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大环路负反馈可以减小失真、降低输出阻抗,可以扩展放大器的频带宽度,但同时也存在有负面影响,可以说有利也有弊。本文介绍的放大器不采用大环路负反馈,为了减小各种调制失真,电路的输入级和第二级分别采用场效应管和双极型晶体三极管构成对称式的两级放大电路,输出级用双极型晶体三极管做达林顿连接构成SEPP输出级。电路简单、失真小。同时,为了防止输出器件和扬声器遭受破坏,在电路中加入了偏压上限限制电路、输出器件电流限制电路和扬声器保护电路。
The large loop negative feedback can reduce the distortion, reduce the output impedance, can expand the amplifier bandwidth, but there are also negative effects, it can be said that there are advantages and disadvantages. This article describes the amplifier does not use the large loop negative feedback, in order to reduce a variety of modulation distortion, the circuit’s input stage and the second stage, respectively, using FET and bipolar transistors constitute a symmetrical two-stage amplifier, the output stage Darlington bipolar transistor transistor connected to form SEPP output stage. Circuit is simple, small distortion. In the meantime, in order to prevent the output device and loudspeaker from damaging, in the circuit, add the bias upper limit circuit, output device current limit circuit and loudspeaker protection circuit.