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Is there an actual difference between AB and A/AB ?

Almost all high end linear audiophile power amps which are not pure Class A sell some story about being Class A up until a certain power output, then switching to AB.

Excuse me, but isn't this actually AB to start with?

The whole point of AB is that you run with some bias current to prevent complete transistor shut off at the crossover frequency. This whole "our amp is Class A up until n watts" seems like hype.

Am I wrong?

Best,
E
erik_squires
atmasphere's avatar
atmasphere
11,841 posts
 
No- you got it. If its not class A, then its AB (or in some rare cases, B). There is also AB1 and AB2 (which mostly applies to tubes depending on whether grid current exists in the output tubes during part of the waveform).
But there is no such thing as A/AB; that is strictly a marketing term.
tomcy6's avatar
tomcy6
2,597 posts
 
Are you saying that amps like Pass Labs do not  operate in class A up to a certain wattage or are you just saying that those amps should be called AB not A/AB?
stevecham
3,340 posts
 
It’s simply the bias on the output devices that determines the level of power afforded in Class A. Such bias allows, or not, whether the output device can swing a given power level through the entire 360 degrees of the duty cycle. The limiting factor is heat and this must be managed effectively, otherwise, the device will fail, sometimes catastrophically.
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