| 摘要 |
PURPOSE:To set a collector current of an output stage transistor (TR) in matching with each load condition by having only to switch one switch to changeover the operation of both a phase inverting circuit and a bias current switch circuit. CONSTITUTION:In closing a switch 4, an interlocked switch 8 is opened, the same input signal is fed to input terminals 1, 2 via a switch 9 to invert the phase inverting circuit, a signal having an opposite phase to that of an input signal is fed to a low frequency amplifier circuit 7 to allow low frequency amplifier circuits 6, 7 to BTL-drive a speaker 10. In opening the switch 4, the switch 8 is closed, a different input signal is fed to the input terminals 1, 2 by the switch 9 to bring the phase inverting circuit 3 to the noninverting state, a signal in phase to that of the input signal is fed to the low frequency amplifier circuit 7, the low frequency amplifier circuits 6, 7 drive separately a headphone load 11. In order to set the output stage bias current to a proper value, a value of a resistor 143 is changed normally to change the bias state.
|
