Class A Solid State Sound

Generally, there is a small difference between FET type devices and bipolar devices. Sometimes FET devices can have a colored texture to the sound - more of a warm and fuzzy type sonic signature. This is not always the case, but FET does lean this way. The warmth of Pass Labs (and possibly Accuphase) definitely leans this way. I would not say Pass is very warm, but it’s a nice controlled easy listening sound.


Bipolar is usually a lot cleaner sounding (without that warmth influence). Gryphon is an example of this. Sometimes the high bias Class A bipolar devices can present a very smoothed over and liquidy sound (this is also an extreme coloration, but it’s different than the FET warmth). The new Krell sliding bias Class A amps are like this. New Mark Levinson are also very liquidy sounding. There are many others, but I can’t remember them.

I have not heard the amps you mention but I do generally seem to prefer amplifiers that use Bi-Polar output devices, such as Clayton's M300 monos.  One possibly meaningful comparison I have made was when I owned both the M300s and Lamm's M1.2 Reference amplifiers for an extended period of time (i.e., months).  I ended up keeping the Claytons and selling the Lamms but I cannot rule out that my preference may have been due to the difference in power between those amplifiers. 

Thanks for the information about Pass XA, Erik. I also believe the entire design and voicing are what leads to sonic differences. However, even today, I find mosfet based output stages to generally present a smoother, potentially less objectionable sound...just my opinion.

I like talking tech but i don't think attributing a sound to a transistor is useful anymore. 

Pass tunes his amps for high second order distortion and his fans love it.