THEORY OF OPERATION
SERIES A-100
Figure 1
These Models of The Hammond Organ contain the entire tone-producing mechanism, which is
completely electrical in operation. Within it are produced all the tones and tone combinations of the
organ. The electrical waves are made audible by suitable amplifiers and loud speakers, contained
within the console. The block diagram (Figure 7) shows the chief components of the instrument.
Electrical impulses of various frequencies are produced within a unit known as the "tone generator",
containing a number of "phonic wheels" or "tone wheels" driven at predetermined speeds by a
synchronous motor and gear arrangement. Each phonic wheel is similar to a gear, with high and low
spots, or teeth, on its edge. As the wheel rotates these teeth pass near a permanent magnet, and the
resulting variations in the magnetic field induce a voltage in a coil wound on the magnet. This small
voltage, when suitably filtered, produces one note of the musical scale, its pitch or frequency depending
on the number of teeth passing the magnet each second.
A note of the organ, played on either manual or the pedal keyboard, generally consists of a fundamental
pitch and a number of harmonics, or multiples of the fundamental frequency. The fundamental and eight
harmonics available on each playing key are individually controllable by means of drawbars and preset
keys. By suitable adjustment of these controls the player is enabled to vary the tone colors at will.
The resulting signal passes through the expression or volume control and through the preamplifier
(where vibrato is introduced) to the power amplifier and the self-contained speakers.
Reverberation is added electrically by a second amplifier which drives a reverberation speaker, also
located in the console
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