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:This article is about pickups for musical instruments.- For a small truck used by both business and consumers, see pickup truck.
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A pickup device acts as a detector and captures mechanical vibrations (usually from suitably equipped stringed instruments (such as the electric guitar, electric bass guitar and violin) and converts them to an electronic signal which can be amplified and recorded.
Electromagnetic pickups use the principle of electromagnetic induction. The pickup consists of a permanent magnet wrapped with many turns of fine 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 magnetic flux linking the turns of wire. This changing flux induces a voltage in the winding. The signal created is then carried to amplification or recording equipment via a cable (or by radio transmission).
One problem with electromagnetic pickups is that - along with the musical signal - they also pick up mainsMains power plug & socket The term mains usually refers to the domestic AC electrical power supply (as in "I've connected the appliance to the mains"). The term is not usually used in the US and Canada. See also List of countries with mains power plugs, v hum. Mains hum consists of a fundamental signal at a nominal 50 or 60 Hz, depending on local alternating currentAn alternating current AC is an electrical current, where the magnitude of the current varies in a cyclical form, as opposed to direct current, where the polarity of the current stays constant. The usual waveform of an AC circuit is generally that of a pe 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 transformerThe word Transformer can also mean: The Transformers toys, and the related comics and animated television series which have run from the 1980s onwards. A glam rock album by Lou Reed, named Transformer . Transformers ''Typical electrical configurations See action.
To overcome this effect, the "humbucking" pickup was developed, originally by the GibsonFor information on the Gibson Martini, see Martini cocktail. For information on the appliances see Gibson Appliance Gibson is also the surname of two authors William Gibson, the playwright, author of The Miracle Worker William Gibson, the science fiction, company. 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 cancelled out, while the musical signal is reinforced.
The turns of wire in close proximity to each other have an equivalent self- capacitanceCapacitance is the ability of a capacitor to store potential difference or voltage for a given amount of stored charge. The SI unit of capacitance is the farad. where C is the capacitance, measured in farads Q is the charge, measured in coulombs V is the which, when added to any cable capacitance present, resonates with the inductanceInductance is a physical characteristic of an inductor, which is an electrical device that produces at any time a voltage proportional to the instantaneous rate of change in current flowing through it. The symbol L is used for inductance in honour of the of the winding. This resonanceThis article is about resonance in physics. For other uses, see Resonance (disambiguation). In physics, resonance is an increase in the oscillatory energy absorbed by a system when the frequency of the oscillations matches the system's natural frequency o 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 the resonant frequency. Thus a design compromise must be reached.
Electromagnetic pickups are usually designed to feed a high input impedance, typically a megohm or more. A low impedance load reduces the high-frequency response of the pickup because the inductance and input resistance form a low-pass filter.
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.
