Volume Controls


This page is all about wiring and mounting potentiometers (‘pots’) as volume controls in arcade cabinets with PCs as the sound source.  Here are some custom control panels with volume controls that I have done previously:

Admin panel Cassiopea closeup Cassiopea small

Control panel with DVD player Galaxy control panel

What Kind of Potentiometer (pot)?

To start with, lets discuss what a pot is.  It is a variable resistor, which is tapered and adjustable.  That is, it provides variable resistance against an electrical current and therefore divides the voltage between the desired audio signal level and ground. This allows us to vary the active audio signal’s voltage up and down within a range.  Pots come in many shapes and forms, but here we are going to study a pot designed for fitting a circular knob to as a volume control.

There are two basic kinds of pots – linear and logarithmic.  A linear potentiometer adjusts along a linear range, so that if we were to map the voltage onto a graph we wold have a straight line.  A logarithmic pot adjusts along a curved range that appears like a typical logarithm curve.  For the purposes of a volume control, we would typically choose a logarithmic potentiometer.

For PC sound output, which is fairly low voltage, we would want to choose a pot with a range from 10k to 100k ohms (50k seems to work well), with a power rating of 0.5W to 1W.  Because we will be dealing with stereo output from a PC, we will also want a dual-ganged potentiometer.  So, when we go into the electronics store, we can knowledgably ask for a ‘dual-ganged logarithmic potentiometer’ of ’10k to 100k range’

Here are some typical pots.  The last picture is a ‘dual-ganged potentiometer’, which is what you want for managing two audio channels.

Pot with long taper Potentiometer Dual-ganged pot

Wiring Plan

This is the way that you want to wire up the volume control in your games cabinet:

PC audio output  —->  volume control pot —->  amplifier  —->  speakers

To connect up the volume control, you need to break out the cable for our PC stereo amplifier.  There are many different kinds of cables, but what you should find is two signal wires – for left and right channels (often coloured red and white) – and one ground wire. The ground wire may either be separate, probably black or green, or actually surrounding the two signal wires to protect the signal from external interference (best).

If the amplifier’s original cable isn’t long enough, then get some speaker cable from the electronics store as well.  What you ideally want is dual-core sheathed cable with ground-shield.  This will have two mini-coax cables inside, each sheathed separately, with the ground surrounding it.  This will give the best signal transference and minimal interference.

Connecting the Potentiometer

Refer to the diagram below.  For simplicity’s sake this diagram shows just one gang for one channel.  The same principles apply for wiring a dual-ganged pot for stereo, just do the same for both left and right channels (it doesn’t matter which gang you use for which channel). The red wire is input and the blue is for input, which is only used in this diagram to make it easier to read.  In practice, you would likely have one colour per channel.  Note the pin numbering because that is going to be very important to us.

Potentiometer wiring diagram

There are three numbered terminals.  For our volume control application, the terminals correspond to:

1  -  ground

2  -  output or ‘wiper’ (blue wire)

3  -  input (red wire)

So for each channel we need to attach the PC side of the wire to pin 3, and the amplifier side of the wire to pin 2.  We attach the ground wire to pin 1.  Repeat this for the second channel, if you are using a dual-ganged pot.

The thing to remember about the ground wire is to ensure that it remains connected all the way from the PC to the amplifier, while also connecting with both pin 1 terminals on the potentiometer.  Use the same ground wire for both left and right channels.  This is to ensure that everything is grounded properly.

There are fancier ways of wiring volume controls, particularly for high-end audio applications.  Nonetheless, the method described above is the simplest and most satisfactory for 99.9% of arcade cabinets and general audio applications.

Now, lets move on to mounting the volume control.

Continued on page two

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