JP6635755B2 - Condenser microphone circuit - Google Patents

Description

  The present invention relates to a condenser microphone circuit.

  A condenser microphone (hereinafter, referred to as “microphone”) needs to supply power for operating an impedance converter and the like included in the microphone. The phantom power supply method specified in JEITA RC-8162A (microphone power supply method) is used for power supply of the microphone.

  In the phantom power supply system, a DC power supply (phantom power supply) provided on an external device side such as a mixer or an amplifier unit is used to output a microphone audio signal through a hot signal line and a cold signal line, which are output signal lines. Supply DC current to microphone. The phantom power supply is connected to each of the hot side signal line and the cold side signal line via a power supply resistor. Therefore, the phantom power supply can supply a direct current equally distributed to the hot side signal line and the cold side signal line.

  The connection and disconnection between the microphone and the external device are usually performed when a phantom power supply for supplying power to the microphone is in an off state. However, the connection and disconnection of the microphone from the external device may be performed when the phantom power is on due to contact between the microphone and the body of the microphone user or insufficient confirmation of the on / off state of the phantom power. There is. In this case, if the timing of connection or disconnection between the terminals connecting the microphone and the phantom power supply is different between the hot-side terminal and the cold-side terminal, a pulse-like current (hereinafter referred to as a “pulse ) Is output.

  This pulse-shaped current flows to the output signal line of the audio signal of the microphone, and is input to an output device such as a speaker via an external device together with the audio signal. In this case, a loud sound, a so-called pop sound, is generated from the output device. The output device breaks down depending on the loudness of the pop sound.

  As a technique for reducing the generation of pop noise when the microphone and the phantom power supply are connected or disconnected, a phantom including a detection circuit for detecting a pulsed current and a limiting circuit for limiting the output of the microphone is provided. A power supply circuit has been proposed (for example, Patent Document 1).

  The detection circuit has a transformer, a capacitor, a resistor, and a first transistor circuit. The transformer is connected between the hot side signal line and the cold side signal line of the microphone, and when either the hot side terminal of the microphone and the phantom power supply or the cold side terminal is disconnected or connected first, a pulse is generated. A current. When a pulsed current flows through the transformer, the detection circuit turns on the first transistor circuit in which the current flows.

  The limiting circuit includes a second transistor circuit, a light emitting diode, a photo MOS relay, and a resistor. When the first transistor circuit of the detection circuit is turned on, the limiting circuit turns off the light emitting diode and releases the contact of the photo MOS relay provided on the hot side signal line and the cold side signal line. When the contact of the photo MOS relay is released, the voice signal and the pulse current from the microphone are attenuated by the resistances respectively bypassed to the hot side signal line and the cold side signal line. That is, the input of the audio signal and the pulsed current to the output device is limited. As a result, generation of pop noise from the output device is suppressed.

Patent No. 5545859 specification

  However, the phantom power supply circuit disclosed in Patent Literature 1 requires a detection circuit for detecting a pulsed current and a limiting circuit for attenuating an audio signal. Therefore, the circuit configuration becomes complicated. The audio signal is attenuated by passing through the bypass-connected resistor, but is not cut off.

  SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems of the related art, and has as its object to prevent pop noise with a simple circuit configuration.

A capacitor microphone circuit connected to a phantom power supply, comprising: a first signal line and a second signal line through which an audio signal from a microphone unit flows; and a photo relay connected between the first signal line and the second signal line. Wherein the photorelay includes a contact, and the contact closes when a switch of the phantom power supply is in an off state.

  According to the present invention, generation of pop noise can be eliminated with a simple circuit configuration.

FIG. 1 is a circuit diagram showing an embodiment of a condenser microphone circuit according to the present invention.

● Condenser microphone circuit ●
Hereinafter, embodiments of a condenser microphone circuit according to the present invention will be described with reference to the drawings.

  FIG. 1 is a circuit diagram showing an embodiment of a condenser microphone circuit according to the present invention. FIG. 1 shows a state in which a condenser microphone circuit (hereinafter, referred to as “microphone circuit”) and a phantom power supply circuit that supplies power to the microphone circuit are connected.

First, a phantom power circuit to which the microphone circuit according to the present invention is connected will be described.

  The phantom power supply circuit FC supplies power to the microphone circuit MC. The phantom power supply circuit FC has a terminal T, a signal line L, a phantom power supply PW, a switch SW, a first supply resistor R1, and a second supply resistor R2.

  Each of the microphone circuit MC and the output device is connected to the terminal T. The terminal T includes a first terminal T1, a second terminal T2, and a third terminal T3, which are input terminals, and a fourth terminal T4, a fifth terminal T5, and a sixth terminal T6, which are output terminals. A microphone circuit MC is connected to the input terminal. An output device is connected to the output terminal.

  The signal line L connects the input terminal and the output terminal. The signal line L includes a hot-side signal line Lh, a cold-side signal line Lc, and a reference potential line Lg. The hot side signal line Lh connects the first terminal T1 and the fourth terminal T4. The cold side terminal Lc connects the second terminal T2 and the fifth terminal T5. The reference potential line Lg connects the third terminal T3 and the sixth terminal T6. An audio signal from the microphone circuit MC flows through the hot side signal line Lh and the cold side signal line Lc.

  The phantom power supply PW is a DC power supply that supplies power to the microphone circuit MC. The switch SW switches between the on state and the off state of the phantom power supply PW. The phantom power supply PW and the switch SW are connected in series between the reference potential line Lg and each of the hot side signal line Lh and the cold side signal line Lc.

  The first supply resistor R1 is connected in series between the switch SW and the hot side signal line Lh. The second supply resistor R2 is connected in series between the switch SW and the cold-side signal line Lc. The first supply resistance R1 and the second supply resistance R2 constitute a supply resistance having the same resistance value. The supply current from the phantom power supply PW is equally divided into the hot side signal line Lh and the cold side signal line Lc via the supply resistance.

● Microphone circuit ●
Next, the microphone circuit MC according to the present invention will be described.

Configuration of Microphone Circuit The microphone circuit MC converts sound into an electric signal and outputs a sound signal. The microphone circuit MC includes a condenser microphone unit (hereinafter, referred to as “microphone unit”) 1, an amplifier circuit 2, an output terminal 3, a signal line 4, a constant current diode 5, a light emitting element 6, and a relay contact 7.

  The microphone circuit MC according to the present embodiment has a microphone unit 1. However, the microphone circuit according to the present invention may not have the microphone unit.

  The microphone unit 1 converts sound into a sound signal. The microphone unit 1 has a diaphragm 11 and a fixed pole 12 that are arranged to face each other. The diaphragm 11 is connected to a third output terminal 33 of the output terminal 3 described below. The fixed pole 12 is connected to the amplifier circuit 2.

  The amplification circuit 2 includes an amplification unit that amplifies the audio signal from the microphone unit 1 and an impedance conversion unit that converts the impedance of the audio signal from the microphone unit 1. The amplifier circuit 2 is connected between the microphone unit 1 and the output terminal 3.

  The output terminal 3 is connected to an input terminal of the phantom power supply circuit FC. The output terminal 3 includes a first output terminal 31, a second output terminal 32, and a third output terminal 33. The first output terminal 31 is a hot-side terminal connected to the terminal T1 of the phantom power supply circuit FC. The second output terminal 32 is a cold-side terminal connected to the terminal T2 of the phantom power supply circuit FC. The third output terminal 33 is a ground terminal connected to the terminal T3 of the phantom power supply circuit FC.

  The signal line 4 connects each of the microphone unit 1 and the amplifier circuit 2 to the output terminal 3. The signal line 4 includes a first signal line 41, a second signal line 42, and a third signal line 43. The first signal line 41 is a hot-side signal line that connects the amplifier circuit 2 and the first output terminal 31. The second signal line 42 is a cold-side signal line that connects the amplifier circuit 2 and the second output terminal 32. The third signal line 43 connects the diaphragm 11 and the third output terminal 33. The third signal line 43 is a reference potential line connected to the reference potential. The first signal line 41 and the second signal line 42 are output signal lines through which audio signals from the microphone unit 1 flow via the amplifier circuit 2.

  The constant current diode 5 converts the current supplied from the phantom power supply PW into a constant current having a constant current value. The constant current diode 5 includes a first constant current diode 51 and a second constant current diode 52. The first constant current diode 51 and the second constant current diode 52 are connected in series between the first signal line 41 and the second signal line 42.

  The anode of the first constant current diode 51 is connected to the first signal line 41. The anode of the second constant current diode 52 is connected to the second signal line 42. The cathode of the first constant current diode 51 and the cathode of the second constant current diode 52 are commonly connected to form a common cathode of the constant current diode 5.

  The light emitting element 6 emits light by the constant current from the constant current diode 5. That is, the light emitting element 6 emits light when the phantom power supply PW of the phantom power supply circuit FC is on. The light emitting element 6 is, for example, a light emitting diode. The light emitting element 6 includes a first light emitting element 61, a second light emitting element 62, and a third light emitting element 63. The light emitting element 6 is connected in series between the common cathode of the constant current diode 5 and the third signal line 43.

  The relay contact 7 is a normally-on type relay contact. The relay contact 7 is connected between the first signal line 41 and the second signal line 42. Specifically, a connection point P1 between the relay contact 7 and the first signal line 41 is a connection point P3 between the first constant current diode 51 and the first signal line 41 of the first signal line 41, and an amplifying circuit. 2 are connected. The connection point P2 between the relay contact 7 and the second signal line 42 is between the connection point P4 between the second constant current diode 52 and the second signal line 42 of the second signal line 42 and the amplifier circuit 2. Connected to.

The first light emitting element 61 and the relay contact 7 constitute a photo relay PR in which the relay contact 7 opens and closes according to the light emitting state of the first light emitting element 61. The photo relay PR is connected between the first signal line 41 and the second signal line 42. The relay contact 7 opens when the first light emitting element 61 emits light . Relay contacts 7, the first light emitting element 61 stops emitting light (dark) Then Close. When the relay contact 7 is closed, the first signal line 41 and the second signal line 42 are short-circuited.

  The second light emitting element 52 and the third light emitting element 53 constitute a light emitting section. The light emitting unit emits light toward the outside of the microphone including the microphone circuit MC. The light emitting unit functions as, for example, an indicator that indicates that the microphone is in a state capable of outputting sound collected by the microphone. The light emitting unit is connected between the first light emitting element 51 and the third signal line 43.

Operation of Microphone Circuit Next, the operation of the microphone circuit MC connected to the phantom power supply circuit FC will be described.

  First, the operation of the microphone circuit MC when the switch SW of the phantom power supply circuit FC is on will be described.

When the switch SW is on, the phantom power supply PW is on. That is, the current from the phantom power supply PW (hereinafter referred to as “supply current”) is supplied to the microphone circuit MC via the supply resistance, the hot side signal line Lh, and the cold side signal line Lc.

  The supply current supplied to the microphone circuit MC is input to the constant current diode 5 and the amplifier circuit 2 via the output signal line. The supply current input to the constant current diode 5 becomes a constant current by the constant current diode 5. The constant current flows from the common cathode to the first light emitting element 61, the second light emitting element 62, and the third light emitting element 63. The first light emitting element 61, the second light emitting element 62, and the third light emitting element 63 emit light with a constant current.

  Light from the first light emitting element 61 is applied to the relay contact 7. That is, the switch SW is on, and the relay contact 7 is open. At this time, the audio signal flowing through the first signal line 41 flows through the first output terminal 31 to the hot side signal line Lh of the phantom power supply circuit FC. The audio signal flowing through the second signal line 42 flows through the second output terminal 32 to the cold-side signal line Lc of the phantom power supply circuit FC. The audio signal flowing through the hot side signal line Lh and the cold side signal line Lc is input to an output device.

  As described above, the second light emitting element 62 and the third light emitting element 63 emit light with a constant current. That is, the current that causes the light emitting unit to emit light is the same as the current that drives the photorelay PR. Therefore, the microphone circuit MC does not require a separate power supply for causing the light emitting unit to emit light.

  Next, the operation of the microphone circuit MC when the switch SW is switched from the on state to the off state will be described.

When the switch SW switches from the on state to the off state, the phantom power supply PW switches from the on state to the off state. Therefore, no supply current is input to the constant current diode 5. Therefore, the first light emitting element 61, the second light emitting element 62, and the third light emitting element 63 are turned off. When the first light emitting element 61 is turned off, the relay contact 7 is closed.

  When the relay contact 7 is closed, the first signal line 41 and the second signal line 42 are short-circuited via the connection point P1, the relay contact 7 and the connection point P2. Therefore, the audio signal flowing through the output signal line is cut off by the short circuit. That is, the audio signal is cut off by the microphone circuit MC. That is, the audio signal is not input to the output device via the phantom power circuit FC.

  Here, when the switch SW switches from the on state to the off state, the switch SW causes so-called chattering for an extremely short time. During this time, a pulse-like current is generated in the phantom power supply PW. The pulse current flows through the hot-side signal line Lh and the cold-side signal line Lc of the phantom power supply circuit FC via the supply resistors R1 and R2. At this time, the audio signal is cut off by the microphone circuit MC as described above. Therefore, the pulse current is not input to the output device together with (superimposed on) the audio signal. That is, no pop noise is generated.

Conclusion According to the embodiment described above, when the switch SW is turned off, the audio signal flowing through the output signal line is cut off by the microphone circuit MC by closing the relay contact 7 of the photo relay PR. This interruption of the audio signal is realized by a simple configuration in which the constant current diode 5 and the photo relay PR are connected to the microphone circuit MC. That is, the microphone circuit MC does not generate a pop sound when power supply to the microphone is stopped, with a simple circuit configuration.

  The interruption of the audio signal is performed instantaneously when the switch SW is turned off. That is, the microphone circuit MC has a mute function.

  Further, the first light emitting element 61 which is a light emitting element of the photo relay PR, and the second light emitting element 62 and the third light emitting element 63 which are light emitting elements of the light emitting section are connected in series. Therefore, the current for driving (light emitting) the light emitting unit and the current for driving the photorelay PR are common. That is, the microphone circuit MC does not require a separate power supply for causing the light emitting unit to emit light. That is, the microphone circuit MC can suppress the current consumption of the entire microphone circuit MC while having the light emitting unit.

  Note that a resistor for adjusting the voltage balance of the output signal line may be connected to the relay contact 7 in parallel. For example, even if a DC voltage is generated at the output of the amplifier circuit 2 for some reason, that is, a DC voltage is generated between the first signal line 41 and the second signal line 42, the resistance of the first signal line 41 And the second signal line 42 is short-circuited to prevent an excessive current from flowing to the output terminal 3.

MC microphone circuit 1 condenser microphone unit 2 amplifier circuit 3 output terminal 31 first output terminal 32 second output terminal 33 third output terminal 4 signal line 41 first signal line 42 second signal line 43 third signal line 5 constant current diode 6 light emitting element 61 first light emitting element 62 second light emitting element 63 third light emitting element 7 relay contact PR photo relay FC phantom power circuit PW phantom power SW switch

Claims (5)

A condenser microphone circuit connected to a phantom power supply,
A first signal line and a second signal line through which an audio signal from the microphone unit flows;
A photo relay connected between the first signal line and the second signal line;
Having,
The photorelay includes a contact,
Equipped with a,
When the switch of the prior SL phantom power is on, the contact is opened,
When the switch is off, the contacts close;
A condenser microphone circuit, characterized in that: The photo relay,
A light-emitting element that emits light when the switch is on,
With
The contact opens when the light emitting element emits light ,
The condenser microphone circuit according to claim 1. A third signal line connected to the reference potential,
Having,
A first constant current diode and a second constant current diode are connected in series between the first signal line and the second signal line,
The cathode of the first constant current diode and the cathode of the second constant current diode are commonly connected,
The light emitting element is connected between a common cathode of the first constant current diode and the second constant current diode, and the third signal line,
The contact is connected between the first signal line and the second signal line,
The condenser microphone circuit according to claim 2. A light emitting unit connected between the light emitting element and the third signal line;
Having,
The condenser microphone circuit according to claim 3. The light emitting unit is an indicator that emits light to the outside to indicate that the microphone unit is in a state capable of outputting sound collected by the microphone unit.
The condenser microphone circuit according to claim 4.

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