Stereo to Mono box.
I have a single channel amp at my desk at work. I used to have a single channel SET amp and it's entirely possible it failed because I killed it but I will never know. I recently noticed the output I was hearing from my speaker at work was sounding funny. It never entered my mind that I couldn't use a Stereo to Mono cable to sum the signals from my stereo output from my pc to a single channel. Well I was wrong, which might explain why it was sounding funny. After doing some research online I found the Why Not Wye article which does a much better job of explaining why this is not a good idea than I ever could.
I also found a premade box at one of the vendors who I have purchased transformers from in the past. However, the cost of the device was reasonable, but shipping was retarded and for the cost of 1 + shipping... I could build a half dozen of these myself. So... a trip over to Mouser and $10 later including shipping... 2 project boxes and parts enough to make a dozen of these, I just happened to be out of these resistors so I got a handful of each.
Parts were very inexpensive, the RCA's are cheap, the project boxes were $3.00 each and the resistors were .11 for the 2 Dale 470ohm and .16 Dale 20kohm. So all told we're talking less than $6.00 to make this little gem.
So, if you run a single mono channel anywhere, and this includes most sub woofers, and don't have this type of device, toss one together it was a snap. The single RCA connector was my inner Audiophile crying out for help lmao. I love the new Black Neutrik REAN connectors. The small 6" connector is also shielded, cool right? :)
I did a how-to a while back on making your own RCA interconnects. Many Thanks to Rane Audio for the info and schematics for this project.