A tonewheel or tone wheel is a simple electromechanical apparatus used for generating electric musical notes in electromechanical

organ Organ may refer to: Biology * Organ (biology), a part of an organism Musical instruments * Organ (music), a family of keyboard musical instruments characterized by sustained tone ** Electronic organ, an electronic keyboard instrument ** Hammond ...

instruments such as the Hammond Organ and in telephony to generate audible signals such as Ringing tone. It was developed by Thaddeus Cahill for the

telharmonium The Telharmonium (also known as the Dynamophone) was an early electrical organ, developed by Thaddeus Cahill c. 1896 and patented in 1897. , filed 1896-02-04. The electrical signal from the Telharmonium was transmitted over wires; it was hear ...

c. 1896 and patented in 1897. It was reinvented around 1910 by Rudolph Goldschmidt for use in pre– vacuum-tube radio receivers as a beat frequency oscillator (BFO) to make

continuous wave A continuous wave or continuous waveform (CW) is an electromagnetic wave of constant amplitude and frequency, typically a sine wave, that for mathematical analysis is considered to be of infinite duration. It may refer to e.g. a laser or partic ...

radiotelegraphy (

Morse code Morse code is a method used in telecommunication to encode text characters as standardized sequences of two different signal durations, called ''dots'' and ''dashes'', or ''dits'' and ''dahs''. Morse code is named after Samuel Morse, one ...

) signals audible.

Description

The tonewheel assembly consists of a synchronous AC motor and an associated

gearbox Propulsion transmission is the mode of transmitting and controlling propulsion power of a machine. The term ''transmission'' properly refers to the whole drivetrain, including clutch, gearbox, prop shaft (for rear-wheel drive vehicles), diff ...

that drives a series of rotating disks. Each disk has a given number of smooth bumps at the rim; these generate a specific frequency as the disk rotates close to a pickup assembly that consists of a

magnet A magnet is a material or object that produces a magnetic field. This magnetic field is invisible but is responsible for the most notable property of a magnet: a force that pulls on other ferromagnetic materials, such as iron, steel, nicke ...

and electromagnetic coil. 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 Electromagnetic or magnetic induction is the production of an electromotive force (emf) across an electrical conductor in a changing magnetic field. Michael Faraday is generally credited with the discovery of induction in 1831, and James Cle ...

. 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

fundamental frequency The fundamental frequency, often referred to simply as the ''fundamental'', is defined as the lowest frequency of a periodic waveform. In music, the fundamental is the musical pitch of a note that is perceived as the lowest partial present. I ...

can thus be combined with one or more harmonics to produce complex sounds.Tonewheels were first developed for and used in the impractical

Telharmonium The Telharmonium (also known as the Dynamophone) was an early electrical organ, developed by Thaddeus Cahill c. 1896 and patented in 1897. , filed 1896-02-04. The electrical signal from the Telharmonium was transmitted over wires; it was hear ...

circa 1896, filed 1896-02-04. and later in the original Hammond organs. ''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 Rudolph Goldschmidt as a beat frequency oscillator in early radio receivers to make

radiotelegraphy (

) signals audible, before the existence of the

vacuum tube A vacuum tube, electron tube, valve (British usage), or tube (North America), is a device that controls electric current flow in a high vacuum between electrodes to which an electric potential difference has been applied. The type known as ...

Notes

References

{{Electronic organs Electronic organs Electric and electronic keyboard instruments

Description

Early uses

See also

Notes

References