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For people with experience with Class-A amps

Hi All,

I had a question for all you audio folks who have experience with Class-A power amps as I am new to this myself.

This is bugging me so I finally decided to ask - I have a class-A power amp (name will be with-held to protect the innocent) where I notice with no shade of doubt that the right heat-sink is warmer to the touch than the left heat-sink after about 2 hours of play/program material.

I got hold of a thermometer & measured the heat sink temperature (stuck the thermometer probe deep into the heat-sink fins & waited for the temperature read-out to increase/decrease by 0.1 degree Celcius).
What I found was that the right heat-sink was 1.5 - 2 degrees Celcius HIGHER than the left heat-sink. I have about 4 readings so far. Altho' not a lot of data points, each measurement has the identical trend - right heat-sink was 1.5 - 2 degrees Celcius HIGHER than the left heat-sink.

This indicates to me that the right channel current bias is more than the left channel current bias. Am I correct in my thinking?
2ndly, should I be worried about this?
(in that, over time, this temperature differential could diverge & the amp could run away thermally?).
Should I get the dealer to adjust the bias so that both channels are more or less equal?

I realize that "more or less equal" is a fuzzy term. To that effect, in your respective experiences, what should the temperature differential be between the 2 channels? 0.5 degree Celcius? Less? More OK? if more, upto what point OK?

Thanks very much in advance for your help.
128x128bombaywalla
rleff
1,065 posts
 
Were your measurements taken during playback or idle state?
I think I would agree with ralph's response from atmasphere
that there is nothing to worry about; if you notice some audible changes then I would investigate more.
bombaywalla's avatar
bombaywalla OP
1,958 posts
 
Rleff,

they were taken soon after playback state (during the time I changed CDs or LPs).
bombaywalla's avatar
bombaywalla OP
1,958 posts
 
Thanks very much everyone for responding to my question.
atmasphere's avatar
atmasphere
11,841 posts
 
Elevick and John, many Krell amplifiers have a patented (although not patented by them) sliding class A system that cuts back on the idle current at low volume levels. As the signal increases, the bias current is increased with it.
ngjockey
1,042 posts
 
Krell, Coda and some Thresholds use a "sliding" bias, so they can run cooler at idle. It's still class A, but bias is automatically adjusted on demand.

How much class A is another question that has a lot to do with the load. For example, my amps run hot and are rated for 100W @ 8ohms, however, bridged into 4 ohms, 650W of class A is just unrealistic.
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