An electrostatic pickup converts mechanical motion to an electrical

signal A signal is both the process and the result of transmission of data over some media accomplished by embedding some variation. Signals are important in multiple subject fields including signal processing, information theory and biology. In ...

by means of varying electrical

capacitance Capacitance is the ability of an object to store electric charge. It is measured by the change in charge in response to a difference in electric potential, expressed as the ratio of those quantities. Commonly recognized are two closely related ...

. This type of pickup, in which the moving plate is a vibrating metal reed, is used in some types of electronic pianos and organs as an inexpensive method of generating tones.

Principle of operation

The electrostatic pickup consists of a

capacitor In electrical engineering, a capacitor is a device that stores electrical energy by accumulating electric charges on two closely spaced surfaces that are insulated from each other. The capacitor was originally known as the condenser, a term st ...

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. Wurlitzer Model 44 Electrostatic Reed Organ

Wurlitzer Model 44 Electrostatic Reed Organ

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

overtone An overtone is any resonant frequency above the fundamental frequency of a sound. (An overtone may or may not be a harmonic) In other words, overtones are all pitches higher than the lowest pitch within an individual sound; the fundamental i ...

s to be generated from a single reed by placing several fixed plates in different locations, as seen in

Wurlitzer The Rudolph Wurlitzer Company, usually referred to as simply Wurlitzer, is an American company started in Cincinnati in 1853 by German immigrant (Franz) Rudolph Wurlitzer. The company initially imported stringed, woodwind and brass instruments ...

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 and overdrive are forms of audio signal processing used to alter the sound of amplified electric musical instruments, usually by increasing their gain (electronics), gain, producing a "fuzzy", "growling", or "gritty" tone. Distorti ...

distortion pedal.

References

External links

Wurlitzer Electrostatic Organs by Eric Larson
{{DEFAULTSORT:Electrostatic Pickup Musical instrument parts and accessories

Principle of operation

Variations

See also

References

External links