Non ADA Gear > Amps

Marshall 9100 bias adjustment

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vmaxvmax:
Thanks all for your answers...

I have no problems biasing my amps. Done it many times - I use a bias probe.

The Marshall 9100 has a 'balance' trimpot on each channel. It is for setting the PI balance. Trouble is, ideally you need an oscilloscope to balance the onset of distortion at the top and bottom of the sine wave.

I was just wondering if anyone has done this and found another way...

One side of the phase inverter has a 100k resister on its output and the other has a 47k resister and 100k trimpot in series. I figure that setting the trim halfway would set the basic balance of the PI but Marshalls tend to be set slightly offset for tonal complexity... I.e. 100k and 82k resistors from the PI.

I have tried to set it by ear at 'household' volume but makes little difference. Maybe not worth worrying about!
 

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