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stokessd 25th March 2003 03:36 PM

Best amp choice for driving NASTY speaker loads
As some of you may know, I'm a big fan of electrostatic loudspeakers. I've been repairing the Quad ESL and Quad ESL-63 for about 10 years now. Last fall I finally got off my butt and built a set of hybrid ESL's which are quite satisfying. The problem is that they are very nasty reactive loads; see:

I've been a tube and tube amplifier fanatic for quite some time (with forays into solid state design). But with the amazing resolving power of these speakers, I'm hearing colorations in my source components like never before (the quads come with rose colored glasses, so tubes tend to be a bit more of the same). I'm now thinking that a low distortion, but polite solid state amplifier would be just the ticket.

I have been using a set of rebuilt Heath W5M's on the panels, and a Pass Aleph 3 on the bass modules (I know, it's a crime to use such a great amp only on the bass).

Currently the Aleph doesn't sound nearly as good on the panels as the Heaths (or citation II or Citation V) or a first generation Adcom 555. I've used the Aleph on less nasty loads and I know it's an amazingly good amplifier, that should be at the top of that list.

So my question is, given my nasty load situation, which pass design (or amplifier design in general) would you guys recommend?

I have been seriously thinking of the Citation 12 design (I've already got a citation 12 earmarked for it); it looks like it would be stable into reactive loads, has a simple short signal path, and strikes me as an all around good design.


SY 25th March 2003 04:20 PM

It doesn't look THAT nasty; no dips to 1 ohm or weird drive angles. That 555 ought to work very well indeed.

What kind of voltage does it take to arc the panels? If they can take more than the Quad, this might be a good candidate for a Circlotron-type OTL. Or you can wait until summer, when my direct-drive ESL amp is up and running and try that out...

jleaman 25th March 2003 04:22 PM

I think that i will be contacting you tonight to get some questions answered. Id like to try to build a pair of these Pannels.

roddyama 25th March 2003 05:25 PM

I think I remember comments on the forum that the Pass A40 did a good job on electrostats. I'll try a search and see what I can find.

Rodd Yamashita

peranders 25th March 2003 06:01 PM


Originally posted by SY
It doesn't look THAT nasty; no dips to 1 ohm or weird drive angles. That 555 ought to work very well indeed.
Exactly, what is nasty about this curve? Any normal amp should be able to drive this speaker.

dhaen 25th March 2003 07:03 PM


No advice, sorry, just some comment:


I've watched your pages for a year with interest, and learned a lot. Thank you.


I'm "all ears" for your ES direct-drive system. I'm sure it'll be worth the wait.


Nelson Pass 25th March 2003 08:31 PM

I don't consider electrostats as nasty loads. They do often dip to a low impedance above 10 KHz, but the energy up there is low enough that it's not a problem for a stable amplifier.

Electrostatic speakers do want voltage, however, and it's usually wise to have a reasonable 8 ohm power to get them going.

ultrachrome 25th March 2003 10:39 PM

I notice some amps claim doubling as the impedence is halved while other amps don't quite double.

Going by this alone, which amp would be better suited to an ESL load?

Curiously, Mr. Stokes didn't like the Aleph 5 on his ESL. What could be done to an amplifier design such as an Aleph or Zen to make it more sound better with ESLs?

I'm a bit confused by all of this so much so that I don't know how to ask the right questions let alone understand the answers.

stokessd 26th March 2003 12:32 AM


The load is almost entirely reactive (inductive at low frequencies, capacitive at higher frequencies). I had a fellow Albuquerque Speaker Society member bring over a big pair of Cary SET's and they sounded awful and at higher than quiet levels it sounding like it was clipping badly. Don't let that smoothly rising and falling impedance lull you into a false sense of security, those things really are nasty to drive.

My panels have 1/8" stator spacing and powder coated stators, you can't push enough power through them to arc. You've got 3mm Xmax and the same Sd as 24 8" woofers. This isn't your dad's quads. :) I'd like to see what you come up with in the ESL amplifier department.


yes, you'd think any amp would drive it, but lots seem to have problems.


Compared to your ionic speaker, I'd say ESL's are a walk in the park. Interestingly, these ESL panels are about 90 dB/watt at one meter. Looking at the speaker inputs with a scope, even my 20 watt W5M's drive them to a lot louder volumes than I need before the amps clip. But you are right, tube amp damping factors are crappy at best, and I can't help but think with such a reactive load, the more control I have over the speaker the better.


I have an aleph 3, and it sounds veiled and rolled off at the top end. Before I had the shunt resistors on the speaker to tame the rising response, the aleph 3 would sound like it was clipping at low to moderate listening volumes.

That's the problem I've got, the aleph designs are great for cone and domes (or at least all speakers which aren't mine), and if my aleph 3 is an indication, that topology isn't working so well for me. So I've got to head down a different path.

Thanks for all the inputs.


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