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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

Showing 6 responses by bombaywalla

bombaywalla's avatar
bombaywalla OP
1,957 posts
 
Shadorne,

very funny!! ha, ha, ha!! :-)

OK, I get the point.
My inexperience w/ class-A amps "forced" me to ask the audio community at large.
Newbie to class-A cutting his teeth/getting his feet wet. Cut me a little bit of slack, chief!
bombaywalla's avatar
bombaywalla OP
1,957 posts
 
Elevick,

>> Have you opened up the amp? Maybe things are not
>> symetrical inside?
I've opened the amp & done a very good inspection - things are very symmetrical inside.

>> Are your speakers drawing the same power? Check the
>> impedance on them.
Not sure 'cuz I did not check but I'll do so.

>> Is the balance off or is the sound even out of both
>> sides?
The sound is even out of both sides.

>> Is this difference when listening quietly or loud?
I've played it at lower & modest levels.
At lower levels it takes a lot more time for the heat sinks to heat up.
I've measured after 2+ hrs of program material at whatever level I was listening depending on time of day (lower at night time, louder during the day).

>> Is your pre-amp the culprit?
can you elaborate on this one? thanks!

Just FYI: with the prev class-AB power I did not have this issue. Both heat sinks were as hot after 2+ hrs of program material.
bombaywalla's avatar
bombaywalla OP
1,957 posts
 
Gs5556,

thanks for your response.
you bring up some good points. Maybe it's the different thermal resistances?
bombaywalla's avatar
bombaywalla OP
1,957 posts
 
Larryi, Aball,

you guys have caught me on my symantics!! :-)

1stly, this IS a class-A amp. The manuf reassured me several times. I had similar doubts hence I did communicate w/ the dealer on this.

what I meant to convey when I wrote "At lower levels it takes a lot more time for the heat sinks to heat up" is that altho' I can feel the heat rising up thru the vents in the top-plate, the heat sinks are relatively cold. As the amp is played longer & longer, the heat sinks begin to warm up.
I agree with both of you that class-A amps are hotter at idle than when they are playing.
This bit of info was incorrectly communicated by me. Sorry!

Aball,
I have a Fluke thermometer that comes with a 2-pin fairly long probe. The probe end is a bit of exposed metal. I will have to look @ it to give you the model #.
So, I just stick the probe between the heat sinks or thru the top-plate vents to take the temperature.

Both heatsinks have identical support & air-flow around them.
bombaywalla's avatar
bombaywalla OP
1,957 posts
 
Rleff,

they were taken soon after playback state (during the time I changed CDs or LPs).
bombaywalla's avatar
bombaywalla OP
1,957 posts
 
Thanks very much everyone for responding to my question.
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