nope, not the cables either; I just tested them. But I think you might be write about the opto I do get a buzz, or rather a hum, from the output, but I figured this was because the MBS wasn't grounded. BTW, I tried the midibox chained after my dx200 and it performed the same as when it was chained after the q, so I know for sure it's not the q. so... time to order a opto.