This circuit with the CA3059 was found in the July 1995 Elexctronics Now magazine. The signal must be DC, and the circuit is not isolated from the mains.
We found this configuration of band rejector filter or band rejector with operational 741 in a...
This oscillator can use any CMOS inverter. The circuit is crystal controlled and was found in the...
This circuit was found in a 1967 US documentation. It shows how to build a gain control by digital...