Design and production of audio preamplifiers

The main technical specifications required for the preamplifier are as follows.
Voltage amplification factor: 10 times:
Pass frequency band: 50Hz ~ 20kHz.
Knowledge points that should be mastered during the study of this project. The principle of transistor amplification, the performance characteristics of common-emitter, common-collector, and common-base amplifier circuits, simple analysis and calculation of common-emitter amplifier circuits, and the characteristics and applications of multi-stage amplifiers. Integrated operational amplifier principles and applications, etc.

1. Circuit Design
This project is designed and produced as the preamplifier part of a two-channel amplifier. Each channel includes a preamplifier and a volume adjustment circuit. The preamplifier is implemented by an integrated operational amplifier, and the volume control is implemented by a dual potentiometer.
The circuit is shown below. The integrated operational amplifier uses NE5532.
NE5532 is a dual operational amplifier, which is a high-performance low-noise operational amplifier. It has good noise performance, excellent output drive capability and quite high small signal and power bandwidth.
The circuit is two in-phase input amplifier circuits. Through analysis, it can be seen that the voltage amplification factor of the circuit is about 11 times, corresponding to the two channels respectively. The function of the 200k potentiometer in the picture is to ensure that the gain of the two channels is the same; the function of the double potentiometer is to simultaneously adjust the output voltage of the two channels, that is, the volume of the two channels; the function of the voltage regulator tube is to ensure The voltage supplied by the power supply is ±15V; the function of the capacitor on the power supply is to eliminate the influence of ripple and high-frequency noise and prevent self-excitation; the capacitance at the input and output ends serves to block DC.