Simple Passive A/B pedal with no ground loop

[Dagan8]

Hello

I apologize if this is already posted somewhere. I did a quick search and found nothing.

I decided to build myself a simple A/B selector so I can switch between my 2 amps for clean vs dirty. I first built a passive A/B using the popular circuit found on most forums but this created a ground loop issue between my 2 amps. I added 2 insulated output jacks and added switching to only connect one ground at a time. Works great and maintains the muting of the output not in use.

I attached a drawing for anyone looking for the same device.

[Mark Black]

Nice! Thanks for sharing.

[Dagan8]

No problem Mark.

Just realized that I posted this under the wrong category. Meant to post under Guitar Effects. Hopefully one of the mods will be able to relocate it.

[David Schwab]

If you want to use a standard A/B switch box and avoid ground loops; all you have to do is disconnect the ground to one of the cables going to one of the amps. You leave the shield on the cable connected on the amp end, but not on the switch end.

[pdf64]

Not sure, but if there's a ground differential then the muted amp (with the open ground) may hum, eg if the input is shorted to the ground of the other amp?
Also Dagan's method allows standard cables to be used, which is always a bonus.
Pete.

[Dagan8]

Not sure, but if there's a ground differential then the muted amp (with the open ground) may hum, eg if the input is shorted to the ground of the other amp?

This is exactly what I found when trying the ground lift method. The amp I had plugged in to the output with the ground lift would hiss when "bypassed". There was also some additional hiss when not "bypassed" as well. It was still an improvement over the ground loop hum but I found the only way to totally reduce the noise was to build it the way I did.

[tedmich]

congrats on the successful A/B I am currently working on Y

(because I have 3 amps I like)