Adding Contact Mic to Electric Guitar - OK to share TRS jack?

[bowanderror]

So I want to add a separate piezo disk contact mic output to a Stratocaster, but am trying to avoid drilling holes.

I was thinking I could use a TRS jack for the guitar output jack, and send the magnetic pickups & contact mic signals separately on the Tip & Ring, sharing ground between them. The signal would leave on a TRS cable to a splitter box, where the magnetic & piezo signals would be split, with a preamp to massage the piezo impedance before it's output. Blue is the regular Strat pickup signal and Red is the piezo signal:



Ideally, I'd like to still be able to use the guitar normally when I plug in a standard TS instrument cable instead of a TRS one. But as the piezo signal would then be connected to sleeve/GND, I was wondering if dumping that pretty large piezo output to ground would cause any problems?

I haven't decided if I want to have separate magnetic and piezo outputs from the splitter box, or if I want to use a footswitch to toggle between them. If anyone has any suggestions, especially about preventing magnetic/piezo interference or potential ground loops, that would also be appreciated!

 

[nvsalgn]

Hey, I just found this post because I am looking to do something similar. Did this end up working out for you?

 

[bowanderror]

Hey, I just found this post because I am looking to do something similar. Did this end up working out for you?

Yeah, worked out great!

I'm actually about to do the same piezo mod to my main guitar. I don't think the mounting location I chose for the first guitar was ideal (center of pickup cavity), so I plan to test a bunch more spots before installing. I 3D printed some piezo mounts to try as well, but I'll have to see if screwing them in sounds OK versus gluing it in like before.

 

[Passinwind]

Hey, I just found this post because I am looking to do something similar. Did this end up working out for you?

I have a Goldtone Dojo (banjo dobro hybrid) wired like that, it works great. One caveat is that you want to keep the output cable as short as is reasonably possible if using an unbuffered piezo element. I've done a variety of breakout boxes and blend/EQ boxes and settled on this one for the moment:



Top row is the mag pickup EQ, in my case the piezo pickup is on the resonator and doesn't really make any low end to speak of, so just a dedicated resonant LPF is sufficient EQ for that side. After the blend section it outputs to a mono jack, if I want to use two separate amps I have a different pedal for that. I can also use this box for bass and other mono wired instruments very easily since the top row comes off the tip connector of the TRS input, so for me it's kind of a Swiss Army knife appliance.

 

[nvsalgn]

Yeah, worked out great!

I'm actually about to do the same piezo mod to my main guitar. I don't think the mounting location I chose for the first guitar was ideal (center of pickup cavity), so I plan to test a bunch more spots before installing. I 3D printed some piezo mounts to try as well, but I'll have to see if screwing them in sounds OK versus gluing it in like before.

Awesome, so I would like to add an active piezo pickup to an electric guitar with passive magnetic pickups. Ideally I would be able to blend the signals together with separate volume knobs. Do you think this would be achievable with a TRS output jack and splitter box? Or would I need to split the signal to just one at a time? Any help is greatly appreciated! (I'm new to this)