What is a guitar pickup?
A pickup is one of those little rectangular things on the body of an electric guitar, directly under the strings. It will either be covered in a metal case, or in a plastic bobbin with some metal pole pieces or a bar magnet exposed.
What does it do?
A pickup is what makes an electric guitar electric. It takes the physical vibration of the string and turns it into an electric signal. With this key component, your amplifier and any effects you use then have a signal to shape and amplify.
Most electric guitars use magnetic guitar pickups. They consist of either a single magnet, or a magnet for each strings, each with thousands of turns of fine wire wrapped around it. When the strings are played, the vibration in the strings produce a corresponding vibration in the magnet’s magnetic field, which then induces a vibrating current in the coiled wires.
Single coil pickups
The first type of pickups were single coil pickups, which as the name suggests consists of a single coil for each string. These have a very clear bell-like tone, but are prone to noise and interference, because as well as picking up the change in the magnetic field from a moving string, they will pick up a change in the magnetic field from mains power, strong lights and so on. This noise was not a big concern for many early guitarists, as their non-master volume amplifiers would produce a mostly clean tone, with the volume level of the noise being well below that of the sound of the strings being played. With the advent of high gain amplifiers, overdrive, distortion, fuzz and compression pedals, the noise of single coil pickups became a much greater problem, as all of these things often made the noise much louder relative to the sound of the guitar being played. Single coil pickups remain popular today with a lot of guitarists who either use a mostly clean tone, or who just don’t mind the hum.
To get around the noise problem of single coil pickups, Seth Lover of the Gibson guitar company wired two pickups with reversed magnetic polarity electrically out of phase with each other. This caused the noise hitting the coils to be cancelled out, while the signal induce by the vibration of the strings were added together. These pickups were called Humbuckers, because they “buck the hum”. They are useful for players who use a lot of overdrive, or those who need their guitar to be silent during quiet sections of music. Humbuckers typically have a darker, raunchier sound than single coil pickups.
Active and passive pickups
Guitar pickups are typically passive – that is, they don’t require any power source, beyond the vibration of the strings. These guitar pickups provide a raw but consistent and punchy sound, with the extreme highs and lows somewhat attenuated. Some guitar pickups use 1 or 2 9 volt batteries to amplify the signal, and provide a much lower impedance signal to the amplifier. This makes for a much more full range, “hi-fi” sort of sound. Active pickups tend to be unpopular on guitar, but are much more common on bass guitar.
Some electric guitars have a Piezoelectronic pickup, often just called a piezo. These pickups are mounted on the bridge. Piezo pickups are much more commonly found on acoustic guitar, and when on electrics they generally are found as an addition to regular magnetic pickups, rather than as a replacement for them. Piezo pickups produce a sound similar to a steel string acoustic guitar, which makes them useful in live performance when an electric guitar player needs to play an acoustic part for a short section of a song. By switching to the piezo system, the guitarist can play the acoustic part without having to change guitars, and can then change back just as easily. Piezo pickups are designed to be attached to a full-range system, such as a PA, rather than a regular guitar amp.
There is another type of pickup known as an optical pickup, that works by sensing the effect on a light beam by the vibration of a string. It is not in common use.
Some guitars have only one pickup, but more commonly they will have 2 or 3. The pickup closest to the bridge is known as the bridge pickup, while the one closest to the neck is called the neck pickup. On a 3 pickup guitar, the one in the middle is known as the middle pickup. Pretty easy huh? The position of the pickup has a big effect on the tone it produces. The bridge pickup will sound brighter and edgier, while the neck pickup is darker and more mellow. The middle pickup will have a sound in between the two. Many guitars will have different types of pickups in each position, further changing the sound of each position.