noob - debugging hum in my Les Paul

[lazybones]

I hear hum from my Les Paul which goes away when I touch any of the metal components. I know what all the components do in theory, but I've never really played around with circuits & used multimeters before. How do I debug this with a simple digital meter? Where do I probe & what readings should be appropriate?

Thanks all - I'm learning a LOT by lurking on this forum!

[Jazz P Bass]

Does the"hum" occur on other amplifers.
Just a thought, It may be the amp.

[lazybones]

Yep - both through my Pod/PC and my practice amp.

[cagamp1]

It may not be components or connections. I'd say depending on the model and year of the LP, the pickups may not be waxed. Waxing and/or shielding them may help. Also shielding the circuit compartments will help even more.

[cminor9]

I thought that was the whole point of grounding the bridge and therefore the strings: when you're playing you don't hear that hum. I have a guitar with some Bill Lawrence pickups in it, and it is the quietest guitar I have ever played with those pickups in terms of hum. But even with those, when I take my hands off the guitar and the volume knob is up, there is a 120 cycle hum.

It's not humming when you are playing, right? If not, I wouldn't worry about it. I think that's normal.

[lazybones]

It doesn't hum while playing. The pickups are wax potted - I found wax when adjusting the pole-screws. Does anyone have any pointers on shielding?

[pdf64]

How does the hum level compare to other guitars?

[cagamp1]

Some pickups are better shielded and everything should be grounded. But that doesn't do the trick for every situation.

Case in point:
I have one of those $4k+ Historic Gibson's. It is made to '57 specs. Every time I plugged it in...hummmmm! The closer you got to electrical stuff or the more lights in the vicinity, the more noise it would pick up. So, I shielded all the compartments and 99% of the hum was gone.

I use easy to get stuff but you can use whatever you feel most comfortable with. You can use that special copper shielding...a little stiffer and more expensive. You can use conductive paint...easy to apply...but has a little higher resistance to ground. I use a tacky glue and aluminum foil...easy to shape and mold & is common household stuff. Just cover the compartments and make sure paint/shielding touches ground. Pay attention not to let any signal carrying components touch the paint or foil, like the bottom of pots. I usually stick a piece of electrical tape under the solder lugs for isolation. Easy and you will be satisfied!

I shield all of my guitars.

[David Schwab]

It may not be components or connections. I'd say depending on the model and year of the LP, the pickups may not be waxed. Waxing and/or shielding them may help. Also shielding the circuit compartments will help even more.

None of that has anything to do with his problem, which is a ground issue.

It's probably not the guitar, but the rest of the rig; patch cord, house grounds, etc.

[lazybones]

Thanks for the tips. I'll try putting some foil in there with tape and see if that makes for any improvement before doing a full shielding.

Can grounding issues be identified/isolated with a multimeter?

[cagamp1]

Lazybones, you should check everything like was mentioned...the guitar, the cables, the eqp., the AC outlets.

Conductive paint for shielding is most reliable. If foil is used, you will have to check periodically to make sure it stays stuck and not touch anything.