Just another amp build. nothing special about the circuit. the Power supply on the other hand is a different story. I picked up a little iphone speaker box from the dollar store that took only one aa battery. after tearing it apart i found a little opamp and a buckboost converter. the converter takes 1.5volts from the battery and turns it into 5volts that the op amp requires. So for 1 dollar I got a switch, battery snaps, and a dc-dc converter.