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The circuit is shown in Figure 3-8. The input signal passes through a low-pass filter and is input to a differential amplifier composed of field effects for pre-amplification
. The output of the differential amplifier is input to the non-inverting input terminal and the inverting input
terminal of the operational amplifier respectively. Since the input end of the operational amplifier is a differential circuit, the signal output by the FET differential circuit is differentially amplified at least once after being input to the operational amplifier.     The phono equalizer RIAA circuit is composed of R7, C6, C7, etc.     The differential input field effect transistor can be 3DJ4F or other low-noise high-quality field effect transistors , IDSS ≥ 2mA, and paired according to IDSS. The error is <3%. The operational amplifier can choose high-performance operational amplifiers such as TL0 72, TU082 or NE5532 . The resistor is a metal film resistor with level I accuracy. The capacitor should be a high-density capacitor, and the coupling capacitor should be a polyester capacitor. The power supply adopts a positive and negative symmetrical regulated power supply.