This tone control was obtained in the Audio Handbook of the National Semiconductor of 1977. The circuit controls the signals of medium frequencies in a wide dynamic range as shown in the diagram.
We found this symmetrical regulator in a documentation from the 70s. The circuit uses components...
This circuit was found in a 1995 documentation. It drives a set of sequential LEDs from the sound...
This sophisticated remote field strength meter circuit was found in a 73 magazine for radio...