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Prior to World War II, Hammond organs featured a tremolo system that would change the loudness of the organ at a periodic rate. This was to simulate a similar feature on pipe organs (almost exclusively theater organs) that would shake the wind regulator to deliver a periodic change in air pressure. This would effect the volume as well as the frequency of the pipe. Of course, this imitates, in a crude way, the vibrato that a singer or violinist uses to add color and interest to their performance.

In the Hammond tremolo, a cam near the RunMotor is rotated by the ToneGenerator drive shaft. As the cam revolves, a series of sequential contacts open and close which changes the output level of the signal passed to the pre-amp. Ideally, this change should be a very low frequency sine oscillation. The actual waveform of the Hammond tremolo, because of the switch contacts, is closer to that of a trapezoid.

Tremolo is not very interesting to the ear and many performers expressed dissatisfaction with the sound. JohnHanert developed the Hammond Vibrato during World War II and the tremolo was discontinued.

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