This is another project that I put together for Mike. He is working on an idea to build 20 tape loops and mix them together, and wanted to start with combining the inputs so...

Voila, twenty headphone inputs all merge into a 1/4" output jack.
The inside is a work of art, I promise.  What?  You don't believe me?
All right, then look for yourself..

Pretty enough for you?  I'll bet you don't think that it really works, right?
You'll have to trust me.  Have a look at the schematic.