We obtained this circuit from Popular Electronics from 1993. The operational amplifiers can be 741 and the 6 to 12 V supply need not be symmetrical. The circuit only lets signals whose frequencies are close to 1kHz pass through.

We obtained this circuit from Popular Electronics from 1993. The operational amplifiers can be 741 and the 6 to 12 V supply need not be symmetrical. The circuit only lets signals whose frequencies are close to 1kHz pass through.