| 摘要 |
PURPOSE:To suppress the occurrence of click noise by impressing a phantom voltage to a microphone through a switching circuit which is turned on when the charging voltage of a capacitor to charge a current to a constant-current circuit reaches a fixed value. CONSTITUTION:When a switch SW1 is set to 'on' and a control circuit to 'off', a capacitor C3 of a constant-current circuit 12 starts being charged, and according to the increase of the voltage at a point a, a switching circuit 10 is activated and the potential of a point b is increased by a certain time constant until it reaches to a phantom power source voltage, and stops increasing. At that time, as a change in potential at the point b is prevented by capacitors C1 and C2 and no input signals come into a microphone amplifier circuit 14, click noise does not occur at a point d. Then, when the switch 1 is set to 'off', a control circuit 11 is turned on, the charge of a capacitor C3 is discharged and the circuit 10 is biased to 'off'. Therefore, the potential of the point b drops rapidly, the charge charged to a capacitor C4 drops by a certain time constant until it reaches 0V, the potential change at the point C becomes minimum, and thus click noise does not occur in a circuit 14. |
