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 :)

It may well be that the original CLS 1 had a lower impedance at high frequencies. Usually how that behaves with any tube amp is that the amp will be rolled in the highs.

Our amps did not roll off with the CLS 1, the same as with other tube amps, but when you put those same amps on the later CLS models, they all rolled off.

So empirically it is logical to assume that the original model had a higher impedance. Based on this experience, I am inclined to think that ML's history of their products is not accurately portrayed, but if it is, then they had something quite unusual- perhaps an increase in efficiency that compensated for the lower impedance.

At any rate: the CLS 1 was an easy load for tubes where none of the succeeding models were.