Sounds like you are talking about two SS amps, so probably from Pass but that is just a guess.
To your question, the Class A amp will likely have a stiffer power supply and more capacitance. Also, IME, I like the sound of Class A better since to me they sound more fleshed out than the best AB amps I have heard and so may sound more harmonically complete when pushed. A last observation based on experience is that really good Class A amps do not get strident sounding as Class AB amps can when they are starting to get stressed, the Class A amps simply run out of steam - at least that is how the two different sets of Lamm hybrid monos I owned used to behave. My 300 wpc Class A Claytons have yet to run out of steam, even driving my new lower-efficiency (85dB) speakers.
To George's response, my listening has resulted in a preference for bi-polar output stages vs. mosfets. I believe some designers use mosfets to try and emulate a "tube sound" but to me they do not control the output as well.
To your question, the Class A amp will likely have a stiffer power supply and more capacitance. Also, IME, I like the sound of Class A better since to me they sound more fleshed out than the best AB amps I have heard and so may sound more harmonically complete when pushed. A last observation based on experience is that really good Class A amps do not get strident sounding as Class AB amps can when they are starting to get stressed, the Class A amps simply run out of steam - at least that is how the two different sets of Lamm hybrid monos I owned used to behave. My 300 wpc Class A Claytons have yet to run out of steam, even driving my new lower-efficiency (85dB) speakers.
To George's response, my listening has resulted in a preference for bi-polar output stages vs. mosfets. I believe some designers use mosfets to try and emulate a "tube sound" but to me they do not control the output as well.