Grounding problem

[Bobby8]

Hey guys

I have a grounding problem in my Kelly. It's wired for 2hum-3way-2vol and everything works fine except i have a constant hum when I'm not playing. Both pickups are grounded to their pots, as well as the output jack. The hum is little bit louder on the bridge pickup than on the neck. When the three-way switch is in the middle position, the hum stops. Now I know I need to ground something somewhere, I just forget what and where. The guitar has the brass (?) plate inside control cavity and the ground wire from the bridge is soldered onto it. The bridge is Kahler so the ground wire is just pressed down with the bridge itself. I tried to touch different parts of the components with a piece of wire without soldering to check if something happens but nothing. Last thing I shielded the control cavity with copper tape with no result. What am I doing wrong? :dunno:

[bratfink]

Ground the shielding as well.

Two things I always do is:

1. Add shielding to the pickup cavities and ground them as well.
2. On a kahler I will scratch off some of the black coating to ensure metal to metal contact with the ground wire.

On an RR I will ensure using shielded cable to the input jack since the cable runs behind the bridge pickup. I will ground the shielding.

Interesting you note that the hum is cancelled when on both pickups. How are the pickups wired?

[Bobby8]

Isn't the shielding grounded as soon as it touches the brass plate in the cavity? Or it must be soldered too? Yes, I forgot about the pickup cavities.

The pickups are Duncans wired for 2vol with a 3-way switch. Neck is '59 w/single conductor wire, bridge is Custom Custom with standard 4-conductor. Everything is wired according to the diagram

http://www.seymourduncan.com/support...matic=2h_2v_3w

except for that black wire marked "ground wire from bridge", I guessed it's enough it's grounded to the brass plate. Or am I wrong?

[dg]

The brass plate has to be wired to ground. There may be a partial ground due to having contact with the bodies of the pots, but try adding a wire from the plate to the back of the volume pot and see what happens. FWIW, on my guitars with the brass plate, the plate itself is wired directly to the output jack, and then all other grounds go to 1 or 2 central grounding points on the plate.

[bratfink]

I'd ground the plate as well, just to make sure. Trick I learnt building race cars, 'you can never have enough ground points'.

[Bobby8]

Ok so I tried to solder the output jack direct to the brass plate and nothing happens. I even tried to desolder the ground wire from the bridge and nothing happens the hum stays the same, it changes when I carry the guitar around the room, somewhere it's louder, somewhere quiet.

Here's the pic, it may be of some help, I'm starting to get quite irritated by this



Uploaded with ImageShack.us

[DalyTek]

Sounds to me like you have a ground loop. It's hard to see what's going on in the picture though.
If there is more than one path for a signal to get to ground, it forms a "loop" which can act as an antenna and pick up interference.
Try to make all your ground connections go to one single location.

[bratfink]

What on earth is going on there!

I would agree on the ground loop having seen that. Send every ground wire to the same point. That is entriely too much shielding as well!

[dg]

Agreed on the possibility of a ground loop. Pick one point as your central grounding point (this will keep you from accidently creating a closed loop somewhere), then connect that to your output jack. This will also have the added benefit of making you re-solder all of your grounds, in case you have a bad solder joint somewhere.

[Bobby8]

Thanks guys, I will certanly give it a try.

[Xyrium]

While you're at it, it couldn't hurt to check the resistance of the offending pickup.

Bratfink: How can one have "too much" shielding? In fact, I'd say that this is an opportunity to add more copper tape to the base of the cavity by removing the pots and starting fresh. Do some star grounding at a lug on the cavity wall and use a lock washer to penetrate the tape surface and feed it back to the input jack ground. Rewire the postive terminal of the input jack with shielded wire and ground one side of that shield to the jack ground terminal.

[bratfink]

Certainly it can't hurt to have that much shielding around the cavity but IMO it is unnecessary. Agreed on adding more to the base of the cavity, in fact I would have the base of the cavity covered and leave the sides out.

[Xyrium]

Got it. BTW, not sure if it was intended, but if your statement below was a joke, it was very clever given the topic!

What on earth is going on there!

[Newc]

With either pickup as the only one on, try touching the height adjustment screw (with the spring in it) and any other metal part (knob or bridge ideally) at the same time and see if the hum stops.

If it's a KE-1 (with the Kahler) make sure the ground wire is actually touching the bridge and hasn't been pushed so deep into it's own dent that it's not touching (had that issue on a Mustaine Pro).

[bratfink]

Got it. BTW, not sure if it was intended, but if your statement below was a joke, it was very clever given the topic!

Glad you picked that up

Most people of this side of the pond don't use the term 'Earth' for 'Ground'.