Introduction: Passive 3 Input Stereo Mixer
This instructable will show you how to build a simple stereo mixer. Though this box has only 3 stereo inputs, you could easily upgrade it to as many as you need! I wanted to build this box to connect multiple audio inputs into one single output.
I am using RCA panel mount connectors because thats what I have, you could make this all with 3.5mm stereo jacks, 1/4" phono jacks, or even a mix of different types! I want to give credit to Curt @ scribd for his inspirational writeup, I'm essentially adding photos, visual design and diagrams.
Currently I have my mac tower, xbox 360, and laptop connected to the same set of speakers with no problems. I wanted to make a small, non-powered box that looked good sitting on the desk.
Build Time: 1 hour, not including research + documentation
Total Cost: $15
$8 -Diecast Project box
$2.50 -Panel mount connectors, (six RCA female, one 3.5mm stereo female)
$2 -18 or 20 gauge wire, solid strand (this should get you 10-20 ft. I only used 8 inches total)
$2 -4.7k-ohm 1/2 watt Resistors
$.50 - Small Ruber Feet
Drill, 1/4" bit
Soldering iron, Solder
Electrical tape or Heat Shrink tubes
Knife or actual wire stripper
*optional* Dremel to thin out the wall of my project box, yours might be fine without
*optional* Alligator clamps to test connections before soldering everything together
Step 1: Detailed Part List Photos
All parts for this project were purchased at the most honorable Debco in Cincinnati Ohio, except for the resistors from Radioshack.
The Diecast box actually worked out to save me about 20 minutes of soldering because it is conductive enough to ground all of these connections. Win.
Step 2: Drill + Screw + Tighten
Measure, mark and drill holes in your project box. I used the awl to make a small indent in the box so my drill bit wouldn't wander.
You'll need 6 holes for the RCA connections and 1 for the stereo jack. Screw the connectors down tight!
Step 3: Circuit Diagram
Heres the basic circuit diagram. I was having problems when I didn't use these resistors mentioned by Curt. When I connected more than two audio sources, one would be barely audible. This volume drop was being caused by signal interference. Adding the resistors solved the problem by raising the total resistance to interference to 9.4k ohms instead of just 4.7k ohms. I dunno entirely why it works, but just trust Curt on this one.
Basically, all input lines have a wire and then a 4.7k resistor attached. Each side (all 3 Right channels, and all 3 Left channels) are then soldered together after the resistors, and another wire runs from that connection to the appropriate pole on the 3.5mm stereo jack.
Instead of soldering everything at once, I used alligator clips to check as I progressed...but essentially, once things are soldered together, you just need to tape or heatshrink the connections.
Then you are almost DONE!
Step 4: Finish!
So, put on your optional rubber feet!
Then you are DONE! Enjoy!