Pickup (music technology)


A pickup is an electronic device that converts energy from one form to another that captures or senses mechanical vibrations produced by musical instruments, particularly stringed instruments such as the electric guitar, and converts these to an electrical signal that is amplified using an instrument amplifier to produce musical sounds through a loudspeaker in a speaker enclosure. The signal from a pickup can also be recorded directly.
The first electrical string instrument with pickups, the "Frying Pan" slide guitar, was created by George Beauchamp and Adolph Rickenbacker around 1931.
Most electric guitars and electric basses use magnetic pickups. Acoustic guitars, upright basses and fiddles often use a piezo electric pickup.

Magnetic pickups

A typical magnetic pickup is a transducer that consists of one or more permanent magnets wrapped with a coil of several thousand turns of fine enameled copper wire. The magnet creates a magnetic field which is focused by the pickup's pole piece or pieces. The permanent magnet in the pickup magnetizes the guitar string above it. This causes the string to generate a magnetic field which is in alignment with that of the permanent magnet. When the string is plucked, the magnetic field around it moves up and down with the string. This moving magnetic field induces a voltage in the coil of the pickup as described by Faraday's law of induction. Output voltage depends on the instrument and playing style and which string are played and where on the string, but for example, a Samick TV Twenty guitar played on the bridge measured 16 mV RMS for one string and 128 mV RMS for a chord.
The pickup is connected with a 6.35 mm audio jack to an amplifier, which amplifies the signal to a sufficient magnitude of power to drive a loudspeaker. A pickup can also be connected to recording equipment via a patch cable.
A pickup is a part of an electric guitar or bass that "hears" the strings and turns their vibrations into an electrical signal. It’s usually attached to the guitar's body, but sometimes it’s placed on other parts like the bridge or the neck.
Pickups come in different types:
  • Single coil pickups: One coil "listens" to all the strings.
  • Humbuckers: Two coils work together to reduce noise and give a thicker sound.
  • Split coil pickups: Found on certain bass guitars, these have two separate coils, each "listening" to different strings. For example, on a bass with four strings, one coil handles the lower two strings, and the other handles the higher two.
The pickup plays a big role in how the guitar sounds, and different guitars often use unique pickups to create their own signature tone. Guitar companies use this as a key feature to attract buyers.

Construction

Pickups have magnetic polepieces, typically one or two for each string, with the notable exceptions of rail and lipstick tube pickups. Single polepieces are approximately centered on each string whereas dual polepieces such as the standard pickups on the Fender Jazz Bass and Precision Bass sit either side of each string.
On most guitars, the strings are not fully parallel: they converge at the nut and diverge at the bridge. Thus, bridge, neck and middle pickups usually have different polepiece spacings on the same guitar.
There are several standards on pickup sizes and string spacing between the poles. Spacing is measured either as a distance between 1st to 6th polepieces' centers, or as a distance between adjacent polepieces' centers.
1st-to-6thAdjacent
Standard spacing
1.90"
48 mm		0.380"
9.6 mm
F-spacing
2.01"
51 mm		0.402"
10.2 mm
Very close to bridge, extra pickup
2.060"
52.3 mm		0.412"
10.5 mm
Telecaster spacing
2.165"
55 mm		0.433"
11 mm
Steinberger Spirit GT-Pro spacing
2.362"
60 mm		0.3937"
10 mm

Output

Some high-output pickups employ very strong magnets, thus creating more flux and thereby more output. This can be detrimental to the final sound because the magnet's pull on the strings can cause problems with intonation as well as damp the strings and reduce sustain.
Other high-output pickups have more turns of wire to increase the voltage generated by the string's movement. However, this also increases the pickup's output resistance and impedance, which can affect high frequencies if the pickup is not isolated by a buffer amplifier or a DI unit.

Pickup sound

The turns of wire in proximity to each other have an equivalent self-capacitance that, when added to any cable capacitance present, resonates with the inductance of the winding. This resonance can accentuate certain frequencies, giving the pickup a characteristic tonal quality. The more turns of wire in the winding, the higher the output voltage but the lower this resonance frequency.
The arrangement of parasitic resistances and capacitances in the guitar, cable, and amplifier input, combined with the inductive source impedance inherent in this type of transducer forms a resistively-damped second-order low-pass filter, producing a non-linearity effect not found in piezoelectric or optical transducers. Pickups are usually designed to feed a high input impedance, typically a megohm or more, and a low-impedance load increases attenuation of higher frequencies. Typical maximum frequency of a single-coil pickup is around 5 kHz, with the highest note on a typical guitar fretboard having a fundamental frequency of 1.17 kHz.

Humbuckers

Single-coil pickups act like a directional antenna and are prone to pick up mains hum—nuisance alternating current electromagnetic interference from electrical power cables, power transformers, fluorescent light ballasts, video monitors or televisions—along with the musical signal. Mains hum consists of a fundamental signal at a nominal 50 or 60 Hz, depending on local current frequency, and usually some harmonic content.
To overcome this, the humbucking pickup was invented by Joseph Raymond "Ray" Butts, while Seth Lover also worked on one for Gibson. Who developed it first is a matter of some debate, but Butts was awarded the first patent and Lover came next.
A humbucking pickup is composed of two coils, with each coil wound reverse to the other. Each set of six magnetic poles is also opposite in polarity. Since ambient hum from electrical devices reaches the coils as common-mode noise, it induces an equal voltage in each coil, but 180 degrees out of phase between the two voltages. These effectively cancel each other, while the signal from the guitar string is doubled.
When wired in series, as is most common, the overall inductance of the pickup is increased, which lowers its resonance frequency and attenuates the higher frequencies, giving a less trebly tone than either of the two component single-coil pickups would give alone.
An alternative wiring places the coils in buck parallel, which has a more neutral effect on resonant frequency. This pickup wiring is rare, as guitarists have come to expect that humbucking pickups 'have a sound', and are not so neutral. On fine jazz guitars, the parallel wiring produces significantly cleaner sound, as the lowered source impedance drives capacitive cable with lower high frequency attenuation. It is not uncommon for instruments aimed at rock players to have series/parallel switching between the two configurations.
A side-by-side humbucking pickup senses a wider section of each string than a single-coil pickup. By picking up a larger portion of the vibrating string, more lower harmonics are present in the signal produced by the pickup in relation to high harmonics, resulting in a "fatter" tone. Humbucking pickups in the narrow form factor of a single coil, designed to replace single-coil pickups, have the narrower aperture resembling that of a single coil pickup. Some models of these single-coil-replacement humbuckers produce more authentic resemblances to classic single-coil tones than full-size humbucking pickups of a similar inductance.

Notation

Most electric guitars have two or three magnetic pickups. A combination of pickups is called a pickup configuration, usually notated by writing out the pickup types in order from bridge pickup through mid to neck pickup, using "S" for single-coil and "H" for humbucker. Typically the bridge pickup is known as the lead pickup, and the neck pickup is known as the rhythm pickup.
Common pickup configurations include:
  • H-H
Less frequently found configurations are:
  • S
  • H
  • H-S
  • H-H-H
Examples of rare configurations that only a few particular models use include:
  • H-S, but with single coil in the middle
  • H-S-S, but with no space between the middle single coil and the bridge humbucker
  • H-H-S
  • H-S-S-H
  • S-H
  • S-H-H
  • '''S-H-S'''

    Piezoelectric pickups

Sensors

The piezoelectric pickup contains a piezo crystal, which converts the vibrations directly to a changing voltage.
Many semi-acoustic and acoustic guitars, and some electric guitars and basses, have been fitted with piezoelectric pickups instead of, or in addition to, magnetic pickups. These have a very different sound, and also have the advantage of not picking up any other magnetic fields, such as mains hum and feedback from monitoring loops. In hybrid guitars, this system allows switching between magnetic pickup and piezo sounds, or simultaneously blending the output. Solid bodied guitars with only a piezo pickup are known as silent guitars, which are usually used for practicing by acoustic guitarists. Piezo pickups can also be built into electric guitar bridges for conversion of existing instruments.
Most pickups for bowed string instruments, such as cello, violin, and double bass, are piezoelectric. These may be inlaid into the bridge, laid between the bridge feet and the top of the instrument, or, less frequently, wedged under a wing of the bridge. Some pickups are fastened to the top of the instrument with removable putty.