AMP REPAIR
TECH SHOP

If you hear a warm hiss/noise when you turn on your amp and there is no signal at the input,
chances are your unit needs the electrolytic capacitors replaced.

If you hear hum and/or buzz,
it is most likely the filter capacitors in the power supply and/or the rectifier in the supply.

If you just got a transistor amplifier back from a shop a couple of weeks ago, and it went down again,
chances are they did not replace the driver trasistor(s) when they replaced the output transistor(s).

If you are hearing noise/clipping/distortion,
it could be as simple as rebiasing the amp.