Why are most High End Amps class A

Kirkus - Thanks, it makes sense.

the ML-2s were like a high-maintainance chick that looked gorgeous on your arm, but didn't know how to have fun when you got home and turned the lights out.

Kirkus,

How about a design that runs Class A to two thirds power? Is that like a gorgeous chick that also knows how to have fun when the lights are out?

Or like a gorgeous chick that knows how to have fun when the lights are out but doesn't go all the way.

Actually, not a bad analogy, Kijanki. It's just a question of . . . when do you want the bad news? To deliver more than you promise is usually more exciting than the other way 'round.

But with most semiconductor amplifier output stages, the linearity problem around the crossover point in Class B is substantially less severe than the one that occurs at the transition between Class A and Class B operation on an AB amp. If class B operation is thoroughly and rigourously optimized, then its performance will be less dependent on load and output level (which I think is very important), but it doesn't give true Class A performance under any conditions. Again, the particular application makes all the difference.

Kirkus - one of the problems with class AB is required gain to get rid of nonlinearity. Class AB amps have gain (before feedback) of couple thousands while class A couple hundred. Huge gain (before NFB) and delays just invite TIM if input slew rate in not limited. It might be possible to bias amp just a little higher (class A has about 150% of max current) to move the "kink" a little further away and set minimum gain to get minimum spects like 0.1-0.5% THD and IMD and bandwidth of 50kHz. The key, I believe, is compromise without going to over specifying it.

TIM is one of the reason of class AB sound, but it wasn't known until 1972. "experts" in denial claimed then that all parameters of SS amp are as good as tubes and therefore they must sound the same while average person could hear otherwise.