Grounding Crackle in PSG Mechanism

Jon Light · Post by **Jon Light** » 27 Jul 2008 10:20 am

I've had this problem for a while now, using several different pickups--it is not a pickup issue. It has a couple of different manifestations but I think they are all one problem. Sometimes I get a hum/buzz when my hands are off the guitar, silenced when I touch the strings. Sometimes it is quiet. Sometimes I get a static-y crackle sound when I engage pedals or levers. Sometimes not. This is with humbucking pickups and with single coils.
I suspect that there is a less-than-positive ground continuity with the metallic elements (string/changer/mechanisms) and the ground of the output jack.
Any thoughts on where to try to track down or firm up my connections? Seems like I could be running ground jumpers all over the place which I surely don't want to do.
This is on my Fessenden.

John Billings · Post by **John Billings** » 27 Jul 2008 11:25 am

25 years ago, I went to Radio Shack and bought some 1 foot long alligator clip jumper cables. They've been very useful in finding/fixing these sorts of problems.

Bo Borland · Post by **Bo Borland** » 27 Jul 2008 3:42 pm

Jon, I was getting the same kind of thing with my old VP. Still not sure what caused it but I was able to quiet it down with a piece of duct tape and new rubber feet.. it was making metal to metal contact.

Jon Light · Post by **Jon Light** » 27 Jul 2008 4:09 pm

Here's where I'm at----the pickup wire, when I touch the insulation, hums loudly. This is a humbucker with non-shielded twin leads in a single wrap.
The two knee levers in closest proximity to the pickup wire--both RKR's--seem to have the issues. When I touch them I get a buzzing/hum. If I touch any other part of the guitar while the hum is happening it goes quiet.

I played around with a jumper (as per John's radio shack post--I've got a bunch of that stuff laying around) and after some fact-finding I have soldered a jumper from the lever that hummed worst to the ground lug of the output jack and right now it seems to be very effective.

I'm going to need to do some playing to determine if there's other problem areas but my conclusion at this moment: these levers are interacting with the field of the pickup lead.

As to why the pickup hums when I touch (or hover near) the insulated wire------any comments?

Donny Hinson · Post by **Donny Hinson** » 28 Jul 2008 10:15 am

As to why the pickup hums when I touch (or hover near) the insulated wire------any comments?

Simple, your body is acting as an antenna, picking up 60-cycle hum from the surroundings and radiating it via capacitative coupling into the (unshielded) pickup wire.

Make sure your changer and pickup are grounded to your frame/endplate where the jack is mounted. Your knee levers may be mounted into (insulated) plastic bushings, but they should still be picking up the ground through the pull rods and pullers...unless the parts are gummed up or rusted/corroded.

Joe Wildman · Post by **Joe Wildman** » 28 Jul 2008 1:00 pm

Sounds like what is known in the electronics industry as a "ground loop"
The first thing to try would be get a ground buster (an ac plug that converts a three wire connection to a two wire) and see if that helps. Unplug any other equipment that might also be supplying a ground. Be careful you don't complete the circuit with yourself.

The second step would be to check the AC wiring to make sure the socket is wired with the ground, neutral and hot connected properly. you can buy a little device, a plug that plugs into your ac source and has various lights that show you this. They should be available in any electrical supply store and are not very expensive.

good luck,
Joe