| 摘要 |
PURPOSE:To eliminate a shock sound and to obtain the substantially-necessary amount of muting by constituting the variable impedance part of a muting circuit by using the 1st and 2nd circuit parts composed of transistors (TR) of complementary polarities whose emitters are connected directly. CONSTITUTION:An input signal ei from a signal source 24 is transferred as an output signal e0 to an output terminal through a coupling capacitor 23 and a resistance 22. A muting signal is inputted from a terminal 25 to generate a muting control current IM by TRs 12 and 14 and a resistance 16, and thus while a current IM flows through TRs 11 and 18 constituting a current mirror circuit, the current IM flows TRs 19 and 20 forming a current mirror circuit. At this time, a voltage at a terminal 26 rises from an earth point by the base-emitter voltage VBE of a TR13 through the TR13, and drops by the VBE through the TR19 to be held at 0V, so that muting operation generates no switching noise. |
