I'm about to say goodbye to something I built over 10 years ago. This is one of the channels of an Alesis RA 100 amplifier. The tiny circuit board attached to the aluminum bracket is something I added. It generates a small current in equal amounts into the two differential input stages of the amp, thereby cancelling the input bias current. This let me experiment with the amp's feedback network of in ways that disturb the impedance without creating a DC offset at the output. #Guitar #Electronics