| 摘要 |
PURPOSE:To obtain an amplifying circuit having a high efficiency, by providing an impedance circuit which is able to execute a variable operation interlocking with a sound volume controlling variable resistor, on a bias circuit of an amplifying transistor. CONSTITUTION:A signal which applied to a terminal 7 is applied to an amplifier 2 through an amplifier 1 and a sound volume controlling variable resistor VR1. Resistances R1, R2 are a bias resistance for biasing transistors (TR) Q1, Q2, and resistors VR1, VR2 and interlocked with each other. In a state that a sound volume is small [VR1 is set to the side (a)], the resistor VR2 is also set to the side (a), a resistance value between (b) and (c) of the resistor VR2 becomes a large value, and a bias current of the TRs Q1, Q2 is small. Subsequently, when the resistor VR1 is set to the side (c), the sound volume becomes large. As a result, the resistor VR2 is also set to the side (c), and the bias current of the TRs Q1, Q2 becomes large. Accordingly, since a dead bias current is omitted, the efficiency of the amplifying circuit is raised. |
