A single coil pickup is a type of magnetic transducer, or pickup, for the electric guitar and the electric bass. It electromagnetically converts the vibration of the strings to an electric signal. Single coil pickups are one of the two most popular designs, along with dual-coil or "humbucking" pickups.
In the mid-1920s George Beauchamp, a Los Angeles, California guitarist, began experimentation with electric amplification of the guitar. Originally using a phonograph pickup assembly, Beauchamp began testing many different combinations of coils and magnets hoping to create the first electromagnetic guitar pickup. He wound his earliest coils using a motor out of a washing machine, later on switching to a sewing machine motor, and eventually using single coiled magnets.
Beauchamp was backed in his efforts by Adolph Rickenbacker, an engineer and wealthy owner of a successful tool and die business. Beauchamp eventually produced the first successful single coil pickup. The pickup consisted of two massive "U" shaped magnets and one coil and was known as the "horseshoe pickup". The two horseshoe-shaped magnets surrounded the strings that passed over a single core plate (or blade) in the center of the coil.
Beauchamp outfitted the pickup in a custom built lap slide guitar. The production model based on this prototype became the Hawaiian Electro lap steel guitar, nicknamed the "Frying Pan" for its round, flat body.
In 1931 Beauchamp founded the Ro-Pat-In Company with Rickenbacker and his associates. Ro-Pat-In eventually became The Electro String Instrument Corporation and subsequently the Rickenbacker International Corporation. The company introduced its first "Electro-String Instruments" to the public in 1932.
The Gibson Guitar Corporation introduced the "bar pickup" in 1935 for its new line of Hawaiian lap steel guitars. The pickup's basic construction is that of a metal blade inserted through the coil as a shared pole piece for all the strings. A pair of large flat magnets were fastened below the coil assembly.
In 1936 Gibson introduced the ES-150, its first electric Spanish styled guitar. The ES-150 was outfitted with the bar pickup. Jazz guitar innovator, Charlie Christian, began playing an ES-150 in the late 1930s with the Benny Goodman Orchestra. This caused the popularity of the electrified guitar to soar. Due to Christian’s close association with the ES-150 it began being referred to as the “Charlie Christian Model” and Gibson’s now famous bar pickup as the “Charlie Christian pickup” or “CC unit”.
The sound of a single coil pickup can range from the strong, fat midrange sound of the Gibson P-90 to the bright and clear Fender Telecaster single-coil tone.
Common designs 
Gibson P-90 
The P-90 is a single-coil pickup designed by the Gibson Guitar Corporation. These pickups have a large, flat coil with adjustable steel screws as pole pieces, and a pair of flat alnico bar magnets lying under the coil bobbin. The adjustable pole pieces pick up the magnetism from the magnets. Moving the screw closer or further away from the magnet determines signal strength, thus tone as well. There are two variations of P-90 pickup that differ mainly by mounting options:
- Soap bar casing has true rectangular shape and the mounting screws are contained within the coil perimeter, positioned between the pole pieces, between strings 2-3 and 4-5, thus creating irregular and somewhat unusual pattern. Occasionally, they are mistaken for pole pieces; thus, the P-90 is sometimes erroneously said to have eight pole pieces. The "soap bar" nickname most probably comes from its predominantly rectangular shape and proportions resembling a bar of soap, and the fact that the first P-90s on the original Gibson Les Paul Model of 1952 were white.
- Dog ear is a casing type with extensions at both sides of pickup that somewhat resemble dog's ears. These are extensions of the predominantly rectangular cover that encompass the outlying mounting screws. Dog-ear P-90 pickups were commonly mounted on Gibson's hollowbody guitars like the ES-330 and occasionally on solid body models like the Les Paul Junior. The same pickups were also available on Epiphone models (since Gibson was building Epiphone guitars in the 1950s) and the design is best remembered for its appearance on the hollow body Epiphone Casino of the mid to late 1960s.
The sound of a P-90 is somewhat brighter and more transparent than Gibson's later humbucker pickup, and every bit as crisp and snappy as Fender's single-coil pickups despite its high output and big sound.
Despite its tonal qualities the P-90 fell out of favor with Gibson in the early 1950s as a consequence of guitar players complaining about the amount of hum (noise) it put out. Gibson employee Seth Lover solved the hum problem by designing a hum-canceling pickup known as a humbucker, it was supposed to sound like a P-90 but in fact has quite a different sound. It nevertheless became Gibson's mainstay pickup from that point on. The P-90 likely did not become as popular for that reason, although many guitarists still prefer the tone of the P-90.
The hum problem proved extremely difficult to solve and despite numerous attempts by Gibson with their P-100, and the larger aftermarket pickup manufacturers with their stacked and sidewinders noiseless designs, hum-canceling P-90 pickups lost most of their favored tonal characteristics and generally did not gain acceptance among guitar players.
Telecaster design 
The Fender Telecaster features two single coils. The neck pickup produces a mellower sound, while the bridge pickup produces an extremely twangy, sharp tone with exaggerated treble response, because the bridge pickup is mounted on a steel plate. These design elements allow musicians to emulate steel guitar sounds, making it particularly appropriate for country music.
Pickups are selected with a three-position switch, and two wiring schemes exist:
- Vintage: 1) neck pickup with treble cutoff for a bassier sound; 2) neck pickup only; 3) bridge pickup only.
- Modern: 1) neck pickup only, with no treble cutoff; 2) neck and bridge; 3) bridge pickup only.
The Fender Esquire has a variation to the Vintage wiring scheme by using the scheme on a single pickup. This gives a treble cutoff in the first position, normal in the middle position, and a tone control cutoff in the third position.
Stratocaster design 
The traditional Stratocaster design guitar features three single coils. The guitarist can control which pickup or combination of pickups are selected with a lever switch. The pickup positions are usually referred to as the bridge, middle and neck pickups based on their proximity to those parts of the instrument.
Pickup position, number of coil winds, type of magnet wire, magnets and other factors shape the sound. A given pickup in the neck position will give louder, mellower and warmer sound, while an identical pickup in the bridge position will have lower output and produce a brighter, sharper sound. The reason the neck pickup has the most output is that the string's vibration has a higher amplitude at the neck position, being near the middle of the string length. Some manufacturers overwind the bridge pickup for more output to compensate for this difference.
The magnet poles have different heights. This is called a magnet stagger and is done to compensate for the different outputs of the string for two reasons. The first reason is that the fretboard has a radius (also called camber) of between 7 and 12 inches usually. Naturally the strings will follow the radius of the fretboard and so must the top surface of the magnets, generally speaking. The second reason is that some strings have naturally higher output, so a lower magnet pole piece can compensate for this. For example a plain or non-wound G-string has the highest output, and this calls for the corresponding magnet to be further compensated, resulting in an apparent odd looking stagger. Fender staggered pickups generally follow the traditional design and have the G string's magnet pole piece taller than the D-string's, but this causes the G-string of modern string sets to be excessively loud and dominate all the other strings (going against the original purpose of stagger and exacerbating the problem of unbalanced string output more than a non-staggered pickup). This comes about because Stratocaster pickups were designed in the 1950s when string sets came with a wound G-string, but modern rock and blues players found it difficult to stretch or bend wound G-strings across the fretboard because of their inherently higher tension. In the 1970s, string manufacturers responded and introduced the now standard non-wound G-string which has lower tension and can be stretched more easily, but which produces much higher output. In order for the G-string to have the same output the corresponding magnet pole should have the greatest gap between the string and the magnet pole piece.
The first Stratocasters had a three-way pickup selector switch, selecting either the neck, middle or bridge pickup. Innovative guitarists found they could get an interesting sound by carefully positioning the selector switch lever between detented positions, where any two adjacent pickups would be on simultaneously. Some players wedged a plectrum between the pickguard and the selector switch to lock it in these positions. Later on, Fender introduced the now standard five-way selector switch, which uses additional detents between the original three positions to allow the combinations of any two adjacent pickups.
Modern Stratocasters have five-position pickup selector switch. Positions 1, 3 and 5 activate only one pickup (bridge, middle or neck respectively), while positions 2 and 4 activate a combination of two pickups (bridge and middle, or middle and neck, respectively). Some pickup sets have a reverse wound and reverse polarity middle pickup that when in combination with the normal bridge or neck pickups will cancel electromagnetic interference (noise/hum) which single coil pickups suffer badly from. The sonic effect of positions 2 and 4 is sometimes referred to as a "quack" or "notch positions", and some guitar notation includes directions to use these pickup combinations. One example is "Sultans of Swing" by Dire Straits which is played in position 2 (bridge and middle).
Noise problems 
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Two types of noise afflict magnetic guitar pickups. Hum is caused by magnetic fields due to power frequency currents in electrical equipment, whereas buzz is propagated as radio transmissions and sounds more like static. The sources of buzz are many, but one example is an AC power tool with a brush motor. The Brush (electric) makes and breaks electrical contact with the commutator segment several thousand times a second at variable frequency dependent on load thus causing radio frequency noise.
Hum can be canceled by suitable arrangements of two coils within the pickup. The two coils are internally wired so that the desired signal from the string is added, but external interference is cancelled. Hum can not be screened out by conductive shielding. Buzz can not be cancelled, it can only be dealt with by grounded conductive shielding of the signal wiring.
Fender Stratocaster and Telecaster pickups as well as Gibson's P-90 pickup being of the single-coil type, output a type of noise known as mains hum or 50Hz / 60Hz hum. Mains hum has its origin in wiring of a building and electrical apparatus/appliances such as transformers, electric motors and lighting. Hum is undesirable because it pollutes the musical notes being played on the instrument with its own sound of fixed unchanging frequency or pitch (usually 50 or 60 hertz) which is discordant with the musical sounds. To address this undesirable situation various attempts to eliminate mains hum signal from Fender single-coil pickups were made dating back to the early 1970s. DiMarzio, Seymour Duncan and EMG manufacture what are commonly known as stacks, or stacked single coils which cancel mains hum. Unfortunately the design is flawed and these stacks also cancel string signal due to magnetic coupling of the two coils which has a detrimental effect on sound quality. EMG used active circuitry within the pickup to compensate for the losses caused by stacked coils by boosting and reshaping the damaged sound but this required an on-board battery with its attendant inconvenience. The resultant sound is not authentic Fender trade mark sound but EMG pickups became popular for their own sound.
Actodyne General manufactured a low-noise design of single-coil pickup known as Lace Sensors, Don Lace being the inventor. The Lace Sensor pickup had a rubberized particle magnet and used ferrous shielding to reduce hum. Being the best at the time, Fender installed Lace Sensors on the Strat Plus model for many years as a solution to the mains hum problem. However the Lace Sensor was a stopgap solution because the sound was not authentic Fender trademark sound. Fender purists wanted the genuine sound of the original Fender pickups with Alnico rod magnets and Fender eventually discontinued Lace Sensors as their mainstay solution to mains hum circa 1998. Lace Sensors continue to be used by many guitar players regardless.
Kinman Guitar Electrix were awarded 5 or more US patents beginning circa 1996 for innovative design concerned with hum canceling single pole pickups. Kinman at first concentrated on particularly the Fender type single coil pickup and in 2009 the P-90 pickup. One of the most important elements of Kinman's patents is the use of iron in the core of the noise sensing coil. This was absolutely novel in 1996 and without the presence of iron to boost the efficiency of the noise sensing coil differential coil technology would not have been possible. Vertical differential coil technique is also described in Kinman's US Patents 5,668,520 and 6,103,966 with priority date of March 1996. After 1998 DiMarzio and Seymour Duncan also began using iron and differential winding techniques in the noise sensing coils in some of their products. Over the years Kinman has improved and refined their designs to a point where the popular consensus is the sound of some models is indistinguishable from noisy single coils. Kinman also manufactures noiseless P-90 and Telecaster pickups under US Patent 7,022,909
The search for an acceptable solution to mains hum gained new impetus around 1995 as guitar players became increasingly intolerant of degraded stacked single-coil sound. Fender was researching new techniques to solve the loss of tone around that time and eventually came out with their Vintage Noiseless design circa 1998.
Notable single-coil pickups 
There are several well-known single-coil pickups that have a distinctive sound:
- Rickenbacker pickups (including the original 1930s "horseshoe" pickup as used in lap steel and solidbody upright basses, and later 6 string electric guitars, pedal steels, and electric bass guitars; also the "Toaster" and "Hi-Gain")
- Gibson bar pickup (1935) — later called the Charlie Christian pickup (1938)
- Gibson P-90 (1946)
- Fender Telecaster, Stratocaster, Jazzmaster, Jaguar, and other pickups
- Danelectro Lipstick
- Gretsch pickups (including the "HiLoTron")
- DeArmond pickups (found on various 50s and 60s guitars by various manufacturers including Gretsch, Guild, Epiphone, Martin, Kustom, Harmony, Regal, Premier, Silvertone, and others, but produced by the Rowe - DeArmond company of Toledo, Ohio; the trade name is now owned by Fender; single coil models including the 200 aka Dynasonic, 2K, and 2000, "mustache", various "gold foil" types, and many clip on, rail, or screw mount pickups designed for acoustic guitars and other instruments). The Fender "Tele-Sonic" featured large DeArmond single coils.
- Valco single coil pickups by Ralph Keller (1954) can be found in Airline, Supro, National, English Electronics, Custom Kraft, and a few Gretsch models of guitar from the 50's, 60's, and 70's. The majority of these pickups maintain the physical appearance of a larger, double coil humbucker pickup. Although consisting of a single coil, the pickup contains a second, off-set magnet which cancels hum. Early variations on the Valco made over-strings "horseshoe" pickup can be found on a number of similarly branded lapsteel guitars, such as Oahu.
- Epiphone "New York" pickups
- Lace Sensor pickups (1987)
See also 
- Batey, Rick (2003). The American Blues Guitar. Hal Leonard. ISBN 0-634-02759-X.
- Duchossoir, A. R. (1998). Gibson Electrics: The Classic Years. Hal Leonard. ISBN 0-7935-9210-0.
- Millard, Andre (2004). The Electric Guitar: A History of an American Icon. Johns Hopkins University Press. ISBN 0-8018-7862-4.
- Hirst, Tom (2003). Electric Guitar Construction. Hal Leonard. ISBN 1-57424-125-7.
- Smith, Richard R. (1987). The History of Rickenbacker Guitars. Centerstream Publications. pp. 9–14. ISBN 0-931759-15-3.
- Fjestad, Zachary R. (2005). Blue Book of Electric Guitars. Blue Book Publications, Inc. p. 397. ISBN 1-886768-57-9.
- Steve Cobham (June 1997). "NECK AND NECK - Gibson Les Paul and Fender Strat Compared". Sound On Stage.