[LectronFanModerator]

Hi all,

Today we are going to use our improved amplifier module to build a simple VCA.

We are going to use a potentiometer to control the volume of an audio signal. No big deal, I hear you say.

But here we are going to control the volume with a DC voltage !

By adding a transistor to the bias input of our amplifier module, we can control the amount of AC coupling to ground. This results in a varying amplification.

We use here the legacy parts, but PNP silicon transistors will also work. Don’t forget the 100K bias resistors !

To make it pleasant to our ears, the end stage driving the earpiece has reduced amplification. We will be able to hear the working of the VCA without feedback.

Use the earpiece with caution, always start with keeping it a bit away from the ears. Feedback may always occur ! Keep the earpiece as far as possible away from the speaker !

Here’s the diagram :

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