JP5805512B2 - Impedance converter for condenser microphone and condenser microphone - Google Patents

Description

  The present invention relates to an impedance converter for a condenser microphone and a condenser microphone using a vacuum tube, and an object thereof is to reduce noise generated by the physical vibration of the vacuum tube.

  Since a condenser microphone has a small effective capacitance and a high output impedance, it is necessary to receive the output signal of the condenser microphone with a high input impedance in order to ensure a frequency response up to a low frequency region. In addition, in order to input the output signal of the condenser microphone to an amplifier or the like via a cable or the like, it is necessary to lower the output impedance of the condenser microphone. Therefore, an impedance converter having a high input impedance and a low output impedance is built in the capacitor microphone. A field effect transistor (FET) is widely used as an impedance conversion element built in a condenser microphone.

  In order to further improve the sound quality of the condenser microphone and to increase the maximum output level, there is one using a vacuum tube (also referred to as an electron tube) as an impedance conversion element (see, for example, Patent Document 1). In Patent Document 1, as one embodiment, an impedance converter having a plate-grounded amplification tube and a bias circuit for generating a bias voltage applied to the grid of the amplification tube, the bias circuit includes the amplification circuit. A first diode for applying a bias voltage to the grid so that a current flows toward the grid of the tube, a second diode connected in parallel opposite to the first diode, and a cathode of the amplifier tube A third diode connected between the cathode and the load resistor so that a current flows toward the load resistor, and a voltage generated in the third diode by the plate current flowing through the amplifier tube is An impedance converter is described which is applied as a bias voltage to a grid of amplifier tubes via a second diode.

  By the way, the output of the microphone is generally output as a balanced signal that is divided into a hot side and a cold side so that noise is not generated in the audio signal even if an electric field or magnetic field that becomes noise is applied to the transmission path. When outputting with a balanced signal, the impedance on the hot side and the cold side is required to be the same. Therefore, it is widely practiced to use an output transformer having a secondary coil with a center tap in the output circuit portion of the microphone so that the hot side and cold side output impedances are the same.

  However, when a transformer is used in the output circuit, the tone color changes depending on the transformer, and there are users who do not like this, so there is a circuit configuration in which the output transformer can be omitted. For example, two microphone units and respective impedance conversion elements and vacuum tubes are provided, and a bias circuit of each vacuum tube includes a first diode that applies a bias voltage to a grid of the respective vacuum tubes, and a parallel and reverse connection to the first diode. A circuit configuration has second diodes connected in the direction. From the cathode of each vacuum tube, a hot side signal and a cold side signal whose phases are opposite to each other can be balanced and output.

  However, according to the microphone unit having the circuit configuration and the impedance converter as described above, even if the bias voltages of the two vacuum tubes are the same, the currents of both vacuum tubes vary. If the currents of both tubes vary, the impedance of the output circuit connected to the cathode follower also varies, and the balance of the balanced output is lost. is there.

  Therefore, the present inventor has applied a bias voltage to the vacuum tube grid, the vacuum tube in which the output signal of the microphone unit is input to the grid and output from the cathode follower, the FET that is cascade-connected to the vacuum tube and defines the current flowing through the vacuum tube, and A bias circuit to be added, and the vacuum tube, the FET, and the fixed bias circuit are connected symmetrically in pairs, so that the two cathode follower outputs are balanced outputs, and the fixed bias circuit that forms the pair Invented a microphone impedance converter having an adjustment member for adjusting the balance of the balanced output by adjusting the current flowing in the paired vacuum tubes, and a microphone using the impedance converter. (See Patent Document 2).

  According to the invention described in Patent Document 2, a pair of vacuum tubes, FETs, and fixed bias circuits are provided, balanced output is made by the cathode follower output of the two vacuum tubes, and the current flowing through the paired vacuum tubes is adjusted to balance the balanced output. Since the adjustment member for adjusting the impedance is provided between the pair of fixed bias circuits, the impedances of both balanced outputs can be made the same, thereby preventing noise from being mixed into the output signal transmission line. it can.

US Pat. No. 6,453,048 JP 2010-273195 A

  As described above, a vacuum tube is used as an impedance converter for a microphone, and the technology is being advanced while solving the technical problems associated therewith. A vacuum tube has a built-in component made of a metal component in a container such as a glass tube kept under vacuum, and has a larger mechanical dimension than a semiconductor element such as a transistor. The built-in components include a heater for generating thermoelectrons, a cathode constituting a cathode, a plate constituting an anode, a grid between the cathode and the plate for controlling the movement of electrons. When vibration or impact is applied to the vacuum tube from the outside, each of the metal parts vibrates. Since each metal part has a different inertial force, each metal part vibrates while displacing the mutual positional relationship, and the movement condition of electrons in the vacuum tube fluctuates to generate vibration noise. This vibration noise is said to be “microphonic noise” because it makes a sound similar to the noise generated when the diaphragm of the microphone vibrates.

  In a microphone using a vacuum tube as an impedance converter, the above-described microphonic noise generated by external vibration or impact is added to the vibration noise generated by the microphone unit body. Since the microphone unit is in the air, the vibration of the diaphragm caused by external vibration or impact is attenuated in a relatively short time by the viscous resistance of the air, and the vibration noise converges in a short time. However, since the inside of the vacuum tube is kept in vacuum, the built-in components are not braked by the viscous resistance of air, and the microphonic noise caused by the structure of the vacuum tube is more than the vibration noise generated by the microphone unit body. It takes a long time to decay.

  The present invention eliminates the above-described problems of a condenser microphone using a vacuum tube as an impedance converter, that is, a condenser microphone that can cancel out the output of vibration noise caused by displacement of a built-in component of the vacuum tube due to vibration or impact. An object is to provide an impedance converter and a condenser microphone.

An impedance converter for a condenser microphone according to the present invention is:
Two pairs of vacuum tubes that convert the output impedance of two pairs of condenser microphone units into low impedance are provided, and the two pairs of vacuum tubes output balanced electroacoustic conversion signals from the two pairs of condenser microphone units. An impedance converter for a connected condenser microphone,
The two pairs of vacuum tubes are vacuum tubes of the same specification, and are characterized in that they are arranged in parallel in the same direction and connected together.

  The condenser microphone according to the present invention includes the capacitor microphone impedance converter according to the present invention as an impedance converter.

  When vibration or impact is applied from the outside, the pair of vacuum tubes vibrate under the same conditions and generate the same vibration noise. Since each of the vacuum tubes is connected so that the electroacoustic conversion signals from the two pairs of condenser microphone units are balanced and output, the vibration noise generated by the two pairs of vacuum tubes is added in an opposite phase to each other and canceled out. The

It is a circuit diagram which shows the circuit structural example of the impedance converter for capacitor | condenser microphones based on this invention, and a capacitor | condenser microphone. It is a cross-sectional view showing an example of an integral coupling structure of a pair of two vacuum tubes applicable to the present invention. It is a cross-sectional view which shows the example of the single vacuum tube before the coupling | bonding applicable to this invention.

  Hereinafter, embodiments of an impedance converter for a condenser microphone and a condenser microphone according to the present invention will be described with reference to the drawings. First, the circuit configuration example shown in FIG. 3 will be described.

  In FIG. 3, reference numerals 11 and 12 denote condenser microphone units. Capacitor microphone units 11 and 12 each have a diaphragm that vibrates in response to sound pressure, and a fixed electrode that faces the diaphragm with a predetermined interval. The microphone units 11 and 12 have the same design specifications, and both diaphragms are on the same plane and have the same orientation. The fixed electrode of the microphone unit 11 and the diaphragm of the microphone unit 12 are grounded. The diaphragm of the microphone unit 11 is connected to the grid of the first vacuum tube 21 via the coupling capacitor 15, and the fixed electrode of the microphone unit 12 is connected to the grid of the second vacuum tube 22 via the coupling capacitor 25. Therefore, the output signal of the microphone unit 11 and the output signal of the microphone unit 12 are in opposite phases. The output signal of the microphone unit 11 is input to the grid of the vacuum tube 21 via the coupling capacitor 15, and the output signal of the microphone unit 12 is input to the grid of the vacuum tube 22 via the coupling capacitor 25.

  The two vacuum tubes 21 and 22 are both used as impedance conversion elements. For example, a high voltage DC voltage of 120 V is applied to the plate of the vacuum tube 21 from the high voltage power supply input terminal 5 through the resistor 33, and the high voltage DC voltage is applied to the plate of the vacuum tube 22 from the terminal 5 through the resistor 35. Applied.

  The vacuum tube 21 is connected so as to output a cathode follower, and is cascade-connected together with the FET 31. More specifically, the cathode of the vacuum tube 21 is connected to the drain of the FET 31, and the source of the FET 31 is connected to the ground via the resistor 42 for controlling the plate current of the vacuum tube 21. A capacitor 34 is connected between the plate of the vacuum tube 21 and the base of the FET 31, and a resistor 41 is connected between the base of the FET 31 and the ground. An impedance conversion output signal is output from the cathode of the vacuum tube 21, and this output signal is output from the cold output terminal 3 to the outside via the electrolytic capacitor 47.

  A bias voltage is applied to the grid of the vacuum tube 21 by a bias circuit as described below. A DC high voltage is supplied from the terminal 5, and the high voltage is divided by the voltage dividing resistors 37 and 52 connected in series between the terminal 5 and the ground. The diode 18 is connected to the grid of the vacuum tube 21. The diode 17 and the diode 18 are each composed of two diodes connected in series, and the diode 17 and the diode 18 are connected in parallel in opposite directions. The cathode of the diode 17 and the anode of the diode 18 are connected to the resistor 38, and the anode of the diode 17 and the cathode of the diode 18 are connected to the grid of the vacuum tube 21.

  When a connection point between the resistor 38 and the diodes 17 and 18 is a point A, an electrolytic capacitor 45 is connected between the point A and the cathode of the vacuum tube 21. The diode 17 is a first diode and the diode 18 is a second diode. The voltage at the voltage dividing point by the voltage dividing resistors 37 and 52 is applied to the grid of the vacuum tube 21 through the bias resistor 38 and further through the first diode 17 or the second diode 18. An electrolytic capacitor 53 is connected in parallel to the voltage dividing resistor 52.

  The diaphragm of the microphone unit 11 is connected so that a DC voltage is applied from the terminal 5 through the resistor 20 and the diodes 13 and 14 connected in parallel in opposite directions. The diodes 13 and 14 are connected in parallel with the first and second diodes 17 and 18 with the coupling capacitors 15 and 16 interposed therebetween. The diodes 13 and 14 are for supplying a polarization voltage from the DC voltage source to the microphone unit 11. The coupling capacitors 15 and 16 function to separate the DC voltage from the output signal of the microphone unit 11 and input only the output signal of the microphone unit 11 to the grid of the vacuum tube 21.

  The first and second diodes 17 and 18 are both composed of two elements connected in series, and the diodes 13 and 14 are also composed of two elements connected in series. The number of elements constituting each of these diodes is arbitrary and may be only one. If the number of elements constituting each diode is increased, the bias voltage applied to the grid of the vacuum tube 21 becomes deeper (larger).

  The circuit configuration centered on the vacuum tube 21 has been described so far, but the circuit configuration centered on the other vacuum tube 22 is the same as the circuit configuration centered on the vacuum tube 21. The two pairs of vacuum tubes 21 and 22 are drawn symmetrically on the circuit diagram shown in FIG. 3, but are substantially connected in parallel. Hereinafter, a circuit configuration centered on the vacuum tube 22 will be described.

  The vacuum tube 22 is connected so as to output a cathode follower, and is cascaded together with the FET 32. More specifically, the cathode of the vacuum tube 22 is connected to the drain of the FET 32, and the source of the FET 32 is connected to the ground via the resistor 44 for controlling the plate current of the vacuum tube 22. A capacitor 36 is connected between the plate of the vacuum tube 22 and the base of the FET 32, and a resistor 43 is connected between the base of the FET 32 and the ground. An impedance conversion output signal is output from the cathode of the vacuum tube 22. This output signal is output from the hot side output terminal 2 to the outside through the electrolytic capacitor 48.

  A bias voltage is applied to the grid of the vacuum tube 22 by a bias circuit as described below. A voltage dividing point by the voltage dividing resistors 37 and 52 connected in series is connected to the grid of the vacuum tube 22 through a bias resistor 39, a diode 27 and a diode 28. The diode 27 and the diode 28 are each composed of two diodes connected in series, and are connected in parallel in opposite directions. The cathode of the diode 27 and the anode of the diode 28 are connected to the resistor 39, and the anode of the diode 27 and the cathode of the diode 28 are connected to the grid of the vacuum tube 22.

  When a connection point between the resistor 39 and the diodes 27 and 28 is a point B, an electrolytic capacitor 46 is connected between the point B and the cathode of the vacuum tube 22. The diode 27 is a first diode, and the diode 28 is a second diode. The voltage at the voltage dividing point is applied to the grid of the vacuum tube 22 via the bias resistor 39 and further via the first diode 27 or the second diode 28.

  The fixed electrode of the microphone unit 12 is connected so that a DC voltage is applied from the terminal 5 via a resistor 30 and diodes 23 and 24 connected in parallel in opposite directions. The diodes 23 and 24 are connected in parallel with the first and second diodes 27 and 28 with the coupling capacitors 25 and 26 interposed therebetween. The diodes 23 and 24 are for supplying a polarization voltage from the DC voltage source to the fixed electrode of the microphone unit 12. The coupling capacitors 25 and 26 function to separate the DC voltage from the output signal of the microphone unit 12 and input only the output signal of the microphone unit 12 to the grid of the vacuum tube 22.

  The first and second diodes 27 and 28 are both composed of two elements connected in series, and the diodes 23 and 24 are also composed of two elements connected in series. The number of elements constituting each of these diodes is arbitrary and may be only one. If the number of elements constituting each diode is increased, the bias voltage applied to the grid of the vacuum tube 22 becomes deeper (larger).

  As described so far, the circuit example shown in FIG. 3 has two cathode follower outputs by connecting a vacuum tube, an FET, and a fixed bias circuit in parallel with each other in parallel (symmetrical on the circuit diagram). Is configured to provide a balanced output. The variable resistor 40 is provided as an adjustment member for adjusting the balance of the balanced output by adjusting the current flowing through the pair of vacuum tubes 21 and 22 between the pair of fixed bias circuits. This is a feature of the circuit example. More specifically, the fixed terminals at both ends of the variable resistor 40 are connected between the source of the FET 31 and the source of the FET 32, and the variable terminal of the variable resistor 40 is connected to the ground.

  The current flowing through the vacuum tube 21 is the same as the current flowing through the FET 31, and similarly, the current flowing through the vacuum tube 22 is the same as the current flowing through the FET 32. These currents are regulated by the plate current control resistors 42 and 44, and further regulated by the adjustment position of the variable resistor 40. When the variable resistor 40 is adjusted to increase the current of the vacuum tube 21, the current of the vacuum tube 22 decreases, and when the current of the vacuum tube 21 is decreased, the current of the vacuum tube 22 increases. Therefore, the variable resistor 40 is adjusted so that the currents of the vacuum tubes 21 and 22 become equal. By adjusting in this way, the impedance of the hot side and the cold side, which are balanced output by the cathode follower, becomes equal and good balance is maintained, and even if an external electrolysis or magnetic field is applied to the output signal transmission line, the output It is possible to prevent noise from entering the signal. The variable resistor 40 may be a semi-fixed resistor that holds the adjustment position semi-fixed once adjusted.

  The impedance converter includes a heater power supply terminal 4 in addition to the DC high-voltage power supply input terminal 5, the cold-side output terminal 3, the hot-side output terminal 2, and the ground terminal 1 that have already been described. A heater 51 of vacuum tubes 21 and 22 is connected between the heater power supply terminal 4 and the ground terminal 1.

  The ground terminal 1, the hot output terminal 2, and the cold output terminal 3 can be connected to a balanced cable via a connector or the like, and can be connected to an external device via this balanced cable. Alternatively, for example, a transformer is disposed in a microphone case, the output terminals 2 and 3 are connected to both ends of the primary winding of the transformer, and both ends of the secondary winding of the transformer are connected to the cold-side terminal of the microphone connector and hot The ground terminal 1 may be connected to the ground terminal of the microphone connector, and balanced output may be performed by the hot terminal, the cold terminal, and the ground terminal of the microphone connector.

  According to the circuit example described above, the output signals of the high output impedance condenser microphone units 11 and 12 are input to the grids of the high input impedance vacuum tubes 21 and 22 connected to the cathode follower. Since the vacuum tubes 21 and 22 output the cathode follower, the output impedance becomes low impedance.

  The diodes 17, 18 and 27, 28 apply a bias voltage to the vacuum tubes 21, 22 as follows. That is, the bias voltage generated at the coupling points A and B is Vc, and the grid voltage of the vacuum tubes 21 and 22 at that time is Vd. If the grid voltage Vd fluctuates so as to be lower than the bias voltage Vc, current flows through the first diodes 17 and 27 due to the forward voltage / current characteristics in the static characteristics of the diodes, and the diodes 17 and 27. Causes a voltage drop Vf. Since the grid voltage Vd is lower than the bias voltage Vc by Vf, the bias voltage Vc becomes shallow, the plate currents of the vacuum tubes 21 and 22 increase, and the bias voltage Vc increases. Thereby, the fluctuation | variation part of the grid voltage Vd is suppressed, and the electric current of the diodes 17 and 27 reduces. This operation continues until no current flows through the diodes 17 and 27. As a result, the fluctuation of the grid voltage Vd converges so that the current of the diodes 17 and 27 is zero, and thus the voltage drop Vf of the diodes 17 and 27 is zero, and the grid voltage Vd becomes equal to the bias voltage Vc.

  Conversely, if the grid voltage Vd fluctuates so as to be higher than the bias voltage Vc, the second diodes 18 and 28 operate in the same manner as the first diodes 17 and 27 in the above case, and the grid voltage Vd. And the grid voltage Vd becomes equal to the bias voltage Vc. That is, the grid voltage and the cathode voltage of the vacuum tubes 21 and 22 are substantially equal.

  As a result, the first and second diodes 17, 18 and 27, 28 operate in the vicinity of zero potential difference between the terminals with respect to alternating current, and the voltage drop between the terminals is substantially zero. , 18 and 27, 28, it is equivalent to connecting a high resistance.

  In other words, the bias circuits of the vacuum tubes 21 and 22 are constituted by the first and second diodes 17, 18 and 27, 28 connected in parallel in opposite directions and the bias resistors 38, 39. , 22 is configured as a fixed bias circuit for applying a constant bias voltage to the grid.

  Further, the plate current control resistors 42 and 44 and the variable resistor 40 connected between the sources of the FETs 31 and 32 and the variable resistor 40 regulate the plate current of the vacuum tubes 21 and 22, thereby adjusting the variable resistor 40. By doing so, the plate currents of both vacuum tubes 21 and 22 can be controlled to be equal, so that the impedances on the hot side and cold side of the balanced output can be made equal and good balance can be maintained.

  Since the audio signals from the microphone units 11 and 12 pass through the vacuum tubes 21 and 22, there is no deterioration in sound quality. Since the FETs 31 and 32 are used in place of the vacuum tubes as circuit elements that are cascade-connected with the vacuum tubes 21 and 22 and define the current flowing through the vacuum tubes 21 and 22, they are consumed by the heater of the vacuum tube while maintaining high sound quality. The amount of power can be reduced.

  In the circuit example shown in FIG. 3, resistors 20 and 30, diodes 13 and 14, and diodes 23 and 24 are provided from the terminal 5 in order to apply a polarization voltage to the condenser microphone units 11 and 12. In the case of the condenser microphone unit, the voltage application circuit is not necessary.

  By the way, as described at the beginning, when vibration or impact is applied to the vacuum tube from the outside, noise called “microphonic noise” is generated. In order to eliminate the noise called “microphonic noise”, in the embodiment according to the present invention, the two pairs of vacuum tubes 21 and 22 are arranged in parallel in the same direction and integrally coupled.

  FIG. 2 shows an example of the structure of a vacuum tube. The vacuum tube 21 includes a cathode 211, a grid 212, a plate 214, a heater (not shown), and the like in a container 210 such as a glass tube whose inside is kept in a vacuum. The grid 212 has a structure in which wires are wound at a predetermined interval across a pair of grid frames 213 standing in parallel, and the cathode 214 is located in the grid 212. Plate 214 surrounds grid 212.

  As shown in FIG. 1, the other vacuum tube 22 is also a vacuum tube having the same structure and the same specifications as the vacuum tube 21, and inside a vacuum vessel 220, a cathode 221, a grid frame 223, a grid 222, and a plate 224. Built-in heater.

  As shown in FIG. 1, the pair of two vacuum tubes 21 and 22 are arranged in parallel in the same direction and are integrally coupled by an adhesive 23. Therefore, when vibration or impact is applied from the outside, the built-in components of the two pairs of vacuum tubes 21 and 22 vibrate with the same stroke in the same direction under the same conditions and generate the same vibration noise. As described with reference to FIG. 1, each of the vacuum tubes 21 and 22 is connected so as to balance and output the electroacoustic conversion signals from the two pairs of condenser microphone units 11 and 12, and thus the two pairs of vacuum tubes 21 and 22. The vibration noises generated in the above are added in an opposite phase to cancel each other, and the vibration noises mixed in the output of the microphone that is balanced and transmitted can be reduced.

  Since the vacuum tubes 21 and 22 are incorporated in the microphone, it is preferable to use an ultra-small vacuum tube called a “battery tube” driven by a battery. Since the “battery tube” is very small, it is easy to bond with the adhesive 23. If it is difficult to directly bond the pair of vacuum tubes 21 and 22 with the adhesive 23 in terms of strength or the like, a holding body that fills the space of the opposing surfaces to be bonded to each other is interposed. It is good to couple | bond together by an adhesive agent under the intervention of this.

  In FIG. 1 and FIG. 2, the structure of the vacuum tubes 21 and 22 is a triode structure. However, the structure or type of the vacuum tube is arbitrary, and if it has an impedance conversion function, it can be a triode or a tetraode. There may be a pentode or more electrodes.

  The description so far relates to a component including a condenser microphone unit and an impedance converter for the condenser microphone.

  The condenser microphone according to the present invention is characterized by including the impedance converter as described above. That is, a condenser microphone according to the present invention includes a condenser microphone unit that outputs two signals having opposite phases to each other, and an impedance converter that has a high input impedance and a low output impedance and receives each output signal of the condenser microphone unit as an input. A capacitor microphone is provided, wherein the impedance converter is an impedance converter as described above. According to the condenser microphone according to the present application, it is possible to obtain an effect obtained by the impedance converter described above.

11 Condenser microphone unit 12 Condenser microphone unit 21 Vacuum tube 22 Vacuum tube 23 Adhesive 31 FET
32 FET

Claims (8)

Two pairs of vacuum tubes that convert the output impedance of two pairs of condenser microphone units into low impedance are provided, and the two pairs of vacuum tubes output balanced electroacoustic conversion signals from the two pairs of condenser microphone units. An impedance converter for a connected condenser microphone,
The two pairs of vacuum tubes are vacuum tubes of the same specification, and are impedance converters for condenser microphones that are arranged in parallel in the same direction and coupled together.   2. An impedance converter for a condenser microphone according to claim 1, wherein the pair of two vacuum tubes are ultra-compact vacuum tubes that can be driven by a battery.   The impedance converter for a condenser microphone according to claim 1 or 2, wherein the pair of two vacuum tubes are integrally coupled by an adhesive.   4. The impedance converter for a condenser microphone according to claim 1, wherein the pair of two vacuum tubes are integrally coupled by an adhesive with a holding body interposed therebetween. The pair of two vacuum tubes are connected so that the output signal of the condenser microphone unit is input to each grid and the cathode follower is output,
A pair of FETs cascaded together with the vacuum tubes to define the current flowing through the vacuum tubes, and a bias circuit for applying a bias voltage to the grid of the vacuum tubes,
5. Each of the vacuum tubes, FETs, and fixed bias circuits are connected in parallel in pairs, so that the cathode follower output of each vacuum tube is connected to provide a balanced output. An impedance converter for a condenser microphone as described.   6. The impedance converter for a condenser microphone according to claim 5, further comprising an adjusting member for adjusting the balance of the balanced output by adjusting the current flowing in the paired vacuum tubes between the pair of fixed bias circuits.   7. The condenser microphone impedance converter according to claim 1, wherein the vacuum tube is a triode. A capacitor microphone unit that outputs two signals having opposite phases to each other, and a capacitor microphone that includes an impedance converter that has a high input impedance and a low output impedance and receives each output signal of the capacitor microphone unit;
The said impedance converter is a microphone which is an impedance converter for capacitor | condenser microphones in any one of Claim 1 thru | or 7.

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