Class A, AB

Neilmc , if the amp is AB it will be class A (does not go into cutoff) to a certain point and above a certain power the amplifier will operate in the 'B' region, IOW part of the amp goes into cutoff as the waveform amplitude increases. There is no such thing as combining Class A with Class AB- such an amplifier is by definition Class AB only.

Class A means that at no time during the amplification of the signal does the amplifier or a portion of the amplifier go into cutoff, such that only a part of the circuit is handling the signal. All single-ended amps are Class A BTW.

"...There is no such thing as combining Class A with Class AB- such an amplifier is by definition Class AB only."

I beg to differ. I believe quite a few Plinius amps do exactly that, i.e., combine in a single amp either class A operation or class A/B. Which modality one employs/enjoys at any particular time is up to the end user via a simple toggle switch. In my mind, that is a simple yet monumentally significant design feature which even taken alone, shoots the Plinius amps way out in front of their competitors. Hard to fathom why it is not a more universally adopted design.

My Crown D-150 is described as a class AB + B. Which means, I guess, that it is a class AB up to power point and then switches to B.

Salut, Bob P.

I too have Class AB amps that run in class A mode until two-thirds power then run in AB mode. I a not sure of the design principles used - perhaps a sliding bias or the final ouput stage only goes to work at the higher operating range....

Maich, if you were describing two independant amplifiers in one chassis that somehow both drove the same speaker without blowing each other up then you would be right. Personally I've not heard of such a thing. The definition of Class AB is: Class A to some given power, it might be 5% or 75% (doesn't matter), and then 'B' operation after that.

Your amp, Inpepinnovations' amp, and Shadorne's amp all fall within that definition. There may be some nuance - Class AB1 or AB2, but they are all Class AB.

In recent years some companies have sold 'enriched AB' amplifiers, claiming a high level of A operation, but what you have to get about that is that that is marketing. 50% Class A operation is unusual, and I think an amp company would have to come up with *something* to point that out, so I am not saying that this is misleading on their part, but it can cause confusion with the market.