Amp for Martin logan CLS Originals

Atmasphere, you have the impedance thing backwards ;--) The original CLS, CLS I were .5 ohm. The CLS II/IIa were .6 and 1.0 ohm respectively; and the CLS IIz is 1.5 ohm

In all models, this "low impedance" occurred only above 15KHz. Raising it initially resulted from adding a second transformer to the electronics module, starting with the CLS II/IIa. The electronics module for the CLS IIz was a complete re-do and included a more sophisticated crossover network (filter network) and a 'signal sensing' circuit which turned off the high-voltage circuits when the speaker was idle -- a great idea for keeping dust from accumulating on the panels, but a disaster in terms of performance! It takes overnight for an electrostat to fully charge, or "form" -- it's just a big capacitor after all -- so most owners have probably never really heard what a IIz can sound like (unless you keep it playing music 24/7!) People with IIz's who know about this, defeat that function so the speaker is always charged up and ready to go. I never had a dust/smoke problem anyway; and Jim Power at ML said that a dry climate is the most important factor in panel longevity.

The later models were (sligntly ;--) easier on ss amps, but the changes to the electronics module were for the purpose of reducing the high end brightness and improving the upper mid-range. Even with the (1 ohm) impedance increase, you still had to buy an unnecessarily high-powered Krell, Threshold, Bryston, etc. to insure they wouldn't see the low impedance as a short! Tube amps by contrast, can handle shorts, but don't like open outputs (ie, nothing connected to the speaker terminals.)

I actually have a 1992 ML factory memo detailing most of these points, including a recommendation that the CLS be placed on stands.
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Nsgarch you know who atmasphere is right?

No. Why do you ask?

Atmasphere is one of the top 5 amplifier manufactures in the audio industry in my opinion;Ralph Karsten produces tube pre amps and OTL amplifiers for over 30 years.I would find it hard to believe that Ralph would be incorrect in the impedance of these speakers.
Google Atmasphere in St.Paul Mn;Ralph has several good white papers to read and his website in quite informative.

Atmasphere's description of the various models is dead-on right. I was an original owner of the first version of CLS stats, and followed the so-called upgrade path step by step to the CLS-Z. The original CLS was a very easy load for tube amps. I used them mostly with an RM-9 Music Reference, which was a great match, but I also tried them with some Dyna mods (Mk. 4 and ST-70) and they worked great as well. The CLS-II was quite a different story. It had a punishingly low impedance at some frequency due to a notch filter in the crossover. Supposedly it made the speakers more compatible with Krells and Mark Levinson amps, but it didn't like tubes at all. Things got better with the CLS-Z. Unfortunately for me, I was fed up with the CLS by that time. I found I was no longer playing music I liked, just because it didn't sound so good on the CLS. I opted instead for cone speakers that are more universal in terms of music playability, but it is true that the CLS has a special magic on the right types of recordings that none of the cone speakers I've used since then can equal.

Dave