mechanical volume control for computer sound

[DenCollins]

Hello,

I'm trying to build a mechanical or analog volume control for computer generated audio.
Trouble is that I have no idea what the resistance or impedence should be on the the pot.

I found something at Amazon that works
http://www.amazon.com/Koss-155954-VC20-Volume-Control/dp/B00001P4XH/ref=sr_1_1?ie=UTF8&qid=1324331552&sr=8-1

But the dial is way to small. I need something that works with a knob or dial.

Can anyone help?

[DenCollins]

Here's a little diagram of what I'm trying to do.

[Hero999]

It's not too critical.

Just use 20R to 50R and it should be fine.

[DenCollins]

I'm Sorry, But I don't know what you mean by 20R. Are you refering to resistance or a 20 R Pot?
I found something that might work. I cracked open a set of headphones we use for the field at work and it
had a B500k Stereo Pot in it. I couldn't find any here in the USA (or I just didn't know where to look) so I ordered them from China. I may be wrong, but in theory these should work.

[DenCollins]

I did a search for a 20r pot,  but all the that came up is a 20K pot. Is that what you were referring to?

[DenCollins]

I'm Sorry, But I don't know what you mean by 20R. Are you refering to resistance or a 20 R Pot?
I found something that might work. I cracked open a set of headphones we use for the field at work and it
had a B500k Stereo Pot in it. I couldn't find any here in the USA (or I just didn't know where to look) so I ordered them from China. I may be wrong, but in theory these should work.

As it turns out I was wrong. The B500K pot is probably matched for the impedence of the speakers in the headphones, but not for the line out of the computer. I know it can be done, I just don't know what resistance the
Pot should be.

[Hero999]

I mean a 20 to 50 Ohm potentiometer.

It really isn't critical, there doesn't need to be any impedance matching. The potentiometer just needs to have a low enough resistance to avoid being loaded too much by the headphones but high enough not to overload the sound card. If the resistance is too high, the volume will be too low when the potentiometer is in the middle setting, when the output resistance is half its value. If the resistance is too low, it will draw too higher current from the sound card output.

[DenCollins]

I mean a 20 to 50 Ohm potentiometer.

It really isn't critical, there doesn't need to be any impedance matching. The potentiometer just needs to have a low enough resistance to avoid being loaded too much by the headphones but high enough not to overload the sound card. If the resistance is too high, the volume will be too low when the potentiometer is in the middle setting, when the output resistance is half its value. If the resistance is too low, it will draw too higher current from the sound card output.

Thank you very much, Would Any of these Work? http://www.futurlec.com/PotRot.shtml
Particularly, 1/2W Dual Logarithmic Taper Potentiometers?
any Help would be much appreciated.

[DenCollins]

Thank you very much, Would Any of these Work? http://www.futurlec.com/PotRot.shtml
Particularly, 1/2W Dual Logarithmic Taper Potentiometers?
any Help would be much appreciated.

Edit: I originally started out with a 25 ohm potentiometer and I couldn't get it to work. I think the current on that line has a really low rating. I say that because it can power a set of small headphones (ipod) but it will not even budge a 4 ohm speaker on it's own.

[DenCollins]

As a final plea for help, let me explain my situation, I work for a non-profit organization that produces touch screen based educational software for cancer patients. One of the problems that we are facing is that we need a solution to a problem that we have been having with adjusting the sound level when viewing the educational videos.  Currently, the patient has a choice; He or She can listen to sound either through either the speakers or through the headphones. The problem is that it’s a fixed volume level that can only be adjusted in the control panel of the computer. Since our software covers the entire screen and there is no keyboard the patient cannot adjust the sound to their personal preference. 

Even if there was a keyboard, the majority of the users don’t even know how to access the control panel  let alone adjust the sound. That’s why we need a mechanical volume control. It’s something that everyone knows how to use.

I know this can be done. I just don’t have the expertise to make it happen. So I am asking that if someone could please be so kind to just point me in the right direction it would not only solve a major problem,  but also help enrich the cancer patients and their families find useful information that could benefit them.