This filter that rejects a frequency range determined by the double-T was found in the August 1993 Electronics Now magazine. The source must be symmetrical.
We find this circuit in a 1995 documentation. It warns when the timing is nearing its end, with...
This circuit is from the 80's, using an integrated of the time. The circuit serves as a reference,...
We got this circuit in a publication of 1987. This is an audio limiter, a circuit that cuts peaks...