PURPOSE: To ensure the control for both the ascent and descent of the level of the fixed band component for the input signal supplied to the amplifier, by providing the circuit consisting of the capacitor, potentiometer and switch to the output terminal of the amplifier.

CONSTITUTION: In triple circuit 35BS which controls both the ascent and descent of the low range component of sound quality control circuit 35, the voltage obtained at the variable terminal of potentiometer VR1 is extracted in the form of the output signal or supplied as the feedback signal of the amplifier or the output signal is extracted out of the output side of the amplifier. This selection is carried out by switches S306∼S309. Thus the control is given whether the level of the fixed band component of the input signal supplied to the amplifier is increased or decreased to the reference level. And the degree of the level ascent and descent is controlled by meter VR1.