Wiring Problem please advise

[80s]

Hey all ! Got a slight problem with me wiring in one of me guitars, I get a constant hum/ annoying noise like its not grounded and it will go once I touch the strings and re-appear when I remove my hand from the strings.
Rather than asking me questions, I have drawn up a wiring diagram so hopefully you can see where the problem Lies.

3-way Gibson USA Switch

Neck - Jazz

Bridge - JB

2 Volume

1 tone

Mono Input jack

Jackson Randy Rhodes with Metal Sratchplate

Thanks for your surport

 

[octavedoctor]

Re: Wiring Problem please advise

You have a problem with your guitar's electrical screening.

Looking at your schematic i don't think you've got a problem with your wiring, although i hope your soldering's neater than your drawing!

The problem you describe is very common. It's caused when the wiring in your guitar acts as aerials and picks up ambient electromagnetic radiation from your environs.

The solution is to enclose the guitars circuitry inside a contiguous conductive "screen" (in the states you call this "shielding" but it's just a difference in terminology).

My guess is that you have a metal scratchplate but no cavity screening. This can actually intensify the noise as the scratchplate will tend to concentrate the interference rather than eliminate it.

Have your guitar screened with graphite or comminuted nickel paint. I feel graphite paint is better as the nickel flake tends to oxidise over time, and the increased resistivity causes the screen's effectiveness to break down.

It's very important that all parts of the screen are continuous and connected to the guitar's earth circuit.

I may submit a post showing the procedure in due course...

 

[80s]

Re: Wiring Problem please advise

So am i right in thinking that the scratchplate needs to be shielded ? And it cant be copper sheilding either ?

Or the actaul Rout for the electronics ?

 

[octavedoctor]

Re: Wiring Problem please advise

So am i right in thinking that the scratchplate needs to be shielded ? And it cant be copper sheilding either ?

No your actual scratch plate doesn't need to be shielded 'cos it's metal, but at the moment it is only half a shield; on the other side of the scratchplate the wiring is exposed and the presence of the large metal plate to which it is all attached is acting a bit like a dish aerial and intensifying the effect of the stray EM wavefronts that are passing through the exposed wiring.

The cavity screening can certainly be copper foil, or any conductive material. In my experience though a conductive paint is easier to apply and there is less risk of the screen becoming discontinuous. I've used both and i haven't found conductive paint to be inferior to copper tape. In fact, copper tape often causes problems when the adhesive layer breaks down and the screening comes adrift, causing shorts when it touches exposed signal points.

Or the actual Rout for the electronics ?

Yes, that's the bit you need to screen

 

[80s]

Re: Wiring Problem please advise

Used Copper shielding as thats all I have at the moment, def seems better thanks alot man, would it be better with a plastic pick guard ? I have some scratchplate material lying around and could make one. Be better maybe ?

 

[octavedoctor]

Re: Wiring Problem please advise

A plastic pickguard won't improve things, you can't get better screening than that offered by solid metal, however aluminium isn't the best as the surface of aluminium begins to oxidise almost immediately and while this feature is very useful if you want to colour it (it's the basis for anodisation) it doesn't lend itself well to electrical conductivity. You may want to try taking the pots off and giving the underside of the plate a good scrub with a wire brush or wire wool to ensure good electrical conductivity between the pots and the plate. Maybe put a piece of copper tape on it and burnish it down hard to ensure it makes good contact. You must use genuine screening tape as only this has an electrically conductive adhesive. Ordinary decorative copper tape used for making leaded lights etc. won't work as well because the resistance offered by the adhesive layer introduces cumulative discontinuity into the screen

The other thing to remember is that the cavity screening must also be connected to the plate and the pots so that there is a continuous conductive "box" around the electrics. It's worth soldering a lead wire to the screen and attaching it to a pot casing to be on the safe side.