Hammond Model A, Руководство пользователя, Страница: 286 / 298

5-23. A vibrato chorus effect, similar to the effect of 2 or 3 slightly out-of-tune
frequencies mixed together, is obtained when the vibrato output signal is mixed with
a portion of signal without vibrato. For vibrato chorus, part of the incoming signal
appears across the vibrato line and the rest across a resistor in series with the
line. As the vibrato effect is applied to the part of the signal appearing across
the line, but not to the part appearing across the resistor, the combination
produces a chorus effect. For normal vibrato, this resistor is short-circuited. In
the Model C-3 console the vibrato effect can be applied to either manual separately
or to both at once.
5-24. Figures 2, 3, & 3a in the Vibrato and Percussion section shows the vibrato
line box. Each of the inductance coils is connected with one or more capacitors to
form one filter section.
5-25. Figure 4 in the Vibrato and Percussion section shows the construction of the
vibrato switch.
5-26. The scanner, shown in figure 5 of the Vibrato and Percussion section, is
mounted on the main generator synchronous motor and driven at 412 revolutions per
minute. It is a multi-pole variable capacitor with 16 sets of stationary plates and
a rotor whose plates mesh with the stationary ones. In Index B of the same figure,
two sets of plates have been removed to show the rotor.
5-27. Signals coming from the line through the vibrato switch appear on the
stationary plates and are picked up, one at a time, by the rotor. Connection to the
rotor is made by carbon brushes, as shown in figure 5, Index A of the Vibrato and
Percussion section. Two brushes touch the sides of the contact pin and a third
presses on the end, in order to eliminate the possibility of contact failure.
5-28. Figure 1 in the Vibrato and Percussion section shows the vibrato circuit.
5-29. The vibrato switch has no OFF position, and 3 vibrato chorus positions (C1,
C2, and C3) are included in it as well as the 3 vibrato positions (V1, V2, and V3).
The vibrato effect is turned ON and OFF for each manual separately by means of
VIBRATO SWELL and VIBRATO GREAT tablets on the manual assembly.
5-30. The preamplifier used with this circuit has two separate channels into which
signals from the VIBRATO GREAT and VIBRATO SWELL tablets are fed. (Reference
paragraph 5-37.) The VIBRATO signal goes through a preliminary amplifier, through
the vibrato system, and then into additional stages of amplification. The NO VIBRATO
signal also has a preliminary amplifier, but bypasses the vibrato system and goes
directly into the additional amplifier stages.
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