Hammond A-162, Owner'S Manual

Page: 79 / 122

79
Setting the P
aramet
ers
Vibrato and Chorus of Hammond Organs
On string instruments, the vibrato eff ect is created by changing the vibrating length of
the string by one’s fi ngers. On wind instruments, by changing the strength of breath. On
electronic instruments with analog circuitry, by modulating the oscillator. As the rotation
of the tone wheels of the original B-3/C-3/A-100 was stabilized by the synchronous mo-
tor, it was not possible to provide a vibrato eff ect. On these models, the vibrato eff ect was
obtained by modulating the signal post-generator.
Th
e vibrato & chorus system of the original B-3/C-3/A-100 consisted of a 9 stage delay
line using LC phase shift circuits. Th is produced a very short delay of about 1 ms. Tones
were passed through coils, delaying the phase. Several coils were connected in tandem
and when the output of each tap was passed from the top to the last by turns, the pitches
gradually lowered. By taking the output of each tap from the last to the top by rotations,
the pitch would gradually rise. Th
ese operations were made by means of a rotating device
called a “scanner” which intercepted the output of each tap. Th e scanner would scan the
entire length of the delay line for V3/C3, approximately half of it for V2/C2 and about a
third of its length for V1/C1.
Th
e scanner was used to select one of multiple input terminals by the static connection.
As each terminal was selected by the “blades” which approached each other, and the sig-
nals of neighboring terminals cross-faded and switched themselves.
As this system modulated the produced tonal signals and not the oscillator, the original
sound could be heard without the vibrato eff ect. By mixing the sound with the vibrato
eff ect and the original sound, the chorus eff ect was obtained.
On this model, the chorus and vibrato eff ects are replicated in the original fashion digi-
tally by our proprietary DSP, without using moving parts.
Hammond Classic “Scanner Vibrato” (Physically Modelled on the A-162)