tone selector circuit

Figure 4-12 is the schematic diagram of the five-speed tone selector. The analysis is as follows:
    In the circuit, IC1 and other components form the electromagnetic phono equalizer amplifier, and I bar, its peripheral resistor-capacitance components and the selector switch form the tone selector
circuit .     Press the "Straight" button, sAl and SA2 will act, and SAi will move c8 in the T-shaped network in the negative feedback loop. ． Rs is disconnected, SAz short-circuit C7, the circuit becomes a typical linear amplifier, the gain is determined by (R5+R6)+3, and the output has flat characteristics.     Press the "Language" button, SAi~SPk will move, and the positions of SAl and SA2 are the same as the "Flat" button, making the amplifier's frequency response flat. SA3 and SA4 connect the amplifier to a band-pass filter at the input end, and the pass-band is. 200～3000Hz:, the signal outside the frequency band is attenuated by 6dB/f audio frequency.     When the "Play" key is pressed, the action of the sculpture causes a resistor R4 to be connected in parallel to C7, slightly increasing the high and low frequencies.     When the "Orchestral" key is pressed, SA7 moves, the pins in the T-shaped network are short-circuited, C8 is grounded, and the high and low frequencies are boosted .     When the "Bass" button is pressed, S:Ag and SAio move, and the switch b causes the negative feedback loop capacitors & and C to be connected in series. The treble negative feedback is enhanced and the bass is improved. SAio connects the T-type resistor R7 to the network, so that The treble is slightly improved to balance the playing pitch and bass.     The electronic uses 5×4 interlocking key switches.