Howdy Stitch. Those lovely A and B pads can be found on many of Barry’s boards. Their main function is to provide us with an easy method of moving the clipping diodes off the main board, and onto a sister mod board, where different options or flavors of diode combinations can be tried by the flick of a switch or the turn of rotary switch. Check out the DPDT board and the Roto-Tone for lots of options and get ready to have fun.