Dual gang potentiometer for 'mixer'

unbwogable

Member
2013-02-07 2:47 am
Forgive me if I'm posting in the wrong place.
I've got two radioshack 100k dual gang stereo volume control (cat# 271-1732) I'm trying to use as volume controls between two computers.
The simple version is that I'm trying to input both audio sources, and be able to increase the volume of one over the other, and vice versa.

The audio signals are sent through the wiper pins seperately, out one side, then combined into a single signal into my headphones. I've got the opposite pins tied to ground, as per the instructions found http://www.beavishifi.com/articles/Volume_Control/.

My issue is I have very little control over the volume until about 2/3 of the way through the pots turn, that last 1/3 gives me a choice between about 20% volume and 100%.

Any suggestions? This happens with both pots, so I'm relatively sure it's not defective parts. I've tried multiple audio sources, and checked all my connections with my trusty multimeter.
 

Mooly

Administrator
Paid Member
2007-09-15 8:14 am
A couple of things come to mind. Firstly, have the pots a logarithmic law or are they linear ?

You really need log types for audio volume controls to match the way our hearing behaves.

The other problem is that by combining like this you are "fighting" any output impedances of the two PC's audio stages. The results of that would be unpredictable.

What you really need to do is connect each pot as a pure volume control and then take the signal from the wiper into a mixer type circuit to avoid any interactions and allow any combination of levels of the two sources to be selected. Two dual opamps would do it all nicely.