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The Hammond Organ

(Excerpted from the OriginalHammondLeslieFaq.)

The Hammond ToneWheel organ, first introduced by LaurensHammond in April 1935, is the one against which all contenders are measured. For this reason its technology is outlined below, and not the technology used in more recently manufactured (non-ToneWheel) Hammond organs.

Types of Hammond Tonewheel Organs

What Makes a Hammond Special?

The secret of the Hammond tonewheel organ lies in its method of tone production. The ToneGenerator assembly consists of an AC SynchronousMotor connected to a geartrain which drives a series of ToneWheels, each of which rotates adjacent to a MagnetAndCoil assembly (similar to an electric guitar pickup). The number of bumps on each tonewheel in combination with the rotational speed set by the GearRatio between the DrivingGear and the DrivenGear determines the pitch produced by a particular tonewheel assembly. The pitches approximate even-tempered tuning, (it's done with integer (rational?) math after all).

The Hammond organ creates its tone colors through additive synthesis. A note on the typical Hammond organ consists of a user defined mixture of the fundamental and eight harmonics, or multiples of that frequency. The harmonic mixture is controlled by means of Drawbars and Preset keys or buttons. Harmonic content for the manuals, Great or Swell, and the PedalClavier can be adjusted independently.)

When a key on a Manual is pressed, nine switch contacts (on most organs), one for each harmonic, closes on the nine Busbars under the manual. In ConsoleOrgans, each busbar is connected through the contacts of one of the depressed preset keys to one of two sets of drawbars or the PresetPanel. In most SpinetOrgans, the busbars are wired directly to a single set of drawbars for each manual. The level of each harmonic is set by the position of the drawbars or the connections on the preset panel which selects one of the nine input taps on the MatchingTransformer. The output of the matching transformer mixes all the harmonics together.

Other Hammond innovations which are important parts of the character of the Hammond Organ are Vibrato, Percussion and HarmonicFoldback. KeyClick and HarmonicLeakage were originally unwanted side-effects. However these have become a sought after part of the "Hammond Sound".

Hammonds are heavy. See WhatDoesAHammondWeigh to see how heavy.

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