The EarthQuaker Devices® A/B Box is a simple, compact tool that lets you choose between two of almost anything. Due to its completely passive design, there is no circuitry between the input and outputs, meaning it can be used in both directions. Use it to switch between two amps! Switch between two channels on a multi-channel amp! Use it as a tuner out/mute switch! Switch between two instruments! Run a dry path and a wet path! The time to passively choose is now!
 
https://www.earthquakerdevices.com/ab-box