GCX with 2 Preamps Issue (JMP-1 & ADA MP-1)

[xPilotx]

Hello All, new to the forum and hoping to get some ideas/help with my setup. First of which is a squealing noise issue / feedback type and the other is general signal flow for my rack gear and pedalboard. I also have the Ground Control Pro along with some overdrive pedals, eq and a looper.

So my first question is regarding an issue that recently started or that I noticed. Here is my signal flow from start to finish followed by a description of my issue :

Guitar > Pedalboard > Guitar Input (on GCX) > Guitar Out > ADA MP-1 and also for A/B selecting as shown in manual > Guitar Thru (on back of unit) > Marshall JMP-1 then back in to > Loop 1 Input > and also ADA MP-1 back in to Loop 1 Return > then from here I have all signal routed out of Loop 1 out going to :

Axe FX 2 - BBE Sonic Maximizer - Rocktron Intellifex > back to Loop 2 In > Loop 2 Delay Pedal in Rack Shelf connected as send/return> Loop 3 Reverb Pedal in Rack Shelf connected as send/return > Loop 4,5,6,7,8 controlling axe fx as stomp boxes on/off > out of GCX to > Marshall 9200 In > Out to Fractal X-Load LB-2 > DI to Recording Interface and Speaker Thru to Marshall 4x12 1960A Cab.

Ok, So I hope that makes sense more or less.

Now my issue is happening when I connect the ADA MP-1 front input cable *** AND *** the Jmp-1 front input cable. When both cables are connected in the above mentioned signal flow - I get a very sensitive squealing type feedback from the JMP-1 - not the ADA. I've set it up like this to be able to utilize the ADA and JMP-1 A/B switching on Ground Control button 1. On is ADA MP-1 , off is Marshall JMP-1. When I disconnect the cable from the ADA input - the problem goes away. However, if both units are connected the JMP-1 squeals like the feedback you would get standing in front of your amp at 10 with no noise gate.

Just to be clear - if I connect my pedalboard direct to jmp-1 it sounds fine. Same for ADA. It only happens when I run them in the 2 preamp method using the guitar out and guitar thru ports into the inputs of each unit. I hope this makes sense.

Any ideas? Am I doing something wrong here?

Second part of the question is : is this the best way to run my signal? Any recommendations? This is my first rack based guitar rig and I would really like to set it up optimally and then just leave it that way.

Thanks in advance for any help on the matter! Looking forward to getting this sorted.

[Marlboro05]

Hi xPilotx,
First off, the noise you are getting is a ground loop. To stop this, the first thing to do is to isolate each rack unit from each other, in the rack. I use Middle Atlantic Shoulder Washers and screws so with nylon washers.

https://www.legrandav.com/products/acce ... Results=20

https://www.legrandav.com/products/acce ... Results=20

After this, you can see if swapping the preamps around, MP1 to loop 1 in and the JMP-1 to the return. The GCX return does not have a earth to ground.
If this does nothing, you need to get an isolated box, an Ebtech hum eliminator or something like it. You can make a audio cable with the ground removed to see if it fixes it to.

As for your other GCX loops, they seem fine. I don’t know what you mean with loops 4,5,6,7 & 8 controlling stomp boxes in the axe fx?
I’d also not use the Sonic Maximizer, to me a waste of space, but each to there own. I’d also run the Intellifex in the loop of the Axe FX or in a loop on the GCX to turn it on or off. But also, this is up to you.

See how you go, get back to us if you need more help.

Cheers