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.
The S-meter is signal strength meter, coupled to telecommunications receivers to indicate the...
This power supply can be implemented with a TIP32 providing an adjustable output at the 2k2...
This circuit was obtained from a 1967 magazine. The magazine no longer exists, but the circuit can still...