Mr Sulu, raise the shields!

Ok, ok,  it’s a bit of a far-fetched analogy, and it does reference the original Star Trek series (so some of you might not even get it), but this is a guitar blog and ‘raising the shields’ can only mean that this month’s subject is guitar/bass shielding.  Hope you are all surviving the winter and using your time to build modify and play your instruments.

Like a lot of the subjects we talk about in this blog, there is a whole book of knowledge that can go along with the question we have in front of us. Since this is just a quick info blog, we will skim the surface for you and hopefully, if you have more questions, you will be encouraged to do some more research. Do any of you have a car/truck that starts with a button?  Did you go get one of those faraday bags to store your fobs in? Well, the farrady bags are used to create a faraday cage which protects your fob from outside interference or radio signals or any would-be thief with tech knowledge wanting to steal your car.  They work…if you haven’t you should get one. Guitar shielding in essence does the same thing….it creates a faraday cage around your electronics to protect them from EMI (electro-magnetic interference) and RFI (radio-frequency interference). Why does this happen you ask?  Well since the wiring in your instrument is all positive to positive, negative to negative, it creates a form of antenna which attracts these nasty little rascals (EMI & RFI).   That leads to humming and buzzing inside your electronics and gets amplified along with your signal.  It’s much worse in a single coil type guitar since the humbucking pickups are already hum-cancelling, right?  Now, there are a couple things to consider with this …. unless you have a cover on your pickup which is connected to a base plate and then grounded, you can’t shield a pickup….even just exposed poles will attract interference.  However, if you have properly shielded your electronics inside the guitar you will minimize this issue, and in fact, modern pickups are less likely to cause a problem than some of the old ones.  True story, many many years back I took my old Harmony Rocket out to a gig.  The guitar was built in 1967 and had a bit of shielded wire, but also had extremely microphonic pickups…the old DeArmond Mustache single coils.  Anyway, every time this specific taxi drove by the pub I was playing at, the guy was on his radio and his voice was picked up by my guitar and broadcast through my amplifier! RFI……

Ok so what do we do?  We create a faraday cage right? We start with a product to line the control cavity, and there are 3 options I am aware of. Copper shielding tape, aluminum tape (duct tape) and carbon based shielding paint. My choice between the three is copper shielding tape for one main reason, both the copper and the adhesive on the back are conductive, so when you use a hundred little pieces of tape to line the cavities, you create a proper shield.  Aluminum tape or foil is only 61% as conductive as copper, so less efficient, and the adhesive is not conductive, so you must maintain a wide overlap in order to be  effective. So why not just use the paint?  The carbon based shielding paints are a simple solution, and one used by many guitar companies as an added feature. The 2 downfalls I have with the paint are the price for one, and also to create a proper shield you will likely have to apply several coats, which will cost more and possibly make the job a lot longer.  To one degree or another they all of the work, and which one you use is up to you.  You will find a lot of manufacturers install an aluminum foil on the back of their pick-guards (as do many of ours here at SOLO), and this is great as long as that foil is connected to the shielding in the cavity (ie make sure the tape in the cavity overlaps the body surface to ensure contact with the pickguard). If I am being paid to shield a guitar (of which I have done a lot) I will resurface the back of the pickguard with copper tape (even if I have to apply this over the aluminum).

Now, excluding hollow-bodies and semi-hollow-bodies, any guitar or bass can be shielded.  Hollows and semi’s will have to be addressed in another blog as the theory is the same but the parts and costs are different. As I said earlier, you are welcome to shield the pickup cavities, but it won’t make a lot of difference. You could argue for the shielding in a strat type guitar where the pu cavities and the control cavity are all one…your choice.  Since there is no signal going through this area, the trem cavity is also not required in the cage (but can be at your choice).  Remember, if you choose to do all the cavities, they have to be connected to each other with soldered wire connections in order to be part of the ‘cage’. Use as many big pieces of the tape as you can to save time and work, but make sure all pieces are slightly overlapped to ensure contact, and that your pots and switches and your input jack are all touching the tape, and that the tape overlaps the edges of the cavity onto the top of the guitar or the surface of the cover plate recess.  It takes a bit of time but its not difficult.  Flatten as well as possible. It won’t look ‘pretty’ but it does kinda look cool….the shielding paints are cool for the look as well. Now you can re-install the electronics.  The shielding has to be connected to the ground at some point in order for it to be effective because your guitar will be plugged in to a cable and amp.  You can add a ground wire from the back of a pot to the shielding and it should work out just fine.  If you still have major humming or buzzing however, you may have created a ground loop somewhere, and the detective work will start to find the culprit.  The other way you can install the electronics however, is to connect the ground lug on your input jack to the shielding (faraday cage).  This makes the shielding a ‘ground bus’.  (The ground from the building you’re in will be connected to the ground in the outlet, then the ground in your power cord to the ground in your amp and through the ground in your cable to the guitar…right?)  This allows for the elimination of all the inter-connected ground wires on your pots and switches (as long as they have good contact… as in metal to metal with the shielding.  Ground wires from bridges and trems get connected in the usual way but can also be soldered to the shielding. That’s it…you will hopefully have eliminated the rascals we talked of earlier.

There is a caveat to all this. Once the work is done, you may or may not notice a difference in your guitar or bass. Modern instruments have arguably less issues with EMI and RFI than the old ones. Modern wiring in buildings is also much more controlled than in the past, and my favourite, flourescant lighting is all but gone. So when you might notice the difference because you shielded your guitar is when you go out to play and your guitar is not affected…..but your buddies guitar is almost un-usable due to the noise from the interference.  You could go a different route and get into shielded switches and pots, and of course shielded wire to connect them, but it’s a whole different world as far as cost.  Just a quick note on shielded wire…insulated wire is not shielded…..cloth covered wire is also not shielded.  Shielded wire is a typical pvc coated wire (either solid or stranded) that is covered in braided metal.  That metal braiding must be soldered to ground in order to be effective.

So there you have it.  Shielding.  It’s really a personal choice depending on where you play your guitars and whether you have had a problem with interference. Remember, that interference could come from lighting, bad power, poorly wired PA systems, microwaves appliances etc, so pretty much anywhere you go. Some shielding is better than none so a layer of paint or aluminum foil is better than nothing at all, but we have discussed the proper method.  Check out this link here for shielding products and send in your questions if you have any.  I hope I have covered the surface of the subject for you.  Hey, there’s a NAMM report coming and Feb is also the launch of an exciting new product!!  Stay tuned and keep playin!