Shielding the Guitar

Background

After having been a guitar player for many decades, I actually started building guitars and therefore got very interested in different aspects of the guitar world. Besides the specific mechanical issues and data involved in guitar building and design, I started looking into the details concerning electronics, pickups and shielding or putting it differently, the signal quality of the entire system. Deciding to do this was based on a few aspects, first and foremost because of a formal education and long work experience in the area of electrical noise (EMI, RFI, EMC etc.) designing three phase motor controls running off 480VAC and up. The idea was that there was most definitely a bunch of experience that could be applied and passed on in this case. Another big reason was after watching several videos online and reading about the specifics, it was my conclusion that there is a lot of misinformation floating around out there. The reason for this is not so much that people do not want to help others to understand and perform the actual shielding and dealing with the associated electronics, it is because the people that make these videos do not have deeper background so they are basing their statements on myths, hearsay and tradition. It looks like a lot of ways the internal wiring of the guitar is performed has pretty much been unchanged for many, many decades and is performed in this way because “this is the way it was always done”, in other words, tradition. This is, of course, the way you would do it, because you do not possess the knowledge to change the way it is done.

There is a long list of issues in the guitar world that by video makers have been described as “myths” and it appears to me that some have done a great job at debunking these myths, but way too many have survived and even been revived. The sad reality is that we are drowning in a sea of myths The list is long, but we will leave it to another section. Pickups that are based on magnetics follow the same laws of physics after all.

Introduction

This is about shielding, and performing it in a way that has the biggest impact on noise reduction and still keeping it simple. This is because it is possible to simplify the internal wiring and the shielding and at the same time achieve the maximum of noise reduction with a minimum in alteration of sound output. The ways you, in most cases, see this performed in books, articles and videos, is to some extent overkill. You also see that someone puts a lot of work into shielding the guitar, but again tradition sets in and the wiring does not take full advantage of the shielding that has been done or simply does certain things that can ruin the elaborate shielding that has just been performed. The purpose of this page is to give direct guidelines to make it much easier and better for guitar players out there. Now, since the shielding process and the guitar control electronics go hand in hand, it will be necessary from time to time to go a bit beyond what is the scope, the shielding. It is the hope that this will be informative, it might, however, be necessary to branch into a different section that is specifically concentrating on guitar electronics. To get deeper into the electronics, please see the specific page covering this subject.

General Shielding and Noise

First of all, it hurts an old electronics engineer with substantial background in electrical noise to hear the word “ground” and especially the way it is used to describe parts of the guitar control circuit. As a very wise professor informed us at a seminar about these issues, “the only thing that qualifies as ground is the Earth and the closest we get to it is a copper rod rammed deep into it. That is Ground!” Other parts of the circuit is not Ground, so call it something else. We typically call it Common, “0”or something similar. Chassis is sometimes used, but not in connection with noise and shielding, simply because chassis is mostly Ground which is typically not connected to circuitry at all. So, please do not call it ground and calling it “cold” is misguided because that lead is just as important as “hot”. There is a long technical reason for this terminology concerning ground, something we can get into later, some other place. Obviously, do not use the ground symbol for this purpose as well. Only use the Ground symbol when it is actually Ground! Or more accurately: Safety Ground.

Now on to shielding, so let us start with the basic rules that govern shielding of electronics and point out that the higher the frequency the stricter you have to be in observing these rules.

In order to be able to understand why this is done this way, let us briefly describe the noise (EMI) characteristics that we are shielding our electronic control circuitry from. There are fundamentally two kinds of noise, “differential mode” (DM) and “common mode” (CM). Differential mode is not important here and will not be described any further, common mode, however, is extremely important in our case, because unlike DM, CM uses Ground as a return path, which means that any noise radiated into our guitar (or amp for that matter) must be returned to Ground the most reliable and low impedance way possible and the control circuitry must be shielded from this noise in such a way that it is conducted to Ground without even connecting to the circuitry.

Something that is part of the picture, but only sort of relevant to the shielding is the guitar cable that connects the guitar and the amplifier. This cable is for the most cases a single conductor surrounded by a shield, for good cables this is braided, but for cheap ones, this is a tin foil wrapped around the single wire. Personally, I would not consider a single conductor with a “shield” around it a shielded cable, for one important reason, the “shield” is an equal signal conductor similar to the single conductor. Remember a shield shall not carry anything other than collected noise directly to Earth Ground, there is no room for the real signal unless you want it noise infested, which we do not want as it is the reason for shielding in the first place: To keep noise from interfering with the signal. Well, you might say, “I get cable TV through that kind of cable”. I say, there are several reasons why there is a big difference between the two types of signal, one being that the audio (guitar) signal is low frequency where as the  Cable TV is extremely high frequency signal. In the first case the cable is a two wire conductor in a frequency range where the noise level is very high and the Cable TV cable is a so called wave guide in a very high frequency range where the noise level is extremely low. Big difference. As we will discuss later, the perfect shielding of a signal is a completely isolated, independent shield not connected to the signal wires at any point and completely surrounding these. The cable question is easily solved, use a good quality wireless and you will resolve both the noise and the capacitance problem. This was probably “jumping the gun” a bit, so we will leave it at that for now.

Below we will illustrate the best practices of electronic shielding. Beware, the shielding is almost entirely for the “E” rather that the “M” in electro-magnetic. Shielding against magnetic interference is quite a bit more elaborate and luckily not our most significant concern in this case.

First, we will discuss the simplest (but most correct ways) of shielding.

As mentioned earlier, the shield must not at any time or in any way be conducting path for the signal we are attempting to shield. This is being violated to such extent (just watch YouTube videos and read books) that it is found necessary to mentioned it here. It is for pretty obvious reasons. The noise radiated into the system is supposed to be absorbed by the shield and conducted to Ground (not signal common) without interfering with the signal from the pickup. Because of this, it is a bit disturbing to se pickups sold with a single “shielded” conductor, which means that this shield is in fact carrying the pickup signal and noise radiated onto the shield will interfere with the signal also conducted by the “shield”, making the system noisy. Other problems can arise having an exposed signal conductor that touches terminals of opposite “polarity” will create a short circuit causing signal interruption.  Even more troubling is seeing humbuckers with one lead soldered to the base plate and if that was not enough, the “shield” is also soldered to the base plate, the latter is correct do not do the first. The shielding example in Fig 1 has a problem, it shows how limited the situation can be because the guitar cable is only 1 conductor and a “shield”, so the guitar jack will be our virtual grounding point, where the actual grounding point is at the amp chassis or more accurate at the wall socket.

As it was suggested earlier, the way the signals are described needs to be updated, because calling the two wires from the pickup “hot” and “ground” (sometimes “cold) is simply wrong or at best misleading. Some of this has been brought up earlier, but if we take a look at the signal in form of the two wires from the pickup they are basically representing the two ends of the coil that picks up the voltages induced in it by the changes to the magnetic field that the pickup coil surrounds. This should clearly show that there is no difference what so ever between the two wires, which also means that these two wires should not be treated differently since they are carrying exactly the same signal. So when you see one acting as shield for the other, it makes people like myself very sad because you know that the noise induced in the shield now becomes part of the total signal meaning that the total signal becomes noise infested contributing to the noise of the total signal. This pretty much defeats the purpose of the shield, making the signal noisier. A good quantity that you never see in connection with guitar electronics is the S/N, the signal to noise ratio. It is our intent to make this number as large as possible, mainly by reducing the noise since there not much to do about the signal source if we want to maintain a good quality sound, well, we could change pickup, but that is for a different section. There are, however, methods to overcome the effect of system components that we want to reduce, for example by boosting signal to minimize effect of guitar cable capacitance (as in cable length) or to avoid the loading of the pickup by inserting a difference amplifier at the pickup output (active pickup) that separate the pickup signal from the volume control and the “tone” because these will in the typical (passive, non-active) circuit represent a load to the pickup that will change its characteristic, “tone” if you wish.

The mission here is not only to suggest effective shielding but also to simplify the wiring of the guitar. As mentioned earlier, there is too much “tradition” that has been carried up to this point and for no reason, really. Take for instance a Strat that is a few years old, the controls (pots, caps and wires) are all mounted on the pick guard, no aluminum foil on the inside. Now notice that there is a bunch of wires running around and a great deal of them are connected to the volume pot (assuming a 1 volume and 2 “tone” arrangement) case, there are also wires to the two “tone” pot cases from this point on the volume pot. To top things off, the three black pickup wires are also connected here. Finally, this point has a wire representing the signal to the ring of the output jack. This is totally crazy doing it this way even though it is violating the guidelines for good shielding and thereby noise reduction it still has a whiff of something in the right direction and it can be assumed that it is done this way for a good reason. The sad part is that if you buy a modern Strat or even a cheap imitation Strat they all have aluminum foil on the inside of the pick guard in the area of the controls (some covering a larger part of the pick guard), but the control wiring looks exactly like the old ones without the aluminum foil. There is still wiring between pot cases and other places, for no reason. The foil in itself represents no shielding, but it does connect the pot cases and switch as well as any wiring would. Take advantage of that, only one connection is needed, besides, multiple parallel connections can create circulating currents (more noise). Now as a stepping stone to the next, the pot cases (and switch) will be connected by the foil, it is not connected to the interior (the resistive element) so it is beginning to take shape of a shield. Now, if we take this a few steps further, we can completely avoid the tedious task of soldering all these wires to the case of good quality potentiometers. The step now is to keep the signal and the shield apart and get the shield part connected to Earth Ground.

Let us discuss Earth Ground (let us call it Ground) for a moment. When we consider all the noise the guitar is bombarded with whether it is radiated or capacitively coupled or both, Ground is a part of that circuit, Ground is the common point, so to speak, for the return to source to complete the circuit (hence the name), it is a complete cycle. So this noise must be returned to its origin by being conducted to Ground first. There is nothing that dictates that the shield and the signal path need to be connected at any point and if they need to be for practical reasons it must be as close to the grounding point (Ground) as possible. To get the abstractness down to earth (no pun intended), let us look at a practical example. Looking at your average guitar amplifier, the power cord that you use to plug it into the wall is a three prong one, where one of the prongs is Ground. The wire that is responsible for the ground connection is connected to the amplifier chassis with a bolt or screw (good solid connection). If you take a look at the guitar input jack ring on the amplifier it is also hard-connected to the chassis of the amp. This means that we have our Ground connection here. Let us now regard this point as our Ground so this is where our shield should be connected. Now, you might notice that the input is a mono jack so the signal also has one wire connected to this point. That is the best we can get and if the internal circuit in the amp is done correctly and there is an actual Ground to connect to in the outlet, it can be much better with the means at our disposal. We will leave it at that, since very few people will have the knowledge to mess with the amplifier, but most people will be comfortable with working on their guitar. So we will concentrate on the guitar. On the other hand, now that I have gotten this deep into it, the amp is something that I might dig into at some point in the future. For now, we can say that the shielding rules mentioned above for the guitar are valid for the amp as well. Where the rules fall short, where the amp design falls short, rather, is the fact that amp chassis becomes part of the signal path as well as acting as Ground.

To establish a good solid Ground we will pick the Amp input since this is the closest we come to the actual Ground, short of using the wall outlet ground prong. Besides the shielding of the “interior” of the guitar which we will describe with some different methods later, we will need a re-wiring of the interior guitar wiring, the output jack needs to be a stereo jack and the cable to the amp needs to be a shielded stereo cable with the receiving end (amp end) plug can be a mono plug with the common wire connected to the sleeve of the plug and well as the shield of the cable. The shield is now connected to the Ground and the connection of common to the sleeve completes the signal path. This cannot be accomplished with a stereo plug in a mono input (amp) since the signal path would not be connected because there is typically not a stereo jack in the amp.

The next step would be to shield the Amp in such a way that the chassis of the Amp becomes shield and safety ground without the signal being connected to it at all. Since no amps known to this author have this option yet, we will discuss this in the future. The purpose of this would be to completely separate signal and shielding. The safety ground will be combined with the shielding and we will have arrived at a complete system with signal and shield/safety ground separated. Remember, everything metal you can touch must be connected to ground!

You have a few ways to go about this. You can follow the guidelines you find in videos online or in articles or in books. These basically have all the flaws mentioned above. Here is the best way I hereby suggest doing the shielding.

First, we need to revise the guitar wiring. The wiring has traditionally been done in a very peculiar way, as mentioned above, but now that we intend on shielding the signal from noise, it is necessary to take a critical look at the wiring and get rid of wiring and connections that are no longer needed and that will do more harm than good, so why keep them. The end result should be total separation of shield and signal wiring.

Let us start with a humbucker pickup. It has a metal base (typically brass) to where the coils are mounted, this pickup can have a metal cover of german silver (60% copper, 20% nickel, 20% zinc). Both types are good conductors and non-magnetic. With the cover soldered to the base plate, we have ourselves an excellent shield, a very good start to our shielding project. Now let us take a look at the wiring. The typical way a humbucker is wound, we end up with two wires out of the pickup, but what is really sad is that one of these wires is connected to a shield and the other wire is connected to the cable center conductor. Even worse, the shield or part of it is connected to the base plate. As you can see, this is what was referred to earlier as “bad practice” since the one conductor is now both a signal conductor and a shield (or at least trying to act as one). In case you have one of these “vintage” wires that has an exposed shield over a single wire, pretty much cut it off at the coil lead wires and throw it away. If it is a single wire with shield and this shield is covered by an isolating cladding, it can still be used. Next we make sure the shield is not attached to one of the coil lead wires and not touching any metal cover or base plate. The part of the “shield” that is soldered to the base plat needs to be cut out completely. Now we have two wires that have no connection to anything other than the pickup coils.

Next step is very important, we need to purchase a braided copper shield (tinned copper braid shield, flexible) and solder it to the base plate using one of the (typically two) holes that the wires normally go through. Make sure that the shield leaves an opening that the leads can enter, an 1/8” diameter is perfect. An eyelet (3mm or 1/8”) same style as used to solder wires to a Strat pickup can be of big help in this soldering process, the holes in the base plate may have to be opened up to fit braid and eyelet. Now, what we have is a completely enclosed pickup and wires that can be connected to another cavity holding the pots. Next step is to look at the wiring in the potentiometer cavity, along with a much simplified wiring in this area. Eventually we need to look at the wiring to the output jack. This is easiest done by some pictures.

As an alternative connection from pickups to the rest of the circuit, I have found that the two or three conductor shielded cable used for e.g. head phones can be used instead of the braided shielding and existing wires. This type of cable can be soldered into the pickup replacing all the outgoing wiring. It is important to select the type wire that has a shield of a lot of strands of wire, NOT a foil shield with a drain wire. I strongly recommended braided shielding at some point, it is still the best, but can be a bit hard to work with compared to the multi conductor cable. This is the EMI engineer talking again!

Looking at Fig 4, we see the major components from left to right, pickup (PU), potentiometer arrangement with a volume pot (V) and a “tone” pot (T) and the output jack. The pickup is, as described earlier, fully enclosed with a cover, base plate and the braided shield is attached to the base plate, best solution soldered, but the signal wiring is completely independent from the shield.

The section with the pots is fully enclosed in its own shielded cavity where the other end of the braided shield from the pickup is attached, soldered or otherwise. The jack has its own cavity of shielding material of copper. These two cavities are connected with a braided shield that is connected at each end to the cavities, as indicated on the drawing. This is more or less traditional guitar wiring meeting new shielding method. Big difference though, nothing is soldered to the pot cases and even better, the pot cases now become part of the shielding and NOT part of the circuit.

So far we have discussed shielding with humbucking pickups. Same approach can be taken with single coil, but this involves complete enclosure as is the case with e.g. Telecaster neck pickups, but in case you do not want to alter the looks of your Strat pickups, we need a different approach.

This pretty much boils down to shielding the coils as an alternative to completely enclosing the pickup which we will avoid to maintain the Strat look. So instead of the rather dubious shortcut of making the coil be its own shield (that is the common thing), insulate the coil and wrap fitting copper foil around the coil and make this the shield and connect this as suggested above in the totally enclosed pickup, at the same time keeping the shield separate from the coil wires. The rest of the wiring is similar to what is described above by using a shielding braid around the wiring and having a completely shielded cavity for pots, switch and output jack. It is essential to avoid soldering anything to pot cases or anywhere else where it would represent an electrical connection to the shield. One exception though, the strings should be connected to the shield, but make sure that it is not connected to anything else.

As an alternative, it would be a better idea to use one of the single coil pickups that has noise canceling already built in or some external noise gate device. You should consider following the guitar wiring suggestions given elsewhere for the best result.

One thing to consider, if shielding the pickups is not desired or convenient, is to thoroughly shield the rest including the wiring, pots, switches and output jack as described above. Concerning the shield at the pickups, here is a trick that has been used by EMI engineers, including myself, you can use the copper braid shielding and run it all the way to the pickup(s), but leave the shield unconnected (“floating” as we pros would say). It may seem strange to leave the shield unconnected at the pickup, but the shield is of course connected at the output jack and completely enclosing everything else. This is easily to understand if you have experienced noise coupling directly into the wires even where the wires are twisted or other attempts have been made to minimize wire loop area.

Personally, I am experimenting with a single coil pickup shielding that maintains the “the original” look of the pickup that can have a traditional cover of plastic.

Until I have more, this is the place to stop, but before I go to the next subject, here is what I saw lately watching a video on YouTube. For me, just another technical horror story, I think it was what you call a Video Blog (please correct me if I’m wrong). This guy spent rambling on for about 55 minutes about guitar shielding, very inefficient use of your time compared to the information included which was mostly wrong. It is my hope that if you read and understood the above text you would agree with me! One whopper of a “fact” he came up with was an analogy between guitar shielding and a satellite dish! Kept saying that it was about the “square footage, man”. Such analogy is totally bogus, there is absolutely no commonality between a satellite dish and shielding and square footage has nothing to do with the effectiveness of the noise mitigation. I shall not reveal this person’s name, but I can say that he has published a ton of misguided videos including some about how pickups work, demonstrating that he knows nothing about it, and he is a pickup maker that “talks tone”.

Oh, I take that back for the case where you put a lot of labor into shielding every cavity in your guitar with copper foil or tape, meticulously solder everything together, even shielding wire channels between cavities and the whole nine yards. And then…and then completely neglect the control circuitry wiring, you maintain a lot of wires soldered to the back (case) of the potentiometers. The cases of the potentiometers are connected to the shield where they are attached to the body or pick guard of the guitar, so now you have a connection between the shield and your signal path! Yes, here square footage matters, the more of that the more noise you get injected into your signal that you just put a lot of work into getting free of noise!

Here is a few other things from other video makers that have recommended doing things like shielding the spring cavity, not necessary because there is nothing to shield! Another one, some guy put copper tape on the bottom of a Tele control cover, which by the way is already metal, just connect it to the shield!

Humbuckers

Certain pickups actually do some of the work for you, let us look at these! Here are a couple of pickups that I actually bought as shown.

It is probably the best to look at a “bad” example of a pickup wiring first, Fig 5. In this example, we have the dreaded single wire with a apparently braided shield around it, what I would call a non-shielding shielded cable, where the “shield” is actually carrying signal, because it is one of only two conductors. Notice that the “shield” is split up into two, one soldered to the frame pretending to be acting as shield, the other soldered to the output lead from the pickup coil. As I said earlier, a very big no-no!

It should be visible right where the screw is where the cable cladding is trimmed to, you can see the braid is split in two. The “shield” half of it is soldered to the frame by the hole in the lower right corner. That blows the basic concept of shielding, lucky for us it is easy to fix.

The next example is a humbucker that actually came with a 4-lead shielded wire, and it was actually wired correctly! This is actually the first one I have seen being delivered like that. I wish that there would be a whole lot of pickups out there made like that. It would make shielding so much easier and better.

You can clearly see in Fig 6 that the entire shield is wired to the frame, and nothing else is soldered to the lower right hand of the frame. The other wires are black and white from the left side pickup and red and green from the other side. All four wires and the shield is brought out, so far so good. On the output end the white and green wires are soldered together, leaving the black and red wires as signal wires and they are completely separate from the shield, the way it should be! Now, nothing is perfect because the output end of the cable also had the black wire soldered to the shield braid. Why exactly did they do this, now that everything was so perfect? To be nice, I would say that not everybody has their guitar shielded so this is a poor attempt at doing something even though they add noise to the signal! If you do not know anything about shielding or otherwise, you do not have to wonder what to do with the braid sticking out. Needless to say, I separated the shield and the black wire to do proper shielding. Like I said, the white and green wires came soldered together, but you could separate them, of course, if you are into this idiotic coil splitting stuff of a perfectly good humbucker.

In case a pickup has no multi wire shielded cable with separate shield, of course, it is possible to replace the existing wiring with a multi conductor shielded cable and attach it as shown in Fig 6 and Fig 7 or you can provide shielding for pickup and wire by adding a separate braid and press it into the base plate as shown in Fig 8. The braid could be a 1/8″ type with an eyelet to match, you might have to open up the hole in the baseplate a bit. Use insulated wire to run the signal out of the guitar. This can also replace a lot of copper tape in the cavities of the guitar, most likely with a better result.

You may go ahead and solder the braid to the baseplate unless you have a very snug fit. After soldering it is a good idea to trim the braid around the eyelet a bit, a cover for the pickup will be easier to mount. Wait until after soldering to feed the pickup signal wires through the braid. Shielding the cavities as shown on many a video now becomes unnecessary, the braid becomes the shield and a much better one too. Run the braiding shield to a cavity created for the control circuitry and also the output jack as shown in previous figures. All the signal wires need to be contained in the shield and completely separate from it electrically. Do not solder any signal wire to any pot cases!

The braid method can also be used for other pickups that have some kind of shielding measure applied, examples I could mention a lipstick pickup or a Tele bridge pickup baseplate. Just DO NOT forget to remove any connection to the wires from the pickup coil. Only the shielding device must be connected to the braid.

Conclusion

The attempt here is to give an overview of the general guidelines for shielding a guitar and also proposing an alternative to the way the wiring is done in connection with the shielding to take the full advantage of all your hard work. I have included a few examples to show a little of the considerations put into this. It is impossible, of course, to show all variants here, but I think with these guidelines you will be off to a great start.

Speaking of hard work, you can save a lot of time and aggravation by doing the shielding the way described here instead of struggling with copper tape or sheets and there is no need to worry about the adhesive, whether it is conductive or not and about all the pieces of the shielding to fit in a conductive whole. That and a total separation between signal and shield as described above, there is no need to be concerned about changing the sound of the guitar! Saved your day, huh?

Finally, you may have noticed that I have not mentioned “conductive” paint in any way shape or form. A few reasons, I have very little experience with it because I remember when it was introduced we tried it and it did not work too well for our applications. It is, of course, not metal, it is conductive particles in a thick solvent and since EMI shielding requires the best possible conduction at a small thickness several coats of paint is needed and even that does not give you what metal foil will yield. Now, you can say that my applications have been high frequency where paint definitely does not cut the mustard, which is true so it might just work at low frequencies, right? Well, I would not bet on it, because the EMI field strength increases drastically when the frequency gets so low as we are talking here. Besides, I have given you a shielding method that is much simpler that paint or foil here. Enjoy!