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Aside from the clear difference in ease of use, is there a performance difference? Surely paint can't be as good as putting actual metal in there, can it?

Thanks for taking the time to separate the topics - hope my suggestion didn't come off as too harsh, but it's just for the sake of maintaining clarity now, and future reference when others search the forum.

This is actually one of the simpler topics to address. In short, no, there's no meaningful difference in effect on noise suppression. Best to choose by ease of application and durabity.

If we were talking about highly sensitive equipment with circuits operating in the mega or gigahertz frequency range then materials, layouts, mesh size, etc, can certainly affect results. In the range of hertz to a few kilohertz we're working with though (extremely low frequency in terms of typical shielding concerns), there is no appreciable difference - they all do a pretty mediocre job.

Several years ago I got curious about this myself and devised a somewhat crude but reasonably effective test rig for this. I wound a simple receiver coil, mounted it in a box, an set up a slide channel with a contact spring to slide plates with different shielding materials between the noise source and the coil.







For noise sources I used various fluorescent lamps, transformers, computer monitors (this was before we had flat screens) at various distances. Most of the tests were simply listening, coil plugged in to an amp as I slid different plates back as forth. I did plug it in to some FFT programs to look for changes as well, but did not record any data. It was admittedly a fairly quick and crude test with nothing calibrated or measured, but I believe still served as a reasonable comparison with for this application with good controls and instant change for real time comparison.

With the materials I tested (.003" copper foil, kitchen aluminum foil, metal HVAC tape, and nickel based shielding paint in single, double, and triple coats) I found no appreciable difference at all. They all suppressed a bit of noise, but none could come close to blocking it out entirely.

Now as I said, this changes with more complicated circuits, so if you are running an active system and need to block out radio or microwave frequencies then it may make some difference. For standard passive guitar electronics and extreme low frequencies we're fighting to block, I don't believe there is any difference until your shielding plates approach thicknesses of inches rather than thousandths.

So my advice is not to worry about it too much, but just use whatever is easiest for you.

And welcome to the forum!

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Thanks. No, not harsh at all. I just needed to type it all out fast or I'd forget things I wanted to ask. It makes more sense to post specific questions that people with the specific knowledge will see.
That demonstration would make a good Youtube video.
Anyway, I think I'll give the paint a try, since some of my cavities are hand chiseled.
What about ground loops? People always advise not to rely on a metal control plate for connecting all the pots to ground, but to also wire the chassis of each pot together and wire them to ground. I know it's only creating a very small loop, but is it audible?. Might it not make sense to isolate the pot from the plate and just wire them together?
It's not a huge deal...in the studio, You can cut out the buzz, and live...well, who cares about a bit of noise live?
The pickup coils are unshielded anyway. I was going to shield them, but I hear you lose some treble, so I'd rather not bother.

Paint is a good choice, usually my default because it's the simplest to apply to cavities with complex shapes.

As to ground loops, it's not something you need to worry about. There is much confusion about this likely due to several misguided articles from the past which have been repeated so often they are easily mistook for fact. Ground loops simply do not, and indeed can not exist in a passive guitar circuit like this - they are entirely a myth.

Ground loops require a different potential from different power sources. If you have an amp plugged in to one outlet and a preamp plugged in through an extension cord, or different pedals running off different power supplies, you can end up with the ground on one being a few volts off from the ground on another. This is the difference in ground potential, and that power can "loop" through the ground circuit and result in noise. Unless you have different active circuits built in to your guitar powered by separate external power supplies though, a ground loop in your guitar is not possible.

Now there can be Eddy currents, which is something entirely different. With a broad shielding surface it is possible for signals it intercepts to circulate within those surfaces, which in turn can act something like a repeater antenna and retransmit the signal it is trying to block. This is why more advanced shielding systems use perforated sheets or screens, so that signals of certain frequency ranges can not loop to form Eddy currents. Again though, in the low frequencies we're most concerned with this is not so big a concern, and even if it were would be extremely complicated to address. With more complex shielding where this is a concern there is a lot of engineering that goes in to these patterns dependent on frequencies of concern and materials being used.

So no ground loops to worry about, and Eddy currents (if really a concern to begin with at 60-16kHz) are really not worth going after (both for the complex and precise engineering required to address, and their lack of significant influence here even if you did).

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David, interesting to hear your take on ground loops. So I have a question - When I had a hum/buzz problem on my guitar, why did it go away when I removed all the grounds from the top of the pots and wired them to common ground post? This is the reason I was convinced ground loops did exist and have since wired all my electrics this way. Was something else going on?

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Tim Benware
Creedmoor, NC

Well, Passive pickups do create an electrical voltage.
The "ground" is a return conductor for the pickup voltage.
Multiple return paths can introduce voltage differences and thus noise.
Just my opinion, and I could be entirely wrong, but it's good practice to use a star ground scheme, especially with highly amplified small voltage levels.
Dan

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I'm not being cheep but aluminum foil and wood glue work real good no buzzing my shop is just full of florescent lighting. and there's plenty of work time before the glue dries usually let it set over night any way.

Foil isn't really an option in this case, because of the very uneven nature of the cavities. I don't even own a router.

I guess the ground loop thing is another of those things that people can argue about all day. I've read more than once that a proper guitar cable should have two internal conductors, and the exterior shielding should only be connected to ground on the end you plug into the amp. Yesterday, I came across huge threads where people are arguing over this.
My take on it is: if it's not obvious enough that everybody agrees on it, it's not noticeable enough to care about. There are no arguments about whether sliced bread makes a good plectrum.

(True guitarists accept no substitute. Though buttered or un-buttered is a different matter)

Ben - one cause I could possibly see is a ground issue somewhere at the other end of the cable. The same features which cut noise on a well grounded system can leave more noise in a well grounded system if the ground is left open or poorly grounded at the amp/power side. Tele's vs Strats for example - if both guitars are perfectly wired but the earthing in the building's electrical is bad, then the Tele is more often likely to show noise than the Strat. This is because the Tele has a metal cover surrounding the neck pickup and a metal bridge and copper base plate directly adjacent to the bridge coil. If the system is not well grounded, this extra surface will collect the noise so to speak, but have nowhere to drain it off too (not a perfectly suited electrical metaphor, but functionally sufficient). Both guitars wired perfect, but more metal on the ground bus in one leaves it more prone to display issues resulting from ground flaws from the amp side.

Actuay I'm really not optimistic this could explain the issue you experienced, as there's really not that much more metal near anything critical with standard vs star grounding, but perhaps. The only other thing I can think of would be some other peripheral problems in the old circuit that while unnoticed, were coincidentally resolved when the wiring was redone.

Dan - although pickups do generate a very small signal voltage and current, it's not the same as a power supply, and incapable of producing an electrical ground loop. Star grounding is a great practice for purposes of simplifying the process (easier for some to solder some star washers or a single grounding plate than each individual casing), or as a preference of aesthetics for some. Wiring between the components though, whether there they are connected through a single metal wire path or a dozen ways back and forth, a ground loop is impossible.


Simply put, ground loops can not be created by what we see as physical loops we imagine a signal could follow - there has to be a difference in potential as provided from separate power sources. Once you have one conductor connecting any passive components (unpowered, whether signal-generating or not) their ground potential will be the same and every additional conductive path created is simply an inconsequential redundancy. Ground loops only exist when components with different power sources have a difference in potential in the neutral side of their power supply.

If ground loops could occur wherever the ground bus connected in multiple ways, imagine all the places problems would be unavoidable. Between the strings on locking nuts, strip tuners, or string trees, the physical construction of the switches and pots with all the different tabs that fold over connecting ha kings to the from plate, saddle height and intonation screws on Fender bridges, tailpiece to Tune-O-Matic and all the scores of potential "loops" inside the bridge itself. These are all physical loops we can see in the ground bus of the guitar, but fortunately they can not create loops because they are not components powered by different sources. The multiple conductive paths here are no different from multiple cuductive paths between pots and switches.

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Thanks, David,
If I may skew the topic, who makes good guitar cables?
I have a non brand and a Fender cable. Both hum like a mofo with or without guitar plugged in.
I'm using a Vox tube amp with the gain cranked up.
No hum with cable not plugged in.
Is there a certain cable I can try that my be less prone to hum?
Or, is there something I can try at the amp end?
Dan

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Wah