Pickup (music technology)

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Three magnetic pickups on a Fender Stratocaster with the pickup configuration of a fat-strat (H-S-S). The bridge (right) pickup is a humbucker and the neck (left) and middle pickups are single coils.

A pickup device acts as a transducer that captures mechanical vibrations, usually from suitably-equipped stringed instruments such as the electric guitar, electric bass guitar, Chapman Stick or electric violin, and converts them to an electrical signal which can then be amplified, recorded and broadcast.

[edit] Magnetic pickups

A magnetic pickup consists of a permanent magnet such as a AlNiCo, wrapped with a coil of a few thousand turns of fine enameled copper wire. The pickup is most often mounted on the body of the instrument, but can be attached to the bridge, neck and/or pickguard, as on many electro-acoustic archtop jazz guitars and string basses. The vibration of the nearby soft-magnetic strings modulates the magnetic flux linking the coil, thereby inducing an alternating current through the coil of wire. This signal is then carried to amplification or recording equipment via a cable. There may also be an internal preamplifier stage between the pickup and cable. More generally, the pickup operation can be described using the concept of a magnetic circuit, in which the motion of the string varies the magnetic reluctance in the circuit created by the permanent magnet.

[edit] Output

The output voltage of pickups varies between 100 mV rms to over 1 V rms for some of the higher output types. Some high-output pickups achieve this by employing very strong magnets, thus creating more flux and thereby more output. This can be detrimental to the final sound because the magnets' 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/impedance, which can affect high frequencies if the pickup is not isolated by a buffer amplifier or a DI unit.

[edit] Pickup sound

Single coil pickups, Fender Stratocaster (1963)

The turns of wire in proximity to each other have an equivalent self-capacitance which, 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 inductive source impedance inherent in this type of transducer makes it less linear than other forms of pickups^{[citation needed]}, such as piezo-electric or optical. The tonal quality produced by this nonlinearity is, however, subject to taste, and may therefore also be considered by some^[who?] to be aesthetically superior to that of a more linear transducer^{[citation needed]}.

The external load usually consists of resistance (the volume and tone potentiometer in the guitar, and any resistance to ground at the amplifier input) and capacitance between the hot lead and shield in the guitar cable. The electric cable also has a capacitance which can be a significant portion of the overall system capacitance. This arrangement of passive components forms a resistively-damped second-order low-pass filter. Pickups are usually designed to feed a high input impedance, typically a megohm or more, and a low impedance load will reduce the high-frequency response of the pickup because of the filtering effect of the inductance.

[edit] Humbuckers

PRS's Dragon humbucker

Single coil pickups pick up mains hum along with the musical signal. Mains hum consists of a fundamental signal at a nominal 50 or 60 Hz, depending on local alternating current frequency, and usually some harmonic content. The changing magnetic flux caused by the mains current links with the windings of the pickup, inducing a voltage by transformer action.

To overcome this effect, the humbucking pickup was developed, concurrently and independently by Seth Lover of Gibson and Ray Butts who initially developed one on his own and later worked with Gretsch^[1]. Who developed it first is a matter of some debate, but Seth Lover was awarded the first patent (U.S. Patent 2,896,491). Ultimately, both men developed essentially the same concept.

A humbucking pickup, shown in the image on the right, is composed of two coils. Each coil is wound reverse to one another. However, the six magnetic poles are opposite in polarity in each winding. Since ambient hum from power-supply transformers, radio frequencies, or electrical devices reaches the coils as common-mode noise, it induces an electrical current of equal magnitude in each coil. Because the windings are reversed in each pickup coil, the electro-magnetic interference sine wave signals in each pickup are equal and 180 degrees out of phase to one another, resulting in them canceling each other. However, the signal from the guitar string is doubled, due to the phase reversal caused by the out of phase magnets. The magnets being out of phase in conjunction with the coil windings being out of phase put the guitar string signal from each pickup in phase with one another. When the two in-phase guitar string sine wave signals meet, the amplitude of the wave doubles, and as does the signal strength.

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. Because the two coils are wired in series, the resulting signal that is output by the pickup is larger in amplitude, thus more able to overdrive the early stages of the amplifier. This is the essence of the "humbucker tone."^{[citation needed]}

An alternative wiring places the coils in buck parallel. The equal common-mode mains hum interference cancels, while the string variation signal sums. This method has a more neutral effect on resonant frequency: mutual capacitance is doubled (which if inductance were constant would result in a lowering of resonant frequency), and inductance is halved (which would raise the resonant frequency without the capacitance change). The net is no change in resonant frequency. This pickup wiring is rare^{[citation needed]}, as guitarists have come to expect that humbucking 'has a sound', and is not neutral. On fine jazz guitars, the parallel wiring will produce significantly cleaner sound^{[citation needed]}, as the lowered source impedance will drive capacitive cable with lower high frequency attenuation.

A side-by-side humbucking pickup senses a wider section of the string (has a wider aperture) than a single-coil pickup. This affects tone.^[2] By picking up a larger portion of the vibrating string more lower harmonics are present in the signal produced by the pickup resulting in a "fatter" tone. Stacked humbuckers have the narrower aperture of a single coil and sound closer to one.

[edit] Construction

Split pole pickups, Fender Jazz Bass

With the notable exceptions of rail and lipstick tube pickups, pickups have magnetic polepieces — one or two for each string. These polepiece centers should be perfectly aligned with the strings, or else sound will be suboptimal as the pickup would capture only a part of the string's vibrational energy. An exception to this rule are the J- and P-style pickups (found on the the Fender Jazz Bass and Precision Bass, respectively) where the two polepieces per string are positioned on either side of each string.

String spacing is not even on most guitars: it starts with minimal spacing at nut and ends with maximal at bridge. Thus, bridge, neck and middle pickups usually have different polepiece spacing 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.

[edit] Notation

Usually an electric guitar has more than one magnetic pickup. A combination of pickups is called a pickup configuration. It is usually notated by just writing out the pickup types, using "S" for single-coil and "H" for humbucker, in order from bridge pickup to neck pickup. Popular pickup configurations include:

S-S (Fender Telecaster)	S-S-S (Fender Stratocaster)	H-H (Gibson Les Paul, Fender Double Fat Stratocaster)	H-S-S (Fender Fat Stratocaster)
H-S-H (Superstrats)

Less frequently found configurations are:

• S (Fender Esquire, early Gibson Les Paul Juniors, Gibson Melody Maker, some Telecasters)
• H (some hollow body guitars like Gibson ES-165 Herb Ellis; minimalistic rock/metal guitars like Kramer Baretta; later Les Paul Juniors)
• H-S (minimalistic guitars like Hamer Californian Deluxe and Les Paul BFG, entry-level guitars like Squier '51)

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

• H-H-H (some Gibson Les Paul Gold Tops and Customs, Gibson SG-3, Gibson ES-5 Switchmaster, Kramer Jersey Star, Ibanez Destroyer)
• H-S-S-H (Music Man Steve Morse Signature)
• H-H-S (some ESP Stephen Carpenter Models and Alembic Jerry Garcia Models)

[edit] Piezoelectric pickups

A piezoelectric pickup on an acoustic guitar.

A piezoelectric Dual pickup by peterman.com.au in Australia.

More recently, 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 which some might prefer, and also have the advantage of not picking up any other magnetic fields, such as mains hum and feedback from monitoring loops. This system allows switching between magnetic pickup and piezo sounds, or simultaneously blending the output.

Most pickups for traditionally acoustic instruments such as Cello, Violin, and Double Bass, are piezoelectric pickups. These usually fit onto the bridge, where the strongest vibration is present. Ideally, however, there would be several transducers in various places to capture a more well rounded sound that is closer to the acoustic (unamplified) tone of the instrument^{[citation needed]}.

[edit] 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 full frequency response. Piezo pickups are usually mounted under the bridge and sometimes form part of the bridge assembly itself.

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. Some musicians prefer a preamp that isn't as linear (like a single-FET amplifier) in which the clipping is "softer"^{[citation needed]}. 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^{[citation needed]}. However, at least one study ^[3] indicates that most people can not tell the difference between FET and op-amp circuits in blind listening comparisons of electric instrument preamps, a finding which correlates with results of formal studies done in 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 pick-up devices using the piezoelectric effect, see phonograph.

[edit] Multi-transducer pickups

Hexaphonic pickups (also called divided pickups and polyphonic pickups) have a separate output for each string (Hexaphonic assumes six strings, as on a guitar). This allows for separate processing and amplification for each string. It also allows a converter to sense the pitch coming from individual string signals for producing note commands, typically according to the MIDI (musical instrument digital interface) protocol. A hexaphonic pickup and a converter are usually components of a guitar/synthesizer.

Such pickups are uncommon (compared to normal ones), and only a few notable models exist. Hexaphonic pickups can be either magnetic or piezoelectric.

[edit] Optical

Optical pickups are a fairly recent development that works by sensing the interruption of a light beam by the string. The light source is usually an LED, and the detector is a photodiode or phototransistor. These pickups have complete insensitivity to magnetic or electric interference and also have a very wide and flat frequency response unlike magnetic pickups.

Optical pickup guitars were first shown at the 1969 NAMM in Chicago, by Ron Hoag.^[4]

[edit] Active and passive pickups

Pickups can be either active or passive. Pickups, apart from optical types, are inherently passive transducers. "Active" pickups incorporate electronic circuitry to modify the signal. "Passive" pickups are usually wire wound around a magnet, and are the most common type used. They can generate electric potential without need for external power, though their output is relatively low, and the harmonic content of output depends greatly on the winding.

EMG 81 and EMG 85 — pair of popular active pickups

Active pickups require an electrical source of energy (usually one or two 9V batteries) to operate and include an electronic preamp, active filters, active EQ and other sound-shaping features. They can sometimes give much higher possible output. They also are less affected in tone by varying lengths of the electric cable connecting the guitar to the amplifier, and amplifier input characteristics. Magnetic pickups used with 'active' circuitry usually feature a lower inductance (and initially lower output) winding that tends to give a flatter frequency response curve^{[citation needed]}.

The disadvantages of active pickups are the power source (usually either a battery or phantom power), higher cost, and less defined unique tonal signature^{[citation needed]}. They are more popular on bass guitars, because of their solid tone; most high-end bass guitars feature an active pickup. Most piezoelectric and all optical pickups are active and include some sort of preamp.

The main advantages of active pickups are that they can be louder than a similar grade passive pickup. They also allow more "headroom"^{[citation needed]} and dynamic range. Active pickups produce less noise and hum compared to their passive counterparts.

[edit] Stereo and multiple pickups with individual outputs

Rickenbacker was the first manufacturer who began producing stereo bass guitars with a stereo output for each pickup section^{[citation needed]}. The neck pickup had one output and the bridge pickup had one. Also Teisco produced a guitar with a stereo option^{[citation needed]}. Teisco divided the two sections in the upper three strings and the lower three strings for each individual output. The Gittler guitar was an experimental guitar with six pickups, one for each string, with six outputs^{[citation needed]}. The Go! Team have modified a Fender Telecaster with an additional rotated pickup for the upper string, causing a simulation of a one string bass sound^{[citation needed]}.

[edit] See also

• Single coil
• Humbucker
• EMG
• Seymour Duncan
• DiMarzio
• Lace Sensor
• Magnetic circuit
• Lipstick pickup
• List of electronics topics
• Transformer
• Nominal impedance
• Reverberation
• Instrument amplifier
• Preamplifier

[edit] Notes

[edit] References

• Brosnac, Donald (1980 a). Guitar Electronics: A Workbook. Ojai, CA: d.B. Music Co.. 

• Tillman, Donald (2002). Response Effects of Guitar Pickup Position and Width

• Wheeler, Tom (1992). American Guitars: an illustrated history. Harper. New York ISBN 0-06-273154-8

[edit] External links

Wikimedia Commons has media related to: Guitar pickups

• Guitar Pickup Simulation
• Guitar Pickup - Interactive Java Tutorial National High Magnetic Field Laboratory
• Properties of Magnetic Materials (chapter)