popping noise tone bypass switch preamp proton ap 1000

[hironimo]

Hallo

I have a Proton AP 1000 preamp wich has a switch to bypass the tonecontroll circuit .
I dit a restoration caps, relay cleaned input switches and replaced the switches at the front for mono bypass etc anyway .
The tonecontroll switch when pushed makes a popping noise, it did it also before the replacement of switches the switch is a shorting type .
The noise is normaly not that loud sometimes it is very loud .
I don‘t like that
some help to determine the problem would be great

best

hironimo

 

[hironimo]

 

[steveu]

I would suspect C413 is bad or reversed, but just take a meter and follow the DC the voltage. You could also have an open bass pot since that is the only DC path on that side of the switch, in which case probing with a meter would drain C507 and C509.