This circuit, from the manual of the integrated circuit used, is a bass and treble control for common amplifiers. The circuit must be supplied with a relatively high voltage but has low consumption. The CI is no longer very simple to obtain, but equivalent operational amplifiers can be tried out. The potentiometers must be linear, and the signal cables must be shielded. C7 is the capacitor coupling to the amplifier and the 500k potentiometer can be replaced by the current commercial value which is 470k.
