Circuit operation is as follows: negative peaks in excess of -8.25V cause D1 and D2 to conduct, charging C4.The charge stored in C4 provides bias to Q1, which determines amplifier gain.

• 电路原理如下：超出-8.；25V的负电平使D1和D2导通，给C4充电，C4储存的电荷为Q1提供偏置，从而控制放大器的增益。