This filter, which rejects frequencies around 1 kHz, was found in the August 1993 Electronics Now magazine. The fine tuning is done at R3, and the source must be symmetrical.
This preamplifier circuit with a CK722 transistor appeared in Radio Electronics magazine in...
We found this circuit with several types of sensors in a 1995 documentation. The circuit also has...
This circuit was found in an American documentation from the 90s. It consists of an optical memory...