Pickup (music technology)

Split pole pickups, Fender Jazz Bass

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 (this is also called "E-to-E" spacing), or as a distance between adjacent polepieces' centers.

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 (called string capture[5]) 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.

Single coil pickups, Fender Stratocaster (1963)

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[6] 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.

PRS's Dragon humbucker

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 (for Gretsch), while Seth Lover also worked on one for Gibson.[7] Who developed it first is a matter of some debate, but Butts was awarded the first patent (U.S. Patent 2,892,371) and Lover came next (U.S. Patent 2,896,491).

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 (i.e., "fatter") 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,[8] 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,[8] as the lowered source impedance drives capacitive cable with lower high frequency attenuation.

A side-by-side humbucking pickup senses a wider section of each string than a single-coil pickup.[9] 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.

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 pickup(s) 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.[10]

Common pickup configurations include:

• 
  S-S (Fender Telecaster, Jazzmaster and Jaguar, Peavey Reactor, and some Rickenbacker guitars)
• 
  S-S-S (Fender Stratocaster)
• 
  H-S-S (Superstrats like Fender HM Strat, Peavey Raptor EXP, Peavey Destiny)
• 
  H-S-H (Ibanez RG, Ibanez S, other superstrats)

• H-H (Gibson Les Paul, many others including superstrats)

Less frequently found configurations are:

• S (Fender Esquire, early Gibson Les Paul Juniors, Gibson Melody Maker, Danelectro U1, some Telecasters)
• H (Gibson ES-165 Herb Ellis, Kramer Baretta, later Les Paul Juniors)
• H-S (Hamer Californian Deluxe, Les Paul BFG, Squier '51)
• H-H-H (some Gibson Les Paul Goldtop and Custom models, Gibson SG-3, Gibson ES-5 Switchmaster (after 1957), Kramer Jersey Star, Ibanez Destroyer, Ibanez PGM200)

Examples of rare configurations that only a few particular models use include:

• H-S, but with single coil in the middle (one model of Fender Jazzmaster, Ibanez RG2011SC, Fender Player Jaguar)
• H-S-S, but with no space between the middle single coil and the bridge humbucker (Hamer Phantom with angled neck pickup)
• H-H-S (Mayones Legend “22” Anders Nyström signature, some ESP Stephen Carpenter Models, and Alembic Jerry Garcia Models)
• H-S-S-H (Music Man Steve Morse Signature)
• S-H (some Telecasters, Music Man “Valentine” James Valentine signature)
• S-H-H (some early seven-string ESP Horizons)
• S-H-S (Fender Wayne Kramer Signature)

Piezoelectric pickup on a classical acoustic guitar

Dual pickup by Peterman in Australia

Piezoelectric violin bridge pickup

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.

Piezoelectric pickups have a very high output impedance and appear as a capacitance in series with a voltage source. They therefore often have an instrument-mounted buffer amplifier fitted to maximize frequency response.

The piezo pickup gives a very wide frequency range output compared to the magnetic types and can give large amplitude signals from the strings. For this reason, the buffer amplifier is often powered from relatively high voltage rails (about ±9 V) to avoid distortion due to clipping. A less linear preamp (like a single-FET amplifier) might be preferable due to softer clipping characteristics.[11] Such an amplifier starts to distort sooner, which makes the distortion less "buzzy" and less audible than a more linear, but less forgiving op-amp. However, at least one study[12] indicates that most people cannot tell the difference between FET and op-amp circuits in blind listening comparisons of electric instrument preamps, which correlates with results of formal studies of other types of audio devices. Sometimes, piezoelectric pickups are used in conjunction with magnetic types to give a wider range of available sounds.

For early pickup devices using the piezoelectric effect, see phonograph.