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 source with the CI 723, common at the time, in a 1989 paper. Power transistors must be...
Often, unauthorized people use the phone to make improper calls. A control for this is achieved with...
Found in an 80's documentation this circuit uses an integrated from the uncommon era today. Other...