in article  <735604750.28979.0@unix5.andrew.cmu.edu>,  Mark Yeck

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Hey, can someone clue me in on these and other weird types of amplifiers?  Just
a brief intro to the concepts behind these would be cool.  I have the clues 
on type A, B, and AB already and stuff, but these other ones are mentioned 
occasionally and I dont know what they do.  I think type D is like a PWM scheme
or something.  Thanx in advanced.

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The whole point to these weird amplifier types is improved efficiency.

Class D amps *are* PWM (pulse width modulation) amps which work very much like
switching power supplies. I think I've seen these things called "class S"
before as well. They're capable of very high efficiencies, and would be suitable
for very high power. I've yet to see anything like this used in an audiophile
amp, though.  I've been trying to design a three-kilowatter for the last year
(to be used as an inverter for an UPS), but have been having serious problems
with layout parasitics (10 IRF 450's in parallel... any help  with a  do-able
isolated drive ckt would be appreciated :) ) 

I'm not absolutely positive about this, but I beleive a 'class G' amp is one that
operates off a variable- or switched power supply rail voltage. The Carver
amps do something like this. They use some sort of phase-control circuit 
(I do not fully understand its operation) to reduce the transformer size, and
I beleive that is patented. I had an M400 apart (trying to fix) and found that
it had three rail voltages that it switched between. I ran a simulation on
PSPICE and found that the topology would greatly reduce power dissipation (heat)
under large-signal conditions, or when driving reactive loads (which draw high
current at the zero-voltage crossings). 