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KAC-X201T bias voltage problems

I'm having issues setting the bias voltage for the right channel. The service manual says to set it to 2.5mVDC. I can set the left channel with no problem, but the right channel drifts badly with warming up/cooling down etc. The left channel drifts around 2.1-2.8mV whether it is just warmed up from cold or just cooled down from hot. If I warm up the amp completely, set the right channel to 2.5, turn it of and let it get cold, turn it back on & let it warm up, it will be

1.1mV. If I then set it to 2.5, let it sit, it will be up around 9mV. These aren't exact figures, it drifts pretty widely. It isn't a dirty pot, the readings aren't jittery or erratic, they just drift with temperature variations.

I'm not sure what class this amp is, it's definantely not D, it looks like a standard analog transistor audio amp. What would a normal cause be for this kind of drift?

Thanks for any help, I'll gladly get more specific definite readings if they will help.

Thanks, Steve

Reply to
Steve
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Poor thermal contact of the output transistors with the heatsink. Poor thermal contact of the bias stabilizer transistor or diode with the heatsink. An abnormally thermally sensitive bias transistor or diode in the external part of the bias stabilization network. An abnormally thermally sensitive output or driver transistor. An abnormally thermally sensitive resistor. In fact, any amount of things. Shouldn't be that hard to find with the tip of a soldering iron, and a can of freezer. A set of schematics would be helpful, but not essential, with another channel for comparison. I would think that the amp is probably a standard class B or AB type.

Arfa

Reply to
Arfa Daily

Thanks, that's what I figured. You're probably right, I just need to bite the bullet and start heating/cooling components. Luckily, I do have a schematic, I was quite suprised that the service manual was available and has parts list, board layout, & schematic.

Thanks, Steve

Reply to
Steve

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