| 摘要 |
PURPOSE:To prevent the generation of a transient sound attended with the switching of a power switch by connecting a resistor in parallel with a constant current source flowing the operating current to a differential amplifier so as to constitute a bias circuit flowing a current at the start of operation. CONSTITUTION:The constant current circuit 56 is provided as a constant current source to draw the operating current of the differential amplifiers 6, 8 between a midpoint of resistors 48, 50 of an operating switching circuit 42 and a reference potential point. The resistor 62 is connected in parallel with this constant current circuit 56 so as to constitute the bias circuit flowing the current at the start of operation. Thus, since the operation switching circuit 42 is brought into the operating state in response to the application of a power switch 34, that is, corresponding to the leading of a bias voltage VB2, the fluctuation in an output DC level is suppressed and the output V0 has no steep peak point but transits to the steady-state with a smooth change. As a result, no fluctuation in the DC level exists and the generation of the transient sound, that is, a popping noise is suppressed. |
