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    Guitar Shielding

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    Ravensha

    Posts : 36
    Join date : 2016-09-05

    Guitar Shielding

    Post by Ravensha on Sat Jul 08, 2017 1:47 pm

    There are some really great discussions on this forum helped by some knowledgeable engineers. I would really like to hear your thoughts on guitar cavity shielding - specifically shielding paint vs. copper tape. Most of the discussions I have read online do not seem to be GROUNDED in (see what I did there!?) any actual data.

    Have any of you shielded your own guitars? Have had situations where you have been able to compare shielding paint and copper tape?
    And why not just grab some Aluminum foil instead?

    Guitar shielding discussion GO!
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    bordonbert

    Posts : 815
    Join date : 2015-01-28
    Age : 97
    Location : Southern England

    Re: Guitar Shielding

    Post by bordonbert on Mon Nov 13, 2017 7:23 am

    Duuuuhhhh!  Sorry Ravensha, I completely missed this thread until I came to start another one and saw it.  Yes, as you can imagine I have strong thoughts on the shielding issue and the misinformation and hype that surrounds it.  (And they're off and it's Bordonbert making a strong showing on the back straight.... again.  Embarassed )  Some of the descriptions of people's results online are laughable.  They plain defy Physics!  It is never approached from a factual critical engineering perspective, it's always seen as another guitar Black Art and something akin to mojo magic. The way I view it is, if the guy who listens to the common wisdom and puts his time and money into performing the ritual can remove all hint of interference from his guitar and make it an inky black ninja silent killer, it proves he has attained entry to 'The Priesthood' who advised him in the first place Wink .  With that in mind guess what he is going to convince himself of after he has fitted the foil or paint?  The truth is it isn't anywhere near as effective as people make out.  It can make a difference but ink black silence inside a generator station you just 'aint likely to get.

    There are two types of interference we suffer from, electrical and magnetic.  Electrical comes from things like fluorescent lighting and is generally high frequency.  Magnetic from things like transformers and heavy motors which are low frequency.  They are different.  The well worked half understood phrase by the apostles of the copper foil is "Faraday Cage".  Yes!  For high frequency electric fields but these are usually dealt with by simply playing your guitar. You do touch your guitar when you play don't you? Then a correctly grounded guitar will stop it when you touch the strings, more of that a little later.  For low frequency magnetic fields it can do nothing.  Copper sheet is a non-magnetic material and at those frequencies you need a strongly ferro-magnetic material to touch it.  The magnetic flux lines are then trapped inside the magnetic shield and simply bent around the cavity.  And that would mean thicker shields, not tiny bits of foil.  Try a solid mu-metal case instead, it may help. In equipment which really needs to be silent they often use 3 or 4 different thicknesses of nested solid special metal canisters to cure it, and we think we can do it with a few scraps of thin copper foil?

    Electrical interference is usually high frequency.  The Faraday cage approach is a start but there is still a lot of misinformation on the outskirts out there.  Shock horror another myth to bust, it is absolutely normal for your guitar to buzz when you are wearing it and not touching the strings!  That does not indicate a problem with your guitar grounding in any way, (and don't even mutter the latest buzz phrase 'ground loop').  As long as it stops when you touch the strings it is perfectly normal.  People often think you are grounding the guitar when you touch it so it must be incorrectly grounded without your contact, you are not.  The guitar is grounding you.  Your body is picking up interference and re-radiating it, and you are wrapped right around your guitar just an inch away from coils designed to pick up signals.  To test it you can try this.  Put your guitar on, don't touch any of its metal parts.  Turn the amp up until you hear that familiar buzz.  Touch something else which is a good earth with your hand, not the guitar/amp.  The buzzing stops or at least reduces significantly?  Once you ground yourself you can see that the guitar has no problem with this effect.

    Certainly screen the cavity with copper foil, it's cheap and easy and it's hard to do something stupid with it, but to get much out of it you will need to take care of a few details.  Firstly and most obviously it needs to be grounded in some way.  Leaving this to a mechanical joint like pressing against it as you mount the output socket is not good.  A soldered lead should be taken to the central grounding point usually on the back of a pot, and that needs to be done for each separate part, like the rear of the scratchplate which is usually just fitted as another mechanical joint, (you did all remember to shield that area too didn't you? Wink )  Mechanical joints in copper corrode very quickly in the atmosphere.  That corrosion is mainly copper oxide and diodes used to be made out of copper oxide at one time.  The slightest film is not good for your noise problem!

    Every piece you use should actually be soldered to the other pieces it laps over for the same reason.  If not then in the future, as the materials age they become less of a low resistance continuous sheet and more a collection of separate areas with resistive connections between them.  And again that 'aint good!

    You have to be careful with any holes in the foil.  Leave it a little untidy around the cable access tunnel and fold the bits around the cable if you can to minimise the hole.  It's inside the cavity, no one is going to see it unless you choose to post the pics of your pretty new mod online for others to envy. Very Happy (We've all done it!)

    It's a dog's breakfast of a solution.  It helps, sometimes a lot, more usually a little.  And the truth is, if it does help a lot then you had other problems which you should have addressed as the root cause.  Like hand wiring!  Why oh why won't the public listen and take in that PCBs are a good thing?  The aerospace and military electronics industry standard way of improving the working of any electronic device is to - - - put it on a PCB.  This isn't purely for cheapness, it's for reliability, repeatability, easy maintenance as well as of course, cost reduction.  What is often missed is that good PCB design work also addresses some of the noise problem we have in our guitars.  Ground planes and proximity effects mean that just having your components on a good PCB actually prevents pickup of interference. But the gurus say it sucks to........ Dooohhh!

    The biggest myth is that a guitar can ever be completely immune to interference.  It is designed to be an open system for picking up disturbances via an open coil and magnets and there will always be a susceptibility to rubbish of all sorts getting through.  The originators were aware of that and designed it to be as silent as it needed to be when playing.  Today's younger players are being sold a pup in the hope of driving up sales and taking on more unhelpful work in many cases. Do I shield my guitars? Yes. Do I claim it made them silent. No. Did it help? Only slightly in one or two cases if I am honest. I'd love to say "yes, I did such a good job they all became much less susceptible" but they didn't. By all means do it just don't get tied up in the hype that comes afterwards. Be prepared to say "not so much after all".
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    Ravensha

    Posts : 36
    Join date : 2016-09-05

    Re: Guitar Shielding

    Post by Ravensha on Mon Nov 13, 2017 11:49 pm

    Awesome, thanks for your feedback!

    I was rebuilding an old guitar, and shielded all of the cavities with copper foil.
    I found it quite addicting!

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