B21126E)
This circuit was taken from an old Popular Electronics. The circuit can have its frequency changed from an external signal. The center frequency is given by C1.
The integrated circuit used in this regulator is not very common today. The circuit is from old...
This tone control was obtained in the Audio Handbook of the National Semiconductor of 1977. The...
We find this circuit in an American 1980s documentation. The circuit can still be assembled...