Differential amplifiers are an internal subsection of many circuits from well, amplifiers to circuits that control speed of motors, power supplies, etc. Here is a nice video on how they work down to circuit level with some nice demonstration of it using audio signals:
It is HTML 5 and can benefit from playing at 1.5X. I posted the same in the balanced/unbalanced thread.
It is HTML 5 and can benefit from playing at 1.5X. I posted the same in the balanced/unbalanced thread.