Detailed explanation of audio preamplifier circuit

The preamplifier circuit is shown in the figure below, using A operational amplifier as the audio preamplifier circuit. Its advantages are small size, low noise, low power consumption and good consistency. Using operational amplifier A can achieve deep negative feedback while improving undistorted output. The signal distortion is less than 1%; the voltage gain of the amplifier can reach 50-80dB.

Among them, cl is the high-frequency compensation capacitor, and c2 and R2 are decoupling filter circuits. Adjusting the potentiometer RPl can balance the common mode rejection ratio. Potentiometer RP2 is a negative feedback element. Adjusting RP2 can change the output level.

Component selection: capacitor cl is 82P, c2 is 100p/25v. Resistor R1 is 27kn, R2 is 100n, and R3 is 50kn. Potentiometer RPl10kn, RP2 is 100kn. Integrated operational amplifier A uses GF2A. Transformer T is replaced by a small output transformer commonly used in transistor radios.