| 摘要 |
PURPOSE:To perform signal switching without causing any crosstalk and to remove a pop noise securely in power-on operation by providing an element which forms a small-time constant discharging circuit composed of an AC coupling circuit and a control means which places a switching means in the 2nd switching state when the power source is turned on. CONSTITUTION:When a low-level muting signal is inputted from a muting signal generating circuit 83 for a specific time during power-on operation, drivers 82L and 82R are driven by NAND gate circuits 84L and 84R. When the power source is turned on, a resistance R2 is connected to a resistance R1 through mode changeover switches 76L and 76R in parallel so as to form the discharging circuit which has a time constant tau2 smaller than the time constant tau1 of the AC coupling circuit composed of a capacitor C and the resistance R1. A charge generated by the capacitor C is discharged principally by the resistance R2, so a pop noise generated in the power-on operation is removed completely in a short time without extending a convergence muting time. |
