This circuit is from an ancient American documentation. The integrated circuit is 741 and the power supply must be symmetrical. The passing band is centered at 1 kHz.
This notch filter was found in National Semiconductor documentation from the 1980s. Operational...
This circuit for the logic control of the 555 in a power supply was found in the October 1989...
Found on an 80's Radio Electronics, this circuit is designed to pass the 300 to 34,000 Hz voice...