This high input impedance circuit is suggested by Motorola's 1993 Linear Interface ICs. The power supply must be symmetrical. The circuit has a differential input.
The diagram shows a tone control with the LM381 IC. The circuit is from a Radio Electronics from...
Very simple, this radio control circuit for short distances was found in an Electronic Design from...
From an article in Radio Electronics magazine, May 1989, this circuit requires a dual power...