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DESCRIPTION JP2012175129

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DESCRIPTION JP2012175129
A condenser microphone operated by a phantom power source, which is replaceable with respect
to a microphone main body, is configured such that the contact between the unit and the
microphone main body is removable with low impedance at one point. SOLUTION: A microphone
unit MU, an FET Q1 and an emitter follower transistor Q2 are included in the unit unit 10, and an
audio signal is taken out from a drain D of the FET Q1, and a second pin of a microphone body
20 having a three pole output connector 22. The constant current diodes D2 and D3 are
connected to 22h and the third pin 22c as a feed circuit for the drain D of the FET Q1, and one
constant current diode D2 is connected to a first electrolytic capacitor C3 for AC coupling and
the other constant current diode D3. A series circuit of a second electrolytic capacitor C4 for AC
coupling and a resistance element R3 is connected between the anode of the second stage and
the ground L3, and the resistance element R3 has an impedance substantially equal to the output
impedance of the transistor Q2. [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 a condenser
microphone operated by a phantom power unit whose unit part is replaceable with respect to a
microphone body.
[0002]
In the condenser microphone, a unit part (head part) having a condenser microphone unit as an
electrostatic type acoustoelectric converter is exchangeable with respect to the microphone main
body (grip part in the case of a hand-held type) to make directivity. There is one that has been
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made to switch.
[0003]
However, in such a model, the signal output portion of the condenser microphone unit having a
very high impedance serves as an electrical connection portion between the unit portion and the
microphone body, so that noise due to an external electromagnetic wave is likely to occur.
An extraneous electromagnetic wave that is particularly problematic is a strong electromagnetic
wave emitted from a mobile phone.
[0004]
Therefore, as a patent document 1, the applicant of the present invention has proposed a method
in which an inductor acting as a choke coil is connected in series between the grounding on the
unit portion side and the grounding on the microphone body side.
[0005]
However, since the signal level of the condenser microphone unit is low and the impedance is
extremely high, in fact, it has not been possible to suppress the noise to a low level.
[0006]
In a condenser microphone, an FET (field effect transistor) is usually used as an impedance
converter. However, when the FET is mounted on the unit portion side, a method of extracting an
audio signal from the drain side of the FET is used for signal extraction. And a method of
extracting an audio signal from the source side of the FET.
[0007]
In the method of extracting the audio signal from the drain side of the FET, the drain wiring is
shared by the feed line and the signal output line, so the contact point between the unit portion
and the microphone main body can be one place, simplifying the structure. However, there is a
problem in that the audio signal is distorted from a low level.
[0008]
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On the other hand, in the case of the method of extracting the audio signal from the source side
of the FET, distortion of the audio signal does not occur to a large level.
However, since it is necessary to separate the power supply and the signal, there are two contact
points and the structure becomes complicated.
[0009]
By the way, when designing a condenser microphone operating with a phantom power supply, it
is necessary to consider a power supply voltage from the phantom power supply.
[0010]
According to EIAJ RC-8162A (power supply system for microphones), three allowable rated
voltages of 12 ± 1 V, 24 ± 4 V, and 48 ± 4 V are defined in phantom power supplies for
condenser microphones.
[0011]
As described above, the present applicant has proposed Patent Documents 2 and 3 in order to
operate such that the maximum output level is increased in each voltage range even if phantom
power supplies with different rated voltages are used.
[0012]
JP-A-2006-313952 JP-A-2006-352622 JP-A-2007-6178
[0013]
Therefore, an object of the present invention is to provide a condenser microphone operating
with a phantom power supply, in which the unit unit is replaceable with respect to the
microphone body, to make the unit unit and the microphone body detachable with low
impedance at one contact point. It is in.
[0014]
In order to solve the above problems, the present invention relates to a capacitor microphone
unit, an FET for converting a capacitance change of the capacitor microphone unit into an audio
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signal, and an emitter follower current for amplifying an audio signal appearing at a source of
the FET. A microphone body including a unit portion including an amplification transistor, a 3pole output connector to which a phantom power is connected, and a constant current diode for
supplying a predetermined drive current to the drain of the FET by feeding from the phantom
power; And the unit portion is electrically and mechanically detachably connected to the
microphone body, and on the unit portion side, the current amplification transistor is between
the drain of the FET and the ground. Connected to the above FET A drain wire connected to the
rain is shared by a feeder and a signal output wire, and the drain wire has a first connection
terminal to the microphone body, and the microphone body side has a hot side of the three-pole
output connector. A first constant current diode connected to the second pin and a second
constant current diode connected to the third pin on the cold side are provided, and each cathode
side of the first and second constant current diodes is both the above A first capacitor element
for AC coupling is connected between the cathode and the anode of the first constant current
diode, which is connected to the second connection terminal that is the other of the first
connection terminal, and the anode of the second constant current diode A series circuit of a
second capacitor element for alternating current coupling and a resistance element is connected
between the terminal and the ground, and the unit portion is connected to the microphone body
With it, it is characterized in that the first connecting terminal and the second connecting
terminals to each other and their ground are connected to each other.
[0015]
According to a preferred aspect of the present invention, the impedance of the resistor element is
approximately equal to the output impedance of the current amplification transistor.
[0016]
In addition, even when phantom power supplies having different rated voltages are used, the
second connection terminal may be connected between the drain wiring and the ground in order
to ensure a maximum output level corresponding to each of the power supplies. The phantom
power supply to be supplied is divided, and a voltage dividing resistor serving as a bias voltage
for the base of the current amplification transistor is connected.
[0017]
In addition, equal voltages are applied to the second and third pins from the phantom power
supply.
[0018]
According to the present invention, since the FET as the impedance converter is mounted on the
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unit side and the audio signal is taken out from the drain side of the FET, the number of signal
system contacts may be one, and for current amplification The output impedance at the output
section of the transistor can be as low as, for example, 200 Ω regardless of the feed voltage from
the phantom power supply, so it is possible to attach and detach the unit section and the
microphone body with low impedance at one contact point. .
[0019]
FIG. 1 is a circuit diagram showing a condenser microphone according to an embodiment of the
present invention.
[0020]
Next, an embodiment of the present invention will be described with reference to FIG. 1, but the
present invention is not limited to this.
[0021]
Referring to FIG. 1, the condenser microphone of the present invention includes a unit (head
unit) 10 and a microphone body 20 (grip unit in the case of a hand-held type). It is removable
(replaceable).
[0022]
Although not shown, the unit portion 10 and the microphone main body 20 both have circular
identical casings made of a metal material such as aluminum or a brass alloy, and these casings
are, for example, screws of male screw and female screw. They are linked together.
The housing is used as a ground.
[0023]
The unit unit 10 includes a condenser microphone unit (which may be referred to as a
microphone unit hereinafter) MU, an FET (field effect transistor) Q1 as an impedance converter,
and a transistor Q2 for amplifying a current of an emitter follower. A circuit and a built-in.
[0024]
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The microphone unit MU is preferably an electret type, but may not be an electret type.
The fixed pole side of the microphone unit MU is connected to the gate G of the FET Q1, and the
diaphragm side is connected to the ground line (housing) L2.
[0025]
In this embodiment, the FET Q1 has a built-in bias circuit, and includes a bias circuit in which two
diodes and one resistance element are combined between the gate G and the source S.
[0026]
The condenser microphone adopts a method of extracting an audio signal from the drain D of the
FET Q1. The drain wiring L1 connected to the drain D is used as a feed line and a signal output
line, and one end of the drain wiring L1 is used. The first connection terminal 11 to the
microphone body 20 is provided.
[0027]
In this embodiment, the transistor Q2 is a PNP type, the emitter is connected to the drain wiring
L1 through the electrolytic capacitor C2 for AC coupling, and the collector is connected to the
ground line L2.
The source S of the FET Q1 is connected to the base of the transistor Q2 via an electrolytic
capacitor C1 for AC coupling.
[0028]
The source S of the FET Q1 is connected to the emitter of the transistor Q2 via the output
resistive element R2.
Further, between the drain D and the source S of the FET Q1, a diode D1 is connected which
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holds the voltage between the drain and the source constant.
[0029]
Further, between the drain wiring L1 and the ground line L2, voltage dividing resistive elements
R0 and R1 for dividing the voltage of the phantom power supplied from the connection terminal
11 to apply a bias voltage to the base of the transistor Q2 are connected. There is.
[0030]
Thereby, even when phantom power supplies (12 V, 24 V, 48 V) having different rated voltages
are used, the bias voltage of transistor Q 2 changes accordingly, and the maximum output level
corresponding to each power source is secured. Therefore, even if any voltage phantom power
source is used, the output impedance at the output of the transistor Q2 can be as low as about
200 Ω.
[0031]
On the other hand, the microphone body 20 is provided with a three-pole output connector 22 to
which the phantom power supply 30 is connected, and two constant current diodes D2 and D3 as
a feeding circuit for the unit unit 10.
[0032]
The three-pole output connector 22 is a connector defined in EIAJ RC-5236 “Latch-lock type
circular connector for audio equipment” or a connector equivalent thereto, and the first pin 22
e of the ground and the second side of the hot side of the signal It has a pin 22h and a third pin
22c on the cold side of the signal.
[0033]
The anode side of the constant current diode D2 is connected to the second pin 22h, and the
anode side of the constant current diode D3 is connected to the third pin 22c.
The cathodes of the constant current diodes D2 and D3 are both connected to a second
connection terminal 21 which is a counterpart of the first connection terminal 11 of the unit
section 10.
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[0034]
In addition, an electrolytic capacitor C3 for AC coupling is connected between the cathode and
the anode of constant current diode D2, and an electrolytic capacitor C4 for AC coupling and a
resistor are connected between the anode of constant current diode D3 and ground line L3. A
series circuit of elements R3 is connected.
The ground line L3 may be a housing of the microphone body 20, and the ground line L3 is
connected to the first pin 22e.
[0035]
The phantom power supply 30 has a DC power supply E set to any of 12 V, 24 V, and 48 V, and
the negative side is connected to the first pin 22 e.
The positive electrode side of the DC power supply E is connected to the second pin 22h and the
third pin 22c via the resistance elements R4 and R5 having the same resistance value.
As an example, when the DC power supply E is 48 V, 6.8 kΩ is used for each of the resistance
elements R4 and R5.
[0036]
According to the above-described configuration, as the unit portion 10 is connected to the
microphone body 20, the first connection terminal 11 and the second connection terminal 21
and their ground lines L2 and L3 are connected.
Since the ground lines L2 and L3 connect the casings to each other, the contact of the signal
system is only one place of the connection terminals 11 and 12.
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For the first connection terminal 11 and the second connection terminal 21, for example, a
predetermined connector member formed of a combination of a terminal pin and a plate spring
piece may be used.
[0037]
When the microphone with the phantom power supply 30 connected is used, current is supplied
from the constant current diodes D2 and D3 to the drain D of the FET Q1 through the connection
terminals 11 and 21 and the drain wiring L1.
The change of the capacitance of the microphone unit MU due to the incoming sound wave is
output as an audio signal from the source S of the FET Q1.
[0038]
This audio signal is amplified in a predetermined manner by the transistor Q2 of the emitter
follower, and is output from the emitter side to the side of the microphone body 20 through the
drain wiring L1 and the connection terminals 11 and 21.
[0039]
On the side of the microphone body 20, the audio signal reaches the second pin 22h via the
electrolytic capacitor C3 for AC coupling.
As a result, the audio signal is output from the output terminals T1 and T2 having electrolytic
capacitors C5 and C6 for AC coupling connected to the second pin 22h and the third pin 22c
toward an audio output circuit such as a mixer. .
[0040]
In this embodiment, as described above, the output impedance at the output portion of the
transistor Q2 is as low as about 200 Ω, while the constant current diodes D2 and D3 have high
impedance in AC, so the signal system contacts 1 The unit portion 10 and the microphone body
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20 can be attached and detached with a low impedance at a place.
Also, no output transformer is required.
[0041]
The resistance value of the resistor R3 connected to the third pin 22c is matched with the output
impedance at the output of the transistor Q2 in order to achieve impedance matching between
the second pin 22h and the third pin 22c. In the embodiment, it is preferable to set about 200 Ω.
[0042]
DESCRIPTION OF SYMBOLS 10 unit part 11 1st connection terminal 20 microphone main body
21 2nd connection terminal 22 3 pole output connector 22e Grounded 1st pin 22h Hot side 2nd
pin 22c Cold side 3rd pin 30 Phantom power supply MU condenser microphone unit Q1 FET
(Field effect transistor) Q2 Current amplification transistor C1 to C6 Electrolytic capacitor for AC
coupling R0, R1 Voltage dividing resistor R3 Resistance element for impedance matching R4, R5
Feeding resistance element for phantom power L1 Drain wiring L2, L3 Ground line (case Body)
D2, D3 constant current diode
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