Eliminating noise: need advanced help


So I have a pretty involved setup but I have it so that I do not get any ground loop noise but I have some questions about some noise and some static noise I cant get rid of.

Quick rundown in guitar into gcx through all loops then out to a suhr buffer that splits the signal to a PT100 and Bogner xtc.

So the iso of suhr buffer is feeding the xtc while the direct out is feeding pt100.

Now there is a slight, slight injection of some hum into the pt100. When I bypass the effects loop and go straight into amp it is dead quiet even on channel 2 with the boost on. Just can't seem to nail this one. Ripped apart my rack a million times and drove poor John Clark Crazy at voodoo labs asking for help in the past. I am using a pro rack G before amp and in loop but this isn't causing any issues.

Now when I have it switched to the bogners preamp I got a slight static that got worse when I touched the custom patch panel I use for all ins and outs with my hand. All this noise went away when I pushed in the phase button on the Suhr buffer. Why?

One thing to note is that when I unplug the cable that is between the input of the suhr buffer and the last loop output of the gcx at the GCX side. I get all kinds of emi noise and it really fluctuates when I move the unplugged end all around in back of my rack.

Help Please? All GCX's and ISP ProRackG are powered by a Voodoo lab pedal power AC. Doesn't matter if all pedals are removed from rack either.
Is it just the nature of the beast having AC devices before the amp input?

c diddy 5000

I've had huge struggles with my GCX. One thing to try if you haven't already is to open up the GCX and locate the ground lug that is screwed into the pcb into the chassis. Remove the screw, and use electrical tape to prevent any unintended contact with the board. This made a huge difference for me. It unfortunately did not solve all my problems, but helped a lot. Let me know if this changes your situation.


I can't say I'm following the diagram 100% (tried, but my head hurt :D), but the general idea of letting the Suhr buffer isolate one of the amps is correct. But you'll also need to make sure you're not re-connecting the grounds when you introduce the effects loops. Otherwise you'll undo the isolation provided by the buffer. You might need to add isolation to the send/returns as well, at least on the Bogner.

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