Crackling noise from Bose 901 equalizer

Thomas Oder

New Member
I have a Bose 901 series 3 active equalizer that has a crackle in the left channel.The unit has been recapped, and all transistors in the left channel outside of one 2n3906 have been replaced. I swapped the 2n3906 with the identical transistor from the right channel (which does not produce this crackling noise) and the crackle remains.

It will disappear at certain times only to reappear after being on for a couple hours.

Looking for any advice on how to get this issue resolved. Or how to track down the noisy component.
 
Welcome to AK... Did you swap speakers from Left to right and right to left?
 
Was the issue present before swapping out capacitors and transistors?
 
The sliders and any switches need a good cleaning just to eliminate that possibility. I'd use faderlube on the sliders.
 
So the solder wasn’t the problem, the problem cropped back up shortly after. I then replaced almost all of the old resistors with new carbon film pieces, which eliminated a lot of background static. Waiting on one last pack of resistors before I call it good.
 
So the solder wasn’t the problem, the problem cropped back up shortly after. I then replaced almost all of the old resistors with new carbon film pieces, which eliminated a lot of background static. Waiting on one last pack of resistors before I call it good.
Lets hope for the best..
 
Look at the solder connections on all your inputs and outputs too. Not sure if these equalisers have RCA sockets soldered directly into the PCB or not, but if so, this could be a good place to look
 
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