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.

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.

Maich, it was not clear to me initially that you were talking about a switch on the amp to change class of operation.

There are a variety of amplifiers made over the years with this feature- we have built a few ourselves.

Generally, when switching to Class AB, the power supply voltage is increased and the bias current is decreased whether the amp is tube or solid state.

However to be accurate, the amp when in the AB mode is that and that only. FWIW most amplifiers have noticeably smoother sound and greater authority in Class A, as distortion cancellation occurs throughout the entire waveform where in AB mode it does not.

Shadorne, I used the example of 75% to make a point- I don't think there are any amps out there that operate with that much 'enrichment' in AB mode.