| 摘要 |
PURPOSE:To execute amplification efficiently, by controlling supply voltage in proportion to a value of a resistor for controlling the sound volume. CONSTITUTION:When a rotary shaft 6a of a variable resistor for controlling the sound volume is rotated to the right, input voltage to a power amplifier becomes high. In this case, a disk 9 is also rotated to the right. When a slit 10 provided on the disk 9 passes through the positions of photocouplrs 11a, 11b and 11c, a signal according to an angle of rotation of the variable resistor is generated from the photocouplers, and is provided to a voltage controlling circuit provided on an electric power supply circuit 3. As a result, in case when the resistor has been controlled so that high input voltage is applied to the power amplifying circuit, the supply voltage applied to the power amplifying circuit is heightened. |
