Voltage Controlled Amplifier

The voltage controlled amplifier or VCA is quite a simple module and the simpler examples of VCAs have basically an audio input, an audio output and a control voltage input which controls the output level of the VCA. It’s sort of like a volume control that can be turned up and down automatically by the control voltage.

Apart from being automated it can also be controlled much quicker by a voltage than you could manually alter it by turning a control. That will come in very useful when we come to employ it in its main use but for now let’s consider its role by using it with a module we have already covered and that’s the LFO.

If we connect the output of the LFO to the input of the VCA, then by using the sine wave from the LFO you can achieve a volume modulation effect, also known as tremolo. Incidentally, the term tremolo is often misused in music. It’s technically a modulation of volume whereas the tremolo arm on a guitar actually affects the pitch mainly.


If you used the square wave output and increased the level that it was controlling the VCA you could get it to produce an on off effect that can be quite effective when synchronised with the tempo of the music.

Some of the more versatile VCA’s are able to control the level of low frequency DC sources so you could have an LFO going through the signal path so the level of the LFO was being controlled by the Control voltage of the VCA. So in effect you could voltage control the level of the LFO’s modulation.

Envelope Generator