| 摘要 |
PURPOSE:To prevent generation of a shock noise at the release of muting by applying gradually muting control and suppressing the fluctuation of a DC potential at the release of muting. CONSTITUTION:A capacitor 50 is charged gradually by an output of a bias circuit 16 via a resistor 47. The charging voltage is compared with a reference voltage Vc by a comparator 18. When the voltage is the reference voltage Vc or below, the comparator 18 generates a muting control signal to throw a switch 54 to the position of a contact point (y) and to conduct a switch 52. When the charging voltage rises and exceeds the reference voltage Vc, the comparator 18 releases gradually the muting control signal in response to the deviation to throw the switch 54 to the position of a contact (x) and to open the switch 52. Since there is no DC potential difference of the output between an amplifier 2 and the bias circuit 16, the shock noise at the release of muting die to the DC potential difference is not generated.
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