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Audio Volume Control

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Recipe #18 — audio volume control

A potentiometer makes a simple audio-level control when it is wired as a voltage divider. The full input signal is placed across the resistive track and the wiper selects how much of that signal continues to the output.

AUDIO VOLUME CONTROL AUDIO IN P1 100 kΩ audio taper AUDIO OUT Turn the wiper toward ground → less output signal
Follow the signal: AUDIO IN is applied to the top of P1. The bottom of P1 is grounded. The wiper becomes AUDIO OUT.

At the two extremes

With the wiper near the input end, the output is close to the full input signal. With the wiper near ground, the output approaches zero.

Another way to think of it

The potentiometer is not creating a stronger or weaker source. It is selecting a fraction of the available input voltage, much like the ordinary voltage divider studied earlier.

Why audio taper?

A linear potentiometer works electrically, but a logarithmic or audio-taper pot usually gives a more natural-feeling change in loudness as the knob is turned.

The source impedance, potentiometer value, and input impedance of the next stage all affect the actual result.

For stereo, two matching potentiometer sections can be moved by one shaft. That dual-gang arrangement will make more sense later, after the basic mono mixer has been completed.

Try these yourself

Which potentiometer terminal provides the adjustable audio output? AUDIO VOLUME CONTROL AUDIO IN P1 100 kΩ audio taper AUDIO OUT Turn the wiper toward ground → less output signal
The wiper moves along the resistive track and selects a fraction of the input voltage.
What happens as the wiper moves toward ground?
The wiper selects a voltage closer to ground, so less audio signal reaches the output.
Why is audio taper commonly used for volume controls?
Audio taper changes resistance non-linearly with shaft position so the control feels more natural to human hearing.
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