GCX-Ground loop help..

[Captain Chunkulus]

Okay, I'm at my end with this, hopefully you guys can help.. I have gone through my rack and completely isolated all of my gear from each other and the rails and all of my gear is on the same power, I have all brand new cables and still I get a ground hum.. Here is my set up.. Peavey 6505 plus, gcx, rocktron replifex, keeley compressor, mxr flanger, mxr chorus, boss 59 fender bass man pedal..
Loop 1. Keeley comp
Loop2. Mxr Chrorus
Loop3. Fender Bassman pedal
Loop4. Mxr Flanger
Out of loop 4 into loop 5, Loop 5 send into the front of my amp, The send from 6505 back into Loop 5 return, loop 5 out into loop 6.
Replifex into loop 6 and then loop 6 out back into the return on the 6505..
I did this so I could insert my amps preamp into a loop and still use the power amp of the amp while bypassing the front of the amp because the clean channel sucks on this amp.. Anyway, I have gone through and taken all of the pedals out of the gcx and just left the amp insert and effects loop set up the same and still getting hum. I tried just running the replifex into the effects loop of the 6505 and no hum.. So the hum is being created in this preamp insert in a loop / replifex combo setup.. I tried lifting the ground on the cables going in and out of the effects loop of the 6505 and this helped but did not get rid of the problem. Side note, when I play straight through the gcx straight into the 6505 no hum at all either so, there is something about this set up that is creating a ground hum.. I have been thinking about the ebtech hum eliminator but what do you guys think? Thanks..

[JohnClark]

This is a little on the strange side... so when you bypass the preamp section, you are just sending your guitar signal (with or without effects) directly to the power amp section? ...and this sounds better than the clean channel itself? Is it just that the clean channel does not get super clean?

Anyway, the buzz you are hearing is likely not a ground loop in this case. It is actually a lack of ground that is causing the problem. The Return jacks on the GCX loops are ground lifted. Try connecting a piece of wire between the sleeve connections of the cables connected to the Return and Out jacks of GCX Loop 5. This should complete the normal ground path for your effects loop with no other modifications needed. I hope that helps!

[Captain Chunkulus]

I know it sounds funny about the whole bypass the front of the amp thing but the clean channel on these amps just arnt that great..I am trying what you said to do as we speak.. Let me see if I have this correct.. The cable that is comming from the effects send on my amp that is going back into the return on the gcx loop 5 and the output of gcx loop 5 should have an extra wire soldered between them on the sleeve connection??

[Captain Chunkulus]

Tried what you said and no difference was achieved. That is if I did it right.. Just a side note., all of the cables I am using have a ground.. I had just tried the ground lift thing in the past and it didn't help so I just went back to all grounded cables, just to clarify from my previous post..

[JohnClark]

Well I guess it is time to simplify this setup a little so we can find the source(s) of the buzz.
As a test, connect your guitar to the In of GCX Loop 6. Leave the Replifex connected to the Send and Return of GCX Loop 6. Connect the Out of GCX Loop 6 to the FX Return on the amplifier.

[Captain Chunkulus]

Okay, here's the scoop. I took everything out of all of the loops.. I then just plugged my guitar cord into loop 6 in and then inserted the replifex into the effects loop, then plugged the out put of loop 6 into the return on my head, not only a hum but a buzz also.. I tried running the same guitar and cord directly into the replifex and the out into the effects return of my amp and no hum or buzz of any kind.. I think at this point something may be wrong with my gcx?

[Captain Chunkulus]

okay, as long as I plug my guitar into the guitar in on the front of the unit and then go guitar out in loop 6 inserting the replifex into loop 6's effects loop then out of loop 6's out into the return on my head with nothing else plugged in anywhere no hum issues.. The minute I plug the guitar into the front, feed through into loop 5 send out of loop 5 into the front of my amp, then send from my amp send into the return of loop 5 then out of loop 5 into loop 6 with the replifex hum and buzz issues occur.. Side note, this is an original DMC gcx unit I am using..

[JohnClark]

Okay, here's the scoop. I took everything out of all of the loops.. I then just plugged my guitar cord into loop 6 in and then inserted the replifex into the effects loop, then plugged the out put of loop 6 into the return on my head, not only a hum but a buzz also.. I tried running the same guitar and cord directly into the replifex and the out into the effects return of my amp and no hum or buzz of any kind.. I think at this point something may be wrong with my gcx?

Nothing points to anything being wrong with your GCX. When you are using the GCX Loop as described in the above test, there is no ground reference being made to overcome the ground Lift on the Return jack. With the setup still done as the above test, try connecting the sleeves of the cables going to the Return and Out of GCX Loop 6. Let me know what happens.

Ultimately, you may have to do this with both Loops 5 and 6. But I want you to try it one step at a time to ensure we know when the buzz begins entering the system.

[Captain Chunkulus]

Okay, Guitar in front, patched through to back into loop 6 in, replifex in loop, output of 6 into effects loop of amp.. Dead quiet with out grounding the return plug and the output plug.. Next test, guitar in front patched through to back into loop 5 input, amp input fed by the send of loop 5, amp send to return on loop 5, loop 5 out put to loop 6 in. huge ground loop buzz what ever you want to call it.. Next used a wire to connect the sleeves of the return and output of 5, does nothing but left it in place anyway, next do the same for loop 6 same no change..

[JohnClark]

Well it seems then that I am wrong all around... Let me do some head scratching, and I will try to come up with a better solution.