home | tumblrblog | musics | electronics | ask | about | more
The guitar pickup is the core of the electric guitar’s circuit. It is probably the most important part of defining a guitar’s tone. There are too many types and variations of guitar pickups to discuss all of them, so I will limit the discussion to pickups based off the generic single coil and the popular humbucker.
The Single Coil
The single coil pickup is possibly one of the simplest elements of the electronics in a guitar. Electrically, it can be considered a non-polarized, passive, magnetically-coupled inductive voltage source. I know that actually makes it sound very complicated, but it’s actually pretty straightforward once you work through the nomenclature:
It is “non-polarized”, simply meaning that signal can flow in either direction through the pickup. This means that you can wire a pickup “backwards”, and it will still work.
It is “passive”, meaning that it doesn’t need to be powered by an external source to do its thing. So, you don’t need a battery or something to get a pickup to make a signal.
When we get to “magnetically-coupled inductive voltage source”, this is where people tend to get lost. However, if we understand this bit, we’ll be a lot less confused later. When the string vibrates, it can move a magnetic field in a certain way. Magnetic fields can be either North or South*, so we have to remember that a single coil—since it contains a magnet—has magnetic polarity. Now, an inductor is a coil of wire around something, and you can either wrap the coil clockwise or counter-clockwise. An inductor just so happens to be good at making an electrical signal when there’s a fluctuation in a nearby magnetic field. This is why we call a pickup a “magnetically-coupled inductor”. We get a magnet, put it near an inductor, move the magnet’s field with a string, and we get an electrical signal. Yay! One last thing: because we can wrap the coil either clockwise or counter-clockwise, we have to remember that the direction of the coil affects the polarity too. So there are two polarities going on: the magnet (N or S), and the coil (CW or CCW).
The most important part is that a single coil pickup creates a signal, and signal can flow through it. A single coil by itself is not complicated, and you can’t really mess up connecting it to a circuit because it only has two wires: one for the signal, and one for the return. Remember: a circuit is basically a circle; a signal comes out, and it needs some path to return. This is usually through a “ground”.
Rarely, a single coil can have a third wire called a “coil tap”. This is a connection that reduces the number of loops of the coil in the pickup. Basically, the fewer the number of coils, the smaller the signal that comes from the pickup, but the tone will be a little different. True coil-taps are much less common than coil-splits, which will be discussed later.
The trickiness comes from wanting to use more than one single coil at the same time, but then again, this is when things get fun. Now we have to concern ourselves with the magnetic polarity and the coil polarity of the pickups relative to each other. Before, it didn’t matter because polarity of a single signal doesn’t change the way it sounds. But if you add two copies of the same signal together that have the opposite polarity, they will destructively interfere, i.e., they cancel out. This is bad.
Unfortunately, pickup manufacturers don’t print the pickup’s magnetic polarity or coil polarity on the pickups. They usually just recommend one end of a single coil goes to ground (negative) and the other goes to the rest of the circuit (positive), though we really need more information if we want to mix and match pickups. For it to work, the resultant polarity of the signal needs to match. This happens in two cases: One way is if the magnets have the same polarity, then the coil winding needs to be the same. The other way is if the magnets have opposite polarity, then the coil winding needs to be the opposite as well, that way the resultant signal from both pickups has the same polarity. The polarity of the string gets flipped twice, basically.
We might be able to break out a magnetic compass to determine the magnetic polarity of a single coil (yes, it really works). Two magnets with opposite magnetic orientation will have opposite directional readings on the compass. But how do we determine the direction of the winding? The standard terminology is to call one end of a single coil the “start”, and the other the “finish”. These are supposed to be the same “places” regardless of coil winding. So, given that we have, for example, a North single coil and a South single coil, we can assume their coil windings are in opposite directions and connect the output of the North at the Start, and the output of the South at the Finish; the rest of the connections to ground. This will provide the same electrical polarity from both pickups. Assuming the pickups are known to be opposite magnetic polarities, we can know if we wired the starts and finishes correctly if the combined tone is good and full (start of North and finish of South), or is thin and weak (start of both). If they have the same magnetic polarity, we’d use the same start, that way the polarity isn’t flipped any extra times.
Let’s clear up one issue in terms of nomenclature: we are talking about just polarity here. Sometimes you hear—from amateurs and experts alike—the word “phase” get substituted for “polarity”. Often “phase” is used to specifically refer to the coil’s polarity (CW or CCW), and “polarity” is used to refer to the magnet’s polarity (N or S). I strongly recommend against using the word “phase” altogether, because phase is actually used to describe a complicated concept: the time-domain difference of components of a signal in terms of angular displacement. Whoa! Let’s not get into that just yet, shall we? That topic is better for a electrical engineering course at a university. As a final note, it is a coincidence that if one frequency is 180º out of phase, it will have an inverted polarity. This is probably why the two get confused, even by the pros.
Anyway, let’s switch gears. Single coil pickups can also be either in series or parallel. The key to understanding if two things are in series or in parallel is if signal goes through both components to get to another place (series) or if signal combines (or splits) at a junction (parallel). The typical arrangement for multiple single coils is to wire them in parallel, and it is much like what we already described when talking about polarity. The signals from both single coils come out of the coils separately, then “sum” on the common wire they are all connected to. Sometimes there are components like switches and pots in the way, but eventually the signals have to come together somewhere if there’s only one output on a guitar.
Now, wiring a pickup in parallel with another pickup will actually affect the signal that comes from the first pickup. Think of one pickup being represented by what it basically is: an inductor. Signal is generated in the first pickup, and before the signal leaves the guitar, it has to interact with the inductor—the other pickup. Keep this in mind: low frequencies like to flow through inductors; high frequencies do not. So, some of the low-frequency information will “drop” through the pickup that we’re pretending isn’t making a signal at the moment (the inductor). In reality, both single coils interact with each other simultaneously, but thinking about it this way shows us how wiring two single coils will change the tone of the guitar.
If the pickups are wired in series—that is, the finish of one is connected to the finish of the other—the frequency interaction is reversed. For a signal in one pickup to flow out of the guitar, it has to go through the other—either on its way out or on the return. Again, since pickups are basically inductors—and high-frequencies don’t like to flow through inductors—some high-frequency information will “drop” across the pickup.
So, let’s review a few things. A single coil by itself is basically an magnet plus an inductor and works even when it’s wired “backwards”. It sometimes has a coil-tap. Two single coils can be wired with the same polarity or opposite polarity, depending on the polarity of the magnets relative to each other, or the directions of the coil winding. It can be tempting to say “out-of-phase” because saying “the polarity is flipped” is kind of awkward, but saying the wrong thing could lead to confusion. Finally, two single coils can be wired in series or parallel—with parallel being more typical—and high frequencies don’t like to go through inductors.
The Humbucker
A humbucker is quite simply two single coil pickups wired so that their coils are wound in opposite directions. The idea here is to “buck” the hum inherent in single coils. This hum is caused by the coils picking up stray electrical fields nearby, usually from TVs, amps, lights, etc. If the coils are wound opposite relative to each other, then this noise gets “canceled-out”. To prevent the guitar signal from canceling out, the magnets also have their polarities flipped. The result is all the guitar signal and none of the hum.
To know which single coil is which is very important. When you look at a humbucker made to go at the bridge position without a metal cover, you will see a row of flat poles (metal circle thingies) on the top, and a row of poles that look like flat-head screws on the bottom (that’s because they actually are screws). By the way, the screws are adjustable, allowing you to fine-tune the distance from the strings if you wish, but generally it will be a subtle (though potentially useful) change. Anyway, this single-coil with the screws is conveniently called the adjustable coil, and it usually has a South polarity. The other one on top is called the slug; it usually has a North polarity.
But which coil is wrapped in which direction? Actually, it doesn’t really matter, as long as we follow the Start and Finish guidelines. Luckily for us, manufacturers usually tell us this for humbuckers. Just like with single coils with opposite magnets running in parallel, we want to use the opposite ends as outputs: start of north and finish of south, for example.
Even though wiring a humbucker’s single coils in parallel sounds good, it is more common to wire them in series. To do this, we wire the North’s start to be the output. Then, the North’s finish is wired to the South’s finish because we want the polarities to be correct. Finally, the remaining South’s start is connected to the ground.
It’s worth noting that manufacturers have not established a set color code system, and they usually make up their own. You just have to look up their codes and take their word for it, unless you can open up the pickup’s housing and see which wire goes to which end.
Additionally, you can always convert a humbucker into a single coil by disconnecting one single coil and making sure the other is grounded. This is called “coil-splitting”, NOT “coil-tapping” (we already talked about what that is). I would not recommend grounding both ends of the unused single coil because this creates a small ground-loop, which is bad circuitry layout practice and has the potential to cause noise.
Humbuckers are often combined together in pairs. All the same combinations that were available with single coils are also available with humbuckers, increasing the complexity of possible combinations. All the same generalizations can be held, too; when wiring in series, there may be less high-frequency response but “warmer”, when wiring in parallel, there may be less low-frequency response. Like with single coils, parallel configurations of whole humbuckers are more typical.
When experimenting, also take note that the neck pickup is often rotated such that the adjustable single coil is now “on top”, or the opposite orientation from the bridge pickup. A quick look at many dual-humbucker guitars reveals this consistent practice. The South poles then usually lie on the outer sides of the humbuckers, and the North poles lie on the inner. Take note that this does not actually change the polarity of anything; it’s just simply in a different arrangement under the strings.
Ok, so let’s review: a humbucker is two single coils with one coil wound opposite of the other. The slug is the one with smooth poles and is usually North; the adjustable single coil is the one with screws and is usually South. Exceptions to this apply, as manufacturers all have their own way of doing things. Figuring out the magnetic polarities and starts/finishes solves this confusion. The usual approach is to wire a humbucker’s coils in series, but parallel is an option too. Disconnecting one of the coils and making sure the other is grounded creates a coil split. When using multiple humbuckers together, the typical configuration is in parallel, though series is an option.
back to basic passive guitar electronics
*2023 note: I probably could have mentioned that I’m not an experienced electrical engineer or scientist, so I gloss over some foundational concepts from time to time. Here, what I mean is when a metallic body like a metal string vibrates a certain way when a magnet is aligned with the string’s motion, the magnet can induce a signal in a coil of wire wrapped around the magnet, which can create a signal in the wire connected to the rest of the circuit. This induced signal has a phase component compared to the original string vibration due to the electromagnetic nature of the signal’s creation, and this phase depends on the polarity and angle of the magnet with respect to the string AND the direction the wire is coiled around the magnet. This is why we say part of a magnet’s orientation can be “north” or “south” in order to disambiguate its physical magnetic orientation with the string and therefore induced signal polarity. Also, as mentioned above, a coil can be “righty-tighty” or “lefty-tighty” (my silly brain’s way of thinking about “clockwise” and “counter-clockwise” wrapping along a cylindrical shape) around the magnet, and we disambiguate this wrapping by saying a coil is wrapped clockwise (CW) when the start is the intended (+) signal output, and a coil is wrapped counter-clockwise (CCW) when the finish is the intended (+) signal output. This way manufacturers can just indicate signal (+) & start/finish nodes on their specs and imply the magnetic polarity and wrapping details of their products. I know I go over this above too but I just wanted to write this up in a hopefully slightly clarifying way, but actually i just re-wrote it in about the same amount of confusing language anway oops oh well