My new A-B switch box for comparing pedals.
The in and out jacks from the pedals being tested are connected to the 4 jacks on the top. The input from guitar is on the right side and the out to the amp is on the left.
Inside is one the AMZ DPDT relay switching pc boards.
When you hit the footswitch, the box seamlessly alternates between the 2 pedals connected to it. You play some riffs, then hit the switch while playing to hear how the other pedal sounds, then quickly go back again to the first pedal.