| 摘要 |
PURPOSE:To attain optimum signal amplification to a power supply voltage by setting an amplification gain to a degree where a signal waveform of an amplified output is not clipped to a maximum power voltage to an amplifier and applying a signal subjected to level adjustment to the power voltage to said amplifier. CONSTITUTION:An audio signal to be amplified is fed to a level adjusting circuit 6 via a variable resistor 4 from an input terminal 2. The level adjusting circuit 6 consists of an electronic volume circuit to detect a fluctuation of the power supply voltage Vcc fed to a power terminal 8 and the level is adjusted to the input signal in response to the fluctuation. The audio signal fed to the input terminal 2 is adjusted to a prescribed level by the variable resistor 4, then fed to the level adjusting circuit 6 and when the signal is changed to a level in response to the fluctuation of the power voltage Vcc and fed to an amplifier 9, where the result is amplified. Thus, even when a power supply whose terminal voltage is changed due to a discharge of a battery is connected to the power terminal 8, the amplified output with an optimum level is obtained corresponding to the fluctuation of the power voltage. |
