| 摘要 |
PURPOSE:To avoid the interference with other circuits and occurrence of unsteadiness due to the floating capacity for the amplifier containing the bias circuit by securing the electric isolation for the bias change-over switch via the opto-coupler in the amplifier. CONSTITUTION:For the amplifier conatining bias circuit 4, light emitting diode D2 has no light emission in opto-coupler OC along with photo transistor Q3 turned off each when switch S1 is off. Thus transistor Q4 is biased via resistance R7 to be turned on, and the base bias value of transistors Q1 and Q2 are decided by resistance R5. Then with S1 turned on, diode D2 emits the light to turn Q3 on and Q4 off respectively, and thus the base bias value of Q1 and Q2 are decided by resistance R5 and R6. Then R5 and R<6> are set properly and with S1 turned on and off, and as a result the amplifier can feature the optional amplifying action from the A-class to B-class amplification. |
