Pass Labs XA30.5 and ModWright KWA150

Because it might still sound great with an autoformer. For instance, it is still a Class A, triode amp. But I do agree with the general idea (not based on any technical knowledge at all)that there is some dissonance in the idea of using an autoformer when you have purposely decided on an OTL amp.

I agree with all of the statements about using an Autoformer (I don't use one and this is one of the reasons I went from M-60's to MA-1's) with Atma-Sphere amps.

When I ran tests with and without the Speltz Autoformer, I could always pick out when the Speltz Autoformer was being used. Anybody who tells you that it doesn't have a sonic signature is definitely fooling themselves - it is there.

However, Atma-Sphere amps + the Speltz Autoformer still sound better to my ear than most amps I have tried. The sonic penalty you pay for inserting the Speltz Autoformer isn't huge and is far less significant than the sonic improvement one gets by raising the impedance that the amp sees via the Speltz Autoformer.

George

OP, if tubes are out of the question for you, I would go with the Pass XA.5, it really does not get better than that if 30 Class A SS watts is enough to drive your speakers.

Like Zybar, I have also tried Atma-Sphere amps with and without ZeroFormers. The amps were M-60 monos and the speakers were Silverline Sonata III. Unlike Zybar, I did not find the improvement with the Zero/M-60 combo to be preferable to an entirely different amp (which happened to be a solid state model). The differences were substantial. I also tried the ZeroFormers with the solid state amps as an experiment, and I still preferred the system without the Zeros.

ZeroFormers are something that are system and listener dependent, IMO, which makes the Speltz home trial offer valuable.

All good points Tvad. I tried the Speltz Autoformers with the following speakers:

Vandersteen 5A's
Emerald Physics CS2's
Omega Revolutions (8" Alnico driver)

Ultimately, trying things at home is always the best course of action.

George