| 摘要 |
PROBLEM TO BE SOLVED: To provide a more efficient power saving circuit for microphone amplifier. SOLUTION: A signal of a microphone amplifier is given to a jack 1 for a microphone with a switching contact, and a gate circuit 5 controls turning on/off of a drive power supply between a power input terminal of the microphone amplifier 6 and a terminal of a drive power supply 8. An inverter circuit element 9 is provided between a gate control terminal of the gate circuit 5 and a changeover contact B of the microphone jack 1. Furthermore, a resistor 4 is connected between an input terminal of the inverter circuit element 9 and a negative terminal of the drive power supply 8. According to this configuration, when a microphone 2 including a plug is not plugged into the microphone jack 1, that is, when the microphone amplifier 6 is inoperative, power supply to the microphone amplifier 6 can be stopped automatically to save power.
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