| 摘要 |
PURPOSE:To prevent pop noise at application of power by adding a bias circuit to an output circuit of an acoustic amplifier so as to control the output circuit even before generation of a muting pulse. CONSTITUTION:A transistor (TR)34 is turned off, because the bias circuit comprising a resistor 35 and diodes 36-39 is not operated until a power supply voltage is >=4VBE even if power is applied and a time t1 is elapsed. Thus, a TR33 and an output TR24 are turned off also and no charging current flows to an output capacitor 28. In selecting t3 as t1<t3<t1+t2 (time of time constant decided by a resistor in a muting pulse generating circuit 1), the muting pulse generating circuit 1 is activated at the application of power until the power supply voltage is increased to the 4VBE, and an output voltage keeps the state of GND level even if the TRs 33, 34 are turned on with the power supply voltage increased >=4VBE. Since no impulsive output voltage is generated at the instance when the time changes from t1 to t2, pop noise is not generated.
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