DIY Pedal Help: Shielding

[Dom Phenom]

Hi all,

So i built myself the simplest of all pedals, an A/B switch. I alternate between playing Bass and using a Moog Little Phatty at shows, and I figured having a nice true bypass pedal would be ideal. I got the kit from General Guitar Gadgets, and built it and it works fine generally... except....

The problem that I've encountered is in certain venues i was getting a serious buzz out of the amp. I realized that when i switched out the a/b pedal i made for my backup Boss switcher, the buzz dissapeared. I figure I need to do some shielding to fix the problem, did a couple google searches and didn't see anything too helpful, so i figure i'd pick all you brains here in effects land. Any suggestions?

Thanks

Dom

[Silent Fly]

Do you use a metal box (supplied with the kit) or a plastic box?

I may be wrong but I think the schematic on General Guitar Gadgets is wrong, J1 has tip and ring reversed. The wiring diagram looks ok.

[rcubed]

It's likely not a shielding issue but a signal flow issue.

[Dom Phenom]

Signal flow? The plot thickens. It definitely has a metal box. I'll check the schematic, wiring diagram and my wiring when i get back to my practice space where the pedal is.

[niftydog]

It's neither - it's called a ground loop and simple switch-based AB boxes are notorious for causing them.

There's a good post on geofex.com about ground loops, please read it if you're after the details. Suffice to say that wherever you have two or more paths to ground in your signal path you have the potential for ground loop hum.

It doesn't happen in every venue, and it can even come and go at whim, but the only proper solution is to eliminate multiple ground paths. In the case of signal splitting/routing the best solution is to use transformer-based splitters; the transformer essentially isolates the input ground from the output ground eliminating the problem.

[Dom Phenom]

Thanks. Once again, impressed and thankful for the quick help available on this forum.

Looks like I've got some learning to do about ground loops.