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JP2005064714

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Notice
This translation is machine-generated. It cannot be guaranteed that it is intelligible, accurate,
complete, reliable or fit for specific purposes. Critical decisions, such as commercially relevant or
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DESCRIPTION JP2005064714
PROBLEM TO BE SOLVED: To provide an apparatus having a horn jack as an audio monitor
output terminal, wherein the S / N ratio of an audio signal inside the apparatus is lowered with a
simple circuit configuration, and a pop noise occurs when an external plug is removed. It is an
object of the present invention to provide an audio circuit which can avoid the occurrence of
contact noise such as a gossacker. In an audio circuit in an apparatus in which a stereo horn jack
is used as an audio monitor output terminal, each contact of the stereo horn jack is always
grounded via a resistor. [Selected figure] Figure 3
Voice circuit
[0001]
The present invention relates to an audio circuit in an apparatus having a stereo horn jack as a
monitor output terminal.
[0002]
A stereo horn jack provided in a conventional TV, radio or audio device is for connecting an
earphone or a headphone.
An audio signal for an internal speaker is supplied to such a stereo horn jack, and when no
external plug is inserted into the stereo horn jack, an audio is sent to the internal speaker via the
stereo horn jack. A signal is given. When a plug is inserted into the stereo horn jack from the
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outside, the contact between the outer contact piece and the inner contact piece of the horn jack
is released, so that the audio signal is not supplied to the internal speaker.
[0003]
FIG. 1 shows the general configuration of a conventional audio circuit in an apparatus having a
horn jack as a monitor output terminal.
[0004]
Stereo input audio is supplied to the horn jack 2 via the input signal selection and volume control
circuit 1.
When the plug 3 connected to the external device is not inserted into the horn jack 2, the stereo
audio signal supplied to the horn jack 2 is sent to the stereo / monaural conversion circuit 4 and
converted to a monaural audio signal. . A monaural audio signal output from the stereo /
monaural conversion circuit 4 is supplied to the internal speaker 6 via an audio output IC (audio
output circuit) 5.
[0005]
When the plug 3 is inserted into the horn jack 2, the contact state between the outer contact
pieces 21L, 21R of the horn jack 2 and the inner contact pieces 22L, 22R is released, so the
stereo audio supplied to the horn jack 2 The signal is not sent to the stereo / monaural
conversion circuit 4 but supplied to an external device through the plug 3.
[0006]
FIG. 2 shows a specific configuration of a conventional audio circuit.
[0007]
A plurality of input audio signals are input to an input signal selection and volume control circuit
1.
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The input signal selection and volume control circuit 1 selects one input audio signal from a
plurality of input audio signals and controls the gain thereof.
[0008]
The left channel signal of the stereo audio signal output from the input signal selection and
volume control circuit 1 is a horn jack 2 through an emitter follower circuit consisting of a
resistor R1, a transistor Tr1 and a resistor R3, a capacitor C1 for cutting a DC component and an
output resistor R5. Is sent to the outer contact piece 21L.
[0009]
The right channel signal of the stereo audio signal output from the input signal selection and
volume control circuit 1 is a horn jack 2 through an emitter follower circuit consisting of a
resistor R2, a transistor Tr2 and a resistor R4, a capacitor C2 for cutting a DC component and an
output resistor R6. Is sent to the outer contact piece 21R.
[0010]
The capacitors C1 and C2 and the resistors R5 and R6 are provided to protect the circuit in the
device when the output signal output to the device is shorted to GND or an external power
supply.
Further, a resistor R7 provided between a midpoint between the resistor R5 and the horn jack 2
and GND and a resistor R8 provided between a midpoint between the resistor R6 and the horn
jack 2 and GND are capacitors C1. , C2, and is provided to stabilize the output potential.
[0011]
The left channel signal sent to the outer contact piece 21L of the horn jack 2 and the right
channel signal sent to the outer contact piece 21R of the horn jack 2 are sent to a stereo /
monaural conversion circuit to be converted into a monaural audio signal. Ru.
[0012]
That is, the left channel signal sent to the outside contact piece 21L of the horn jack 2 is sent via
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the inside contact piece 22L of the horn jack 2 to the emitter follower circuit consisting of the
resistor R9, the transistor Tr3 and the resistor R11.
Similarly, the right channel signal sent to the outer contact piece 21R of the horn jack 2 is sent
via the inner contact piece 22R of the horn jack 2 to an emitter follower circuit consisting of a
resistor R10, a transistor Tr4 and a resistor R12.
[0013]
The output of one emitter follower circuit and the output of the other emitter follower circuit are
added via resistors R13 and R14 respectively to be monaural, and then an emitter follower
circuit consisting of a resistor R15, a transistor Tr5 and a resistor R16, a capacitor C3 And is
supplied to the internal speaker 6 through the audio output IC 5.
The resistor 15 is provided to reduce and adjust the amplitude of the audio signal in order to
meet the rating of the device since the audio output IC 5 generally has a large constant gain of
+20 to +40 dB.
[0014]
In a small liquid crystal projector used for presentation and the like, a monaural small one is used
as an internal speaker in order to reduce the weight and size of the device, and the volume is not
large.
On the other hand, the audio signal input to the liquid crystal projector is a stereo audio signal,
and the internal speaker is supplied with an audio signal after the stereo audio signal has been
converted to monaural.
[0015]
However, as an external audio output to an external audio apparatus such as an audio amplifier,
not a monaural speaker output but an audio monitor signal whose volume is controlled in stereo
is used.
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[0016]
Further, in a small liquid crystal projector, since the device itself is small, in order to reduce the
area occupied by the input and output terminals, a stereo horn jack is often used as an audio
output terminal, not an RCA jack.
Then, unlike a low impedance signal such as a speaker output signal, an audio monitor signal
whose volume is controlled in stereo is supplied to the horn jack, so that the S / N ratio of the
audio signal inside the device is lowered or At the time of plugging and unplugging, contact
noises such as a popping noise and a rattling noise are easily generated.
[0017]
The present invention is an apparatus having a horn jack as an audio monitor output terminal,
and has a simple circuit configuration, such as a reduction in S / N ratio of an audio signal inside
the apparatus, a popping noise, a rattling noise, etc. when inserting or removing a plug from the
outside It is an object of the present invention to provide an audio circuit capable of avoiding the
generation of contact noise of
[0018]
The invention according to claim 1 is an audio circuit in an apparatus in which a stereo horn jack
is used as an audio monitor output terminal, the first circuit for supplying an input audio signal
to the stereo horn jack, and a stereo A second circuit for supplying an audio signal supplied to
the stereo horn jack to an audio output circuit for generating a speaker audio signal when no
plug is inserted into the horn jack; When a plug is inserted into the horn jack, supply of the audio
signal to the second circuit is cut off, and in the audio circuit in which the audio signal supplied
to the stereo / horn jack is supplied to the external device through the plug, the stereo An audio
circuit characterized in that each contact of the horn jack is always grounded via a resistor.
[0019]
The invention according to claim 2 is the audio circuit according to claim 1, wherein as the
contact piece of the stereo horn jack, an outer contact piece for the left channel, an outer contact
piece for the right channel, an inner contact piece for the left channel and It is characterized in
that there is an inner contact piece for the right channel, and each of these contact pieces is
grounded via a separate resistor.
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[0020]
According to the present invention, in an apparatus having a horn jack as an audio monitor
output terminal, the S / N ratio of the audio signal inside the apparatus is reduced with a simple
circuit configuration, and a popping noise or noise is generated when plugging in and out from
the outside It can be avoided that contact noise such as sound is generated.
[0021]
Hereinafter, embodiments of the present invention will be described with reference to the
drawings.
[0022]
FIG. 3 shows the configuration of the audio circuit in the embodiment of the present invention.
In FIG. 3, the same components as those in FIG. 2 are denoted by the same reference numerals,
and the description thereof will be omitted.
[0023]
The circuit for supplying an audio signal from the input signal selection and volume control
circuit 1 to the horn jack 2 is the same as that of FIG.
In this embodiment, the inner contact piece 22L of the horn jack 2 is grounded via the resistor
R31, and the inner contact piece 22R of the horn jack 2 is grounded via the resistor R32.
More specifically, the connection point between the inner contact piece 22L and the resistor R9
is grounded via the resistor R31.
Further, a connection point between the inner contact piece 22R and the resistor R10 is
grounded via the resistor R32.
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The resistors R31 and R32 are resistors which were not provided in the prior art of FIG.
[0024]
In general, assuming that the output resistances R5 and R6 are 1 K.OMEGA., Resistances of 100
K.OMEGA. Or more which are much larger than the output resistances R5 and R6 are used as the
discharge resistances R7 and R8. Also in FIG. 2, this point is the same.
[0025]
In the present embodiment, as the added resistors R31 and R32, one having a resistance value of
about 10 KΩ smaller than the discharge resistors R7 and R8 is used. The signals sent to the
transistors Tr3 and Tr4 via the horn jack 2 by these resistors R31 and R32 are smaller by about
10% compared to the conventional one, but the resistance value of the resistor R15 for amplitude
adjustment at monauralization It is possible to compensate by making
[0026]
In general, the cause of the pop noise of speech is that the DC potential of the speech signal is
disturbed. Although the disturbance of the DC potential occurs also at the rise / fall of the power
supply of the circuit, it often occurs due to an impedance change such as a load fluctuation at the
time of plugging in and out of the horn jack 2.
[0027]
In this embodiment, the outer contact pieces 21L and 21R of the horn jack 2 are grounded via
the resistors R7 and R8, respectively, and the inner contact pieces 22L and 22R are also
grounded via the resistors R31 and R32, respectively. ing. That is, in this embodiment, since the
potential of GND is always applied to the contact pieces 21L, 21R, 22L and 22R of the horn jack
2, the DC potential is stabilized, and the contact noise of the contacts due to plugging and
unplugging is suppressed. The circuit operation is stabilized and the signal S / N ratio is also
stabilized.
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[0028]
Further, generally, since the voice input resistance is 10 KΩ or more, substantially equivalent
resistance exists in the horn jack 2 at the time of plug insertion which is connected to an external
device and at the time of plug non-insertion. This means that the load change of the contact piece
on the monitor output side at the time of plug insertion and removal is small. Therefore, the pop
noise can be suppressed also on the external device side receiving the monitor output.
[0029]
According to the above-described embodiment, mechanical contact noise caused by passing a
signal through the horn jack 2 and load change due to the presence or absence of external plug
connection can be suppressed. It is possible to suppress the pop noise due to the transient DC
potential fluctuation due to the decrease of the / N ratio and the plug removal and insertion.
[0030]
It is a block diagram which shows the whole structure of the conventional audio | voice circuit in
the apparatus which has a horn jack as a monitor output terminal.
It is an electric circuit diagram showing the concrete composition of the conventional voice
circuit. It is an electric circuit diagram showing a concrete composition of an audio circuit which
is an embodiment of the invention.
Explanation of sign
[0031]
DESCRIPTION OF SYMBOLS 1 input signal selection and volume control circuit 2 horn jack 3
plug 5 audio output IC 6 internal speaker 21L, 21R outer contact piece 22L, 22R inner contact
piece Tr1, Tr2, Tr3, Tr4, Tr5 transistor R7, R8, R31, R32 resistance
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