Got it for practicing with two different bass guitars running off one amp. Discovered that when we have an active guitar plugged into A and a passive guitar plugged into B, A's volume knob controlled B's output. As long as A was turned up, B could control its volume with its volume knob, but when A's volume knob was turned down, B's volume went down with it. Literally, A turning itself down could totally mute B. This really isn't a problem as long as you know that. If you want total, independent control, you might want to look for a buffered ABY solution. We also tried it running a Fender Strat guitar into the Y, and the AB outputs were run into a dual input tube preamp that had a Fender input and a Marshall input. Running the AB outputs of the switch into each of the amp's inputs allowed us to very quickly compare the difference between the two inputs and it was very noticeable. One input was very clean and the other had a little distortion added. We got the fattest, richest sound running both inputs simultaneously.
Green Sea, SC