Acoustat Electrostatic spearkers

I sold them, it wasn't until much later that a few guys figured out how to make the OTLs stable

Uh yeah- that would be me... FWIW (one of Atma-Sphere's claim to fame was the first reliable OTL).


Sure- just don't exceed the phase margin of the amplifier when you design the feedback loop (this is really all that was about, and it really shouldn't have been me that solved this, as its standard control theory which has been around for a very long time, and this rule applies to any tube amp or traditional transistor amp!). That was the Achilles heel of many OTLs. The designer(s) tried to get greedy in an effort to send the output impedance down, but the price for that wasn't worthwhile. However, OTLs don't need feedback to drive the Acoustats quite nicely! A good friend Frank (RIP) had a set and I heard them many times.

I still own 2+2s perhaps for another three weeks or so until the Sound Labs arrive. I actually helped design the frame for the Monitor 4s (long story) 6's are not two pairs of 2+2s. They are two Three's stacked one on top of the other. Unless you have a very powerful amp capable of handling low impedances you do not want to parallel the interfaces. That would be asking for it. The intent was to use two channels of amplification per speaker. You are supposed to use a stereo amp behind each speaker instead of a mono amp. Put subwoofers under them and you'd be rocking for sure. 
Once I recover from the expense I plan on getting a pair of Atma-Sphere MA 2's. Our friend here would need 4 of them. Imagine that!

Roger Modjeski (Music Reference, RAM Tubes) very much liked the Acoustat drivers, but considered the company's interface transformers junk. He designed and built a replacement, but unless you already own a pair that is academic; Roger left none behind when he died in late 2019.

@bdp24 That does not sound like it would be all that hard to come up with something. People have done that successfully for the Sound Lab.

He designed and built a replacement, but unless you already own a pair that is academic; Roger left none behind when he died in late 2019.

Actually he did leave one behind. It was his personal unit and it's sitting in my living room. This one was designed for use with Roger's own ESLs. He did build some for a group of Acoustat owners (in Australia IIRC) as well. I have the Model 2 speakers and use the Acoustat servo amp with them. I wish Roger could have done the tube input mod to it but he ran out of time. There is a company in the Netherlands that will do this but I'm not inclined to send the amps over there.