Ground loop with a amp and a preamp in a GCX

[Steven Latch]

I did try just now and it doesn't change. Still have the hum coming when the input jack is connected.

I also unscrewed the gcx from the rack. So the amp head, the gcx and the preamp's chassis are not connected together in any way.

[JohnClark]

Interesting, to say the least. Can you perhaps take a picture of this setup and post it here?

Alternatively, if you would rather we just get the GCX in here for inspection, feel free to give us a call or write to info@voodoolab.com. Be sure to mention this thread.

[Steven Latch]

Hi John,

I will clean up the setup tomorrow for a photo and post it.I'm in Europe but if it comes to it, I willl ship it over.

Cheers

[Steven Latch]

Hi John,

I hope you are well today.

I did some more tests and couldn't come up with a solution. Here is what I have tried.

- Swapping the preamp with a POD that is two meters away from the rack, plugged in a different wall wart. No difference
- Swap the marshall head for another one. Same symptoms
- I tried an even simplier setup, involving just one loop. Guitar out and feed trough into the inputs of both amps. Return of the preamps into the input and returns feeds of loop 1. Exact same thing.

All trough the test, I have used a variety of cables, both with the shield lifted or not.

I have taken a shot of the wiring as well as a short video. At which adress could I send it to you?

Cheers

[JohnClark]

Great! Please send to info@voodoolab.com

[carstenlange]

You need to get a lehle p splitter. If you randall out is going to the return of the loop then the randalls input needs to be fed a ground lifted signal/ISO.

See the returns of all of the gcx loops are lifted whichs is good.

Do this.

Guitar into GCX input, into channel A of ISP ProRackG, out into input of P splitter (or even a voodo labs amp selecter would work). Have the normaL OUT OF P splitter feed your input of marshall and the ISO out of P splitter feed your Randall. Have Marshall send go to in of loop 5, and the out of RM4 go to return of loop 5, have out go to channel be of proRackG channel B, and the to your return of effects loops.

I am doing this with CAA PT100 and CAA 3+SE preamp with 0 hum