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DESCRIPTION JP2009147859

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DESCRIPTION JP2009147859
The present invention magnetically shields an inductor (a high frequency choke coil) provided in
a signal pin of an output connector and a microphone circuit portion in a high frequency manner
without separately using a magnetic shielding member. SOLUTION: An electrostatic microphone
unit 10 and at least a microphone circuit unit 24, an output transformer 25 and an output
connector 26 are accommodated in a shield case 21 in a state of being electrically connected via
predetermined wiring. In the condenser microphone including the power module unit 20 and the
microphone unit 10 electrically connected to the microphone circuit unit 24, soft magnetic
powder is included in a synthetic resin bobbin around which a coil wire in the output transformer
is wound. [Selected figure] Figure 1
コンデンサマイクロホン
[0001]
The present invention relates to a condenser microphone, and more particularly, to an output
transformer used for the condenser microphone.
[0002]
The condenser microphone includes an electrostatic microphone unit in which a diaphragm and
a fixed pole are disposed to face each other. However, since the impedance of the microphone
unit is high, an impedance converter is incorporated.
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In most cases, an FET (field effect transistor) is used as the impedance converter, but in rare
cases a vacuum tube may be used.
[0003]
Further, in order to satisfy the performance and function as a microphone, a microphone circuit
unit including an output circuit and a low cut circuit, an output transformer, an output connector
and the like are built in the microphone.
[0004]
In general, a condenser microphone is used by being connected to a phantom power supply via a
microphone cable (balanced shield cable), and while the polarized power is supplied from the
phantom power, the microphone output (voice signal) is output to the phantom power side. Ru.
[0005]
For example, in a recording studio or the like, the microphone cable is extended and used for a
long time.
When an electromagnetic wave is applied to the microphone cable, a high frequency current
flows into the inside of the microphone from the output connector side of the microphone along
the cable.
[0006]
Then, the high frequency current may be detected by the FET or the like, and the noise due to it
may be mixed with the sound output and output.
Mobile phones that are rapidly spreading in recent years have considerably strong
electromagnetic waves during use (for example, within a few cm to a few tens of cm, they reach
tens of thousands times the electric field strength generated in the market by commercial power
sources Since the electric field intensity is emitted, the problem due to the electromagnetic wave
is increased.
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[0007]
As a countermeasure against electromagnetic waves, it is effective to block the penetration of
high frequency current into the inside of the microphone at the part of the output connector.
Therefore, the applicant attached a shield plate to the output connector in Patent Document 1 to
perform electrostatic shielding. It is proposed that.
[0008]
Normally, a 3-pin (grounding pin, hot side pin and cold side pin of signal) type output connector
specified by EIAJ RC-5236 "Latch lock type round connector for audio equipment" is used for
condenser microphone There is.
[0009]
Among these, since the ground pin is connected to the ground (shield enclosure), there is no
possibility that high frequency current may enter from the ground pin, but an inductor (high
frequency choke coil) is connected to the signal pin (signal system) to It is necessary to prevent
the entry of current.
[0010]
However, a high frequency leakage magnetic field generated from an inductor may induce a high
frequency current in a microphone circuit portion such as an output circuit or a low cut circuit
built in the microphone, which may cause noise.
[0011]
In order to prevent this, a magnetic shielding member such as an electromagnetic wave
absorbing member may be provided between the inductor and the microphone circuit portion,
but providing a separate magnetic shielding member requires a design change, and Not desirable
in terms of cost.
[0012]
JP 2005-94575 A
[0013]
Therefore, the subject of the present invention is that, in the condenser microphone, without
using a magnetic shielding member separately, the inductor (high frequency choke coil) provided
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on the signal pin (signal system) of the output connector and the microphone circuit unit are
magnetically magnetized in high frequency It is to shield.
[0014]
In order to solve the above problems, according to the present invention, an electrostatic
microphone unit and at least a microphone circuit portion, an output transformer, and an output
connector are housed in a shield case in a state of being electrically connected through
predetermined wiring. Soft magnetic powder is included in a synthetic resin bobbin around
which a coil wire in the output transformer is wound, in the condenser microphone including the
power module section and the microphone circuit section electrically connected to the
microphone circuit section. It is characterized by
[0015]
In the present invention, the output transformer is disposed between a high frequency choke coil
provided in a signal system of the output connector and the microphone circuit portion.
[0016]
According to the present invention, the bobbin for winding the coil wire of the output
transformer contains soft magnetic powder, and the bobbin itself has an electromagnetic wave
absorbing function of high frequency magnetic shielding.
Therefore, simply by arranging the output transformer between the high frequency choke coil
provided in the signal system of the output connector and the microphone circuit section, an
inductor (high frequency choke coil) provided in the signal pin (signal system) of the output
connector and the microphone circuit It is possible to magnetically shield the unit in a high
frequency manner.
[0017]
Next, an embodiment of the present invention will be described with reference to FIGS. 1 and 2,
but the present invention is not limited thereto.
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1 (a) is a transverse sectional view showing the internal structure of a condenser microphone
according to an embodiment of the present invention, FIG. 1 (b) is a longitudinal sectional view
thereof, and FIG. 2 is an exploded perspective view of an output transformer provided in the
condenser microphone. is there.
[0018]
First, referring to FIGS. 1 (a) and 1 (b), as a basic configuration, this condenser microphone 1 has
a microphone unit 10 of electrostatic type that converts sound waves into electrical sound
signals, and a microphone unit 10 And a power module unit (audio signal output unit) 20
connected to the output side of the circuit.
[0019]
The microphone unit 10 has a unit case 11 made of metal such as brass, and the unit case 11 is
provided with a front acoustic terminal hole 11 a and a rear acoustic terminal hole 11 b for
obtaining single directivity.
[0020]
In the unit case 11, an acoustoelectric conversion unit 12 including a diaphragm and a fixed
electrode is accommodated in a state of being supported by a pedestal 13 made of synthetic
resin.
An electrode rod 13a connected to the fixed electrode is pulled out from the center of the
pedestal 13.
[0021]
The power module unit 20 includes a shield case 21 made of metal such as brass.
First and second two connectors 22 and 26 are provided at both ends of the shield case 21, and
the circuit board 23 is supported between the connectors 22 and 26.
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[0022]
The electrode rod 13 a is connected to the first connector 22.
The second connector 26 is a 3-pin type output connector defined by EIAJ RC-5236 "Latch lock
type round connector for audio equipment" (hereinafter, the second connector is referred to as
an output connector).
The output connector 26 is connected to a phantom power supply (not shown) via a balanced
shield cable.
[0023]
The microphone circuit unit 24 and the output transformer 25 are mounted on the circuit board
23.
Although not shown in detail, the microphone circuit unit 24 includes an FET as an impedance
converter, an output circuit, a low cut circuit, and the like.
[0024]
The output transformer 25 is connected to the hot side pin (No. 2 pin) of the signal of the output
connector 26 and the cold side pin (No. 3 pin), and supplies power from the phantom power
supply to the microphone unit 10.
Further, the audio signal from the microphone circuit unit 24 is given to the 2nd pin and the 3rd
pin of the output connector 26 through the output transformer 25.
[0025]
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A protection circuit 27 is attached to the output connector 26 to prevent high frequency current
from external electromagnetic waves from entering the power module unit 20 from the output
connector 26.
The protection circuit 27 includes a harmonic choke coil (inductor) 27a connected to the second
and third pins of the output connector 26, but may also include a capacitor, a Zener diode, and
the like.
[0026]
When a high frequency leakage magnetic field is generated from the harmonic choke coil 27a, a
high frequency current may be induced in the microphone circuit unit 24 by magnetic coupling,
so that the microphone circuit unit 24 and the harmonic choke coil 27a are magnetically
shielded in a high frequency manner. There is a need.
[0027]
Therefore, in the present invention, the output transformer 25 provided between the microphone
circuit unit 24 and the harmonic choke coil 27a is provided with a magnetic shielding function to
make the microphone circuit unit 24 and the harmonic choke coil 27a have a high frequency. To
magnetically shield the
[0028]
As shown in FIG. 2, the output transformer 25 is attached to the magnetic core main body 251
formed substantially in a U shape, the yoke 252 extended between both ends of the magnetic
core main body 251, and each arm of the magnetic core main body 251. The coil wire 254 is
wound around each bobbin 253, but in the present invention, each bobbin 253 contains soft
magnetic powder.
[0029]
The bobbin 253 can be obtained by dispersing soft magnetic powder in a thermoplastic resin
such as polypropylene to form an electromagnetic wave absorbing composite material and
molding it.
In the example of FIG. 2, the bobbin 253 molded in advance is fitted into the magnetic core main
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body 251, but may be integrally formed with the magnetic core main body 251 in an insert
molding die.
[0030]
As described above, according to the present invention, the soft magnetic powder is included in
the bobbin 253 of the output transformer 25 so that the microphone circuit unit 24 and the
harmonics can be generated without the need for a magnetic shielding member such as a
magnetic shielding plate separately. Magnetic shielding can be performed with the choke coil
27a in a high frequency manner.
[0031]
In the above embodiment, although the microphone unit 10 and the power module unit 20 are
integrally connected, the microphone unit 10 and the power module unit 20 are separated as in a
gooseneck microphone or a tie pin microphone. It may be configured and connected via a
microphone cord.
[0032]
(A) A transverse sectional view showing an internal structure of a condenser microphone
according to an embodiment of the present invention, and (b) a longitudinal sectional view
thereof.
The disassembled perspective view of the output transformer with which the said capacitor |
condenser microphone is equipped.
Explanation of sign
[0033]
DESCRIPTION OF SYMBOLS 10 Microphone unit 20 Power module part 21 Shield case 23 Circuit
board 24 Microphone circuit part 25 Output transformer 251 Magnetic core body 252 Yoke 253
Bobbin 26 Output connector 27a High frequency choke coil (inductor)
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