Hammond Model A, Manual, Page: 288 / 298

5-37. VOLUME CONTROL AND PREAMPLIFIER ASSEMBLY.
5-38. Typical Circuit Before Pre-amplifier.
5-39. Each voltage of predetermined frequency produced by the tone generator is
connected to one or more key contacts. When the associated playing key is depressed,
this voltage is impressed upon the bus bar and is carried through the preset key
switch to the preset panel. The voltage is then fed to one of the several taps of the
matching transformer which is associated with the manual being played. From the high
impedance secondary of the matching transformer, this voltage (combined with others
which may be fed through simultaneously) passes to one of the preamplifier input
circuits. (Vibrato ON or OFF circuit).
5-40. Power to operate the preamplifier and power amplifier is supplied through the
run switch circuit as shown in the console schematic.
5-41. Preamplifier Circuit, Input.
5-42. The signal from each mixing transformer is sent to the Vibrato ON-OFF tablet
associated with its particular manual, and is then carried to the VIBRATO or NO
VIBRATO preamplifier input, depending on the position of the tablet.
5-43. The input circuits are similar, with one extra stage of amplification in the
VIBRATO channel to compensate for the loss that occurs through the phase shift
network and associated scanner. The input tube V4 receives the signals from VIBRATO
and NO VIBRATO circuits and further amplifies them. The signal then is impressed on
the LOUD stator of the volume control, and on the SOFT stator through a compensating
network.
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