In the last section, we discussed the different kinds of pickups available to the guitar player. So now, we should have a good idea of why we would use each type and we should also have a rough idea of how each type works. And from that last article, we probably also remember that the most popular kind of guitar pickup is the passive type, and that it uses a magnet and the windings of a wire coil to create your sound.
In this article, we’ll discuss the magnet and the coil and how the interaction between them creates your sound. Essentially, the wire coil and the magnet create a simple electronic transducer, which is a device that changes one form of energy into another; in this case, we change string vibrations into an electrical voltage.
- The guitar pickup starts with the magnet. Magnets create a magnetic field of varying strengths and sizes.
- A wire coil, made from very thin, insulated wire, creates a device called an electromagnetic coil. An electromagnetic coil is a device that becomes magnetically charged when electricity is applied to it. Alternatively, when a coil passes through a magnetic field, electricity is created in the coil through inductance. This is called Faraday’s Law of Induction.
- To take advantage of Faraday’s Law of Induction, we place a wire coil inside the field of a magnet (or magnets). A stationary coil inside a stationary magnetic field will not create electricity on its own. In order to create electricity, either the wire coil or the magnetic field needs to be put in motion. To put the magnetic field in motion, we place our steel guitar strings into the magnetic field, along with the coil. When we pluck the strings, the vibrations disturb the magnetic field and create a sympathetic electrical voltage in the coil. This voltage is sent to our amplifier, where it is amplified into the sound that we hear.
- By using steel or magnetic posts that are lined up with the individual strings, we can fine-tune the “reading” of each string.
It may seem that there would only be a need for one type of pickup design, but that is far from the case. There are many reasons why pickup design can get complicated, and why there are so many different types of pickups to choose from. Some important things to look at first:
Pickup Location – The guitar strings vibrate much less at the bridge pickup than at the neck pickup, and more vibration equals more voltage. If you place two identical pickups in both positions, the neck pickup will be much louder. Most players will try to get the pickups to have a similar output voltage, so the guitar doesn’t suddenly get loud or quiet when switching between pickups.
Musical Style – Guitar pickups can be designed to output more power, which can be used to drive an amplifier harder. A guitar player looking for more distortion might choose higher output pickups for this reason.
Sonic Balance – This refers to the balance of volume and tone between each of the guitar strings. Some players might look for more volume from their lower strings, while others might look for more volume from the higher strings.
Budget – It is important to realize that in many budget guitars, costs have been cut in the pickup design. Often the cheapest of magnets are used and the coil is wound with as little copper as possible. They are oftentimes not wax-potted (something we will talk about later), leading to a more microphonic sound; the other components used in the construction of the pickup are subpar as well. This can lead to a harsh and brittle-sounding pickup, and many times changing to third party pickups can have a dramatic effect on your sound.
The magnet is a very important part of the equation, and while there are many types that can be used, we mostly use ceramic and alnico magnets.
Ceramic magnets are by far the most common type and they are the least expensive. Made from iron oxide, they are usually in the form of a bar, which creates a single magnetic field. This type of magnet is usually placed at the bottom of the pickup and is attached to six steel posts or machine screws that line up with each of the guitar strings. This, in turn, magnetizes the steel posts, changing the shape of the magnetic field and allowing it to get in close proximity of each string.
Alnico magnets are made from aluminum, nickel, and cobalt. These magnets are more expensive to make and are much less common. While these magnets do come in bar form, they are more often arranged in post form. In other words, six alnico post magnets are lined up with the six guitar strings. This creates six separate magnetic fields that can interact with the coil.
Magnets and the magnetic fields they create will definitely affect your output signal. A larger and stronger magnetic field will create a greater electric current in the coil, resulting in a louder pickup. The size of the magnetic field will also affect the area from which vibrations can be detected. A four-string mandolin would need a smaller magnetic field than a six-string guitar, for example.
Magnets will also have a huge effect on your tone, but it is much harder to define or predict exactly how. A quick search of Google will show many results claiming that ceramic magnets sound this way, and that Alnico magnets sound another way, but that has been proven to be false. The magnets need to be heard on a case-by-case basis, as any type of magnet is just as likely to create any type of tone (good or bad).
There are also some negative aspects of the magnets. If the magnet is too weak, the output will be very low, with a higher noise floor. If the magnet is too strong, it will pull on your strings, decreasing sustain and possibly affecting your tonality.
The coil and its windings are the other part of the equation that is very important to the final sound. Coils are slightly more predictable than magnets, but not by much.
The coil, a very thin copper wire, is wound around a bobbin. Other metals, such as silver, can be used, but they are much less common and more expensive. The coil windings are particularly significant: the more turns/winds around the bobbin, the more output/voltage the pickup will produce, and the more “resistance” the coil will have.
The coil by itself, without the presence of a magnet, is actually another electronic component, called a resistor. Two of the common specs to look at when purchasing a pickup is its Output mV, and its DC Resistance. For example, the DiMarzio True Velvet single-coil electric guitar neck pickup has an Output mV of 130 and a DC Resistance of 6.21 Kohm. The Dimarzio Dark Matter 2 passive middle single-coil has an Output mV of 200 and a DC Resistance of 7.33 Kohm. We can tell, by looking at these two examples, that the Dark Matter pickup is going to be louder.
DC Resistance is tied directly to the coil, but the Output mV will be affected by the magnet. If you have two pickups with the same DC resistance but a different Output mV, then the one with the higher Output mV will have the stronger magnet.
The wire is usually 42 or 43 AWG (American Wire Gauge). 42 AWG is used in most pickups, but 43 AWG is often used to get more windings around the bobbin, creating a “hotter” pickup. Other gauges are also used, but much less commonly. Thinner wire has a higher inherent resistance, so the same length of 43 AWG wire will have a higher DC Resistance than a 42 AWG wire.
The wire is coated with an enamel, poly, or a heavy formvar, which acts as an insulation when winding the coil, so the wire does not short itself out. All things being equal, the different insulating materials should have no effect on the final sound. It is possible that various insulating materials might compress differently as they are wound, producing slightly varied sounds, but these are very likely to be minimal against other factors. Some pickups do use a double formvar coating that is said to achieve a brighter sound (due to a change in capacitance), because there is more space between the winds.
The number of winds is going to be a large factor in the final sound. As you add more winds, the space between them creates a capacitor that rolls off more and more high-end frequencies. You can see this in action by taking another look at those Dark Matter 2 pickups we talked about earlier. These pickups are darker in tone, probably in part due to the 7.33 DC Resistance, which we know is the result of its larger-sized coil.
One way to manipulate the capacitance is in the way that the coil is wound. Machine winding is very uniform and can add more capacitance, while hand winding (known as scatter winding) is much less uniform and leads to less capacitance and a brighter tone. This is the reason hand-wound pickups are often described as being brighter and clearer than their machine-wound counterparts. Machine winding leads to pickups that can be mass-produced and counted on to sound a certain way. All Dark Matter 2 pickups, for example, will sound the same. Hand-winding leads to one-of-a-kind pickups, and you never know exactly how they will sound until you try them.
A pickup maker/seeker needs to balance the right type of magnet, with the right amount of winds, in the right way, to create the perfect sound, and in a guitar with multiple pickups, they need to create pickups that complement each other.
Let the fun begin!
In the next article, we will look at the equipment you need to build your own pickup.