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In Reply to: RE: Class A amp keeps shutting down posted by b.l.zeebub on August 03, 2014 at 09:18:14
"Funny thing about Class A amps is that they dissipate more heat at idle than at full power.
There is not a lot in it but the louder you play your music the cooler the amp runs."
So what you are asserting is, if our Belgian friend would like a cooler running amplifier, he should run it at near clipping all day long to keep the amplifier "cool." He could do this easily with a test CD like the Stereophile CD that has test tones. He could disconnect the speakers and use a dummy load for those times he is not using the amp and run it full output into the dummy load hour after hour to keep it cool.
Since this assertion is clearly counter-intuitive, I think it would be a great service to us all if you could describe to us in technical terms why a class A push pull amplifier draws LESS current when passing a signal and the lowest current draw when operating near clipping.
Follow Ups:
Thw writer is correct.
First the anecdotal evidence. We have a Yamaha CA-800 integrated amp that's switchable into class A. It runs hottest at idle and cooleer the louder it's played. We played it loud for about an hour once and it's the coolests it's ever been after being on for a while.
Second: Class A amps dissipate a constant amount of power. The louder they're played the more of that power they dissipate in the load (the speakers) and the less in themselves. They also draw (nearly) constant current and power from the wall. You can check that with a Kill-a-watt or other such device. In fact that's the easiest way to check whether a claimed class A amp is truly class A.
We had a Bedini "Class A" amp in some time ago that didn't sound class A and didn't measure class A. I suspect it used some sliding bias technology and/or sliding rails to claim class A.
Class A is woefully inefficient and generally really good-sounding.
"Class A amps is that they dissipate more heat at idle than at full power."
"Class A amps dissipate a constant amount of power."
These statements are mutually exclusive. The first statement violates the definition of Class A the second statement is correct.
This statement violates the second statment:
"The louder they're played the more of that power they dissipate in the load (the speakers) and the less in themselves."
Say a given Class A amp draws 300W of power from the wall socket.
It will always draw 300W if idling or close to clipping.
When idling all of those 300W get turned into heat, when it is playing some watts go to the speaker and the rest gets turned into heat.
Hope you get the idea because I can't really dumb it down any further but none of the statements violate each other. Kinda obvious if you think about it.
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