What kind of power wakes up electrostatic speakers

Is it wpc, high current, both or what? I've been aud-itioning amps with the Final Electrostatic 0.3's (86 db sensitivity). The manufacturer suggests a minimum of 50 wpc to get them going. So far, I've tried a Nakamichi Stasis (150wpc) and an Electrocompaniet AW250DMB(250 wpc).With both,the speakers sounded dull, yet the Parasound HCA 3500 (250wpc & high current)made them sing sweet as can be.
Could somebody be kind enought to explain to me how this stuff works. I need to purchase an amp to drive the Final 0.4's (the big brother to the 0.3's). I'd love to know what
to look for.
I appreciate in advance your help. The source for this
was a Pioneer PD S95.

Welcome the the world of 'stats. I will never go back to boxes, but we stat owners need to do our homework.

These speakers present a widely varying impedence load to the driving amp, often down the sub 2 ohm range and want lots of voltage to play at louder levels. I have had a sunfire amp (300 wpc) hooked up to my actively crossed over Innersound Eros but found the best match was Innersounds own amp designed for ESL's specifically.

I heartily reccommend jumping over to www.innersound .net and checking out thier white paper on ESL amps. Furhter down be shy about calling the company and talking to the designer, Roger Sanders, who pretty much wrote the book on ESL design. Shoot every time I have called, he is the guy answering the phone.

His amp has loads of power and is quite reasonably priced ( for high-end audio!)

Happy listening and welcome to the "club"

Hello, I think you may need a Berning ZH270, stunning with electrostatics, believe me I know first hand :)

The ZH270 handled the load of my Soundlab Pristine II's with ease to moderately load volumes with outstatnding sonics and musicality.

Check the forum archives here and read up about the 270 with electrostatics and other fine speaker designs, this amp is world class.

Best of luck,

Ooops! A typo. The Parasound HCA 3500 is 350wpc.
Greetings Steakster -

Congrats on you Final purchase! That's one of the few electrostats I haven't heard.

First of all, the Nakamichi Stasis is prone to going into oscillation and self-destructing when driving electrostats. Nakamichi skimped on the output transistors and didn't use the ones designer Nelson Pass specified.

The thing an electrostatic panel likes is a high voltage amplifier. Don't worry too much about the ultra-low impedance at high frequencies (unless your amp is oscillation-prone like the Nak), as there is very little energy up there. It's the high impedance at the lower end of the panel's range, plus the capacitive load, that gives many amps a severe pain in the output stage.

Nearly all of the speakers I sell are full-range electrostats, and by far the best bang-for-the-buck amp I've found is the InnerSound ESL amplifier (good call, Bart!). If you don't have a local dealer, shoot me an e-mail and I'd be happy to arrange a no-risk in-home audition. By no-risk, I mean if you don't like the amp, you won't even have to pay the return shipping.

Best of luck to you in your search!

Arrrgh - sorry for posting again, but I deleted a paragraph to rewrite it and then accidentally posted instead.

What I wanted to say was that there are a number of tube amplifiers that also work quite well with electrostats (some of which I sell), and there are a few that don't. It seems to me that the most critical factor is the quality of the output transformers - "budget" or high watts-per-dollar tube amps usually don't work well with electrostats. OTL's often work quite well - I got good results with the Berning amp mentioned, though in the end I chose to carry a different brand. Also, very high current and/or Class A solid state amps generally work quite well.
Hi Duke: As usual, your response(s) are informative and to the point. My question to you is, what specifications should us 'stat fans look for in an amp? The 'current' rating should be ..... or above? The 'voltage' capability should be....or above? TIA.
I can't speak from personal experience, but some seem to like the "Sim" gear with stats.
Back about 15 years ago ( WOW, was it really that long ago ??? ), J. Gordon Holt found that the only two SS amps that he had tried that could drive Acoustat's well were the Acoustat TNT-200 and a Threshold. I will second that nomination and also add Perreaux to the list. Whether or not any of these amps are to your personal liking in terms of sonic characteristics may be another story though. Sean
The Acoustat TNT-200 has been upgraded and is now the Hafler 9505 DIABLO. It was designed by Jim Strickland who designed all of the Acoustat products made in USA. I have been using a 9505 to drive my Acoustat 2+2s for several years and have no complaints. Don
it's the volts!(watts = amps x volts) Look at the power supply rating on the amps you auditioned and that should give you your answer. -aj
May I join this discussion, since I am a proud owner of Martin Logan Prodigy ESL.
I have recently upgraded my amps and use now two Wolcott tube monoblocks for the panels and have adapted two bridged Bel Canto Evo 200.2 as monoblocks for the bass woofers. Now I have the best of both worlds: Giagantic mid range and treble, plus a bass which finally has body, but is not boomy.
If you cannot afford the Wolcott amps, I would definitely look into the new Bel Canto Evo 200.2.
I had the older version (which serves now for the bass) driving the whole Prodigy speaker and I was very amazed from the sound I got. And you can get a pair of the older Evo 200.2 for less than $3000 per pair here at Audiogon.
They have plenty of power (up to 800 watts, short term) in bridged mode to drive your speakers. I would not suggest just one Bel Canto stereo amp. They really only shine in bridged monoblock mode.
whoo hooo... Prodigy's with Wolcott's! that must be one sweet sound! -aj
It's really not watts or amps but volts. ESLs are mostly voltage driven devices. However, there is a reactive impedance due to the fact that they are really just capacitors (impedance drops with increasing frequency) that are driven by transformers (voltage step up devices).

Since there is a characteristsic impedance, but one that is reactive - it turns out that in solid state amps it is a good idea to have a large SOA (safe operating area) and a stable design so that the amp doesn't barf on the wierd phase angles and implied current/voltage lead/lag.

In order to move the diaphragm almost only voltage is required - however in practice there is some current wasted in the process. This is why tube amps can be direct coupled to the stators in some designs, even though the plates are actually very high impedance. Current not really required.

For various reasons, imho, there are few solid state amps that shine on ESL loads, while tubes of sufficient power (read power = voltage swing) can often give superior results in the midbass...

There are only a few different variants on the drive transformer circuits used in ESLs. Notoriously bad are the original ML CLS with a nasty dip down into the 2 ohm region, making them a tough to drive speaker in general. Depending upon what the manufacturer of your speaker did in the drive circuit (and there are only a few choices for full range cells - full range cells being like CLS, Acoustat, not Quad 57)you could have a nasty, low Z load to drive. That makes it very hard for all but the very biggest amps to handle, and that narrows the field so much that you may have a hard time finding one that also sounds good.

If you want to do some research look into the patented drive circuit for the Acoustats - it solved this problem very nicely. One can use it for personal use without violating the patents, btw...

For some ESLs it can be a problem to find an amp that will drive the speaker and sound good doing it for the above reasons.
Hahahah... Bear, you bring up a very good and interesting point. It is quite possible for an amp to drive a difficult load like a walk in the park, but the bottom line is, does it sound good doing it ??? : ) Like everything else in life, there are a LOT of factors that add up to make the big picture, not just one or two. Sean
If you are looking for a amp designed for electrostatics the Innersound amps are made for this . They have a Kilowatt Monobloc rated at 1,000 watts at 8 ohms that will really wake up your speakers. WWW.Innersound.net They also have smaller rated amps too.
Tweety speaks the truth! and whoever heard of ESL's at EIGHT ohms, so just THINK of the possibilites!
Innersound also has a electrostatic amp at 2,000 volt-amps at $3000.00 which is a lot less money than the kilowatt monobloc hope this helps
The Innersound amps are pretty nice for the $$... you might
research their heritage though...

There are several ESLs with a benign load impedance curve. The Acoustat stands out as one without any dips below 6 ohms. It all depends upon the drive circuit. I think the Audiostatic has a patented circuit that has similar benefits.

The issue is where do you match the "cells" along their 6dB/oct slope from low freq/high impedance to high freq/low

The idea is to NOT match them at one point but at at least two, keeping the impedances in hand... that's what the better full range panels do. The multiway ones (Quad 57) do that automatically...
Bear, i have seen impedance charts for Acoustat's that show a dip below 1 ohm at appr 10 KHz. From other charts that i have seen, this is pretty normal for a LOT of E-stat's. While the dips may not be quite as extreme or at the same exact frequency, they all tend to frustrate amps at high freq's. The saving grace of all of this is that there is not a ton of recorded info up that high and what is recorded is not of a high current demand like low freq's.

I would also think that a speaker with an impedance of 6+ ohms ( even with a reactive phase angle ) would not be too tough for a decently built amp to deal with. The fact that Acoustat's put MANY, MANY amps to shame and can suck most "high powered" monsters dry somewhat contradicts your previous statements. What i'm trying to get at is, what info did you base your nominal 6 ohm impedance figure on ? As mentioned, i'm going by the test measurements that i've seen and the experiences of more than a few Acoustat owners. Sean
I'm using a Innersound esl amp to drive my Magnepan 1.6's and with good results. Before I bought the Innersound, I was using a Odyssey Stratos amp. The Odyssey was quite neutral, but at the same time, compressed the soundstage when pushed at higher volume. The Innersound compared to the Odyssey exhibited tighter bass control, unrestrained dynamic swings, more air around voice and instruments, better micro and macro details, and overall better control of my speakers. I haven't looked back on my purchuse of this great amp from Duke at Audio Kinesis. I'm in no way affiliated with Audio Kinesis or Innersound audio, but rather a very happy owner of the Innersound esl amp! Thanks again Duke!
Sean, which Acoustat?? All of the Acoustats that used the 121 type interface - that included the II,III, IV, VI, VIIs
absolutely do NOT have any impedance dip below 6 ohms. I am not convinced that any did, unless they stopped using Jim Strickland's patented "bi-former" interfaces with the last of the breed - the hybrid Spectra series stuff.

This is the published data for those speakers. My own tests confirm this. Indeed it is the basis for the patent.

As far as the Acoustats "sucking" amps dry is more due to the large voltage swings required for peak output, and deficits in those amplifiers' design. Since ESLs tend to have lower distortion than many cone speakers, the onset of
"distress" is easily heard.

On the other hand, I know at least one person with a very nicely done 35 watt tube amp that drove them with no trouble at all.

Quite a lot of people ran them with receivers too - as long
as you didn't stress the amp (play too loudly) they sounded pretty much ok.

So, I'm not sure what sorts of problems you've encountered with Acoustats - again if it is the later "Spectra" series, all bets are off, as I have no idea what they ended up doing towards the end of the product's life.
I owned Acoustat IVs for many years. Anyone interested in electrostats should visit this site:


It contains all the original information on virtually every electrostat ever made. It includes a copy of the original paper "The technology of full-range-element electrostatic loudspeakers" by James Strickland, President of Acoustat Corporation.

This paper includes a discussion of the interface and amp requirements. It also shows the impedance curve for the Acoustats which dips to 3 ohms.
I'm very happy with my Mcintosh MA-6500. It sounds great, has more than enough power, and great features. The MA-6900 is another good one to consider.
Bear, i'll see if i can dig up the info on that specific Acoustat. As to running Acoustat's with receiver's, we've all seen systems that worked but were far from optimized. In fact, i think that most of us still own them : )

Pls1, while i haven't had a chance to look at the Strickland paper that you mentioned, i have seen that website. It is a wealth of information for fans of E-stat's. Sean
Bear and Sean, the paper I referenced on that website shows the impedance curve for the specific MK 121 interface as well as the details of its implementation. The impedance is below 6 ohms except for the frequency band between 500 and 4000 Hz.
Yeah... and I looked around for my original brochure and can't seem to find it...

If the curve is the same, then it would explain a lot about why some amps don't do well on the Acoustats...

My recollection was different, but I have not seen that brochure's file around for a number of years.

oh well, "swiss cheese" syndrome is setting in!

:- )
Try to find some Counterpoint power amps. Unfortunately, they are no longer in production so you might have some trouble locating them but it is worth it.
I have two Counterpoint NPS400's (recently upgraded by Mike Elliott, the designer-- he can be reached at altavistaaudio.com) and they sound great. In my experience, bi-amping electrostatic speakers is really the way to go, because they are notoriously inefficient. High capacity power amps really help the speakers to perform to their full potential.
Bear is right, its current.

I'll probably get some flack here, but driving Quad 989's the Innersound amp sounded , well, brittle - kinda like a Coda amp, who I think makes it for Sanders...

I've seen the Berning ZH270 easily drive a pair of Acoustat 1+1 Medallion transformer elctroststat spkrs - a very tough load. My advice is get the Berning. No big tube hassles either, run warmish not hot, don't weigh much, great reliability - what do you need to know?

If not, and you like SS, the Sim suggestion above looks good.
Respectfully disagree, but no flack. The InnerSound seems to need major break-in. Now usually I'm a little skeptical of all this break-in bidness, but, I personally experienced a break through with the InnerSound after a minimum of about a hundred hours, plus, you need to drive the s**t out of it to get the goodness. Warmer is better. Soon I will carry by InnerSound over to a SoundLab UL-1 owner and we will compare it to some Boulder mono-blocks. Could be interesting.
Try tube amps. The previous owner of my Acoustats commented that his Acoustat seemed more at ease with tube amp of decent size and power. I've tried my Acoustat Model 3 with an Audio Alchemy OM-150 (150wpc) and an Acurus A150 2 stereo amp. The 'stats were more at ease with the OM-150, since it was quite a buiser. I tried my Quicksilver silver mono 90's, and even thought I had less power (some 90wpc), that 'stats were driven with even more ease. No sure if it's the volts, current, or the fact the tubes can just deal with load the 'stats present (better overloading?). I think this helps drive home the point of Jim Strickland's direct drive tube amps.

I you're looking for a big tube amp, try the Wolcott. It was designed for drive ESLs, in particular the Soundlab models.
I have owned stats for 14 years now, Beveridge and Martin Logan. I have made the switch over to tubes and am currently running a Decware Integrated SET @ 7W. Yes, 7W! Gets much louder than it has any right to, not to mention sounding infinately more engaging than the 150W SS amp it replaced. One factor to keep in mind is that most tube amps (Deware is a notable exception) like to drive higher impedance speakers.

Good luck, Paul
Travis, they were sent in for review at the time; they were properly burned in. Coda, Innersound, Boulder are all detailed oriented, energy loaded at the transient-type SS amps - quite similar. Not sure that's a great comparison...

Paul, 7W!!? You've got more courage than me! :0)

Seriously though, Paul, you might find a nice balance with the Berning - and maybe a bit of tube rolling the inputs yo siut.
A friend of mine recently was trying to upgrade the amplifier to drive his Martin Logan CLS speakers, he was driving them with a Quad 606 (original version) and it was sort of managing OK. He was really looking for a substantial upgrade and he tried a Krell 300i which was onsale.

The Krell was not in a position to drive them at realistic levels even at full volume. The Quad somehow was playing much louder and still had room to spare. We were really surprised. Switched his two CD players, three speakers, and the two amps. None of the equipment had any problem including the Krell which was driving the Maggies as well as large dual concentric Tannoy speaker. We were unable to figure out why Krell on Martin Logan CLS sounded like a 25 watter. Nothing made sense to us.

What could be the reason for such low volumes on the CLS? Is Krell 300i a bad match for CLS? Is the power supply of just 400v in Krell not able to cope with the load? Is it the matter of voltage versus current?

Can anyone shed some light on this issue for our better understanding?
Bear - what do you mean regarding the "history" of the innersoud amp?
Hey, Asa, you heard what you heard. I've never heard the new QUADs so no comment. I'm still glad I found the InnerSound for my 3.6s, though.
Scotty: I think Bear meant that one might want to do some research and find out who actually builds the amp for them i.e. Innersound does not build their own amp or preamp. As far as i know, it is built by Coda for them. On the same hand, Coda also builds the amps / preamps for Legacy too. Something about Coda and speaker manufacturers i guess....

Quadophile: While i don't know if the 606 is similar in design to some of the older Quad amps, the use of "current dumpers" helps the amp load in a more linear fashion to speakers with wild impedance curves. As such, the power transfer ( or "apparent volume" ) seems to be more consistent regardless of impedance or frequency. From what i've read about the 606, it appeared to be of similar design to what i'm talking about but with a "beefier" power supply.

Krell and other "brute" SS amps simply respond to the varying impedances at different frequencies in a more mechanized manner. It is possible for such an amp to be delivering BIG wattage at X frequency while only being able to muster a few watts at another frequency at any given time due to the impedance. As such, the output levels won't be as consistent due to the loading characteristics that the amp sees varying so much.

With an E-stat, it is not so much high current as it is high voltage over most of the range. Since tubes are more of a voltage amp, they tend to work pretty well. Only problem is, some E-stats drop in impedance, so they need a lot of current. Finding an amp that can deliver both high voltages AND high currents and do so at any given time and frequency with any level of reactance / impedance thrown at it would put you in "E-stat heaven" : ) In effect, you would have the effects of a tube amp that sees the constant impedance of an output transformer and the current of a BIG solid state amp as it needs it on demand. No simple trick and that is why some of these speakers are hard to find suitable amps for. Sean
Van Alstine makes the 440hc to drive loads from 1 ohm, it uses 12 MOSFETS in the output stage rather than the 8 devices in the regular 440.
I have owned electrostats for around 12 years and found they all like lot's of power, they DONT do well with entry level high power amps. I have Martin Logan Ascents and driving them with two Classe 25 power amps in mono about 1000 watts per channel and sounds great. If you choose tube amps check out Audio Research, VTLboth sound very nice. GOOD LUCK
Travis, sorry so long to get back; forgot about this thread actually. Glad you are happy. Hey, lots of guys with Soundlabs seem to like the new Parasounds. Maybe you might like those too on the 3.6's? Just an idea down the road if you get the itch...
From what i've been told, both Sound Labs & Martin Logan ( as companies and manufacturers ) have ordered or already have the new Parasound JC-1's in their reference systems. As i mentioned in another thread before, if i had the money, i'd have a pair of these mono-blocks too.... : ) Sean
Sean, I have the Martin Logan Odysseys which replaced the Ascents.I ran a Pass Labs X250 with both and still have it for the Odysseys. I called Martin Logan the Other day to ask about amp's and the new Parasound JC-1 and they told me THAT they have not ordered or heard the Parasound JC-1 on there speakers. When i told them people were saying that the company ( Martin Logan ) had these amps on order they said that they do NOT have them on order at all, and didn't know that much about them?? They did by the acknowledge the other amps i had mentioned and even gave one a compliment?? Just A FYI.
Hmmmm.... Thanks for the info Btstrg. I'll have to check with my sources and see what the deal is. Sean
You need high current for the reasons Audiokinesis so aptly stated above. However, high voltage is necessary as well and that is why tubes generally are a good match with stators, as Sean so rightly points out. The Innersound amps, though a little roughshot in their interpretation will do well, so do the Wolcotts with their better transformers, if not so much in the highs, defenitely excellent in their bass rendering and if you want to spend some more, the Jadis 200 is wonderful and liquid on most stators and if you want to go SS, the Spectral 360, but also their old 200 are both dynamic as well as refined. And yes, before I forget, I have an ancient Threshold Stasis, still made by Nelson Pass, the man, before Nakamichi gave Threshold a bad name and that drives Quads, Staxes, Sound Labs and whatever stators you throw at them beautifully...and it is more than 20 years old now and never saw a technician so far. I use it every time, one of my other amps decides to give up its ghost with excellent effect. It set me back $1800 at the time when I bought it. (I've just sold my Gryphon Referenes, which were just so so with stators, as well as all the Krell and Levinson stuff I auditioned with them, but I'll never part with that one. I love it.)
As I understand, switching amps (such as Bel Cantos, Spectrons or Ps Audio HCA-2s) are very load insensitive. Does anyone have any actual experience though?
I don't know about the Bel Canto's or Spectron's but the PS HCA-2 does not respond very linearly as impedance is changed. Both frequency response and distortion are effected as impedance varies. Sean
Yesterday I was at the friends place as he invited me to listen to his new find. I was surprised to see a vintage Sansui Au-111 tube amp which was glowing and driving the CLS in a way which was shocking. This combination was so far the best we came across. I was accompanied by another friend who is actually into the bottles (Cary 2A3, Alon Adrianna's, Wadia 850) and he too was very impressed with the sound that was coming out of the CLS.

Now the friend with the CLS knows which direction he needs to go. Tubes and nothing else.

Meanwhile the Sansui which is a vintage model circa 1965 is under servicing and cleaning, including changing to new set of tubes. We will have a go at it again and see what the results are.

I thought I should update my finding on this thread.

Sean, if you are reading this, thanks for the detailed explanation. I appreciate it>
Btstrg, I spoke with Dennis Chern of Martin Logan this afternoon and they just got the JC-1s hooked up last week in their ML reference system and he just listened to them this past Tuesday and just loves them....He said fine to quote him BTW :-)
To corroborate what Bob stated, ML is in fact using the JC-1's as their reference amplification within their test lab / listening room. Even in a large room, ML stated that these amps are fully capable of providing any SPL range that they desire and can do so with absolute control and do so while sounding superb. Sean

PS... I posted this not to jump on the band wagon, but simply as a "witness" to verify / support the statements being made. Some might feel that such information was tainted coming from Bob or that Bob was blowing his own horn. To clarify things, Bob was involved with designing the amps, primarily selecting the individual components used to voice the sonic signature of the amp. For the record, i do not own or sell any Parasound gear or the JC-1's in specific. Having said that, i would like to own a pair of these amps and am accepting funds on a donation basis so that i can afford to buy a pair or two : )
By the way, Innersound told me that their ESL amp is indeed a "switching" amp. That's why it runs so cool. How does this relate to switching amp's generally poor capability to deal with wide impedence ranges? Clearly the ESL handles this kind of variability fairly well.
That's a new one on me. My two ESL amps run very, very hot when I'm cranking the 3.6s, impedances are low but flat. Another friend drives his EROS MKII panels with an ESL and plays the music very loud. The amp runs cool. Another friend runs Clements RT-7s (ribbon tweeter, cone woofer) with his ESL and the amp can get warm, but not hot, with loud volumes.