Tonewheel
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A tonewheel or tone wheel is a simple electromechanical apparatus used for generating electric
Tone wheels are also an important component in many wheel speed sensors.
Description
The tonewheel assembly consists of a synchronous
As each bump in the wheel approaches the pickup, it temporarily concentrates the magnetic field near it, and thus strengthens the magnetic field that passes through the coil, inducing a current in the coil by the process of electromagnetic induction. As the bump moves past, this concentrating effect is reduced again, the magnetic field weakens slightly, and an opposite current is induced in the coil. Thus, the frequency of the current in the coil depends on the speed of rotation of the disk and the number of bumps.
Typically, the coil is connected to an amplifier through a network of switches, contacts, resistor banks, and transformers which can be used to mix the fluctuating current representing the note from one coil with similar currents from other coils representing other notes. A single
Tonewheel leakage occurs in the Hammond organ and in similar situations, where the large number of tonewheels causes pickups to overhear tonewheels other than their own. This causes the organ to add chromatics to played notes. In some kinds of music this is undesirable, but in others it has become an important part of the Hammond sound. On some digital simulations of Hammond organs tonewheel leakage is a user-set parameter.
Early uses
The tonewheel was independently invented in 1910 by
See also
Notes
- guitar pickup, in that a permanent magnet is placed within the coil and the moving element is unmagnetized. Unlike most generators or dynamos, there is no external field applied through the moving part.
References
- ^ U.S. patent 580035A
- ^ US patent 580035, Thaddeus Cahill, "Art of and apparatus for generating and distributing music electrically", issued 1897-04-06, filed 1896-02-04.