| 摘要 |
PURPOSE:To enable to completely zero the sound volume, by decreasing the flowing-out base current of an input transistor to a negligible small amount, in a DC control circuit which receives a DC voltage from a variable resistor at the base of the input transistor. CONSTITUTION:Transistors Tr8, Tr9 are differentially operated, the base potential of Tr9 is determined with resistors R17, R18, and Tr9 is switched in response to the current change of the transistor Tr8. The slope of switching can be made smooth with the resistors R14, R15. The emitter output potential of an input transistor Tr7 is changed with the potential Vr at an input terminal (a). When the output voltage of the variable resistor VR for volume control is made to zero, the residual potential of the variable resistor VR can be made to 0.07 volt with the effect of improvement of the base current of a transistor Tr1. |
