| 摘要 |
PURPOSE:To eliminate unpleasant sound produced through a headphone by providing a negative feedback circuit which reduces the output of an amplifier in response to the headphone in case the output of the amplifier is connected to the headphone. CONSTITUTION:When a headphone is used, a headphone plug is inserted to a headphone jack 9. In response to this action, movable contact bars 5c and 14c of changeover switches 5 and 14 are switched to the sides of fixed contacts 5b and 14b respectively. Thus an audio output is delivered to the headphone, and at the same time a part of the audio output is negatively fed back to amplifiers 1 and 10 via resistances 18 and 19 respectively. Then the outputs of amplifiers 1 and 10 are reduced. Therefore an output waveform is never clipped to a fixed input signal. It is possible to apply audio signal containing reduced distortion to the headphone via the resistances 7 and 8 by selecting feedback resistances 18 and 19 as well as resistances 20 and 21 so as to eliminate the distortion of the output waveform. As a result, no unpleasant sound is produced through the headphone even though the volume is set maximum by volume resistances 16 and 17. |
