Accustic Arts Power 1 - operates in Class A?

To the best of my knowledge (as I recall speaking to the people in Germany), their top of the line amps are biased for a few watts in pure class A. Your lack of additional wattage draw registration from your PS Audio is due to the amps' massive storage energy bank, and perhaps the relatively benign load of your speakers. Just my two cents.

Best regards.

Csontos, I don't know. Things I've read apply to bipolars only. In my opinion it should also apply to Mosfets but design might be completely different possibly equalizing gain. Assuming that overbiasing of Mosfets might reduce distortions the question would be "by how much". The main problem I see with class AB is that because of inherent nonlinearities feedback is usually 10x deeper than one in class A amps. This feedback might create odd order harmonics because of Transient Intermodulation. Once you have this feedback set in your amp by design changing bias won't help TIM. Your improvement in distortions might be miniscule and not worth the heat dissipated not to mention possibility of increased distortions if we got it wrong. Increasing bias current and heatsink size seems to be inexpensive proposition and if designer decided against it I wouldn't touch it.

What I've done is reduce it slightly to around 290ma from 300. The thread I'm referring to concludes it's not quiescent current that matters but instead the voltage drop across the emitters is the important number. So optimal bias with bipolars may be a reduction in current after all. But the mosfet amps I have don't have emitters and must be biased at the rails.