Preamp solid state GK 2000CPL hiss problem

hello everyone, I start by saying that I'm not an electronics expert but I really like it and I would like to give it a try to try and find a solution to the problem, practically the GK and a preamp that I connect to the marshall 9200 power amp and you hear a strong hiss that increases as the volume increases, both clean channel A and distorted channel B, both with guitar connected and not connected, I am attaching a video for now I have limited myself to trying to replace the components of the power supply stage because I thought they were the cause of the problem, the replaced components are circled in red, but the problem evidently persists not in the power supply stage. Thanks

 

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Agree with Osvaldo that is Hum/Buzz, not Hiss.

You have half a Guitar Shop in that rack setup, ALL noises add up.

I much suspect grounding around your GK preamp, but more important: we NEED a clear detailed drawing of your setup.

For example, I do NOT know how is your JMP1 preamp connected to the 9200 Power Amp, even less how the GK is simultaneously connected to it, those are 2 separate independent preamps and usual would be connecting either one or the other to the power amp, through some kind of switching/patching, yet here you simply rise one or the other volume.

Again: we need the full map, on a nice and clean sheet of white paper.
 
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