Hi there!

First of all pardon me speaking in English, but I don't know German and this is the only website I found info about the schematics of my amp!

I'm quite new regarding electronics and amps but all my life I have fiddled with circuits and tried to repair them.

Recently, my Blackstar One s104 6L6 started developing a kind of "white noise" hiss, the noise is not there in clean channel, but appears very loudly in crunch, OD1 and OD2. Power amp seems isolated from this issue, as connecting something to the loop return doesn't produce any noise.

Effects send also has the mentioned hiss, so the noise seems to come from the preamp section. I have replaced all the preamp tubes with a working amp ones, and the hiss is still there. I've tapped all the connections with a pencil, but no change in the hiss.

At this stage I am suspecting it is the TL072 chip in the input stage, but I have no evidence of this - I have also replaced the 1M resistor of the input circuit, but no results either.

Any ideas of what I should look up next? This amp is making my head hurt!

Thanks for your help!

PD: I only have schematics of the 200w version, but seems similar on the preamp section...

Heres the schematics