Class A, AB

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.

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

Surely an amp that is capable of operation to 75% of power in Class A is much more expensive to build than one that runs only Class A to 5% of same rated power.

Why does it not matter or am I missing something?

From a Plinius manual:

"The Plinius [model] power amplifier operates in class A and is therefore capable of generating a moderately high temperature..."

Later in the same manual referring to the toggle switch I referred to:

"...A/B position reduces the bias on the output stage to operate in class AB. This is a bias configuration used by the majority of High End amplifier designers for their products."

Sounds to me like it operates in class A as well as A/B.