Electrostatic pickup

An electrostatic pickup converts

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

, 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.[1]

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 overtones 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.

References

Miessner, Benjamin F. (1936). "Electronic Music and Instruments". Proceedings of the Institute of Radio Engineers. 24 (11): 1427–63.

^ US 2542611, Zuck, Victor, "Pickup for Electric Organs", issued February 20, 1951

External links

Wurlitzer Electrostatic Organs by Eric Larson

[1] US 2542611, Zuck, Victor, "Pickup for Electric Organs", issued February 20, 1951

Principle of operation

Variations

See also

References

External links