Ecstatic Electrostatic

I had the opportunity to spend Sunday with a colleague to audition and experiment a bi-amped system comprising some locally made 5' high electrostatic panels in combination with 8" long throw isobaric subs and 150Hz crossover point.
Amplifiers used were very nice 80W tube monoblocks, IcePower 250W monoblocks, Carver pm-1201 (600W+600W) and an EV power amp (600W+600W) in different combinations.
The tube amps were used only on the electrostatics, and the Carver went into clipping/limiting prematurely when driving the subs, so was used only with the electrostatic panels.
The isobarics are around 4 ohms load impedence, and the electrostatics droop from around 8 ohms at 500 Hz to around 1 ohm at 20 kHz.
The first combination was LF IcePower and tube HF, and this gave a rather nice presentation overall, except for HF response drooping by 1 dB at 10 kHz and 4 dB at 16 kHz, caused by the transformer output resistance.
This gave a very nicely clean combination sound, and the HF droop was not really objectionable but did make the highs a little tameish.
The IcePower monoblocks did not really cope with the low load impedence of the HF panels, and became subtlely but audibly distorted.
The EV amplifier handled the HF rather well and sounded flatter and crisper than the tube amp.
With the EV on the LF, and the Carver on the HF the system could be driven to -3 dB indicated on the Carver before flashover*.
At these power levels in a very large room, we were getting over 120 dBA of the biggest nicest and totally non ear hurting sound that I/we have been near for quite a while.
The very low overall distortion and total lack of any peakiness, belied this pretty high SPL - the power delivery into the room was abundantly apparent but did not sound quite so LOUD as is the manner of a dynanic driver HF section.
Male and female vocal, pop, rock, classical and jazz were all reproduced very pleasingly, and loudly.
Microdynamics are just plainly and clearly audible.

Question is - anybody here have good info on SS and tube amplifier designs and electrostatic panel coupling transformer circuits to help with the electrostatic drooping load impedence characteristic problem ?.
Any info, links, experience or advice will be very much appreciated.


* - really pretty blue flashes. :) :(
Acoustat used a dual trafo setup to extend both ends of the spectrum (also means you can put 2 amps on a single panel -- worked really well with my NAIMs (before a channel went bye-bye).

A lot of good ESL info at the ESL Circuit including a schema of the acoustat setup i got for Hans.

I also always thot that Menno van der Veen's toroidal matching transformers would be worth a good look.

roddyama said:
I think it was Sanders that did a DIY electrostat project in Speaker Builder back in the 80's or early 90's. I'll check back to see if I can find it if your interested.

It was, he also did an extended version in the form of a book. There is also another DIY ESL book as well. I have both of them round here somewhere.

The problem of low impedance at higher frequencies
plagued me for quite some time during my speaker
building. I couldn't find a good solution. I
just used an equalizer to level the sound out and
hoped that my cheap commercial amp didn't complain
with smoke. Roger Sander's book didn't treat or
even acknowledge this problem.

BTW, If you look at Martin-Logan's specs you can
see that they suffer from the same problem.

There are amps that can handle capactive loads
better than others. I'd stick to these if I had
an option.

If you come across a good solution let me know.