stereo looper use - ground loop?

[Tim Toberer]

I am trying to put together a small pedalboard with a stereo looper. My guitar is an acoustic with a sound hole pickup and a triple disc piezo (on bridge plate) both wired to a stereo endpin jack. The magnetic pickup volume and tone is on the guitar, but the piezo is wired straight to the jack. Volume is controlled on the amp. having it this way allows me to blend the sounds by turning the volume down on the guitar, which brings in more piezo. Works like a charm. I want to setup my acoustic lap steel with this same setup.

My question is, can I split the signal so I can route the magnetic pickup through a couple effects pedals to go into one input of the looper while carrying the piezo signal separately to the other input? Here's the potential problem, I want to rejoin the signal after the looper to carry it to my stereo amp in a TRS cable. I see a ground loop issue because they share a common ground. Seems like I would have to wire them with separate mono jacks on the guitar in order to avoid this. (which I don't want to do!) Hope that makes sense. I want to wire it like this so I can make acoustic and electric loops with the same guitar at the same time. I also want to use the percussive sounds of thumping on the top to make percussive loops.

[George Biner]

I see a problem in that you are taking two outputs, one from the magnetic effect boxes and one from the piezo guitar pickup, and connecting them together -- one usually doesn't connect one output to another, the stronger one will win and you won't hear (and may damage) the other one -- I think you're going to have to keep them separate or send them through a mixer (with gain elements like op amps or resistors buffering one output from the other). Then you also won't have any ground loop issues.