Noise after shielding

[Booooooom]

I’m nearing completion on my rc4 build (build diary http://www.buildyourownguitar.com.au...ead.php?t=8523 here) and had the bass wired up and working... spent about a week noodling around on it with a great deal of satisfaction! The only issues were when the switch was selecting both pick ups there was a slight dip in volume and also with both pups selected, when either volume pot was zeroed it killed all sound (below last 10% of travel). The tones were clean and clear and good differentiation between pups.

Since then I have stripped it down to give it another couple of coats of oil, waxed it and copper taped the control cavity, both pup cavities and the back of the scratchplate.

Once I reconnected everything there is a lot of noise unless both tone controls are zeroed. If the switch is set to both pups either tone pot can be adjusted without noise but as soon as the second gets moved - noise. The same volume issue as before occurs when zeroing one or other volume pot with both pups selected.

Wiggling the lead in the jack socket reduces but does not eliminate noise. I’ve rewired this with new wire with no improvement. I’ve also replaced all other hot wires and checked all connections for connectivity. All cavities are soldered together and there is connection amongst all cavities. The wiring is the same as here although I have the volume pots closest to the strings and the tones at the bottom as this makes more sense to me.

I’m considering replacing the jack socket and all pots but any ideas what’s causing these issues?

Thanks

Dave

[Rossc0]

Had very similar issues, in one case I had a stray earth, had used shielded wire and one of the hots wires was intermittently earthing out, in the other the bridge earth had come lose. Wiggling the lead, if your touching the metal of the jack will reduce the noise as your effectively becoming a conduit to earth.

If you have a multi meter I'd start by checking everything you expect to be grounded is, and there is no stray wires, solder between pot connections.

[Sonic Mountain]

Almost every wiring problem is an earthing issue somewhere, so Rossco is on the money for start points.

It is possible to kill the kit pots with too much heat. I've wrecked a few bits and piece via multiple wiring attempts. I've also had the jack just up and fail - the insulation between the earth and hot connectors isn't amazing. My local guitar shop sells pots and jacks for around $3-$4 for ones similar to the kit or you can lash out for some Real Parts (or similar) ones for around the $12 mark (I see you are in England... so that's AUD I'm talking)

On my first build I had a few problems with the wiring, which ended up being solved by new pots.

[fender3x]

Checking all the grounds with a multimeter is a good start. Had a similar issue and it was a hidden ground. Have you checked the the ground to the bridge/strings?

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[Booooooom]

Thanks for the replies

I’ve checked for continuity for connection of the components and foiled areas with a multimeter. I’ll check the bridge connection again...

[Simon Barden]

Shielding can only do so much and is effective against only certain types of noise, but is obviously better than not having it. But it does have limitations.

I'd run extra copper tape between the control cavity and the neck pickup on both the body and under the pickguard, so they join up. I normally cover all the underside of a flat pickguard with shielding (I always think a bigger ground plane is better and helps stop interference from a wider range of angles). Unless it's a single piece of copper tape, ensure that you've got continuity to all parts of the cavity and on the pickguard.

I often find that parallel strips of copper tape with an overlap don't have continuity between all the strips, so I normally end up with one or two cross-wise strips that seem to then do the job.

I believe the neck pickup should be a mini-humbucker, so that should be silent without any shielding. If it's noisy, it's either because the signal and ground wires have got crossed somewhere, or because there's something making an awful lot of RF noise close by. Any fluorescent lights (some non-LED low-energy bulbs can give off noise) , dimmer switches, other electrical equipment nearby? Can you test in another room or even a different location?

Never hurts to check the amp mains lead ground connection or the guitar lead. The cheap lead that came with the kit should be thrown away, it is that bad! If you are using that for testing, swap to a decent lead.

With both pickups on, I'd expect a very slight drop in volume, partly as there will be some frequency cancelling from the two pickups sensing different parts of the string, and also because both pickup signals are connected together across both volume pots in parallel, the resultant effective resistance to ground of the pots is halved.

[fender3x]

Are you testing continuity at the ring of the jack?

The best antennas for picking up RF noise are the pickups and the strings, I think. So best bet is you have a bad ground to the bridge or one of the pickup shielding wires.

I have heard a ground loop can also cause this if you have components with multiple paths to ground, but I have never actually had this problem. Best to check the easy stuff first ;-)

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[Booooooom]

I didn’t get chance to check anything yesterday but all cavities have a soldered wire connecting them. Also, when I have been checking continuity with a multimeter I’ve just been taking random points between any of the cavities and getting a bleep. Should I be looking for readings and if so what? #certainlynotapromultimeteruser

[Simon Barden]

For good foil shielding, you should be reading one or two ohms at most. My experience is that if sections aren't properly connecting, then I get 'overload' indication on even the high ohm settings on the multimeter, showing no connection at all. Beeping is an indication of good continuity, so I wouldn't worry too much about sections that beep.

The other thing to check is that the foil has a good connection to ground. It should be connected to ground by the pots on the pickguard touching the foil there, and the foil on the pickguard making contact to the foil in the cavities by contact pressure with the pickguard on. Which is why I like as much overlap on the body and pickguard of foil as possible, and use all the space under the pickguard. But worth checking for a connection from the back of the pots to the foil on the pickguard, just in case the pots have some form of insulation preventing a through connection (unlikely but better safe than sorry).

[fender3x]

Your in good company, don't worry. The great thing about these forums is that you can learn as you go.

Everything that is grounded has to get to the ring on the jack, so I think it's a good idea to clip one lead to that. The continuity that you are checking needs to be continuous to there.

Do all the things Simon has suggested with your foil. Test to make sure that everything that should be grounded is continuous all the way to the jack, by beep or very low (near 0) ohms.


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