Spectral DMA-400RS = Class A or Class AB?

AB. Quiescent current consumption is too low for full class A, though high enough that it probably runs class A for 25+ W, more than enough to provide a goodly amount of low-level detail without crossover distortion.

HTH - Don

Don’t really know but would tend to agree. At the same time though, there is also sliding/servo bias.

I am not sure it really matters. One can argue theoretically back and forth, but in the end the practical implementation is what decides. And Spectral is probably among the best and most impressive implementations of solid state technology out there.

My Octave tube amp features both pentode circuits and class A/B mode, both concepts being anathema to some tube lovers. But the implementation and resulting sound are excellent, so I don't care. I did upgrade to the Octave from triode class A monoblocks.