This is a low impedance discrete level control which sits between the preamp active circuitry and the input to your power amplifier 这是一个位于前级有源电路和后级放大器输入端之间的低阻抗的音量控制。
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When the signal source of an op - amp contains an energizing voltage which is much higher than the op - amp supply it is common to use a diode and a current limiting resistor to protect the op - amp in the event of a sensor short - circuit 为了防止信号源窜入高压损坏放大器，常见的做法是在放大器输入端到放大器电源间串接一个二极管，并且在放大器输入端串接一个限流电阻。
