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JPH08205277

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DESCRIPTION JPH08205277
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
power supply circuit of a power supply voltage supplied from the outside to an amplifier of a
capacitive type or electret type capacitive acoustoelectric converter (hereinafter referred to as a
microphone).
[0002]
2. Description of the Related Art As a capacitive microphone, for example, a condenser
microphone requires an amplifier in the microphone and a phantom power supply (power supply
circuit) for supplying a power supply current to the amplifier from the outside through a signal
line The Phantom Power Supply) system and the AB power supply system are known. The
phantom feeding method and the A-B feeding method are defined in RC-8162 of Japan Electronic
Machinery Industry Standard EIAJ.
[0003]
The phantom feeding method is to feed equally divided feeding currents to both signal lines of
balanced output, and to use a shielded cable of a cable as a return conductor. Therefore, the
amplification of the subsequent microphone is a balanced input and an input float type.
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1
[0004]
FIGS. 4A and 4B show the circuit configurations of the power supply side (FIG. 4A) and the
microphone side (FIG. 4B) of the transformer center tap type of the conventional phantom power
supply system.
[0005]
In FIG. 4A, P is a connector defined by IEC 268-12, and a positive electrode of the power supply
U (a pressure in a direction in which the diaphragm of the microphone is pushed down (positive
sound pressure) is applied) , And the negative shield is connected to the connector terminal 3
and the grounded shield of the microphone cord W is connected to the connector terminal 1).
ing.
[0006]
The positive terminal of the direct current power supply U is connected to the primary winding
center point tap of the transformer T via a resistor R, and the start end of the primary winding is
connected to the connector terminal 2 and the primary winding The terminal end is connected to
the connector terminal 3, and the negative side of the power supply U is connected to the shield
of the microphone cord W, and the output of the microphone is taken out from the secondary
winding side of the transformer T.
[0007]
FIG. 4B also shows a circuit configuration on the microphone side of the transformer coupling
type, where P is the same connector as FIG. 4A, and the positive voltage from the connector
terminal 2 is negative at the beginning of the primary side of the transformer T1. The ground
connector terminal 1 is connected to the secondary end of the transformer T1 and to the ground
terminal of the amplifier A, and the center tap of the transformer T1 is connected to the
amplifier. Connected to the hot side of A.
The output of the capacitive microphone M is connected to the start of the transformer T1.
[0008]
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Also, as shown in FIGS. 5A and 5B, the AB power feeding method is to flow the supplied current
only to the signal line a or the signal line b, FIG. 5A shows the circuit on the power feeding side
and FIG. 5B shows the circuit on the microphone side. Is shown.
In these figures, the positive side of the power supply U is connected to the supply line a
connected to the connector terminal 2 via the resistor R8 (180 Ω), and the negative side is
connected to the connector terminal 3 via the resistor R7 (180 Ω) It is connected to the supply
line b.
The connector terminal 1 is connected to the grounded shield wire of the microphone cord W,
but in general, one of the a supply line and the b supply line is used in a grounded state. A
capacitor C is connected between the primary windings of the transformer T.
[0009]
The microphone M side is directly fed to the amplifier from each terminal 2 or 3 of the connector
P. In this method, when connecting to a dynamic type microphone or the like, there is an
inconvenience that an operation of turning off the power supply is required in advance.
[0010]
SUMMARY OF THE INVENTION In the case where, for example, sound is picked up by the stereo
microphones MR and ML in the above-described phantom feeding method, only one power
source can be used as shown in FIG. The divided resistors R1 and R2 supply the supply current I
from the supply power source U, and the left and right stereo signals LCH and RCH are taken out
through the transformer T. As described above, in the case of using the resistance division
transformer coupling type phantom feeding method or the like, it is necessary to prepare two
sets of phantom feeding circuits for the left and right microphones ML and MR. Of course, the
same applies to the transformer coupled phantom feeding method shown in FIG. 4A.
[0011]
In the above case, a virtual ground point can be provided by an operational amplifier etc. on the
amplifier A1 side of the stereo microphone side, and both power supplies can be realized in a
pseudo manner, but the virtual ground point is not necessarily equivalent ground but virtual
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ground and ground There was a problem that you had to pay enough attention to
[0012]
Also, although it is possible to add a DC-DC converter or regulator to the amplifier A1 side to
convert the power supply to dual power supplies, a converter is required, and since this
converter has a noise source, addition of a noise removal filter is also necessary. And there was a
problem that the scale of the circuit became large.
In addition, there is a problem of converter efficiency, and there is a disadvantage that current
consumption increases.
[0013]
The present invention has been made to solve the above-mentioned problems, and the objective
of the present invention is to obtain a microphone power supply circuit with improved dynamic
range by improving the characteristics of the microphone amplifier by dual power supply. It is
[0014]
SUMMARY OF THE INVENTION The microphone power supply circuit of the present invention is,
as an example of which is shown in FIGS. 1 to 3, via a phantom feeding circuit to capacitive
stereo microphones MR and ML, Both positive and negative voltages are supplied via one
connector P1 having at least one ground terminal whose one end is dropped to the ground
potential, a pair of terminals to which a positive electrode voltage is supplied, and a pair of
terminals to which a negative electrode voltage is supplied. The
[0015]
In the microphone power supply circuit according to the present invention, positive voltage is
supplied to one channel and negative voltage is supplied to the other channel when power supply
voltages are supplied from two sets of phantom circuits to a capacitive stereo microphone. Since
the voltage is supplied to make the microphone amplifier dual power supply, the characteristics
of the amplifier can be improved, and a microphone amplifier with a large dynamic range can be
obtained.
[0016]
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DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The microphone power supply
circuit of the present invention will be described below with reference to FIGS.
1 to 3 show the configurations of various systems of this example, and FIG. 1A shows a power
supply side circuit using a transformer center tap system as a fontum feed circuit, and FIG. 1B
shows a circuit on the stereo microphone side. .
[0017]
As shown in FIGS. 1A and 1B, the connector (eg, jack) P1 and the connector (eg, plug) P1 'have at
least five-pole terminals 1 to 5 and the terminals of the connector P1 are connected to the shield
wire of the microphone cord W. Is dropped to the ground potential.
Terminals 2 and 3 of connector P1 are connected, for example, between the primary windings of
transformer TL for the left channel, and terminals 4 and 5 of the same connector P1 are between
the primary windings of transformer TR for the right channel The left and right channel signals
LCH and RCH of the stereo microphones are output from the secondary windings of the
transformers TL and TR.
[0018]
For the left and right channel power supplies UL and UR, for example, the positive electrode of
the left channel power supply UL is connected to the center tap of the primary winding of the left
channel transformer TL via the resistor RL, and the negative electrode is dropped to the ground
potential. ing.
The negative terminal of the right channel power supply UR is connected to the center tap of the
primary winding of the right channel transformer TR via a resistor RR, and the positive terminal
is dropped to the ground potential.
[0019]
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That is, the potential on the current IR side flowing into the connector terminals 4 and 5 on the
right channel RCH side is negative, and the potential on the current IL side flowing into the
connector terminals 2 and 3 on the left channel LCH side is positive .
[0020]
The connectors P1 'on the stereo microphones MR and ML shown in FIG. 1B correspond to the
connector P1, the terminal 1 of the connector P1' is connected to the ground potential of the
amplifier A1, and the terminals 2 and 3 are left-channel transformer TL ' The terminals 4 and 5
are connected to the primary winding of the right channel transformer TR ', the respective
secondary windings are connected to the left and right channel output terminals of the amplifier
A1, and the left and right channel transformers TL The negative voltage (-V) and the positive
voltage (+ V) extracted from the center taps of 'and TR' are supplied to the positive and negative
power terminals of the dual power supply amplifier.
[0021]
Picked-up signals from the left and right stereo microphones ML and MR are converted into
electric signals and amplified, and output through the left and right channel transformers TL 'and
TR'.fwdarw.connectors P1' and P1.fwdarw.
[0022]
The configuration shown in FIGS. 2A and 2B is a connection diagram on the feed side and the
microphone side, respectively, showing another configuration of the phantom feed circuit similar
to FIGS. 1A and 1B. Instead of the taps, this is done by the resistors RR1 and RR2 and RL1 and
RL2, and the microphone side is also divided by the resistors RR1 'and RR2' and RL1 'and RL2'. It
is the same.
[0023]
3A and 3B are also connection diagrams on the feeding side and the microphone side, and
phantom feeding is performed by the dividing resistors RR1 to RR4 and RL1 to RL4 similar to
FIGS. 2A and 2B and capacitors CR1, CR2, CL1 instead of transformer coupling. , CL2 coupled.
The microphone side is also coupled by capacitors CR3 to CR4 and CL3 to CL4.
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[0024]
In the above configuration, the feed side and the microphone side are both center tap
transformer coupling method, resistance division transformer coupling method, and resistance
division capacitor coupling method. However, for example, the feed side is the transformer
coupling method and the microphone side is resistance division method It is apparent that the
configurations of FIGS. 1A and B, FIGS. 2A and B, and FIGS. 3A and B may be combined as
appropriate.
[0025]
According to the microphone power supply circuit of the present invention, the increase in
current consumption at the time of dual power supply at the stereo microphone side which
occurs because only one power supply in phantom feeding can be supplied is suppressed, and
the characteristic of the stereo microphone amplifier is impedance It will be lowered and
significant improvement will be possible.
[0026]
Also, by using a stereo microphone amplifier in a DC amplifier configuration, it is possible to
make a ground reference, and it is possible to omit a coupling capacitor and to significantly
improve the dynamic range as compared with a single power supply amplifier.
[0027]
According to the present invention, dual power supply improves the characteristics of the
microphone amplifier, improves the dynamic range, and the use of a 5-core cable enables stereo
sound collection with one wire.
[0028]
Brief description of the drawings
[0029]
1 is a block diagram showing an embodiment (transformer coupling) of the microphone power
supply circuit of the present invention.
[0030]
2 is a block diagram of another embodiment (resistance division transformer coupling) of the
microphone power supply circuit of the present invention.
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[0031]
3 is a configuration diagram of still another embodiment (resistance division capacitor coupling)
of the microphone power supply circuit of the present invention.
[0032]
4 is an explanatory circuit diagram of a conventional phantom feeding method.
[0033]
5 is an explanatory circuit diagram of a conventional AB power supply system.
[0034]
6 is a feeding circuit diagram of a conventional stereo microphone.
[0035]
Explanation of sign
[0036]
P, P1, P1 'connector W microphone cord T, T1, TR, TL transformer A, A1 amplifier M, ML, MR
microphone U, UL, UR power supply
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