The MXR A/B Box allows you to route your instrument's signal to two seperate amp paths. Use it to switch between amps or run them both at the same time with different effect configurations so you can find your ultimate sound. Use the Thru jack to connect to a tuner, amp or other device that you want to recieve a constant signal. The MXR A/B Box comes in a heavy-duty die-cast housing with hight quality jacks and switches.