croquet hoop
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Sounds likely. I actually read that in a discussion about wiring in high-gain dirt pedals, not in guitars.
Shielding overkill
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Cagey
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This might be helpful. If that makes any sense to you, you can see how it would be impossible for it to be a problem in a guitar.
Now, in outboard gear, it's fairly easy to create loops because power circuits can be many and varied. Then, the high input impedance of guitar amps makes it easy for them to see pretty small signals, so they tend to exacerbate things that would normally not be much of a problem.
Now, in outboard gear, it's fairly easy to create loops because power circuits can be many and varied. Then, the high input impedance of guitar amps makes it easy for them to see pretty small signals, so they tend to exacerbate things that would normally not be much of a problem.
SoundAsAnOldEngineer
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Cagey said:
On the other hand, a ground loop is easily formed if you connect an amplifier, which is of course grounded to the AC supply, to a PA through a DI box. The loop is from the amp, through the DI box, up the snake/multicore, through the mixer, out the AC cable of the mixer, through the AC wiring of whatever venue you have fortune or misfortune to be playing in, and back to the amplifier. That kind of loop is fixed using the ground lift switch on the DI box.
Prometheus
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Hi. I see some other replies have come in while I was getting to this reply, but I'll post it anyway.
Effective RF shielding is comprised of a grounded conductive enclosure, whose largest aperture dictates the longest wavelength (lowest frequency) that it is capable of absorbing.
Shielded wire has the advantage of pretty much ensuring that the apertures are more-than-adequately small. But it has the disadvantage of requiring the extra effort of grounding the shield in every installed wire. Cavity shielding has the advantage of only being grounded once, and all interior conductors may then be single wires - but it requires a lot of up-front work in getting the cavity clad properly. toMAYto, toMAHto .... pick your poison. Those who wire up once and let it live that way forever may prefer shielded wire. Those who want to more easily change around their wiring schemes may prefer shielding the cavity.
There's no harm in "patchwork" cavity shielding, per se. Using a bunch of small pieces does look untidy though. But if the foil has conductive adhesive, and there's some overlap at joints/seams, many pieces is just the same as one contiguous piece. Some people use regular foil and tack-solder the seams, which is fine too, but more work and I think it's less tidy.
I think that BlueTalon's photo displays an excellent job of cavity shielding. I don't think it's "overkill" though, because that's the way that cavity shielding must be done, or else don't bother (see my previous looooong post). On the other hand, any small aperture or pinhole is really fine, so truly watertight is in fact not necessary. But Cagey has an excellent point about the unshielded conductors. An antenna for RF is really just a length of unshielded wire. And the whole point of the cage is to keep out unwanted RF. So if you have an unshielded length of wire exposed outside the cage, and that wire runs into the cage, then it carries everything that it picks up right into the cage. Not good. The benefit of the cage is nullified. This is what a single coil pickups will do. Or an output cable with an ungrounded shield. All "outside runs" of wire must be shielded, either by extending the cage out to fully enclose the routing they pass through, or by using shielded wire.
I am undecided about copper cladding the pickup routes, at least in terms of eddy currents. They are theoretically bad (and in my work application, intolerable). But I have no personal experience with it in a guitar pickup, so I can't say whether it creates an objectionable audible difference in tone. I lean towards thinking that one may as well try to avoid it if one can. But I maintain that shielding the cavity for a single coil pickup is pointless, because that pickup is the mother of all antennae. Cladding the pickup route does not create an effective RF box, because it's open on one side, and the pickup is exposed to the environment. In fact, the shielded cavity's shape may even provide some "focusing" effect of ambient RF onto the pickup (dunno).
At its heart, this topic is physics, so there's really no room for personal interpretation - although there is, naturally, for personal preference. But if you have noise-cancelled input signal, and let the laws of physics guide your implementation of shielding, then you will be able to keep the guitar's wiring from picking up RF. You may, however, have to work at it. And no, SoundAsAnOldEngineer, I can't think of an easier way to clad a cavity.
Good luck to all. And so long as YOU are happy with YOUR axe, then rock on!
Effective RF shielding is comprised of a grounded conductive enclosure, whose largest aperture dictates the longest wavelength (lowest frequency) that it is capable of absorbing.
Shielded wire has the advantage of pretty much ensuring that the apertures are more-than-adequately small. But it has the disadvantage of requiring the extra effort of grounding the shield in every installed wire. Cavity shielding has the advantage of only being grounded once, and all interior conductors may then be single wires - but it requires a lot of up-front work in getting the cavity clad properly. toMAYto, toMAHto .... pick your poison. Those who wire up once and let it live that way forever may prefer shielded wire. Those who want to more easily change around their wiring schemes may prefer shielding the cavity.
There's no harm in "patchwork" cavity shielding, per se. Using a bunch of small pieces does look untidy though. But if the foil has conductive adhesive, and there's some overlap at joints/seams, many pieces is just the same as one contiguous piece. Some people use regular foil and tack-solder the seams, which is fine too, but more work and I think it's less tidy.
I think that BlueTalon's photo displays an excellent job of cavity shielding. I don't think it's "overkill" though, because that's the way that cavity shielding must be done, or else don't bother (see my previous looooong post). On the other hand, any small aperture or pinhole is really fine, so truly watertight is in fact not necessary. But Cagey has an excellent point about the unshielded conductors. An antenna for RF is really just a length of unshielded wire. And the whole point of the cage is to keep out unwanted RF. So if you have an unshielded length of wire exposed outside the cage, and that wire runs into the cage, then it carries everything that it picks up right into the cage. Not good. The benefit of the cage is nullified. This is what a single coil pickups will do. Or an output cable with an ungrounded shield. All "outside runs" of wire must be shielded, either by extending the cage out to fully enclose the routing they pass through, or by using shielded wire.
I am undecided about copper cladding the pickup routes, at least in terms of eddy currents. They are theoretically bad (and in my work application, intolerable). But I have no personal experience with it in a guitar pickup, so I can't say whether it creates an objectionable audible difference in tone. I lean towards thinking that one may as well try to avoid it if one can. But I maintain that shielding the cavity for a single coil pickup is pointless, because that pickup is the mother of all antennae. Cladding the pickup route does not create an effective RF box, because it's open on one side, and the pickup is exposed to the environment. In fact, the shielded cavity's shape may even provide some "focusing" effect of ambient RF onto the pickup (dunno).
At its heart, this topic is physics, so there's really no room for personal interpretation - although there is, naturally, for personal preference. But if you have noise-cancelled input signal, and let the laws of physics guide your implementation of shielding, then you will be able to keep the guitar's wiring from picking up RF. You may, however, have to work at it. And no, SoundAsAnOldEngineer, I can't think of an easier way to clad a cavity.
Good luck to all. And so long as YOU are happy with YOUR axe, then rock on!
SoundAsAnOldEngineer
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Well, this is going nicely, but I'm a bit confused. People have mentioned two interesting properties of a pickup, namely hum-cancelling and shielding. These two properties don't always go hand in hand, because we have shielded single coil pickups like the standard Telecaster neck pickup, and also plenty of open (unshielded) humbuckers. I'm assuming that it's the shielding of the pickup that contributes to keeping out the RF interference.
As far as I know, humbuckers are great at cancelling low frequency magnetic fields, and that's about it.
As far as I know, humbuckers are great at cancelling low frequency magnetic fields, and that's about it.
Cagey
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This might get long, so bear with me.
Shielding and hum-cancelling are two entirely different things.
Simply put, shielding is a method that takes incoming signals and shunts them to ground so they can't influence the circuits you don't want to see those signals. Some people call those signals RF (Radio Frequency), and that almost certainly gets shunted as well, but in the audio world RF is rarely a problem as the frequency is too high to be heard. It's more properly called EMI (Electro Magnetic Interference), but when push comes to shove, it's really the same thing. It's just that EMI is usually understood to be lower frequency where it gets aggravating. Think 60hz power lines, and the harmonics of that.
Since it's basically radiation, it's difficult to seal against. Depending on the frequency, cracks and holes will let it through and it spreads like ink under pressure.
Hum-cancelling depends on something called CMNR (Common Mode Noise Rejection). How that works is you have two conductors with their signals impressed on them out of phase, then reversed to recover them. Any noise imposed on the two lines is in-phase, so it cancels out during reversal. Has the effect of eliminating any signal that didn't originate at the source.
It doesn't eliminate any particular frequency, so it's incorrect to say "humbuckers" lose low end. In fact, generally speaking, the opposite it true, but it's not due to the things being noiseless, it has to do with impedance mismatch. And usually, humbuckers are heavier on the low end. It's the high end you lose, which is what made the "Hot Rails" so popular when they came out. Humbucking, but still somewhat articulate.
There's a lot more to it, but that's food for thought.
Shielding and hum-cancelling are two entirely different things.
Simply put, shielding is a method that takes incoming signals and shunts them to ground so they can't influence the circuits you don't want to see those signals. Some people call those signals RF (Radio Frequency), and that almost certainly gets shunted as well, but in the audio world RF is rarely a problem as the frequency is too high to be heard. It's more properly called EMI (Electro Magnetic Interference), but when push comes to shove, it's really the same thing. It's just that EMI is usually understood to be lower frequency where it gets aggravating. Think 60hz power lines, and the harmonics of that.
Since it's basically radiation, it's difficult to seal against. Depending on the frequency, cracks and holes will let it through and it spreads like ink under pressure.
Hum-cancelling depends on something called CMNR (Common Mode Noise Rejection). How that works is you have two conductors with their signals impressed on them out of phase, then reversed to recover them. Any noise imposed on the two lines is in-phase, so it cancels out during reversal. Has the effect of eliminating any signal that didn't originate at the source.
It doesn't eliminate any particular frequency, so it's incorrect to say "humbuckers" lose low end. In fact, generally speaking, the opposite it true, but it's not due to the things being noiseless, it has to do with impedance mismatch. And usually, humbuckers are heavier on the low end. It's the high end you lose, which is what made the "Hot Rails" so popular when they came out. Humbucking, but still somewhat articulate.
There's a lot more to it, but that's food for thought.
BlueTalon
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Prometheus said:
I do think there is room for one bit of personal interpretation in matters of physics -- "Does it matter?" Specifically regarding eddy currents, I totally believe you that they are bad (probably), and they might even be measurable at the copper shielding of a pickup route. But in my experience, there's not enough of an effect to be able to hear a difference. It's one of those things where if you listen hard enough, you might be able to hear a difference, but then you wouldn't be able to tell if you were really hearing it or just imagining it.
(OK, truth time -- I have only a very vague idea of what eddy currents actually are, and I just thought of a question that illustrates my ignorance. In the case of a shielded pickup cavity, are eddy currents caused by the copper or induced in the copper? In other words, do eddy currents exist in the grounded shielding, or the pickup wiring? or both?)
Now, it may be a little different for guitar than it is for bass. My experience is with bass, and to the best of my ability to discern, the possible presence of eddy currents doesn't make a difference in the sound.
Now, about the open faced shielded pickup cavity -- yes, the pickup is exposed to the elements, but I don't think the shielding creates any focusing effect for EM/RF energy. If it was ungrounded, then I do believe it would act like a dish antenna and focus unwanted energy; but since it's grounded, I think it acts more like a baseball backstop. Same basic shape, but absorbs/shunts more than it reflects.
Question: Why do you see a difference between single coil pickups and humbuckers, with regards to shielding? My understanding is that adding a RWRP coil would defeat magnetic-source noise but not electric-source. Is that incorrect? If it is correct, or close, then why wouldn't humbuckers also be the mother of all antennae?
Cagey
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BlueTalon said:
When it comes to physics, it always matters. They're immutable laws that can't be disobeyed no matter how badass you are. Whether they make a difference in regards to what you're dealing with is where the rubber meets the road. That is, in reference to what we're talking about - can you hear it? Tough to say. You won't see any tests anywhere that objectively plots one situation accurately against the other. So, anything you hear from anybody is always subjective, rather than fact-based.
"I lined my cavities with foil and it was really really quiet!" Ok. What was it like before? Nobody knows. Nobody builds a guitar/bass, shields it, tests/measures it, then removes the shielding and tests/measures it again. For all they know, it was quieter without the shielding (unlikely, but there's no evidence).
Eddy currents are somewhat directionless currents induced in conductors by nearby conductors with current flow through them. They're out of phase with the inducer, so they have a cancelling effect. That's why you wouldn't want them present near an inductive pickup. You'd lose frequency response, which is a Bad Thing. But, you have to keep in mind some things like the intensity of the fields, which degrade at the square of distance. WIth pickups, the field is so weak to begin with, it's hardly worth talking about. Then, pickup rings and shielding materials are usually brass/copper/aluminum/tin, none of which are ferrous metals. Inducing a current in them with a guitar pickup would be akin to barking at the moon to get it to vibrate. Good luck.
As far as why single coils vs. "humbuckers" respond differently to shielding - neither really does. Humbuckers cancel noise because of CMNR (see previous post), not because they're shielded. Actually, they rarely are. Don't need to be. Single coils don't respond to it either, because there's no way to close the aperture. They're always an exposed antenna. Nothing you can do about it. All the "noiseless" single coils you see are actually "humbuckers" using CMNR to quiet down. It's just not obvious. It's a different packaging/manufacturing technique that makes them look/sound like single coils while actually using two coils. Some are better at it than others.
Neo Fender
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My microscopic attention span prohibits me from scouring every detail in this thread but I read a recent short article in Guitar Player by Gray Brawer. If you don’t know about him, he runs a popular repair shop in San Francisco and is also Joe Satriani’s guitar tech.
In essence, Gary said that shielding control cavities is fine. However, if not grounded properly, shielding (paint or foil) in pickup or trem cavities can act as an antenna and make noise matters worse.
Just sharing…
In essence, Gary said that shielding control cavities is fine. However, if not grounded properly, shielding (paint or foil) in pickup or trem cavities can act as an antenna and make noise matters worse.
Just sharing…
All I know is, all stock Telecasters I play or have played have noticable buzz until I touch the bridge / strings etc, some worse than others. The Tele I have just built with SD Quarter Pounder and SD Phat Cat with copper shielded cavities etc is silent. If I turn up the amp real loud I can hear the faintest difference when touching etc. My American Anniversary Strat is noisy by comparison and doesn't have anywhere near as much shielding. My '57 Historic Les Paul is also buzzy, but that might be due to in keeping with authenticity.
I will always use shielded wire as well as conductive paint. Every guitar I've done that to is completely silent at any gain level when not touching it, while every stock guitar will buzz until you touch the strings.
It amazes me that Gibson (and others) run unshielded wire to the selector switch. It doesn't matter if the pickup wire is shielded if the wires running under the pickups are not.
Really, a $1000 build with many hours invested is worth $5 in supplies.
Just my two cents.
It amazes me that Gibson (and others) run unshielded wire to the selector switch. It doesn't matter if the pickup wire is shielded if the wires running under the pickups are not.
Really, a $1000 build with many hours invested is worth $5 in supplies.
Just my two cents.
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