A typical magnetic pickup is a transducer (specifically a
variable reluctance sensor) that consists of one or more
permanent magnets (usually
alnico or
ferrite) 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(s) are played and where on the string, but for example, a
Samick TV Twenty guitar played on the bridge measured 16 mV
RMS (200
mV peak) for one string and 128 mV RMS (850 mV peak) for a chord. The pickup is connected with a
6.35 mm audio jack (instrument cable) to an
amplifier, which amplifies the signal to a sufficient magnitude of power to drive a
loudspeaker (most amplifiers are above 10 watts). 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 (where the strings rest) or the neck. Pickups come in several 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 (this is also called "E-to-E" spacing), or as a distance between adjacent polepieces' centers.
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 (called string capture) 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 (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 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 '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. 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 (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, 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, 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: Image:Pickup-SS-tele.jpg|
S-S (
Fender Telecaster,
Jazzmaster, and
Jaguar,
Peavey Reactor, and some
Rickenbacker and
Gibson guitars) Image:Stratocaster pickups.jpg|
S-S-S (
Fender Stratocaster) Image:Pickup-SSH.jpg|
H-S-S (
superstrats like
Fender HM Strat,
Peavey Raptor EXP,
Peavey Destiny) Image:Pickup-HSH.jpg|
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 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.
Preamps 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. 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 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. ==Other transducers==