WURLITZER 4600 Series Instruments

North Suburban HAMMOND ORGAN Society

This video shows how the two signals which are 90 degrees out of phase combine as they are alternately gated on and off. The resulting signal transistions smoothly from 0 to -90 degrees and back again. If you find this distracting while reading the text, use the stop button to freeeze the video.

vector diagram showing phase transition for 0 to -90 degrees and back

This video shows how the two signals which are 90 degrees out of phase combine as they are alternately gated on and off. The resulting signal transistions smoothly from 0 to -90 degrees and back again.

The constantly changing arrows on the X and Y axes represent the two signals, phase A and phase B that are 90° apart as they are shown by their physical placement in the diagram. The third arrow that rotates forward and back through 90° represents the composite signal, which will have a true, pitch-varying vibrato.

If for some reason, the amplitude of one of the two phases is different from that of the other, this will also introduce a volume-varying tremolo into the tone as well as the pitch varying vibrato. In these older instruments where there can be considerable component parameter changes with time, this is indeed the case. It is also somewhat true even when these instruments were new as it would be very difficult to balance the outputs of the phase splitter over the entire frequency range of the instrument. But the presence of some amplitude-varying tremolo in the signal, as long as not excessive, is not bad by any means.

The above diagram clearly shows how the composite signal varies between 0° and -90° as the two input signals vary in amplitude. On the next page there is a diagram of the final result, the same electrical signal which now has the vibrato applied. The gradual changing of the length along the x axis of the wave shows that its instantaneous frequency is changing. This is the result of combining the gated signals of phases A and B.

 

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