Hammond Model A, Manual, Page: 147 / 298

HOW THE PEDAL SOLO UNIT WORKS
All notes of the pedal solo unit are controlled by a two-triode vacuum tube master
oscillator circuit operating at audio frequencies from 523 to 3136 cycles per
second, corresponding to 1 foot pitch. Thus the master oscillator operates over the
full pedal keyboard range of 32 notes. Each time a pedal is depressed. its tuning
contact tunes the oscillator to the pitch associated with the corresponding key in
this 32 note range.
The output of the oscillator is fed into a series of five cascaded frequency
dividers, each of which divides its input frequency by two and thus produces a note
an octave lower than its input frequency. The five dividers thereby provide pitches
of one, two, three, four, and five octaves below the pitch of the oscillator. In
this way, when the oscillator is tuned to some given note, each divider produces a
note in exact octave relation to the oscillator, thus forming a series of six notes
having exact octave relationships. The particular frequency divider or dividers
selected for sounding through the amplifier and speaker system of the organ will
depend upon which of the stop tablets are used.
A control contact Under each pedal causes the control tube to transmit the signal to
the amplification system with a controlled rate of attack.
COMPONENTS OF THE PEDAL SOLO UNIT
Electrically the pedal solo unit is very similar in principle to the Hammond Solovox
Model L, although there are, of course, many differences. It employs tuning coils,
tuning adjustment knobs, a master oscillator, and frequency dividers similar to
those in the Solovox, and the stop tablets are similar in function to the register
controls of the Solovox.
The Pedal Solo Generator is a chassis which looks like an amplifier and contains the
master oscillator, five frequency dividers, an amplifier, a control tube, and a
power supply. It is located directly above the pedal switch assembly, near the left
side of the console as viewed at the rear.
The Tuning Coil Assembly contains 32 adjustable inductance coils, which tune the
master oscillator to the frequencies of the 32 pedal notes. It is mounted above the
pedal switch assembly, near the right side of the console as viewed at the rear.
The Control Panel, with stop tablets and a volume control knob, is mounted at the
right end lower manual.
The Pedal Switch has nine contacts under each pedal key. One is used for tuning the
pedal solo unit, the second serves to key the amplifier and make the pedal solo note
sound, and the other seven carry harmonics from the main (tone wheel) generator to
the pedal drawbars as in the B and C series consoles.
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