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thaumgarrett

Shielding and Grounding

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Apologies if this has been asked before and my search just didn't turn it up, BUT...

Those of you who saw my 2nd build know that it had a horrendous amount of buzz. I'm sure the cheap amazon pots were at fault and I'll never use them again, but all the same it sent me searching for advice about shielding.

I've seen a few tutorials that recommend grounding the shielding material itself (e.g. lining the control cavity with conductive foil, then soldering a wire from the grounded pot-back straight onto the foil, and then leaving some foil hanging over the lip so that it contacts the foil also on the underside of the cavity cover). And with my very fragmentary knowledge of how these things work, I can sort of see why that would be effective.

The thing is, none of the commercially built guitars I own seems to be built that way. There's always a ground wire running from the bridge to the back of a pot where it contacts all the other ground wires, plus conductive foil on the underside of the cavity cover, but never (as far as I can tell) the extensive "grounding" of shielding material that I've just described. 

So since I trust the fine people on this forum a LOT more than random Google searches, I'm asking right out: do you need to somehow ground the foil you're using for shielding? (and, bonus question: if that's the case, why don't Gibson or Ibanez or the budget manufacturers from whom I've purchased seem to be doing this?)

Thanks as always

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20 minutes ago, thaumgarrett said:

The thing is, none of the commercially built guitars I own seems to be built that way. There's always a ground wire running from the bridge to the back of a pot where it contacts all the other ground wires, plus conductive foil on the underside of the cavity cover, but never (as far as I can tell) the extensive "grounding" of shielding material that I've just described. 

That is generally all you should need to do. The grounding of the shield is performed using the already-grounded conductive body of the pot being in contact with the shielding material by way of the pot nut securing it tightly to the cavity wall. Adding a bonus wire directly from another known-grounded point to the shielding material itself serves no real purpose other than to complicate the installation process. The only reason I can think of to do so would be if the shielding material was unable to be grounded in any other way (eg, non-conductive, plastic bodied pots were used).

As a side note, cheap pots are unlikely to be the cause of buzz. That's not where buzz originates from. Cheap pots just mean higher chances of poor longevity, poor construction, less than optimal electrical specs, or easy to break during use or installation.

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About buzz: My first P90 equipped guitar had a very nice sound and a horrendous buzz. I studied this and that and learned that buzz is a feature for P90's. Yet I found it distracting even in the low volumes of the Blackstar Fly clean channel so I took yet another look at the wiring. I rebuilt the three way switch wiring to another design to no awail. Finally, after having triple checked everything I noticed that the jack wires were swapped, the ground being on the tip and the hot in the body! Fixed that, end of buzz.

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P-90s don't buzz. They bark and howl.....and hum sometimes like any single coil pickup. They typically come with very nice shielded wire, so even that is not particularly noticeable.

On the other hand, I think mis-wired jacks may be the number one cause / fix for buzzing-humming squalling noise.  Checking that ought to be at the top of the list for things to check....up there with "did you re-boot it, is it plugged in"?

SR

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19 minutes ago, ScottR said:

up there with "did you re-boot it, is it plugged in"?

😆 how coincidental! That's what I ask for living...

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18 hours ago, thaumgarrett said:

Apologies if this has been asked before and my search just didn't turn it up, BUT...

Those of you who saw my 2nd build know that it had a horrendous amount of buzz. I'm sure the cheap amazon pots were at fault and I'll never use them again, but all the same it sent me searching for advice about shielding.

I've seen a few tutorials that recommend grounding the shielding material itself (e.g. lining the control cavity with conductive foil, then soldering a wire from the grounded pot-back straight onto the foil, and then leaving some foil hanging over the lip so that it contacts the foil also on the underside of the cavity cover). And with my very fragmentary knowledge of how these things work, I can sort of see why that would be effective.

The thing is, none of the commercially built guitars I own seems to be built that way. There's always a ground wire running from the bridge to the back of a pot where it contacts all the other ground wires, plus conductive foil on the underside of the cavity cover, but never (as far as I can tell) the extensive "grounding" of shielding material that I've just described. 

So since I trust the fine people on this forum a LOT more than random Google searches, I'm asking right out: do you need to somehow ground the foil you're using for shielding? (and, bonus question: if that's the case, why don't Gibson or Ibanez or the budget manufacturers from whom I've purchased seem to be doing this?)

Thanks as always

for the most part I use conductive paint to shield my cavities and run a ground to a screw in the cavity and to each additional cavity to link them all.  as mentioned pots should connect it to ground but over time the pots can wear off the paint or tear the tape so i like to wire it in explicitly.  That said, I think you'd be fine either way.  People tend to overkill the shielding but it's better to be safe then sorry IMO. 

for the record my hamer had ground wire running to the pot and to all cavities from the factory... I think if you look at ten mfg you'd likely find ten dif methods of shielding... all varying degrees of 'fine'.

buzz - it's funny but that can mean a lot of dif things to a lot of dif people.  There is the distinct buzz that comes from a single coil that is operating alone, the buzz that will be there when you aren't touching the strings (assuming no emgs), 'buzz' from emi/rf... buzz from a bad cable... a guitar that is wired perfectly correct will have some of these things so I think you just have to get a feel for when you have the right kind of buzz and not the wrong! 

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On 4/22/2019 at 10:28 AM, mistermikev said:

for the record my hamer had ground wire running to the pot and to all cavities from the factory... I think if you look at ten mfg you'd likely find ten dif methods of shielding... all varying degrees of 'fine'.

And thank you again. What threw me is that I (used to) own one factory-made guitar that had foil on the back of the cover but nothing conductive (that I could tell) on the underside of the control cavity, nor any means of grounding that one chunk of foil.

But the more I think about it, based on these responses, maybe it was just lousy build quality since it was a $50 budget guitar. Should have mentioned that I bought it for parts and didn't plug it in before disassembly so for all I know the thing buzzed always buzzed like heck. :)

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7 hours ago, thaumgarrett said:

And thank you again. What threw me is that I (used to) own one factory-made guitar that had foil on the back of the cover but nothing conductive (that I could tell) on the underside of the control cavity, nor any means of grounding that one chunk of foil.

But the more I think about it, based on these responses, maybe it was just lousy build quality since it was a $50 budget guitar. Should have mentioned that I bought it for parts and didn't plug it in before disassembly so for all I know the thing buzzed always buzzed like heck. :)

who knows... maybe they just wanted the "look" of shielding!

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7 hours ago, thaumgarrett said:

And thank you again. What threw me is that I (used to) own one factory-made guitar that had foil on the back of the cover but nothing conductive (that I could tell) on the underside of the control cavity, nor any means of grounding that one chunk of foil.

But the more I think about it, based on these responses, maybe it was just lousy build quality since it was a $50 budget guitar. Should have mentioned that I bought it for parts and didn't plug it in before disassembly so for all I know the thing buzzed always buzzed like heck. :)

Pretty much every strat-type guitar I've seen has adhesive foil stuck to the underside of the pickguard, I imagine this is down to whomever manufactures it for them putting it on, even a £5 scratch plate from amazon or ebay normally has the foil on it. 

When I was researching grounding a while back for my first build, I saw lots of threads saying that coating the cavities with something conductive was not deemed necessary by manufacturers as it's more down to the power supply in the location than the guitar itself and the faraday cage made no difference in factory conditions, especially on guitars fitted with humbuckers.

Generally I tend to setup my builds prior to finish to make sure I'm happy with neck carve etc, so get them playing before I've painted the control cavities with conductive paint and I've got to say that I've never noticed a difference between a shielded cavity and a non-shielded cavity in terms of noise, but domestic wiring in the UK is a lot better than it is in some parts of the world, which stands up with what I read. I shield all my cavities anyway because you never know when you're going to end up playing in a scabby venue with ancient wiring.

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