This circuit operates from 20 Hz to over 20 kHz and is easily tunable. We found it in a 70s documentation. The circuit can be implemented with modern operational amplifiers.
The LS4558 integrated circuit is a double 741. The filter response curve is given next to the...
This motor control using transistors was found in a recent English publication. The circuit is for...
This circuit from a 90s Popular Electronics, decodes the old analog TV signal. It works with a...