Guitar Shielding and the Capacitor argument against it...

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Guitar Shielding and the Capacitor argument against it...

Postby johnnyg » 23 Nov 2010, 20:13

I'm no EE - but this argument seems like hokum to me... so much so it actually irks me and I'm fed up encountering it. You find some wiring expert pop up on most guitar forums spouting it if you google about for info on guitar shielding. But are these people right and am I wrong - is it possibly true? :hmmm:

The basic idea behind shielding your guitar with either conductive paint or metal foil (usually copper) is to create something approaching a Faraday cage around the internal electronics which will hopefully 'soak in' any RFI and the like that may otherwise work its way into your output signal - right? But the argument against it goes you 'add capacitance' and muddy your 'tone' by reducing treble: the top and bottom of your shielded cavity inside your guitar become a pair of 'plates' and the air between them a dielectric! In other words you effectively create a big fat non-mojo capacitor your signal must pass through....

That sounds like utter bullshit to me - surely if you have shielded correctly you have created, effectively, a metal box around around your internal electronics. Not two separate plates - if you've ended up with that you've done a really bad job shielding your guitar?
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Re: Guitar Shielding and the Capacitor argument against it...

Postby Hides-His-Eyes » 23 Nov 2010, 20:42

There are two capacitors in my guitar and at least one if them is always in the chain via a 500k pot so I'm not worried :)

Plus I can turn the treble up on by amp, I can't turn the noise down on my amp!
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Re: Guitar Shielding and the Capacitor argument against it...

Postby Duckman » 23 Nov 2010, 22:01

I don't know about that "big capacitor effect" (too much distance between plates for such a little voltage, IMO) but if somebody can't shield his guitar correctly, just making pickguard shield connect to cavity shield, maybe hardly can notice any sound difference :lol: and deserves to suffer it :mrgreen:
Ok, just a joke, but I'll sure be following this topic to see where it go.

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Re: Guitar Shielding and the Capacitor argument against it...

Postby johnnyg » 24 Nov 2010, 00:31

I agree with you both H-E-H and Duckman.

I would not be surprised if using a lot of copper foil to shield the cavity/cavities inside your guitar could perhaps have a slight affect on its 'tone' somewhat - for reasons such as altering the resonance of the body perhaps or even affecting the magnetism of the pickups I don't know. But this 'big capacitor' idea I've read a few times seems a bit far fetched - though I'm willing to be enlightened if it can be proven (in layman's terms!). :block:
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Re: Guitar Shielding and the Capacitor argument against it...

Postby Hides-His-Eyes » 24 Nov 2010, 11:30

Being a physicist I thought I would do the calculation.

The value of capacitance of two parallel plates of 20*15cm (rough guess for a cavity) with 25mm of air between them is 10pF. So not laughably small; worth considering, but I'll still take the shielding, thanks.
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Re: Guitar Shielding and the Capacitor argument against it...

Postby modman » 24 Nov 2010, 14:06

You are talking about guitarnuts.com?

Late in 1995 I purchased my first electric guitar (except for a brief fling at 13), a Korean Squier Stratocaster that was unbelievably noisy. When I looked "under the hood" I was appalled to find an unshielded mess of ground loops. Having many years experience as an electronics technician I was flabbergasted that even an inexpensive guitar would be so poorly wired. You can imagine my disgust when I discovered that even many "high-end" guitars costing hundreds or even thousands of dollars were wired no better than that cheap Squier. Naturally I shielded and wired that Strat properly and it became so quiet that I could play it in front of my computer monitor at reasonably high gain without a lot of noise. After hearing horror stories of people being told by their local dealers that guitars equipped with single-coil pickups were supposed to hum, that it was "part of the Fender sound," I became disgusted enough to put instructions for wiring and shielding guitars up on my personal web site.

The response was overwhelming and soon I was exceeding the amount of traffic permitted by the ISP I was using so I purchased a domain and began paying to have the account hosted by a commercial web hosting company.

From those humble beginnings GuitarNuts has steadily grown as I am able to add new features to the site. It is no longer just a wiring site, we now have other sections including a public forum. I've never really promoted the site, have never even submitted it to a search engine, but after Guitar Player magazine featured the site traffic snowballed so rapidly that I had to kick my commercial account up a level because I was again reaching the point where my bandwidth was being throttled before the end of the month.

As for day-to-day operations, GuitarNuts remains mostly a one-man effort. However, I now have a number of people I trust to perform gear reviews and to whom I turn for advice in areas outside my field of expertise. Volunteers also contribute greatly to the site, from sending schematics of their favorite modifications to John Thornburgh's fine article on potting pickups to photographs of a shielding project in progress. If you have something you would like to contribute, I gladly welcome all such input. Just please understand that it may take some time before your submissions actually show up on the site because, when it comes to answering e-mail and updating the site, this is still pretty much a one-man operation, and that one man has to work for a living just like y'all!
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Re: Guitar Shielding and the Capacitor argument against it...

Postby dai h. » 24 Nov 2010, 15:56

so the question is, (basically) "is there validity to the notion that the capacitance increase (from signal wires to ground/shielding) will affect the highs so much that the one will become 'muddy' therefore adding shielding is undesirable?" (Just guessing), but a) I suspect it'd be too small to matter, and b) the pros (reduction of "buzz" would outweigh the cons (possible high freq. reduction). Or, maybe the topic (seen somewhere) somehow morphed from directly shielding pickups with copper foil (on/around them) which (I think) did have a more noticable effect.

re: star grounding (from the quote) (not my original observation, but) I would think the currents inside the gtr. are typically so miniscule that there would not be much point in star grounding (no significantly higher current loops which carry signal that could be superimposed over more sensitive loops via the common ground line to put voltages where they should not be and cause problems such as hum, oscillation).
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Re: Guitar Shielding and the Capacitor argument against it...

Postby roseblood11 » 24 Nov 2010, 17:47

Hides-His-Eyes wrote:Being a physicist I thought I would do the calculation.

The value of capacitance of two parallel plates of 20*15cm (rough guess for a cavity) with 25mm of air between them is 10pF. So not laughably small; worth considering, but I'll still take the shielding, thanks.


This would be true if you had "two parallel plates" with only air between them, but if you shield the cavity completely, all the copper foil (or whatever) is connected together - so there isn´t any capacitive effect, right?
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Re: Guitar Shielding and the Capacitor argument against it...

Postby Duckman » 24 Nov 2010, 17:57

I'm confused :scratch: (or just didn't studied enough :D ) Every box we use in a pedal got his own capacitance that really affect the overall sound?
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Re: Guitar Shielding and the Capacitor argument against it...

Postby FiveseveN » 24 Nov 2010, 18:03

The value of capacitance of two parallel plates of 20*15cm (rough guess for a cavity) with 25mm of air between them is 10pF.

Yes, but the shielding itself does not form a capacitor. Why? Because the two "plates" the OP reffers to are connected together and to ground.
The additional capacitance is between the shielding and the wires signal passes through. This means
1. since a wire has a lot less surface area, the area of overlap is smaller so the resulting capacitance is (much) lower;
2. there are at least two dielectrics between the two "plates": the insulation around the wire and the air between that and the cavity shielding. At least two because some wires have more complex insulation.
If these wires are already shielded themselves (with a screen to ground) I believe there will be no added capacitance. This is also why you eliminate crosstalk between two wires by shielding them.
But would you still benefit from cavity shielding if you already have shielded wires? Yes, because the cavities contain other components that may or may not be individually shielded.
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Re: Guitar Shielding and the Capacitor argument against it...

Postby roseblood11 » 24 Nov 2010, 18:23

Conclusion: The whole "shielding kills your sound" discussion is revealed to be complete bullshit.
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Re: Guitar Shielding and the Capacitor argument against it...

Postby johnnyg » 24 Nov 2010, 18:53

modman wrote:You are talking about guitarnuts.com?


No Modman - I don't trust what I read on that site for reasons given here (my second post in the thread): viewtopic.php?f=2&t=2540

It was just an argument I encountered surfing various guitar forums, I can't recall exactly where - but these are some examples I just found again with a quick google:

http://www.mylespaul.com/forums/tonefre ... knobs.html
http://www.mylespaul.com/forums/tonefre ... lding.html
http://www.mylespaul.com/forums/epiphon ... -tape.html
http://www.strat-talk.com/forum/tech-ta ... ality.html

I decided to paint my own Les Paul control cavity with shielding paint as part of a big rewire of the guitar I'm undertaking - and I had been googling for images of Les Paul wiring and re-wiring for possible ideas (whether to keep the grounding plate in there, go for 50s style wiring etc). It had a grounding issue - too noisy when I wasn't touching the strings. I decided to add the shielding as well - why? Because my US Strat, which has shielding paint and aluminium foil on the pickguard (to create a Faraday cage) put there by the factory, is actually quieter than my Les Paul :shock: ...in the cheap, sleazy, sweaty, smelly rehearsal rooms I often find myself anyway... I can't afford to join a band that plays in the nice £500 a month rooms 8) There is a taxi rank nearby and I think that may create a lot of RFI I don't know... I can't really use a fuzz face there - certainly not a si one anyway.

roseblood11 wrote:Conclusion: The whole "shielding kills your sound" discussion is revealed to be complete bullshit.


Perhaps also this stargrounding your guitar idea from Guitarnuts etc -as Dai H said :wink:

Edit - http://www.youtube.com/watch?v=Jk4k46V0 ... re=related :D
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Re: Guitar Shielding and the Capacitor argument against it...

Postby Duckman » 24 Nov 2010, 19:39

FiveseveN wrote:Yes, but the shielding itself does not form a capacitor. Why? Because the two "plates" the OP reffers to are connected together and to ground.


Now I can sleep :lol: . Thanks
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Re: Guitar Shielding and the Capacitor argument against it...

Postby modman » 25 Nov 2010, 00:43

Shielding is good mostly for single coils. Humbuckers can benefit, but are already humcancelling, having two pickups in counter phase....

johnnyg wrote:I decided to paint my own Les Paul control cavity with shielding paint as part of a big rewire of the guitar I'm undertaking - and I had been googling for images of Les Paul wiring and re-wiring for possible ideas (whether to keep the grounding plate in there, go for 50s style wiring etc). It had a grounding issue - too noisy when I wasn't touching the strings. I decided to add the shielding as well - why? Because my US Strat, which has shielding paint and aluminium foil on the pickguard (to create a Faraday cage) put there by the factory, is actually quieter than my Les Paul :shock: ...in the cheap, sleazy, sweaty, smelly rehearsal rooms I often find myself anyway... I can't afford to join a band that plays in the nice £500 a month rooms 8) There is a taxi rank nearby and I think that may create a lot of RFI I don't know... I can't really use a fuzz face there - certainly not a si one anyway.


http://www.guitarnuts.com/wiring/shielding/shield3.php

Most guitars with single-coil pickups suffer to some degree from hum. Almost all are much noisier than they need to be, because the manufacturers don't bother to shield them well and don't follow simple electronic wiring principles that have been known for decades. This holds true even for many premium guitars costing thousands of dollars. Even some guitars equipped with humbuckers can benefit from good shielding and grounding – guitars that pick up local radio stations are good examples.


Shielding kills a lot of sound indeed - the noise...
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Re: Guitar Shielding and the Capacitor argument against it...

Postby johnnyg » 28 Nov 2010, 01:07

Modman's influence maybe - but I went back to the Guitarnuts site and have modified my opinion about it... not about the benefit of stargrounding in a guitar perhaps, but the site in general. Here I found something very interesting - for me anyway. Seems my original prompt to rewire my guitar was not a correct one! :block:

http://www.guitarnuts.com/technical/noisebucket.php

But the prompt was just to do something I'd wanted to do for a long time - I'd just been terrified to go near my Les Paul as it's too precious to me (too long spent saving for one and too long then spent searching for a good one). I now have a better sounding guitar that's for sure with the changes I've made - it always sounded good, now it sounds even better... I'll discover how much the shielding in the control cavity might help with noise issues next time I'm at a rehearsal.
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Re: Guitar Shielding and the Capacitor argument against it...

Postby azrael » 28 Nov 2010, 02:53

Now...what if we were to shield the actual pickup? Would that do anything?
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Re: Guitar Shielding and the Capacitor argument against it...

Postby RnFR » 28 Nov 2010, 06:07

FiveseveN wrote:
The value of capacitance of two parallel plates of 20*15cm (rough guess for a cavity) with 25mm of air between them is 10pF.

Yes, but the shielding itself does not form a capacitor. Why? Because the two "plates" the OP reffers to are connected together and to ground.
The additional capacitance is between the shielding and the wires signal passes through. This means
1. since a wire has a lot less surface area, the area of overlap is smaller so the resulting capacitance is (much) lower;
2. there are at least two dielectrics between the two "plates": the insulation around the wire and the air between that and the cavity shielding. At least two because some wires have more complex insulation.
If these wires are already shielded themselves (with a screen to ground) I believe there will be no added capacitance. This is also why you eliminate crosstalk between two wires by shielding them.
But would you still benefit from cavity shielding if you already have shielded wires? Yes, because the cavities contain other components that may or may not be individually shielded.

This makes total sense to me. Now remind me never to set foot in that mylespaul forum again. I don't know, maybe it was the massive dogmatic sigs, but that place gave me the creeps.
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Re: Guitar Shielding and the Capacitor argument against it...

Postby aot » 02 Dec 2010, 21:55

Hi Everyone,

Interesting discussion, I love dispelling all the myths that 'experts' have tried to create around the electric guitar. I'm a physicist/RF engineer (I build things for MRI scanners), and it's been really interesting coming back to the guitar with the knowledge I've learnt about RF electronics. I'm repeating what's already been said here, but maybe some of you would appreciate the second opinion.
Most pickups have shielded cables, which should be connected to ground. So there will be no capacitive effect between any cavity shielding (such as copper/aluminium foil) and shielded pickup cables. For unshielded cables there will be an effect, google wire above a ground plane for the answer. It's not likely to be a large effect, shielded cable connecting the guitar to whatever comes next is likely to add a lot more capacitance. For pickups, there is some capacitance between the windings, and if the pickups are shielded then there will be some capacitance there. Apparently shielded pickups are less bright than unshielded, which would make sense (I've never tried them it on the same guitar so I can't comment).

There was a mention of ground loops:

dai h. wrote:re: star grounding (from the quote) (not my original observation, but) I would think the currents inside the gtr. are typically so miniscule that there would not be much point in star grounding (no significantly higher current loops which carry signal that could be superimposed over more sensitive loops via the common ground line to put voltages where they should not be and cause problems such as hum, oscillation).


You definitely want to star ground your guitar. Any loop will act as a small antennae that will pick up the 50/60Hz electromagnetic field from the electric wiring in your house/studio/stage etc. 50Hz has a wavelength of around 6000km, and so you're definitely within the near field regime unless you are in the middle of the Pacific Ocean. Any loop of wire will couple strongly to this field (it's mostly magnetic), this includes a loop in your wiring in your guitar, this causes a common mode signal down what should be a differential (ie single ended) mode and that's why you hear a ground loop. I always star ground my guitars, it makes a hell of a difference.

Oh and how to tell the difference between a ground loop and single coil noise. Single coils pick up the mains frequency from lighting etc, however it tends to be the higher harmonics (100/120Hz+) and so sounds more crackly and thin. Ground loops are predominantly at the fundamental mains frequency and so are very much a low hum.
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Re: Guitar Shielding and the Capacitor argument against it...

Postby dai h. » 02 Dec 2010, 23:57

thanks.

(I think) I get the concept of minimizing area of any loops to reduce hum induction (on those loops--like how a transformer works), but not quite getting my head around the need for a star (individual wires for every ground point).
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Re: Guitar Shielding and the Capacitor argument against it...

Postby mictester » 03 Dec 2010, 02:06

dai h. wrote:thanks.

(I think) I get the concept of minimizing area of any loops to reduce hum induction (on those loops--like how a transformer works), but not quite getting my head around the need for a star (individual wires for every ground point).


This may sound a bit "counter-intuitive" - after all, they're all connected to ground, aren't they? You're eliminating any circulating currents in the earth wiring. However - if you manage to include a loop in your earth wiring, your guitar will be much more susceptible to hum fields.

My guitar wiring (on conventionally wired instruments) uses the ground of the output jack socket as the "star point". It's probably the most convenient place.
"Why is it humming?" "Because it doesn't know the words!"
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