Electrostatic pickup
Encyclopedia
An electrostatic pickup converts mechanical motion
to an electrical signal by means of varying electrical capacitance
. This type of pickup
, in which the moving plate is a vibrating metal reed
, is used in some types of electronic piano
s and organs as an inexpensive method of generating tones.
with one stationary plate and one moving plate. The moving plate is typically a steel or brass reed
, anchored at one end and free to vibrate at the other end. Another fixed plate is suspended near the vibrating reed, but is electrically insulated.
A high voltage is applied between the stationary and moving plates to produce an electric field. The motion of the moving plate induces a varying current through the capacitor formed by the reed and the fixed plate.
The capacitance of the pickup is changed by the motion of the moving plate. As a result of the changing capacitance, a varying current flows into or out of the plates as needed to maintain the proper charge for the new amount of capacitance. This current produces a varying voltage across an external resistor which is amplified to produce a usable output signal.
s to be generated from a single reed by placing several fixed plates in different locations, as seen in Wurlitzer
electrostatic organs.
The electrostatic pickup used in the Hohner Pianet
N electric piano has a fixed plate mounted at a 90 degree angle to the reed, while the fixed plates used in Wurlitzer electrostatic organs are parallel to the reed. The position of the fixed plate in the Pianet is such that the capacitance changes most dramatically when the reed is in the upper portion of its travel. The result is a large second-harmonic content in the resulting signal, similar to that produced by a fuzz box distortion pedal.
Motion (physics)
In physics, motion is a change in position of an object with respect to time. Change in action is the result of an unbalanced force. Motion is typically described in terms of velocity, acceleration, displacement and time . An object's velocity cannot change unless it is acted upon by a force, as...
to an electrical signal by means of varying electrical capacitance
Capacitance
In electromagnetism and electronics, capacitance is the ability of a capacitor to store energy in an electric field. Capacitance is also a measure of the amount of electric potential energy stored for a given electric potential. A common form of energy storage device is a parallel-plate capacitor...
. This type of pickup
Pickup (music technology)
A pickup device is 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 that is amplified, recorded, or broadcast.-...
, in which the moving plate is a vibrating metal reed
Reed (instrument)
A reed is a thin strip of material which vibrates to produce a sound on a musical instrument. The reeds of most Woodwind instruments are made from Arundo donax or synthetic material; tuned reeds are made of metal or synthetics.-Single reeds:Single reeds are used on the mouthpieces of clarinets...
, is used in some types of electronic piano
Electronic piano
An electronic piano is a keyboard instrument designed to simulate the timbre of a piano using analog circuitry....
s and organs as an inexpensive method of generating tones.
Principle of operation
The electrostatic pickup consists of a capacitorCapacitor
A capacitor is a passive two-terminal electrical component used to store energy in an electric field. The forms of practical capacitors vary widely, but all contain at least two electrical conductors separated by a dielectric ; for example, one common construction consists of metal foils separated...
with one stationary plate and one moving plate. The moving plate is typically a steel or brass reed
Reed (instrument)
A reed is a thin strip of material which vibrates to produce a sound on a musical instrument. The reeds of most Woodwind instruments are made from Arundo donax or synthetic material; tuned reeds are made of metal or synthetics.-Single reeds:Single reeds are used on the mouthpieces of clarinets...
, anchored at one end and free to vibrate at the other end. Another fixed plate is suspended near the vibrating reed, but is electrically insulated.
A high voltage is applied between the stationary and moving plates to produce an electric field. The motion of the moving plate induces a varying current through the capacitor formed by the reed and the fixed plate.
The capacitance of the pickup is changed by the motion of the moving plate. As a result of the changing capacitance, a varying current flows into or out of the plates as needed to maintain the proper charge for the new amount of capacitance. This current produces a varying voltage across an external resistor which is amplified to produce a usable output signal.
Variations
The shape, size and position of the fixed plate relative to the reed has an effect on the capacitance change as a function of the reed's instantaneous position during its travel. This allows different combinations of overtoneOvertone
An overtone is any frequency higher than the fundamental frequency of a sound. The fundamental and the overtones together are called partials. Harmonics are partials whose frequencies are whole number multiples of the fundamental These overlapping terms are variously used when discussing the...
s to be generated from a single reed by placing several fixed plates in different locations, as seen in Wurlitzer
Wurlitzer
The Rudolph Wurlitzer Company, usually referred to simply as Wurlitzer, was an American company that produced stringed instruments, woodwinds, brass instruments, theatre organs, band organs, orchestrions, electronic organs, electric pianos and jukeboxes....
electrostatic organs.
The electrostatic pickup used in the Hohner Pianet
Pianet
thumb|Hohner Pianet TThe Pianet was a series of electric pianos built by the Hohner company of Trossingen, West Germany from the 1960s to the 1970s. The designer of the early Pianet models was Ernst Zacharias, basing the mechanism closely on a 1920s design by Lloyd Loar...
N electric piano has a fixed plate mounted at a 90 degree angle to the reed, while the fixed plates used in Wurlitzer electrostatic organs are parallel to the reed. The position of the fixed plate in the Pianet is such that the capacitance changes most dramatically when the reed is in the upper portion of its travel. The result is a large second-harmonic content in the resulting signal, similar to that produced by a fuzz box distortion pedal.
See also
- Everett OrgatronOrgatronThe Orgatron was an electronic organ originally developed in 1934 by Frederick Albert Hoschke, after a Benjamin F. Miessner patent. A fan blew air over a set of free reeds, causing them to vibrate...
- Compton organ
- Wurlitzer electric pianoWurlitzer electric pianoWurlitzer 200A|250px|thumbThe Wurlitzer electric piano was one of a series of electromechanical stringless pianos manufactured and marketed by the Rudolph Wurlitzer Company, Corinth, Mississippi, U.S. and Tonawanda, New York...
- Hohner PianetPianetthumb|Hohner Pianet TThe Pianet was a series of electric pianos built by the Hohner company of Trossingen, West Germany from the 1960s to the 1970s. The designer of the early Pianet models was Ernst Zacharias, basing the mechanism closely on a 1920s design by Lloyd Loar...