Ran across this article a while back when I was reading up on shielding, might be of interest as an alternative perspective on the subject: I Was Wrong About Guitar Shielding
Enjoy the benefits of a premium membership!
Upgrade Account
-
TalkBass has been independent since 1998. Add your voice.
Create a free account to reply to discussions, view embedded media, and browse with fewer display ads.
Join free Log in
Want zero display ads or expanded classifieds tools? Compare plans.
Worst shielding ever?
- Thread starter Daniel B5
- Start date
-
- Tags
- shielding tape
A Faraday cage doesn't need to fully encpasulate to be effective, the gaps just need to be arranged in manner that prevents electric signals entering the protected area. I think that battery IS in the cage.
maybe they used the foil tape as a ground "bus"? the entire chassis of the pot is electrically equivalent, so rather than using a wire to jump between the pots for a ground point, you could rely on the connection between the foil tape and the bottom (in this respect) of the pot for your common/ground. this is just an educated guess since i've never seen the inside of a Ric's control space. but that would be the thing that makes sense to me.
Yeah, Fender was doing that for awhile on some Jazz basses, worked fine until the pot nuts loosened a little.
I wish I still had pictures, but a jazz bass I had years ago had been shielded by a previous owner painting the back of the control plate. Pots, wires, jack, everything just coated in the stuff. The bass still had all the normal hum and the pots were stiff and scratchy. I replaced it with a clean plate and new harness and most of the noise issues went away.
Interesting reply. Let's start by addressing what I actually wrote:
"... shielding the control cavity does not really add much value" does not equal "... shielding doesn't do anything".
I got this from at least one source, and shared what I read here. I also made it clear what my credentials are (or are not, as it were) from the start. Correcting me without the condenscension and false quotes would have been a more appropriate response.
When grounded shielding of any kind (with a separate wire to the output jack), touches something that is already grounded (the back of a pot for example), a closed loop occurs thereby removing the desired hum cancelling effect. Granted, I left this out but my intent was not to write a dissertation. The point of which, since my comment was more of an editorial than a statement of fact, goes back to the juice not being worth the squeeze.
Coinicidentally, I recently brought one of my electric guitars into the shop to have copper shielding tape installed, and all the folks over on the guitar forum were trying to tell me the exact opposite: "Shielding the pickup cavities isn't necessary, just shield the control cavity!"
Fortunately I didn't listen to them.
And every bass or guitar I own that is shielded has shielding in both the pickup and control cavities.
When grounded shielding touches something already grounded, like the back of a pot, it does not automatically create a closed loop, and it does not remove the shielding’s hum-reduction effect.
In a passive electric guitar, the shielding works by acting as a Faraday shield: it intercepts electrostatic noise and drains it to ground. For that to work, the shielding must be connected to ground somehow. If copper foil in the control cavity touches the back of a grounded pot, that is usually fine. In fact, many shielding jobs intentionally rely on contact between the foil and grounded pots, switch frames, jack sleeve, or a common ground wire.
In a passive guitar, those loops are usually very small, carry tiny currents, and are rarely the main source of hum. The bigger issues are usually:
Incomplete shielding coverage
- Shielding not actually connected to ground
- Poor continuity between shielded cavities
- Single-coil pickup hum, which shielding cannot fully eliminate
- Bad solder joints or loose grounds
- A shield accidentally touching a hot signal lug, which can kill or load the signal
Here is a great thread by @Turnaround on the why and how to shield: Shielding - What's to know?
Now when is someone going to share a bass where the body itself has been wrapped completely in aluminum foil, as a way of not having to deal with weird angles in cavities (and creating an, err, eye-catching finish)?
Now when is someone going to share a bass where the body itself has been wrapped completely in aluminum foil, as a way of not having to deal with weird angles in cavities (and creating an, err, eye-catching finish)?
Knightro Custom- J/P Nordys.
Nothing was shielded, not even paint, it was also wired incorrectly. The cavity was bare wood, not even copper on the cover.
It was absolutely unplayable until I redid EVERYTHING.
Nothing was shielded, not even paint, it was also wired incorrectly. The cavity was bare wood, not even copper on the cover.
It was absolutely unplayable until I redid EVERYTHING.
I use the copper foil with the conductive adhesive, the MG Supershield paint is absurdly overpriced, and seems to dry up in the bottle pretty quick, but I can see why Pros would use the spray cans of it when Time is literally money. It doesn't kill 100% of the hum with single-coils, I have a couple old LED lights that still seem to cause it, but it's minor enough, and barely audible.
Last edited:
The control cavity shielding is grounded (or should be, at least) and the pots are also grounded, so if they touch nothing of consequence happens. I do see the value in shielding the control cavity as I have found that input/hot wires are very prone to electro-magnetic "shenanigans".
I see your "tabs" for the pickguard outside the pickup cavities (I do this too). Also, we have the same taste in Mallory caps.I use the copper foil with the conductive adhesive, the MG Supershield paint is absurdly overpriced, and seems to dry up in the bottle pretty quick, but I can see why Pros would use the spray cans of it when Time is literally money. It doesn't kill 100% of the hum with single-coils, I have a couple old LED lights that still seem to cause it, but it's minor enough, and barely audible.
"worst shielding ever" might be what i see in lots of new mid-price instruments, where they paint the cavities with what is in fact shielding paint, but then don't bother to ground it
they've basically installed "antenna paint" at that point, it could add noise
as for shielding control cavities vs pickup cavities, there's an argument for avoiding shielding that's "too good" (i.e., too conductive, like copper foil) right near the pickups themselves; if that shielding is within the magnetic field of the pickups then it can induce eddy currents in the shielding, and said eddy currents can dull the sound of the pickups a little
so yeah, shield the control cavity definitely, shield the pickup cavities with something no more conductive than the graphite paint
they've basically installed "antenna paint" at that point, it could add noise
as for shielding control cavities vs pickup cavities, there's an argument for avoiding shielding that's "too good" (i.e., too conductive, like copper foil) right near the pickups themselves; if that shielding is within the magnetic field of the pickups then it can induce eddy currents in the shielding, and said eddy currents can dull the sound of the pickups a little
so yeah, shield the control cavity definitely, shield the pickup cavities with something no more conductive than the graphite paint
If the pots are secured to it, then the shield is grounded."worst shielding ever" might be what i see in lots of new mid-price instruments, where they paint the cavities with what is in fact shielding paint, but then don't bother to ground it
they've basically installed "antenna paint" at that point, it could add noise
as for shielding control cavities vs pickup cavities, there's an argument for avoiding shielding that's "too good" (i.e., too conductive, like copper foil) right near the pickups themselves; if that shielding is within the magnetic field of the pickups then it can induce eddy currents in the shielding, and said eddy currents can dull the sound of the pickups a little
so yeah, shield the control cavity definitely, shield the pickup cavities with something no more conductive than the graphite paint
correct, but i see it in pickguard-mounted control schemes and in unconnected pickup cavities, situations where there's no ground connection to the shielding paint at all
How many coats of MG super shield does it take to get adequate shielding and continuity? I have had no luck with this stuff. I typically only use it on the “shelf” edges of a control cavity so copper doesn’t show through around the opening, and I can’t get continuity to the copper foil I use inside the cavity. Those tiny little jars only have enough paint to shield (1) cavity with (1) coat. What am I doing wrong? I pull “tabs” of foil up onto the cavity “shelf” at the screw holes, and line the back of the cavity cover with foil as well.
Can't speak to the specific brand but generally three heavy coats with a thorough mixing before each coat and stirring to keep things mixed while applying. That is the minimum but is typically up to the task
