Amp for Martin logan CLS Originals

The CLS 1 (the original) had a high impedance and was a match made in heaven for tubes, even OTLs.

The CLS 2 was an example of Martin-Logan's attempts to make ESLs compatible with transistors. It was very low impedance, 0.5 ohms at 20KHz. Almost any amplifier sounds better on it if using a set of ZEROs to help with the impedance.

The CLS Z and later models do show some moderation with regards to impedance, but still are built to favor transistors.

Its hard to make transistors sound right on a full-range ESL due to the impedance curve. There is a tendency to be weak in the bass and too bright in the highs. As a result many ML owners place the speaker fairly close to the rear wall to try to get back some of the bass, but it is often one-note bass due to the placement (ESLs need to be out in the room at least 5 feet).

But the CLS 1 (which, BTW, it sounds like ML still has parts on hand to build them) is an easy load for most amps and IMO the best of the lot; of course I have a bias :)

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.