From: tj–(at)– (tim stanley)
Subject: Re: How to prevent electrical interference on pickups?
Date: 12 Sep 94 10:22:40
Organization: U of M
Lines: 168
References: <34l117$6r--(at)--igboote.WPI.EDU>
In-reply-to: martin–(at)–pi.WPI.EDU’s message of 7 Sep 1994 18:33:11 GMT
Xref: alt.guitar:23917

In article <34l117$6r--(at)--igboote.WPI.EDU> martin–(at)–pi.WPI.EDU (Robert Paul Martino Jr) writes:

When I play the Kramer guitar I’m borrowing too close
to my computer monitor I get all types of buzz and
hum. Is there a way to prevent this? I need to
be somewhat close to the monitor to do digital


Rob Martino _|_ “Yeah! Then we can get our socks
martin–(at)– |filled with sausages!” -Ren
Worcester, Massachusetts |
John 3:16
Hi Rob,

Here are a few responses I wrote and use as a shielding FAQ to cover
this question.


Tim Stanley
WPI EE 1982


| with noise coming from the pick-ups. I understand this is a fairly
| standard problem with strats. What can be done? Being an EE, but not a
| guitar player, I would say shield the pickup and control cavities. Any
| other recommendations?

Yeah, shield the cavity. IMHO, before you buy new pickups, do what
the manufacturer failed to do properly – i.e., shield the cavity.
That is the basis of the problem – after that – decide if new pickups
are in order.

Stewart-MacDonalds (Athens, OH) sells mail order shielding paint.
That is what I always use. One small can is enough for > 5 guitars at
3 coats per guitar. Get in a patient neat mood. This paint is a bit
nasty and awkward to apply. Paint the entire back of the pickguard,
the entire cavity, and a thin lip on the face of the guitar next to
the cavity. Be careful not to paint this lip anywhere that is not
covered by the pickguard. At the same time, be sure to extend the lip
out and around as many screwholes as possible. Then when you screw
the pickguard to the guitar, a connection is made between the shield
on the pickguard and the cavity. Works great for me.

Also, I use 3 coats for coverage and to reduce the sheet resistance of
the paint-shield. The paint is a bit thick – after it dries, you can
visibly see the direction of your brush strokes. So, e.g., first coat
is left to right; second coat is up and down, and third coat is
diagonal. Thusly, at the end, everything is evenly covered despite
your brush strokes.

Other people like foil/sheet metal. Seems hard to work with to me.
But, no doubt it provides a lower resistance path to ground for that
pesky noise.

One practical matter to remember, even for a college educated EE. All
grounds are not alike. Be *very* careful not to create a ground loop.
Follow these simple rules:
+ All grounds should come together at one and only one point
(usually the back of a pot case).

+ Don’t use the shield as ground, rather, use it to conduct
noise to ground. The sheet resistance of the paint is at least
a few ohms – not a good ground conductor, but low enought to
conduct the noise to ground. Do you see the difference?

+ Thusly, there will *never* be two paths to ground.

OK – all fine and well. You will see significant improvement. Fact
is, single coils always have more noise than humbuckers.




| I’m getting too much stray hum and noise in my guitar, and it’s not the
| pickups (i.e. the identical pickups in another guitar sound just fine) nor

Yuppo – big stratish drag – – –

| is it the wiring, which has been redone several times with new shielded
| wires and new solder. Amp, cable, etc. have been the same.

OK – just be *sure* that the shielding in the shielded wire is not
causing a ground loop somewhere. In nearly all instances, the shield
of the cable should be connected at *one*and*only*one* end. Otherwise
it is a ground loop. It may or may not matter. My philosophy is to
never have one.

I use shielded cable from the input jack to the first connection.
This wire carries hot and ground from the cable into the guitar.
Ground is hooked up at both ends.

That’s it. The rest of my internal wiring is done with regular,
appropriate guage wire. I have done the Dan Armstrong scheme twice
and that is the most intricate and complex (and most cool) wiring
design I know. In both instances, I also added push-pull phase
switches, too. I depend on shielding paint to shield the inside of
the cavity from external noise. I avoid shielded cable except where
I can not shield cavities.
| So I’m thinking of shielding the control cavity. The guitar is a Strat
| Plus, older model, and it doesn’t have any shielding at all. I’m thinking

Why don’t manufacturers simply do the right thing and shield their cavities?

| of getting that copper shielding tape from Stewart-MacDonald (and just so
| folks don’t ask, yes, they’re a good company, no I’m not affiliated, and

Yeah – real good – that’s where I got my shielding paint.
| From what I understand, I just stick in the tape and solder it all
| together? Seems like the solder connections could be iffy. After that I
| would then solder a wire from one of the tape segments to ground? I have

Yup – to one and only one point. A common ground lug – much like the
ones on the back of the one of the pots in most implementations. In
fact, simply connecting the shield to that point will do the trick.

| this weird screw/flange/washer thingy in my pickup cavity that isn’t
| attached to anything — is this thing designed to be screwed down on top of
| the tape and then have a wire soldered from this flange thingy to ground?
| If not, what IS that screw for? Nothing is currently attached to it….

No idea.

| While paint is more expensive, if it makes life simpler I may go with the
| copper shielding paint. Any opinions on that?

It is nickel actually, methinks. Hard to say. Probably not copper though.
See my FAQ.

| Also, it seems that shielding the pickup cavity may have pretty irrelevant
| results because the pickups sit so far out of the guitar (at least
| according to Foley’s book) — any opinions on this?

I disagree. I have Foley’s book. Foley is correct that the part of
the pickup sticking out of the guitar is not shielded and will not be
helped. But part of it is below you pickguard – the back of which
will be shielded – and will be helped. Of course, the pickup has an
*enormous* amount of wire in it, and any non-shielded part may
come to dominate overall shielding impact.

BUT – IMHO – especially with strats – shielding makes a real
difference. Audible. This is not a “silver wire” sort of
improvement, if you have been reading that thread. This is not an
alder vs, ash strat sort of thing. It is positively real.

In fact, FYI – Gibson (used to) shields their cavities with a thin
brass plate. On an old SG I own, with two humbuckers, the brass plate
serves only to shield the cavity wiring. Therfore ergo etc, it must
be of some value.

I have paint shielded two strats and one Gibson SG. I have paint
shielded two additional loaded pickguards that I swap back and forth
on one start. All with one can of paint and there is more left. 3
liberal coats each.


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