This circuit is from a March 1978 Radio Electronics magazine article that showed how to build it. The circuit is TTL based and is powered. The components used can still be found.
This filter for the 300 Hz to 3 kHz range was found in an American documentation from the 90's....
A very interesting integrated circuit for step-down converter designs (voltage reducers) with an...
We found this circuit in the 1994 Linear Applications Handbook from National Semiconductor. The...