The first half of the circuit (IC1a) it has an input sensitivity of 3 mV and has a frequency correction composed of C5, C3, R6 and R8. The bass signal coming from phono input is amplified while the high signal is attenuated. The selection of the input signal sources is done with switch S1. P1 and P2 are parte of a double potentiometer. They contro
l the high tones and bass. There is no risk of overdrive in circuit due to the passive nature of the sound control.