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
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.
Rleff,

they were taken soon after playback state (during the time I changed CDs or LPs).
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.
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.