rf t8004

rrae

Member
2011-03-17 5:14 pm
Got this amp with one bad channel (shorted outputs), replaced the outputs, gate and source resistors.
Now i get squealing - i would say, pitching noise from that channel, with no input source, only when the crossover switch is set on HP or LP - with all pass mode i don't have this problem.
Gain pot makes it louder/quieter, freq. pot changes the frequency of the pitching noise.
Seems like in full range mode the amp plays perfectly fine, only the problem exist on HP/LP mode.
In HP/LP mode it produce the audio, but its not clear and i can hear that pitch noise in background.
Sadly, but i don't have right now scope.
I got schematic.
 
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First check to see if you have any significant DC on the output pins of any of the op-amps.

Next I would check to see if any switches or potentiometers are shorted or defective.

The defective channel and the squeeling could be a coincidence.

If the amp does in fact works as it should in full range, but not in LP or HP this is where I would start.
 

rrae

Member
2011-03-17 5:14 pm
Dont see anything suspicious.
Seems like the frequency pot "generates" the pitching, if i set it to 0 i dont almost hear anything, when i start to turn it, the pitching slowly comes up, and if i more tun it up, the higher are the frequency. Seems like almost i am "driving" input test signal...