This filter was found in a Texas Instruments manual based on an operational amplifier 741. Other operational can be used and, with the indicated components, the rejection frequency is 2 kHz.
This circuit generates sinusoidal signals between 300 and 3000 Hz. We find a 303 Circuits from the 90's....
This amplifier for audio transmission lines was found in a 1961 American publication. The critical...
Old phones with dials can be used in a simple home intercom system, as this circuit from Popular...