Shielding Advice Sought

[ChrisK]

There are layered metal foil methods and conductive paint methods for guitar cavity shielding.

When one looks at the material cost, they are both similar. The labor to apply the paint seems to be much less than the foil (especially if one ensures full edge/perimeter connectivity).

Fender uses conductive paint since it can be automated.


Does anyone have experience with both, and can then recommend one over the other?

Specifically, is the foil method vastly superior to the conductive paint method?

[cynical1]

To me, shielding a bass or guitar is either something you do on a build before all the stuff goes in, or it requires you to dis-assemble everything...which is time consuming and may create problems for you on re-assembly...so I've always done both the conductive paint and copper foil shielding...mainly because once I rip the bass or guitar apart I never want to have to go back in and do it again...

In all fairness, I still have about 9 rolls of 3M correlated 1" copper conductive adhesive tape laying around that I picked up at a about 20 bucks/doz from a music store that went out of business...so using foil isn't a cost issue for me... (the nasty little cuts from the foil are a pain in the _ss, though...) With the conductive adhesive you just overlap your seams by about 1/8" and smooth it down with a pencil eraser or a piece of 1/4" doll rod with the edges sanded over...no soldering required.

The conductive paint varies from different vendors. The metallic stuff is OK, but if there's body paint in the cavity the stuff I used had adhesion problems. (don't recall the brand, sorry) The Stew-Mac stuff seems to stick better. It ain't cheap, but nothing at Stew-Mac is cheap. I'll normally put down 3 coats of conductive paint before the foil, leaving about 3-5 days to dry before applying the foil..

I guess the reason I've always done both comes down to a simple philosophy...If you don't have time to do it right, when are you going to have time to do it again.

This may get shot down as overkill, but I guess I'm just a throwback to the days of over-engineering...

Happy Trails

Cynical One

[newey]

Specifically, is the foil method vastly superior to the conductive paint method?

Superior in ease of installation or in shielding efficacy?

I've not tried the conductive paint. But after several bouts with aluminum foil, gluing, overlapping and taping the ends down, I sprung for the copper tape with the conductive adhesive from Stew-Mac. Pricier than aluminum foil, but the trade off in aggravation is worth it. Got good conductivity with about 10 minutes work. And you can solder to it.

I'll never go back to aluminum foil again . . .

I would assume that at least a couple of coats of the paint would be needed to ensure good coverage. That can't be easier to do than foil.

As far as whether the paint or foil performs better shielding-wise, rather than anecdotal evidence, we should obtain some empirical data. We would need 3 identical guitars, one shielded with paint, one with foil, and an unshielded control.

[westside]

Hi there,

I have an Ibanez from the early 90's that has conductive paint on the cavities, from the factory. It has 2 humbuckers (neck and bridge) and a middle SC. The SC is quite noisy. I haven't gone through the guitar in detail yet to know if the shielding and grounding are well-connected and complete.

I have just applied copper shielding to my modern American Standard Strat. I followed the Quieting the Beast advice on the original GuitarNuts website at . It helped but it's not totally hum free. If I get obsessed enough I may try the coil-shielding method described in the Zero-Hum Strat Coil thread. However, I'm not sure if the wiring to the output jack is correct.

I used a very nice Strat pickguard shield and copper sheeting from www.monteallums.com/ which I found via . I lined the pickup cavity with the copper foil and soldered it all for continuity. The pickguard liner and the body foil are overlapped at several pickguard screws, so I should have a good encapsulation. All the shielding has continuity to ground.

I also used a shielded cable to run the signal from the output to the output jack. I used the shield of this cable as the ground on the output jack and also connected it to the guitar's ground point. I have a question about this.

The installation instructions say to attach the shield on this cable to ground on one end only. I understand that on a shielded cable, attaching the shield at both ends makes the shield itself into a conductor that may be carrying some voltage. If you ground it one end only, then any current induced into the shield flows to ground at the ground point, and there are no steady state currents in the shield. However, that implies that I need an additional wire to ground the output jack, and I didn't do that. Also, I didn't line the output jack cavity, or the tremolo cavity for that matter.

My question is, should you consider each piece of shielded cable as its own system, or should the overall length of the signal be considered? The cable between the guitar and the amp is also shielded, and presumably that should be grounded at one end only. If that is the amp end, then wouldn't the entire length of cable (pot to output jack, output jack to amp) be shielded with a single-point ground? Ultimately the cavity shielding itself should be part of that system.

Any opinions, or better yet, actual knowledge on this subject? Thanks, I really appreciate everyone sharing their experience on all these topics.

[ashcatlt]

westside, this goes a little off the topic of this thread, but that never stopped anybody around here before!

QTB calls for "About 1' of "audio" cable which has two insulated conductors inside a single shield" That's how you can get away with attaching the shield at only one end. Honestly, I'm not sure how much you gain this way as opposed to the way you've got it today.

This seems to be a common misunderstanding. Balanced lines can get away with lifting one end of the shield because the shield doesn't carry any program material. I think this is usually done to break ground loops between active components, rather than to improve RFI rejection.

Breaking the shield on the cable between you're guitar and amp might reduce unwanted noise, but it will also reduce wanted noise to something approaching silence.

[westside]

Yeah, that's kind of what I thought. Anyway, I got on to that doing shielding, so it didn't seem too far off topic. I added a gratuitous reference to my paint-shielded Ibanez.

BTW, I also used aluminum foil to shield a medium-old Guild S-70 I have lying around. I used one of those heavy aluminum foil chafing dishes for the foil, and I used a single piece (pressing it down into the cavity) so I wouldn't have to solder it. I found the copper to be much easier to use, was faster to apply, it looks better (not that you can see it, but hey) and you can solder it. As for the amount of time it takes, just how many guitars do you have? Anyway, you still have to take everything off the pickguard if that's not factory-shielded.

Again, with the Guild, the noise was reduced but not eliminated. Either I'm not doing something right, or I have noisy pickups. The noise is definitely higher for SC versus HBs, no news flash there.

[ChrisK]

As for the amount of time it takes, just how many guitars do you have?

Many. Under construction I have 7.

Anyway, you still have to take everything off the pick guard if that's not factory-shielded.

Most are rear-rout.


Using copper foil seems to be problematic especially in bodies that have a less than flat cavity bottom. Some painted ones have points sticking up.

I just found some 12" by 18" sheets of unetched 1/32" glass epoxy single-sided copper-clad PCB stock in my basement. I think that I'll use this for the cavity bottoms, especially on the rear-rout bodies. This will ensure a good non-tearing surface for soldering the cavity side foil to and for the pot shaft bushings, which will keep it in place.