Soundcraft Powerstation Spirit 600

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saint gillis

Well-known member
Joined
Nov 4, 2012
Messages
871
Location
Brussels - Belgium
  I had to fix of of these, the right side power amp was showing heavy distortion awful sound. I first re-soldered the suspicious points and the amplifier came back to life again.
  After 3 or 4 times using it during few hours each times, the problem came back again.
  There is a negative feedback from the output to a differential pair at the input, I tried to ground or to remove the feedback on the functional left amplifier, but the circuit seems not to work this way (negative -60V rail at the output of the amp). So I measured and compared voltages on the left and right amps (the functional one and the distorted one), they were all the same. Then I put the oscilloscope and realised the distorted amp was working correctly again...
  Is this a bad transistor somewhere?
 
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