High-fidelity power amplifier using switching power supply 02

(1) In the power supply part, a
    high-frequency switching power supply is used to replace the traditional power supply that is bulky, bulky, inefficient and hinders the improvement of sound quality. The sound quality is improved to a certain extent. The
sound of the entire power amplifier makes people feel more friendly and soft. Figure 6-24 is a diagram of a switching power supply with an operating frequency of 100kHz. Its output
DC voltage is continuously adjustable from ±35V to ±45V. The rated output power is 300W, the efficiency is greater than 85%, the load voltage fluctuation
is less than 0.2%, and it is no-load. The ripple voltage is 0.2mV and the full load is 70mVo. It can work normally under the condition of input AC 170V to 270v
. The protection circuit is complete. The thick film component CF8861 has highly sensitive current limiting function internally, and a thyristor permanent shutdown circuit is installed externally
, making the switching power supply overcurrent and short-circuit protection quick and reliable.
    Adjust the DC output of the switching power supply to ±35V and supply it to the LM3875 in the post-stage of the power amplifier. The pre-stage can simply use 7 81 5 and
7 9 1 5 to supply the LM833 ±isv voltage, so there is no need to worry about the signal-to-noise ratio deteriorating.
    (2) Preamplifier and power amplifier part.
    The monolithic integrated power amplifier I.M3875 of the American NSC Company is an upgraded product of the LM1875. It has high performance
indicators. The LM3875 chip has complete overvoltage, undervoltage, overload, and power short circuit inside the chip. It has protection functions such as thermal breakdown and instantaneous high-temperature impact
, and its performance is better than that of amplifiers composed of general discrete components and hybrid devices. The peripheral circuit is simple and easy to assemble.
    The pre-stage uses LM833, which performs well in vocals and violin strings. Round and delicate, it
is better than NE5532. However, it lacks advertising and is not as well-known as NE5532. In terms of performance indicators, LM833 is comparable to NE5532.