustat? - Daniel Poirier on 2007-02-12 20:26:25

    My old trusty power amps (PS Audio) are getting old and their capacitors are drying out... I have had them repaired a few times already, but I think eventually, I\'ll have to face the facts: I\'ll need a new integrated amp (or a pre-amp and a power amp). The dilemma, of course, is to find an amp that won\'t fry when it hits the low impedance of the Acoustats... I\'ve read somewhere that it can be as low as 1 ohm at certain frequencies... I don\'t invest as much in audio as I did when I first bought my Acoustats (in 1983)... so I am not really looking for a $2000 amplifier. Any suggestions for amps that can handle the Acoustats? Am i looking for \"high current\"? Is that synonymous with \"capable of handling low impedance speakers\"? Any typical brands or models that can find their way into eBay (and are not 20 years old)? Or new models that can cut it and still be affordable? If it matters, mine are model 2C (dual panels, with a sub-woofer in the transformer box in the back). Thanks... Daniel

    Andy Szabo (2007-02-24 15:20:13)

    The good news is that there are probably more suitable amplifiers on the market today, than there were when the speakers were new. If you are looking to buy new, there are probably few, if any, good condidates below $1000, especially if you are looking for an integrated amp. Buying used can be a good route to go. Acoustat amplifiers are well suited, of course, but even the newest of them are nearly 20 years old. The Hafler Transnova series (9000 series model numbers) were also designed by Jim Strickland, and are a very good choice, and a bit newer. I use a Halfer 9500 with very good results, but some of the smaller models would work well also. Don\'t overlook the Hafler Pro series - they\'re the same amps inside. Many more brands would work well, but I have no personal experience with them. Anyone else care to comment here?

    Hans Zeeuwe (2007-03-26 19:55:29)

    You may want to take a look at the Quad ESL 57 section. In the \'Reviews\' section there are two or three articles on amplifiers and the Quad ESL 57. As the ESL 57 is famous for being a rather difficult load for amplifiers, the articles may apply for the Acoustats as well. At least it should guide you in the right direction.

    Silvan Karrer (2007-05-10 19:57:12)

    As I have the Acoustat 1+1, the impendance of this model is not going lower than 3Ohm. To my opinion, the amp has to deliver a lot of current. The watt amount is not the point, the amp has to have strong current delivery! I can recommend KR Audio Amps, or Krell as transistor amps. I prefere tube amps for the acoustats! Cheers, Silvan

  • Just got 4400s and seems a problem - Brad M. on 2007-02-07 15:25:46

    I just got a pair of Spectra 4400s that seem to be in really good condition. However; when I compared them to the pair of Spectra 2200 that I already had I found the high frequency response was greatly reduced. All 4 panels per speaker seem to be working properly and I measured the speakers in room responses with a 1/6th octave real-time-analyzer. The measured in room response explains what I hear that above about 4-5khz the speakers are down by about 5 or 6 db relative to the midrange (and even more compared to the bass). Both speakers are behaving similiarly. This is frustrating because I thought going from the 2200 to the 4400 would be more of the same just a bigger sound. Is there some reason why the HF response is so much lower than the midrange? I am checking the high voltage on the panels tonight with a HV probe. As to the bass, I have identified the wires that will reduce the bass by a couple of db and I will also make this change but it doesn\'t change the problem with the highs. Any help on this matter would be greatly appreciated.

    Andy Szabo (2007-02-18 15:38:56)

    You should expect the 4400\'s to sound similar to the 2200\'s - they use the same panels, same sectoring arrangement, and only slightly different interface electronics to account for the increased capacitance of the load, and the need for less bass boost. I doubt very much that you will find a solution in adjusting the bass taps. Very few, if any, owners of the 4400 found it necessary to use anything different than the normal GREEN tap. I also would not expect abnormal bias voltage to produce the effect you describe. Bias voltage is more like a volume control - it affects all frequencies equally. Do make sure that the left and right speakers are on the correct sides. Having them backwards can yield some pretty weird results. Beware of relying on any labels or markings for identifying L & R speakers. If the grille cloth has been changed, those labels may not be have been re-assembled in the correct position. For the right speaker, the high frequencies will be coming from a segment closer to the left side. Also examine the room around the speakers. If the upper portion of the walls or the ceiling absorbs high frequencies more than lower areas, this could throw-off the perceived frequency balance. With speakers this tall, one must think vertically too, when examining room interactions. I can\'t think of much else that could be wrong, unless a previous owner has changed something (always a possibility with used speakers). I too own 4400\'s, having upgraded from 1100\'s, and found the transition a positive change in every respect.

  • Upgrades - Tom Mahaffey on 2007-01-20 17:41:48

    I have a pair of Acoustat model 3 and was thinking about upgrading them, but they sound great and never been a problem, and I have had them for about 23 years. Are there any upgrades for these great speakers anymore?? They are always plugged in and I use them almost daily. Thanks Tom Mahaffey

    Andy Szabo (2007-01-20 18:29:04)

    Were your Model 3\'s originally built, or later modified with the Medallion Transformers? That is the greatest modification that can be done, although getting it down nowadays might be tricky since Acoustat USA has been out-of-business since 1990. Try contacting \'Sounds Like New\' - they do good Acoustat repairs and modifications (and might be able to do Medallions). Contact information is under \"Refurbishing\'. Beware of other persons who claim to do interface modifications - there\'s alot of snake-oil vendors out there. Some of the proposed modifications are merely a waste of money with no improvement, others are downright wrong and/or harmful. Or, if you\'ve been happy with them for 23 years, why change now? Keep on listening!

    Bert Rodriguez (2008-01-03 17:34:37)

    Sounds Like New can do the Medallion Mod. I had it done in 2003 for my MK-121 interfaces for my Model 3s. Job was first rate and the speakers came back with the old parts and wire in a baggy. Only drawback was that it took almost three months because of the time it took to acquire the tranformers. Was it worth the cost and the time? A definite yes!!!! Bert Rodriguez Massachusetts, USA

    Roy A. Esposito (2011-07-17 20:06:55)

    July 17, 2011

    I am very much alive.

    I am No-Where near retiring .... and over many years have
    come up with astounding improvements, variations and restorations
    for the Acoustat MK and Spectra Interfaces
    and even more so the Trans-Nova amplifiers (TNT-200 and TNT-120)
    and Trans-Nova Preamplifier (TNP).
    I also renew the earlier and more rare, Acoustat MRP and RP-2 preamps.

    To my chagrin ----
    Folks don't realize I was many years younger than the
    other principals at Acoustat, back in 70's and 80's Fort Lauderdale.
    About half their age at that time.

    I am happy to continue lovingly working with Acoustat products.
    I do this with a fully functional laboratory and stockroom
    of original .........and improvement parts.

    But please realize that... in 2011....
    this is part-time work.... in addition
    to my regular full-time engineering/consulting work.

    So it can take a few weeks in total, for me to work my
    Acoustat "magic"...... as my client's have often
    described the results.

    I hope the above will help explain why I don't
    provide a phone number, except to established clients,
    and I prefer email contact instead. I also prefer my work
    and "word-of-mouth" to speak for itself
    ....instead of having and spending time maintaining a website.

    There are others that offer work on Acoustat products.
    Fancy words .... Fancy websites.
    But NONE of them worked for the Company.
    And to correct the mess.....
    Folks usually end up with me despite the glowing website tetimonials.
    That's just sad.

    I very much appreciate all of you, who continue to revere...
    and enjoy...
    the magnificent design works of Dr. Strickland,
    and our original Acoustat Engineering Team.

    May we all enjoy the Music,

    Roy A. Esposito /

    Bert Rodriguez (2011-08-11 15:50:54)


    Good to hear that you are still doing business. My Acoustat Model 3s continue to work fine thanks to the modifications you made to them in 2003. They continue to "sound like new". Some people are actually surprised to hear that these are a 30+ years old design. Compared to the stuff put out today, I will take the Acoustats any time.

    Thanks and regards!

    Bert Rodriguez

    Andrei Tudoran (2011-09-10 09:55:19)

    Roy just did a great job upgrading my Model 8 interfaces.

  • Acoustics and panel placement. - Andrzej Kruszewski on 2007-01-20 02:29:40

    by Andrzej Kruszewski (January 20, 2007). Hello again, another day another question. This time it is the acoustics vs. interior design. My Ones are positioned in the big opening (8 x 8 feet) between two rooms of equal size 13 x 16 feet and 11 feet high ceilings, so they play into two rooms. Is this a proper placement of this kind of speaker? Is there a maximum distance from the \"rear wall\", past which the sound will suffer? On the back side of the panels, there are felt strips glued to the grid. I assume it is there for some reason, like tuning of the diaphragm. Please let me know, if I was to remove this strips so the panels would play more evenly on both sides (front and back), would it decrease the quality on the front side, or overall quality in the both rooms. Have anybody tried positioning panels in this way ? If yes, please let me know your opinion. The woofer stands on one side of the opening next to one panel, so it covers more or less both rooms. the idea of this placement came during a recent apartment renovation. I enlarged door opening between two rooms to 8 x 8 feet large on 16 feet long wall. Your help and opinion is very much appreciated. Thanks, Andrzej.

    Andy Szabo (2007-01-20 18:21:17)

    The Acoustat Speaker (or any bi-polar speaker)was not designed to be used as you describe. It is intended to have the front of the speaker project into a single room, with the rear of the speaker facing a wall, about two to four feet from that wall. The idea is for the sound to bounce off the rear wall, giving a greater sense of ambience and soundstage. Having said that, however, there is nothing wrong or harmful about the set-up you describe. If it makes you happy, then it is good for you. Try it both ways to see what works best for your lifestyle and listening habits. DO NOT remove the felt strips on the rear of the panels. They control unwanted resonances in the diaphragm, and the speaker will not sound as good without them. If a piece of felt has come loose, remove it entirely, coat the felt with a spray-adhesive, and then re-apply as before.

  • Woofer problem! - Andrzej Kruszewski on 2007-01-19 21:37:06

    I just discovered the forum (great info. source), so I have few questions for Andy Szabo, or someone else with the knowledge of original design of One\'s woofer and tweaks. As a result of uncontrolled use of my system by my New Year\'s Eve Party guests, I discovered : audio fuse blown in one of the MK -141C , woofer dual-voice coils damaged and possible damage to Air core inductors (chokes?). When testing it, by direct connection of amp. outputs to the woofer, one chanel did not play at all, and other made scratchy noises. I examined interfaces carefully (but have no knowledge or tools to test it properly), and they look O.K. - no visible wire or component damage, no discoloration, and panels seem to play O.K. (but they are 20 or so years old). I have had coils of the woofer repaired by pro-technician. When testing woofer after repair, it started to play in full range. It looks as the crossovers are damaged. From the schematic of MK-141-C, I read (from left to right) crossover parts: L1 4.5 mH/4.3 ohm ; C5 330uF; R6 -10ohm/25w. Strangely, inside the woofer enclosure I have found two (one for each chanel)- what looks like -transformers w/o core, it must be Air Core Inductor (L1 4.5 mH / 4.3ohm) ???... Each of them is marked with numbers LA 002 and 2009128, and no other elements of crossover (C5 ,R6)... Am I missing some parts in my woofer cabinet???... I bought the One\'s \'second hand\" and don\'t know what woofer looked like originally inside. I would like to replace crossover with the original parts, or do you recommend upgrade to some different (newer and better)parts?... Where can I buy them???. I live in Poland, and shipping the woofer to Florida may be an overkill, so if i can get components, I can rebuild crossovers here. If I can not find suitable inductors, technician can rebuild them for me here in Poland, but he needs pertinent values: mH, ohm, wire or foil type and gauge. Please let me know what should be installed inside woofer cabinet - crossover parts ( is my info from the schematic correct???...). Where can I buy the parts?... and what parts (possibly upgrade?). In the future I am considering building of two separate woofers. As Andy Szabo explained, it may improve stereo imaging. If yes, what crossovers should I use (values and types). I have two 8\" woofer drivers that I got some time ago from Rockford. They were sent to me by mistake, as a replacement to my 10\" driver for One\'s woofer. They are \"new in the box\" and never used, so in the future I would like to build cabinets and put them to use. What size (in liters) do you recommend? Another idea, is to build them in to lower section of the One,s frame and put the enclosure behind it?. On the page for Acoustat 1, there are some pictures (2 and 3) and it looks as a good idea. Question to the person contributing this two pictures: are this Model One adapted to include woofer, or is it another model of Acoustat ?... Once again on crossovers - should I consider buying \"ready made\" crossovers, if yes what kind : for 10\" single woofer - \"Parts Express\" has two types 4-ohm and 8-ohm, each 200 watt RMS, designed for dual voice coil subwoofer and 12dB per octave slope ( no other specs).b.) for two 8\" woofers with single coils - no info. or idea on brand or specs. Thanks for any help I can get out there, and please excuse my text book english. Kind regards, Andrzej Kruszewski.

  • Weak output - dan magers on 2006-12-22 17:26:25