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A pickup device acts as a Transducer that captures mechanical vibrations (usually from suitably equipped Stringed Instrument s such as the Electric Guitar , electric Bass Guitar or Electric Violin ) and converts them to an electronic signal which can be Amplified and Recorded . MAGNETIC PICKUPS Electromagnetic pickups use the principle of variable Magnetic Reluctance . The pickup consists of a permanent Magnet wrapped with many turns of fine copper wire. The pickup is mounted on the body of the instrument, close to the strings. When the instrument's strings vibrate in the Magnetic Field of the permanent magnet, they alter the reluctance of the magnetic path seen by the magnet. This changes the flux in the magnetic circuit which in turn induces a voltage in the winding. The signal created is then carried to Amplification or Recording equipment via a Cable (or by radio transmission). 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. These can be detrimental to the final sound because the magnets can tend to attract the strings and Damp them thus ruining sustain. Other high output pickups use instead a much larger number of turns of wire to increase the voltage generated by the string's movement. This however gives the pickup a larger output resistance/impedance and this can affect the high frequencies if the pickup is not isolated by a Buffer Amplifier . Pickup sound The turns of wire in close 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 Resonant Frequency . The Inductive Source Impedance inherent in this type of Transducer makes it less linear than other forms of pickups, 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 to be aesthetically superior to that of a more linear transducer. 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 cable capacitance has a large effect and must not be neglected. This arrangement of passive components forms a second-order Low-pass Filter . Electromagnetic pickups are usually designed to feed a high Input Impedance , typically a Megaohm or more and a low impedance load will reduce the high-frequency response of the pickup because of the filtering effect of the inductance. Humbucking One problem with electromagnetic pickups is that — along with the musical signal — they also pick up Mains hum. 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, originally by Seth Lover of Gibson . A humbucking pickup comprises two standard pickups wired together in series. However, the magnets of the two pickups are reversed in polarity, and the windings are also reversed. Thus, any hum or other Common Mode extraneous noise that is picked up is canceled out, while the musical signal is reinforced. A side effect of this technique is that the overall inductance of the pickup is increased, attenuating the higher frequencies and giving a duller tone. Construction, sizes, spacing With a notable exception of rail pickups, pickups have magnetic polepieces — one or two for each string. These polepiece centers should be perfectly aligned with strings, or else sound will be suboptimal as pickup would capture only a part of vibrational energy. String spacing is not even, on most guitars: it starts with minimal spacing at nut and ends with maximal at bridge. So, bridge, neck and middle pickups should have a 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. 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 neck pickup to bridge pickup. Popular pickup configurations include:
Less frequently used configurations are:
PIEZOELECTRIC PICKUPS More recently, semi-acoustic and acoustic guitars have been fitted with Piezoelectric pickups instead of, or in addition to, magnetic pickups. These have a very different sound which some prefer, and also have the advantage of not picking up unwanted magnetic fields, such as mains hum and feedback from hearing-aid loops. Preamps Piezoelectric pickups have a very high fitted if the sound is to retain its high frequencies. Piezo pickups are usually mounted under the Bridge and sometimes form part of the bridge assembly itself. The piezo pick up gives a very wide frequency range output compared to the magnetic types and can give large Amplitude signals from the strings. For this reason, it is usually necessary to run the buffer amplifier 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) so that the clipping is "softer". (Although such an amplifier starts to distort sooner, this makes the distortion less "buzzy" and less audible than a more linear, but less forgiving Op-amp .) {Link without Title} 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 . 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 an individual string. A hexaphonic pickup and a converter are usually components of a Guitar/synthesizer . Such pickups are relatively uncommon (compared to normal ones), and only a few notable models exists. Hexaphonic pickups can be either electromagnetic or piezoelectrical. Electromagnetic
Piezoelectric
OPTICAL PICKUPS Optical pickups are a fairly recent development that work 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 {Link without Title} ACTIVE AND PASSIVE PICK-UPS Pick-ups can be either active or passive. Pickups, apart from optical types, are inherently Passive Transducer s. So-called ''active'' pickups incorporate electronic circuitry to modify the signal. ''Passive'' pick-ups are usually wire wound around a magnet. 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. Passive pick-ups are very convenient as they require no power source to operate. They are most popular and widely used pick-up type on electric guitars, and their Frequency Response curve is unique to the type and manufacturer. — one of the most famous active pickups in the world]] Active pick-ups require an electrical source of energy to operate and include an electronic Preamp , active filters, active EQ and other sound-shaping features. They can sometimes give much higher possible output (in comparison to passive) and much flatter frequency response curve. They also are less affected in tone by varying lengths of amplifier lead, and amplifier input characteristics. Magnetic pick-ups used with 'active' circuitry usually feature a lower inductance (and initially lower output) winding that tends to give a flatter frequency response curve. The disadvantages of active pick-ups are the power source (usually either a Battery or Phantom Power ), cost, and less defined unique tonal signature. They are more popular on bass guitars, because of their solid tone; most high-end bass guitars feature an active pick-up. Most piezoelectric and all optical pick-ups are active and include some sort of preamp. SEE ALSO Electronic-related
Pickup types and models
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