This box works fine with guitars but it kills the signal from our keyboards. It reduces the volume on our keyboards by about 80. We could compensate on the mixer but it is just too much of a drop. Really strange. Never seen this before. We have 5 or 6 other boxes from various brands and none of them do this. I don't know if we got one that is flawed but I wouldn't buy it to use with a keyboard unless you are using the headphones jack. And yes we had the buttons all set correctly. I've been doing sound for 37 years. It would probably work well with anything with a really hot signal.