On Oct 25, 4:32 pm, robert casey wrote:
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.

You're observably an engineer, Robert, I'm writing about "engineers",
who are observably something else, most easily spotted by their
symptomatic tailoring of electronic truths to their personal
animosities.

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.".

It is such an obvious condition that most texts leave it to the
reader's good sense to add to the definition. This thread is
particularly about Graham Stevenson, Don Pearce and Arny Krueger
explicitly claiming the opposite is true, trying for malicious
personal reasons to redefine Class A operation as one in which "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).

Dream on. I've seen KT66 that after fifty years of use were more
closely matched than new-production EL34.

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.

I wouldn't call it a Class A amp. I would say "it has 1W in Class A
and xWatts in Class B". It seems to me worth keeping the distinction
between an amplifier class and an operatiing class; it pleases me as a
wordsmith that the verbal distinction makes Class AB possible; if we
could not express it, we might not think of it. A Class A amplifier is
one in which up to the maximum specified signal no device ever ceases
conducting.

(Had to get down a new keyboard. Sputtered my wine across the previous
one. First time in years I had poor Australian wine. Some ponce at the
studio recommended it as "earthy". In raal life it tastes like the
peapod peepee made by some vegetarian ladies I dined with once and
never again -- nut cutlets, yech! --, and then only because I owed the
brother of one, who I knew at HP, a favour -- he was one of the
designers of my 400W party amps for entertaining only 800 of my
closest friends. Back to the good stuff!)

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.

Thanks for the straighforward analysis. You realize of course that you
and Phil Allison by demystifying the facts so bluntly are spoling my
fun kicking the enemies of fidelity around.

Andre Jute
Impedance is futile, you will be simulated into the triode of the
Borg. -- Robert Casey