Crackling sound

A

Agoll

New member
Lately I’ve been experiencing crackling noises after playing my amp for about 20 minutes. My current setup is as follows:

Guitar -> Rack pre-amp unit -> effects unit -> rack power amp -> cabinet

The pre amp is tube, so I tried replacing the tubes, no dice
Power amp is solid state, so no tubes to look at there
Cords are only a couple months old

The crackling doesn’t start immediately it takes a little, but once it starts it quickly gets progressively louder until I turn the amp off, any idea what’s the cause?
 
Have you tried it with different guitars? Passive pickups or active pickups? Have you removed the effects chain and ran only the pre-amp into the power-amp? Have you tried unplugging the pre-amp with the poweramp still on to see if it stops? Have you tried (carefully) plugging in the guitar directly to the poweramp with the guitar volume slightly on to see if it still exists?

My initial thought is that the pre-amp needs serviced and possibly re-capped. There might be something funky going on in the heater filament circuit causing voltages to not be correct. It could be running the pre-amp tubes at the wrong filament voltage, or there may be a capacitor altering a certain stage's bias to due acting more resistive than capacitive. Just my initial thoughts - I'd recommend performing the tests, but my guess is that you're going to need to have the pre-amp serviced.
 
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