The circuit is from the 1977 National Semiconductor Audio Handbook. The bass and treble control is Baxandall type. The integrated circuit used is not common today.
This circuit was found in an English magazine Radio & Electronics Constructor of February 1977....
This circuit was found in an American publication from the 70s, but it can be assembled with more...
This microphone circuit was found in a collection of American 80's layouts, using operational...