Andre Jute wrote:

You really have to wonder.

Here we have three self-proclaimed engineers claiming that Class A is
an amplification Class in which "the output device(s)never cease
conducting under any signal condition."


Let's see, I graduated Syracuse University in 1978 with a BSEE, so I'd
be an engineer. For class A, I'd add the condition "if the input signal
level doesn't drive the amp into distortion or clipping" to "_all_ the
output device(s)never cease conducting under any signal condition.". I
also added "all" to make it clear that each and every output device
never turns off. I've seen class A amps that had push-pull tubes, each
tube configured to never shut off, thru out the entire waveform cycle.
This would help reduce 2nd harmonic distortions (or have perfect
cancellation IF both tubes have identical characteristics and fed
identical except inverted signals).

Okay, how about class AB? That's usually a push pull configuration
where, at or near zero crossing, both devices are conducting. But get
above, say 10% of maximum input signal level, one of the devices stops
conducting, and the other device is doing the work. Lets also say that
this is a 100W amplifier, if you run it with an input signal that makes
only 1 watt (the volume control is set low), then, sure you could call
it a 1 watt class A amp. But that'd be rather silly...

Class B is where there is no class A overlap. Sure, you could have low
quiescent current, but you could easily have crossover distortion. And
it'd sound like a cheap op-amp...

And there's class C, but that's not usable in audio work. It's used in
FM RF transmitters, where the distortions are filtered out.

And there's class D, which IIRC is a pulse width modulation scheme with
a clock running at about 10X the highest audio frequency. And heavy low
pass filtering to remove the clock and its harmonics. Mainly used in
solid state amps, and even there it's not real common.