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DESCRIPTION JPS62276909

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DESCRIPTION JPS62276909
[0001]
3. Field of the Invention The present invention relates to an output switching circuit in a power
amplifier to which a headphone as a load and a speaker are switched and connected.
Conventionally, the output switching in the power amplifier shared by the headphone and the
speaker has been switched on the output side of the power amplifier. Hereinafter, a conventional
output switching circuit will be described with reference to FIG. 2 with reference to the entire
drawings. In FIG. 2, the input signal i to the power amplifier 3 is inputted through the input
resistance 1 and the volume volume 2, the output signal is supplied to the common terminal of
the output changeover switch 4 and the speaker is switched by switching the output changeover
switch 4 7 or supplied via an output adjustment resistor S to a terminal 6 to which a headphone
is connected. Problems to be Solved by the Invention However, in the above configuration, since
the button speaker 7 has a small diameter in the case of small-sized audio equipment and the
output itself is small, the power amplifier is operated to secure sufficient sounding of the speaker
7 When the gain of 3 is set, the power amplifier 3 itself is clipped, and when the output selection
switch 4 is switched to the headphone side at the predetermined volume volume 2 position, the
headphone output is clipped. It adversely affects headphone listening, and volume volume 2 must
be adjusted and used. There is a problem in terms of operability that the volume volume 2t-must
be adjusted when switching the headphone and the cuspid force. Means for Solving the Problems
In order to solve the above problems, the output switching circuit according to the present
invention comprises the input of the power amplifier by switching means responsive to the
switching means of the speaker and the headphone connected to the output side of the power
amplifier. It is characterized in that the impedance is changed. Operation According to the abovedescribed configuration, the present invention is capable of automatically setting the output of
the power amplifier suitable for headphone listening by switching the input impedance of the
power amplifier in response to the output switching of the power amplifier. It is possible to
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realize suitable headphone listening even at a fixed position of Embodiment An embodiment of
the present invention will be described with reference to FIG. In FIG. 1, first, an input signal i of
the power amplifier 3 is input through the volume volume 2 at the time of speaker output, and
an output signal is output from the speaker 7 through the speaker output tuning transistor 1o.
FIG. 2 shows the time of speaker output. Next, when the output selector switch 4 is switched to
the headphone output side, the input resistance switching transistor 8 and the feedback
switching transistor 9 operate simultaneously.
Since the input resistance 1 is added as a load, the input signal of the power amplifier 3
decreases from that at the speaker output. The output signal of the power amplifier 3 is supplied
to the headphone output terminal 6 through the headphone output switching transistor 9. That
is, the output of the headphone can be adjusted by securing the gain of the power amplifier 3
sufficiently with the speaker output and setting the value of the input resistance 1 arbitrarily at
the headphone output. It becomes possible to listen to headphones. As described above,
according to the present invention, when the output switching of the power amplifier is
performed, the output impedance of the power amplifier suitable for headphone listening is
automatically changed by changing the input impedance of the power amplifier simultaneously
with the output switching. In this way, it is possible to realize all suitable headphone listening
even at the fixed position of the volume volume.
[0002]
Brief description of the drawings
[0003]
FIG. 1 is a block diagram of an output switching circuit according to an embodiment of the
present invention, and FIG. 2 is a block diagram of a conventional output switching circuit.
1 и и и Human resistance, 2 и и и Volume volume, 3 и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и
и и и output selector switch, 6 и и и и и и headphone output 7 ииииии Speaker, 8, 9 ░ 10 иииииииии Switching
transistor. Name of Agent Attorney Nakao Toshio Other 1 person Figure 2
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