Vibrato And Chorus Of Hammond Organs - Hammond B-3 Owner's Manual

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Vibrato and Chorus of Hammond Organs

On string instruments, the vibrato effect is created by changing the string tension by one's
fingers. 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 was stabilized by the synchronous motor, it was not possible to provide a vibrato
effect. On these models, the vibrato effect was obtained by modulating the signal post-genera-
tor.
The vibrato & chorus system of the original B-3 consisted of a 9 stage delay line using LC
phase shift circuits. This 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 turns on the contrary, the pitch would gradually
rise. These operations were automatically made by turning the scanner with a motor.
The 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, a popping noise like
that of a switch did not occur and the signals of neighboring terminals cross-faded and switched
themselves.
The mode-selection of vibrato effects was made by changing the range of the connecting tap.
As this system modulated the produced tonal signals and not the oscillator, the original sound
could be heard without the vibrato effect. By mixing the sound with the vibrato effect and the
original sound, the chorus effect was obtained.
On this model, the chorus and vibrato effects are simulated and modeled in the original fash-
ion digitally, by the DSP, without using moving parts.
Fundamental diagram of VIBRATO equipment
Setting the Parameters