If you have a significant geek factor, you may have more than one computer in a room at home.  Sometimes you have your old computer plus your new computer, or your home computer plus your laptop from work, or a large stack of machines tracing your computer history over the last decade.

If you find yourself in this situation, you might find a use for a device I have never seen in any computer store or swap meet.  Fortunately, with very minimal soldering skill, you can build it in an evening very cheaply.

The problem this solves is what to do with the audio from both (or all) of those computers.  With this computer audio mixer, you can use one set of powered speakers and have the audio from all of your machines come through them. 

Note: this only works for powered speakers.  The mixer does not work for unpowered speakers.

For my setup, I decided to have four inputs, but you can use the same approach for however many inputs you need.  Here’s the schematic:

Here’s what the circuit board looks like assembled:


 You can use either 1/4 watt or 1/8 watt resistors.  Here’s what the board looks like from the other side, with the locations of resistors shown:


 Here it is built into a box:

 I used some parts I had around the house, but you can build it from the following parts from Radio Shack:

Name Part Number Quantity
Proto Board 276-158 1
10K Resistors 271-1335 2
1/8 inch Stereo Jack 274-246 5
Box 270-1805 1
1/8 inch Stereo Cable 42-2387 4

Just use the stereo cables to connect the speaker outputs of your computers to the inputs of the box.  Then plug the powered speakers into the output.