JPS6184993A - Capacitor microphone - Google Patents

Abstract

PURPOSE:To suppress the occurrence of click noise by impressing a phantom voltage to a microphone through a switching circuit which is turned on when the charging voltage of a capacitor to charge a current to a constant-current circuit reaches a fixed value. CONSTITUTION:When a switch SW1 is set to 'on' and a control circuit to 'off', a capacitor C3 of a constant-current circuit 12 starts being charged, and according to the increase of the voltage at a point a, a switching circuit 10 is activated and the potential of a point b is increased by a certain time constant until it reaches to a phantom power source voltage, and stops increasing. At that time, as a change in potential at the point b is prevented by capacitors C1 and C2 and no input signals come into a microphone amplifier circuit 14, click noise does not occur at a point d. Then, when the switch 1 is set to 'off', a control circuit 11 is turned on, the charge of a capacitor C3 is discharged and the circuit 10 is biased to 'off'. Therefore, the potential of the point b drops rapidly, the charge charged to a capacitor C4 drops by a certain time constant until it reaches 0V, the potential change at the point C becomes minimum, and thus click noise does not occur in a circuit 14.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a condenser microphone device that requires a power source for operation.

Structure of a conventional example and its problems FIG. 1 shows a conventional condenser microphone device. 1 is a balanced input type microphone/amplifier circuit, and 2 is a condenser microphone. 3 is a phantom power supply circuit consisting of a resistor 1 (,, R2, and a switch SW), which supplies a phantom voltage for the capacitor microphone 2 to the balanced input lines Ll and L2 of the microphone amplifier circuit 1. C1 and C2 are line This is a DC capacitor inserted in Ll, L2.

Next, the operation of the above conventional example will be explained. In Fig. 1, when the switch SW is turned on, the phantom power supply voltage (usually -48) is applied to the lines L, , and L2 via the resistor 1 and It2, and is supplied to the electrode of the condenser microphone 2. . However, in the conventional example, although the DC voltage is not directly applied to the microphone amplifier circuit 1 by the capacitor (2), at the moment when the phantom power supply voltage is applied, the transient peak value is approximately . The same state occurs when a +8V signal is applied to microphone amplifier circuit 1. As a result, normally 1.I
The disadvantage is that the microphone amplification circuit, which has an amplification degree of more than OdB, becomes saturated and generates a dog lick sound.

There is a problem in that the generation of this click sound passes through the power amplification amplifier after the microphone amplifier and damages the speaker connected to the amplifier.

OBJECTS OF THE INVENTION The present invention aims to eliminate the above-mentioned drawbacks and to suppress the occurrence of click sounds when turning on and off phantom power.

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a condenser microphone, a microphone amplifier circuit that can be connected to the condenser microphone via a DC blocking capacitor, a switch, and a container that charges current from a constant current circuit when the switch is operated. a switching circuit that is turned on when the charging voltage of the capacitor reaches a predetermined voltage; and a charging circuit connected to the switch and the switching circuit, and applying a phantom voltage to the capacitor microphone through the switching circuit. It is configured to do so.

DESCRIPTION OF THE EMBODIMENTS The configuration of an embodiment of the present invention will be described below with reference to the drawings. In Figure 2, 10 is phantom power (+4
8V) on/off switching circuit, 11 is the control circuit for controlling the switching circuit IO.
12 a constant current circuit for providing a time constant to the potential rise of the id switching circuit 10; 13 a charging circuit for charging the phantom power supply potential; 14 a microphone amplifier circuit; 15
is a condenser microphone, SW, I is also 1, 1 is also 2. C
,.

02, L, and R2 are the same switches, resistors, DC blocking capacitors, and lines as shown in FIG. 1, respectively.

Dl is a diode for backflow prevention, R3 is a resistor +C:l+
-04 is a capacitor.

Next, the operation of this embodiment will be explained. Now, when the switch SW is set to the on side at time t, the control circuit II is turned off and charging of the capacitor C1 of the constant current circuit 12 is started. The charging waveform at point a at this time is shown in the third section. As the voltage at point a increases, the switching circuit 2 becomes active, and the potential at point b rises with a certain time constant as shown in Figure 3 +1.3). The potential at point b is set to a predetermined phantom power supply voltage (usually -14
8V), and stops when the potential of the capacitor C1 reaches the phantom power supply voltage. Here, the capacitor C1 at the input section of the microphone amplifier circuit I
The cut-off frequency fc due to °C2 is: ■ fc=-92πC-ZL ZL: Human power impedance of the microphone amplifier circuit C: Since it is the capacitance of capacitor C1 or C2,
The potential change at point b, that is, the frequency, -\f is l\f<f
If it is c, it is blocked by the capacitor (3, (R2) and does not become an input signal to the microphone amplifier circuit 1.1, and no click noise occurs at point d as shown in Figure 3 (Q). Next, when the switch SW is set to the 0FI- position, the control circuit 11 is turned off and the constant current circuit 1 is turned off.
Dissipate the charge of capacitor B, connected to 2, 11ft, .
Biasing switching circuit 10 off. As a result, 1) the potential at point I drops rapidly, but the diode D for backflow prevention prevents the capacitor.

The electric charge charged in is discharged via switch SW→resistor It, and the potential drops with a certain time constant and finally becomes OV. Therefore, as in the case where the switch SW is turned on, the potential change at the point C becomes extremely small, and no click sound is generated in the microphone amplifier circuit 14.

Effects of the Invention The present invention has the above-described configuration, and since there is no click sound when the phantom power is turned off or turned off in the microphone amplification circuit, even if the phantom power is turned on or off carelessly, it will not affect the subsequent stage. This eliminates the possibility of damaging connected equipment (for example, speakers, etc.).

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing a conventional condenser microphone device, FIG. 2 is a circuit diagram showing a condenser microphone device according to an embodiment of the present invention, and FIG. 3 is a waveform diagram showing waveforms of various parts in FIG. 2. . IO...Switching circuit, I2/constant current circuit, 1/1
゛°°Microphone expansion circuit, 15-conodenser microphone, C1, C2 capacitor. Name of agent: Patent attorney Toshio Nakao and 1 other person for winter 1
Figure 2

Claims (1)

[Claims] A capacitor microphone, a microphone amplifier circuit connected to the capacitor microphone via a DC blocking capacitor, a switch, a capacitor that charges current from a constant current circuit when the switch is operated, and when the charging voltage of the capacitor reaches a predetermined voltage. A condenser microphone device comprising a switching circuit that is turned on, and a charging circuit connected to the switch and the switching circuit, and applying a phantom voltage to the condenser microphone through the switching circuit.