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.
The circuit shown is from an old European publication. In it we have the way to activate a relay...
We found this circuit in a European publication from the 1990s. Transistors are still common types...
This circuit was found in an American documentation and can be added to common amplifiers of any...