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  1. #1
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    Acoustat Spkrs - Info needed

    I recently acquired a set of ACOUSTAT MK-121-2 speakers with a Magne-Kinetic I/F from a friend that unfortunately lost most everything in a recent flood. I plugged them in and got nothing. (no power) He informed me to haul them away. I was not familiar with the ACOUSTAT Corp. being a diehard Klipsch fan from AR, but have since been researching these spkrs and to my surprise like what I am reading. I have pulled the black boxes off and found internal blown (250v slow-blow) fuses. I cannot make out the amps? There is a 1/4 BUSS marking on one end. Can someone inform me what I need to look for in replacing these fuses. Also, can the spkrs be safely connected to a NAD 3150 amp? What if the internal electronics are damaged, say something more than a blown fuse, can the speakers themselves still be salvaged and wired directly with an amp? I am excited
    to bring them to life! Please advise.

    thanks!

    faisonmars

  2. #2
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    I'm not an authority on Acoutstats however, I do know they are a highly respected planar speaker.

    There is a forum specific to planar/electrostatics with people more knowledgeable than I on this subject.
    This question would better be posed in the Planar speaker forum.

  3. #3
    Forum Regular audio amateur's Avatar
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    Quote Originally Posted by squeegy200
    I'm not an authority on Acoutstats however, I do know they are a highly respected planar speaker.

    There is a forum specific to planar/electrostatics with people more knowledgeable than I on this subject.
    This question would better be posed in the Planar speaker forum.
    Regardless of the location, the thread will be scene if users use the 'new posts' link. A few regular users own and enjoy planars and the likes, E-stat being one who i believe knows a little about Acoustats.

  4. #4
    Music Junkie E-Stat's Avatar
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    Quote Originally Posted by Faisonmars
    I recently acquired a set of ACOUSTAT MK-121-2 speakers with a Magne-Kinetic I/F
    Acoustat you say? Yes, I go way back with them. A great source for information can be found over at the Audio Circuit here.

    Quote Originally Posted by Faisonmars
    Can someone inform me what I need to look for in replacing these fuses.
    If memory serves, the interface uses a 3 amp fuse.

    Quote Originally Posted by Faisonmars
    Also, can the spkrs be safely connected to a NAD 3150 amp?
    No problemo. I ran my 2+2s with 500 watt (@ 4 ohms) VTL tube amps. Speaking of models, there were quite a few different models based upon their panel configuration. With the first generation, there were eight different flavors depending upon how many of a common building block panels were used horizontally and vertically. There was the 1, the 2, the 1+1 (one stacked vertically over another), the 2+2, the 3, the 4, the 6 (which was really a 3+3) and finally the 8 (4+4). The largest two used a pair of transformers each.

    Quote Originally Posted by Faisonmars
    What if the internal electronics are damaged, say something more than a blown fuse, can the speakers themselves still be salvaged and wired directly with an amp?
    Wired directly to an amp? No. Electrostatic speakers require a step up transformer in order to work. Rather than using a magnetic force to move a cone and voice coil, 'stats rely on using a high voltage charge to move the thin mylar diaphragm. No bias charge, no output. The good news is there are folks who continue to maintain them today. I understand that replacement transformers, however, are hard to come by.

    You'll find the sound a bit different from horn loaded Klipsch models. While not nearly as efficient, I find they produce a purer, more coherent sound. There is no woofer, tweeter or midrange. There is no crossover as each panel runs full range.

    Great find. I used them for nearly thirty years.

    rw

  5. #5
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    It sounds like something shorted - put in new fuses, and you should be set.

    Each speaker should have a bit of circuitry and two transformers: A big one to step up the voltage from the amp from 20v to 2,000v, and a small one to generate the 10,000 volt bias voltage. Normally, the plates and the mylar diaphragm do not touch each other, but if anything - like water - were to short them out, the fuses would blow instantly.

    Alternately, if you STILL can't get them to work, sell them to me so that I can perform mad DIY experiments on them.

  6. #6
    Music Junkie E-Stat's Avatar
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    Quote Originally Posted by spasticteapot
    A big one to step up the voltage from the amp from 20v to 2,000v, and a small one to generate the 10,000 volt bias voltage.
    In the event there is need for replacement, I think an accurate description would be helpful. Actually, one transformer handles the bass and the other the high frequencies with their output blended for the full range signal. Sound Lab uses the same overlapping approach in their current models although they use toroidal transformers. The fixed bias voltage is more like 3 kV in the Acoustat design. The challenge with running a fixed high bias voltage is that it will arc in conditions of low humidity. While the Sound Lab designs can run very close to 10 kV, the bias control is variable so that you can tailor the setting to the room conditions. You increase the bias until it just starts to crackle, then back it off a bit until that stops. If you follow the link I provided to the Audio Circuit, you will find discussions about the split frequency transformers with Andy Szabo, a former Acoustat engineer.

    There is also a brief tour of the panel fabrication that some may find interesting found here. The older gentleman with glasses and a vest found in two of the pictures is Jim Strickland, the designer of Acoustat. I had the pleasure of meeting him back in 1976 when he and his partner Bob Rieman brought a pair of the original model X to Atlanta for TAS reviewer Dr. Cooledge to sample. I bought my first pair one year later.

    Good luck!

    rw

  7. #7
    Forum Regular Deadeye's Avatar
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    Quote Originally Posted by Faisonmars
    I recently acquired a set of ACOUSTAT MK-121-2 speakers with a Magne-Kinetic I/F from a friend that unfortunately lost most everything in a recent flood. I plugged them in and got nothing. (no power) He informed me to haul them away. I was not familiar with the ACOUSTAT Corp. being a diehard Klipsch fan from AR, but have since been researching these spkrs and to my surprise like what I am reading. I have pulled the black boxes off and found internal blown (250v slow-blow) fuses. I cannot make out the amps? There is a 1/4 BUSS marking on one end. Can someone inform me what I need to look for in replacing these fuses. Also, can the spkrs be safely connected to a NAD 3150 amp? What if the internal electronics are damaged, say something more than a blown fuse, can the speakers themselves still be salvaged and wired directly with an amp? I am excited
    to bring them to life! Please advise.

    thanks!

    faisonmars
    The Mk-121-2 number is the model number of the interface unit. All Acoustats have a model number that corresponds to the number of panels in a side. ex: The Model 2 has two Electrostatic panels per side. The Model 2+2 has 4 panels per side that are vertically stacked. There are also models with anywhere from 1 to 8 panels per side. The models with with 6 or 8 panels have 2 interfaces per side.

    I have replaced the 5 Amp fuses in my Spectra 22 interfaces with solid copper plugs. The fuse holders in my Model ones are currently filled with 5 Amp fuses. I suggest 5 Amp fast blow fuses for your interfaces. The fuse holders are adjacent to the AC power input cord and accessible without any disassembly.

    Acoustat ESL's can safely be driven by any amp in existence. They are extremely difficult to blow up as the driving voltage from the amplifier goes through the interface transformers and applies voltage variations to the stators. No drive voltage or current ever goes through the electrostatic membrane itself.

    If you give the approximate dimensions and appearance of your speakers it would be easy to tell exactly what model you own.

    If I can be of any help at all please contact me through this forum or by email.
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  8. #8
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    Over at theaudiocircuit.com there is a wealth of information about Acoustats mostly provided by Andy Szabo, who worked at Acoustat. He tells the story that originally the Acoustat Magne-Kinetic interface used 3 amp slow blo fuses. But then Acoustat got fed up with all the complaints about people blowing the fuses for no good reason, so the value was upped to 5 amps slow blo. Unfortunately, the 5 amp fuses are not very good protection. You can still burn out the transformers from overheating by playing loud music for an extended time. The 5 amp fuse might protect you from amplifier failure or something like that, very high power for a brief period, but won't protect you from high power over an extended period.

    This was all theoretical to me until two weeks ago. I burned out one of my interfaces after playing some rock for a rock enthusiast who loves louder, louder, loudest. These transformers are virtually impossible to replace. Custom made after years of tinkering with the design, no one knows the secret recipe anymore. The panels are virtually indestructable, so it's always the transformers that fail, so everyone with a bad speaker wants one. Fortunately for me, Sound Values just happened to be clearing out truckloads of junk from Hafler/Rockford on ebay at that time. I managed to snag both a NOS LF transformer and a whole new NOS Red Medallion interface (just like mine). You probably won't see stuff like that on ebay again. It's rarer than unobtanium. And I paid high prices. I could have a pair of used speakers for the price of that one interface. The only other way to get a transformer is to buy someone else's working speaker, but usually they're sold for pickup only from places like San Francisco or Florida, not good if you live in Texas. Also there is a guy in Florida (go to The Audio Circuit to learn more) who does or did repair interfaces, but the latest word is that he's getting hard to get ahold of.

    So be very careful. And I would strongly advise against bypassing the fuses, but since they're not much protection anyway, maybe that's OK if you're careful. If you're worried, use the 3 amp fuses for better protection. Unlike Quad ESL's, acoustats will play very loud, like 100dB peak (measured at my 6' listening position), but don't push your luck with that for too long like I did. Try to keep them at moderately loud levels, not headbanging levels. Actually the speakers sound better at 90dB peak because there is less compression. When they play too loud, they lose their bite and clarity. Even to reach 90dB, you'll need a good amp with 200+W/channel. It's claimed that you may be better off with a higher power amp than a lower power one, due to less HF clipping. However, with my Krell FPB 300 (which has 600W+ into 4 ohms) I don't get clipping which makes it alll too easy to play louder and louder and then too loud. A lesser amp wouldn't let you get away with that. My Parasound HCA-1000A (200W into 4 ohms) shuts down after playing 90dB. That may be safer for the speaker, but who wants that? My evaluations are done with the 2-panel 1+1's. Ironically if your acoustat has more than 2 panels, it needs less power for the same level and (depending on transformer setting) can play louder.

    What these speakers should have had, IMO, was a thermal sensor that directly sensed the temperature of the transformers and shut the speaker down if they got too hot.

    One of Jim Strickland's greatest achievements (he wrote a paper about it) was designing a virtually indestructable electrostatic panel for the Acoustats, and that could play loud enough to satisfy most audiophiles. Unfortunately, he didn't pair it with a transformer interface that was equally indestructable. Although, back in the glory days 1980-1990 there weren't quite so many behemoth amplfiers that could actually break the transformers.

    One more thing, if you've overstressed the LF transformer like I did, it may not break completely right away. It may start blowing fuses at lower and lower levels as some insulation breakdown voltage is reached. Then eventually the transformer opens, and you get no bass. It's funny that this behavior is a somewhat like the old Quad ESL 57's die, with some panel arcing at lower and lower levels until it won't play at all. But for me it only took about a day and two blown fuses for the LF transformer to die completely. Then it no longer blew fuses, but had no bass.

    But they're so good when they're working that you'll do anything to keep them that way.
    Last edited by Charles Peterson; 03-25-2009 at 07:31 PM.

  9. #9
    Phila combat zone JoeE SP9's Avatar
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    Hi there Charles;
    If I may be presumptuous. Thanks for the tip about blowing transformers, although I'll probably never have that problem. The Krells on my want list are the old KSA-100's. The 200WPC into 4Ohms they put out would probably not be enough to blow the trannys. The interfaces on my Spectra's say 5A for the fuses. I put some in as soon as I read your post.

    Two things are in my favor. Sustained levels of 100dB are to loud for me. +100dB peaks are fine. The second thing in my favor is bi-amping. I run mine from 75Hz up. If I ever did blow the transformers I would do just about anything to get my "stats" working again. The only speakers I like as much or more are much more expensive.
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  10. #10
    Forum Regular MrAcoustat's Avatar
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    The best fuse is NO fuse

    Hi i have owned Acoustat's for more than 25 years i presently own my third pair of 1+1s i also have owned 2+2s Spectra 22s and Spectra 33s i have ALWAYS bypass the fuse why because the best fuse for Acoustat's is NO fuse just use what you have on your shoulders.
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  11. #11
    RGA
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    Almost two full years old Mr. Acoustat. A little late I think.

  12. #12
    Forum Regular MrAcoustat's Avatar
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    Quote Originally Posted by RGA View Post
    Almost two full years old Mr. Acoustat. A little late I think.
    No sir, it's never to late for info, i learn every day.
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  13. #13
    Phila combat zone JoeE SP9's Avatar
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    If this thread was about HE speakers or Audio Note gear RGA wouldn't have posted that comment. We would have been inundated with a wealth of information and opinion about HE speakers, Audio Note gear and SET's
    Good to know you're still out there MrAcoustat.
    ARC SP9 MKIII, VPI HW19, Rega RB300
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  14. #14
    Music Junkie E-Stat's Avatar
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    Quote Originally Posted by JoeE SP9 View Post
    If this thread was about HE speakers or Audio Note gear RGA wouldn't have posted that comment.
    What does the topic have to do with his obligatory posting about AN ? Or how he hates Magneplanars? It could be about toenail clippers. Over at AA, the topic was "Audio Shows" and he worked in both themes here.

    rw

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