Hammond Model A Manual page 21

and driven by a constant speed synchronous motor. Their speeds
of rotation and the number of high points on each are so calculated
that each disc produces one of the 91 frequencies necessary for the 91
pitches which are used in the fundamentals and harmonic overtones.
THE GENERAL ELECTRICAL OPERATION.
Ninety-one frequencies are thus continuously available at the generator.
when a key is depressed it selects the proper frequency for the fundamental
of the note it represents, together with the proper frequencies for eight
harmonics of that note as set up on the harmonic controller or on a pre-set
key. These frequencies then flow through the contacts made by the key,
each to its proper drawbar, of the harmonic controller. The position of
the drawbar (which is under the control of the artist) determines the
intensity of each frequency. After leaving the harmonic controller these
various frequencies are superimposed upon one another, or mixed, and
flow as a single complex electrical wave to the pre-amplifier, also located
in the console. From here the wave (amplified somewhat) flows through
the connecting cable to the amplifiers located in the power cabinet where
it is further amplified and caused to operate the speakers.
The swell pedal control is located between the pre-amplifier and the power
cabinet. Its operation varies the strength of the electric wave flowing
to the power cabinet but does not change any of its other characteristics.
Varying the strength of this wave varies the volume of the organ.
Notice that the operation is entirely electrical. No sound is created in
the console-only electrical wave forms. The music first appears as
sound at the power cabinet.
Page Nineteen