Bias current

[peter5]

I just turned on my leach amp to set the bias current but turning the potentiometer didn't do anything. The current was stuck at around 20 ma. Can anybody tell me what's going on?

Thanks.

Peter

 

[serosmaness]

leach bias current

Hello It seems that I may have a problem with adjusting the bias current. The bias current stays around 19 to 25 ma. Please help.
Serosmaness

 

[Jan Dupont]

Most problems with bias current adjustment are caused by the potentiometer........ Carefully try to meassure the output of the potentiometer and check that it actually variates the voltage to the base of the Bias transistor

 

[serosmaness]

Thanks Jan for the reply.I changed the pot and checked on the board for change of resistance. Everything checked good.
I put a squarewave on the input and got a amplified output but it was not clean.
The good channel is biased to 115 ma and works but its response is notably different than my Sumo. Less bass.
Thanks Serosmaness

 

[Jan Dupont]

Did you check for a defect bias transistor ???

 

[serosmaness]

Thanks again Jan for your response. I found the problem. I swapped the B and E on the output transistors. I biases fine now.
Thanks again
Serosmaness

 

[Jan Dupont]

Ok Then happy Amp'ing....