Originally designed for WWV (Standard Time Station) signals, it lets 1 kHz tones pass by rejecting the 440 and 600 Hz tones emitted by the station. The circuit is from a 1964 Electronic Design.
This circuit came out in an American magazine that no longer exists. It's the Electronic...
This circuit can be added to any audio amplifier design, consisting of a good tone control with an...
Using a 741 op amp with symmetrical source, this circuit was found in a 1982 documentation. The...