This circuit is from 1964 documentation but can be easily implemented based on current components. Input waveforms and detection are shown next to the diagram.
This circuit uses PNP transistors that can be BC558, but if the power is reversed, BC548 can be...
This tone control was obtained in the Audio Handbook of the National Semiconductor of 1977. The...
This circuit was found in the Linear Technology Applications of 1997. The circuit uses components from...