OK, here's the deal. The jack itself is a stereo jack, however, the input is set up for mono. It's not a ballanced input--it's just a stereo jack wired with a mono hook-up. Kind of a weird way to do things, and I sure don't know why Yamaha did this, but I tried every wiring configuration and then went to my stereo mixer, fired a mic through it, connected both outputs through a stereo jack (In/out effects cable) and the best I can come up with is mono--not stereo. Sure would like to see a schematic of the board, but unless there's something wrong with my boards, I usually don't take them apart. If anyone has an up to date schematic, I would sure like to see it.

Cheers,

Gary