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Shielding guitar electronics

Postby Lord Of Tea » Sun Dec 16, 2012 3:21 am

Just tried shielding a Strat copy (Aria STG) but it seems to make no difference. I put baking foil around the pot and pickup cavity, the jack connector cavity and on the underside of the scratch plate. I haven't tried putting foil arond the pick ups yet but that's the next thing I'm intending to try.

Does anyone have any advice and or previouse experience? Want to get this right on the Aria before I move on to my Fenders.
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Re: Shielding guitar electronics

Postby Jay Menon » Sun Dec 16, 2012 5:52 am

Take a look at this:

http://www.edgeguitarservices.co.uk/electric/rf_screening.htm

If it's for a guitar without antique value, you'd be far better off with a couple of coats of conductive graphite paint than copper foil...

Remember to paint on to the surface of the body so as to make contact with the foil on the scratchplate. Also do screen the cavity of the jack socket and the 'tunnel' that leads to it from the main control cavity.
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Re: Shielding guitar electronics

Postby ef37a » Sun Dec 16, 2012 12:00 pm

The efficacy of "electrostatic" screening of anything is dependant upon the conductivity of the shield material. Copper will be better than graphite and Silver (used in RF kit) would be better still (of the same coating thickness)but I doubt you would hear much difference for an electric guitar.

The quotes are because screening the cavity does not reduce "electromagnetic" pickup (might if you used "mu-metal"). I have a De Mazio humbucker in a diecast box*. 100% heavy e'stat screening but it still hums if close enough to a 50Hz traff.

*As a "proper" input load for amps. I had to fill the pot with candle fat as well to mitigate microphony.

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Re: Shielding guitar electronics

Postby Gary_W » Sun Dec 16, 2012 12:35 pm

The screening won't do anything if it is not connected to the screen of the guitar cable.

It's well worth investing a tenner in a multimeter. That way, you can make sure that you have decent continuity to your pots in the first place. Once you've established that, you can then use that 'know good earth'...... As long as your foil has a firm mechanical connection to the earth you'll be fine :)

For a Strat, I like to take the hardware off the scratch plate and then apply a layer of foil to the underside of it using spray on glue.

Whilst it's drying, I put foil inside the body cavity. I leave a tiny bit of foil overlapping in a few places so that they are sticking out of the cavity. I also make sure the bridge is earthed - if it isn't I sort that out. Ditto for any dodgy joints on the pots. In fact, I'll often replace all the wiring - the standard of soldering often seems to be poor in cheaper guitars.

Once the scratchplate is dry I bolt the pots back on. Using my meter I then ensure you have an earthed scratch plate. Then I bolt the scratch plate back in, trapping the overlapping body cavity bits in there. Job done :).

Obviously a Strat won't be as quiet as a properly screened humbucker equipped guitar but doing the above turns a buzz monster into something far nicer.
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Re: Shielding guitar electronics

Postby Dr Huge Longjohns » Mon Dec 17, 2012 10:52 am

Yup, Gary is right. I use the self adhesive copper tape you can get on ebay for about £4 a roll. It's really easy to use, just line the scratchplate and all the cavities then solder an earth wire from the foil to the back of the volume pot. It can make a huge difference. Do it on a single coil guitar and it can turn really noisy into really useable. Do it on a humbucker equipped guitar and you'll think your lead has fallen out it's so eerily quiet!
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Re: Shielding guitar electronics

Postby Dr Huge Longjohns » Mon Dec 17, 2012 10:56 am

Copper tape

Here's the stuff I use.
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Re: Shielding guitar electronics

Postby Lord Of Tea » Mon Dec 17, 2012 11:53 pm

I didn't shield the tunnel. Will get some conductive paint.
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Re: Shielding guitar electronics

Postby Lord Of Tea » Mon Dec 17, 2012 11:57 pm

Gary_W wrote:The screening won't do anything if it is not connected to the screen of the guitar cable.

It's well worth investing a tenner in a multimeter. That way, you can make sure that you have decent continuity to your pots in the first place. Once you've established that, you can then use that 'know good earth'...... As long as your foil has a firm mechanical connection to the earth you'll be fine :)

For a Strat, I like to take the hardware off the scratch plate and then apply a layer of foil to the underside of it using spray on glue.

Whilst it's drying, I put foil inside the body cavity. I leave a tiny bit of foil overlapping in a few places so that they are sticking out of the cavity. I also make sure the bridge is earthed - if it isn't I sort that out. Ditto for any dodgy joints on the pots. In fact, I'll often replace all the wiring - the standard of soldering often seems to be poor in cheaper guitars.

Once the scratchplate is dry I bolt the pots back on. Using my meter I then ensure you have an earthed scratch plate. Then I bolt the scratch plate back in, trapping the overlapping body cavity bits in there. Job done :).

Obviously a Strat won't be as quiet as a properly screened humbucker equipped guitar but doing the above turns a buzz monster into something far nicer.


I've checked the foil, pots, screws and bridge with a multimeter and all seems to be earthed.But still the same hum.
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Re: Shielding guitar electronics

Postby zenguitar » Tue Dec 18, 2012 12:26 am

Lord Of Tea wrote:I've checked the foil, pots, screws and bridge with a multimeter and all seems to be earthed.But still the same hum.

I know exactly what you mean. I used to spend hours methodically checking earths with a multimeter without finding any problem. So as a last resort I would strip out all of the wiring loom, clean all the pots and switches, use a nice solder pump, solder wick, and a file to clean the surface of the contacts, I'd use some fine wet & dry paper to clean the jack socket, and would then rewire from scratch with new hook-up cable.

And it always solved the problem.

I have theories why it is the case, but can't be certain. However, experience tells me that if I hear an obvious wiring problem it is a complete waste of time trying to chase it down with a meter. OK, I've rewired a LOT of guitars, but it always takes me less time to draw a schematic of the existing wiring, work out what it is intended to do (and whether it will actually do that), remove the old loom, clean up, and rewire properly.

Yeah, it's nice to know what was wrong, but it can be a serious waste of time tracing it. Only worth doing on an instrument that would be seriously devalued by rewiring from scratch.

Life is too short to waste on tracing a hum that shouldn't be there. Just rip it all out and rewire from scratch. Hook-up cable costs pennies.

Andy :beamup:
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Re: Shielding guitar electronics

Postby Megacurve » Tue Dec 18, 2012 7:58 am

I have a detailed article on shielding a strat, then changing to a bridge humbucker.

http://www.artandtechnology.com.au/guitar/shielding-strat.html

This has a real short hum demo at the end showing that even with complete shielding,single coils still hum.

Even doing a really good shielding job doesn't fix all the hum. The pickups stick out of the body and are great at picking up hum.

I use high gain, and the final fix for me was a DiMarzio single coil format humbucker.
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Re: Shielding guitar electronics

Postby Lord Of Tea » Sat Dec 22, 2012 2:51 pm

zenguitar wrote:
Lord Of Tea wrote:I've checked the foil, pots, screws and bridge with a multimeter and all seems to be earthed.But still the same hum.

I know exactly what you mean. I used to spend hours methodically checking earths with a multimeter without finding any problem. So as a last resort I would strip out all of the wiring loom, clean all the pots and switches, use a nice solder pump, solder wick, and a file to clean the surface of the contacts, I'd use some fine wet & dry paper to clean the jack socket, and would then rewire from scratch with new hook-up cable.

And it always solved the problem.

I have theories why it is the case, but can't be certain. However, experience tells me that if I hear an obvious wiring problem it is a complete waste of time trying to chase it down with a meter. OK, I've rewired a LOT of guitars, but it always takes me less time to draw a schematic of the existing wiring, work out what it is intended to do (and whether it will actually do that), remove the old loom, clean up, and rewire properly.

Yeah, it's nice to know what was wrong, but it can be a serious waste of time tracing it. Only worth doing on an instrument that would be seriously devalued by rewiring from scratch.

Life is too short to waste on tracing a hum that shouldn't be there. Just rip it all out and rewire from scratch. Hook-up cable costs pennies.

Andy :beamup:

Cheers Andy. I'll take your advice. I have some shielded cable, is there any reason I shouldn't use that? Currently all the looms are made up of unshielded single core.
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Re: Shielding guitar electronics

Postby zenguitar » Sat Dec 22, 2012 5:34 pm

Shielded cable can be very useful, especially for the link to the output socket. But it does come with some caveats if you want to use it for all the hook-ups. And to be honest, if the guitar is already screened there is little if any extra value to be had from using screened cable.

The main things to watch out for are ground loops, especially on instruments where the pots and switches are mounted on a metal plate or a foil screened scratchplate/cavity. The metal plate or foil screen will usually link the metal cases of the pots and switches. So, whether you are using new pots and switches or re-using the originals (after carefully cleaning the solder tags/bodies as I described), the best approach is to fit them before making any connections and use your meter to check whether or not the bodies of the parts have a continuity between them. If they do, your guitar is well screened so just use normal hook-up wire and just use the screened cable for the output.

If most are connected, but one or two are not (maybe a tele with a pick up selector on the top horn like a Les Paul, or a switch with a plastic body) use your screened to connect to that part. But take care to avoid creating any ground loops when you do. For example, a strat pick-up selector is connected to all three pots so if your switch body needs a ground connection you only need to connect it to one of the pot bodies using the screened cable. If you connect all 3 with screened cable you risk ground loops.

Hope that helps :)

Andy :beamup:
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