Possible ground problem

[Perry Underwood]

I recently finished a guitar and have discovered a possible ground problem with one of the humbuckers.

The guitar has two humbuckers, a tone and volume control, and a three-way switch.

The problem is that when I touch the neck humbucker, there is a buzz that goes away when I touch the strings or bridge. The bridge pickup is quiet when I touch it--no need to touch the strings.

I tried plugging the amp into a grounded socket, and it helped quite a bit. The buzz when touching the neck pickup was almost gone.

I've gone over my wiring and don't see a problem. The only issue I can think of is that I had to add additional wire to the neck humbucker.

Any thoughts or suggestions welcomed. I don't know if there is a problem at all. The guitar plays and sounds fine otherwise.

Thanks in advance. Perry

[David King]

Hi Perry,

Are the pickups the same make and model? It sounds like they might have been wired differently internally and that the neck one has the metal parts connected to hot instead of ground. Does touching the string to the top of the neck pickup kill the output?

If that's the case you might try swapping the connections of both pickups at the selector switch and see if that helps. It may just move the noise to the bridge pickup. Ultimately you may have to flip the magnet polarities of the neck pickup and then swap it's leads to keep it in phase with the bridge and get the case grounded.

[Perry Underwood]

David, thank you for your reply. I do get sound from the neck pickup when I touch it and play the strings. It sounds fine except for the buzzing.

The pickups are Carvins. Different models, though. The bridge is in the M series, and the neck is in the C series.

I do have the habit of painting the pickup cavities with conductive paint although I do not ground them. I thought that might be the problem, so I removed the screws holding the pickup to the body and raised the pickup. Still buzzes.

When I have time, I check the area where I added wire. Perhaps the problem is there. I have another Carvin M series pickup I can try if nothing else works.

Thanks again for your reply. Perry

[Mark Swanson]

A few things here. David asked if the guitar sound cuts OUT when you touch the string TO THE PICKUP cover. If the string is grounded, and the pickup cover is hot- which it should not be- then the sound (all of the sound, not just the buzz) will shut off.

I do have the habit of painting the pickup cavities with conductive paint although I do not ground them. I thought that might be the problem, so I removed the screws holding the pickup to the body and raised the pickup. Still buzzes.

You shouldn't use the shielding paint if you are not going to ground it. It is worse than useless if it isn't grounded, if it's not it can actually act as an antenna for hum and buzz, making it worse. If your pickup was screwed down to the cavity, then the cavity was indeed grounded through the pickup base. If you raised it, now it is not.
get a VOM (Volt Ohm Meter). then you can use the continuity tester function to test all of the grounds to make sure they are all connected. All of them, all the way through the circuit including the pickup baseplates.

[David King]

According to this link Carvin has a lot of related pickups under the C and M monikers.
http://www.carvinguitars.com/pickups/
They all share a lot in common and I can't imagine that they wouldn't all play well together. Each has a ground wire which should be the only ground connection to the baseplate and pole screws. The tops of these pickups are mostly plastic by the looks of it so it wouldn't be easy to short anything out touching the string except the pole screw if it was sticking out enough. The M series are all two wire buckers

It sounds like the neck pickup's ground wire is not connected. I imagine if they're 2 or 4 conductor cables then the shield drain is the ground wire and it's soldered to the steel (or nickel-silver) baseplate at the pickup end.

I've gone over my wiring and don't see a problem. The only issue I can think of is that I had to add additional wire to the neck humbucker.

You added a 3rd wire to connect to the series link to make the M pickup splittable? Maybe you inadvertently cut the shield wire in the process?

[Perry Underwood]

Mark and David, thank you for your replies. I misunderstood what David had asked about the string touching the pickup cover. I did test that just now and there is no cut out of sound. I touched the string to one of the polepieces.

David you are correct about these pickups not having covers. I will ground the pickup cavities and check the wiring again, especially the ground wire. When I say that I added wire to the neck pickup, I meant that I just added extra wire so it would be long enough to reach the electronics cavitiy. Sorry that that wasn't clear.

By the way, here's a picture of the guitar showing the pickups.

[Mark Swanson]

If the wire you added is not shielded well, that might be the issue. Is the shield connected to ground all along that pickups' cable?

[Perry Underwood]

Mark, thanks for your suggestion. I'll need to check the wiring over the weekend. I'll update then.


Thanks again. Perry

[Perry Underwood]

I believe I found what the problem was. The shield that is soldered to the base of the pickup was broken. I haven't repaired it yet. I'm thinking that since the wire is short, I should just replace the entire length.

Since I haven't repaired the humbucker I had in the neck position, I installed another Carvin pickup.

Thanks again to David and Mark for their suggestions.

Perry