JP5233603B2 - Audio signal adder - Google Patents

Description

  The present invention relates to a technique for reducing noise of equipment.

  In a karaoke apparatus or the like, it has become possible to enjoy singing with a large number of people by connecting a plurality of microphones. This is realized by providing a plurality of input terminals for inserting microphone plugs and providing an audio signal adding device for amplifying and adding the audio signals supplied to the respective input terminals in the first stage amplifier. This conventional configuration will be described with reference to FIGS. 4 (a) and 4 (b).

  FIG. 4A is a diagram showing a configuration of a conventional audio signal adding device 1A. The audio signal adding device 1A adds a plurality of input stages 10A-1, 10A-2,... 10A-n and outputs from the input stages 10A-1, 10A-2,. And an adder 50A for outputting. Each input stage 10A-1, 10A-2,... 10A-n includes an input unit 100A having terminals T1 ′, T2 ′ and T3 ′, and an initial stage for amplifying the output from the terminal T2 ′ of the input unit 100A. An amplifier 200A is provided. Terminals T1 'and T3' are grounded. The input unit 100A is provided with an insertion port 101A into which a microphone plug is inserted, an electrode 102A, and a switch electrode 103A.

  FIG. 4A shows a state in which the microphone plug is not inserted, the electrode 102A and the switch electrode 103A are electrically connected, and the terminal T2 'is grounded via the terminal T3'. Therefore, the input of the first stage amplifier 200A is in a grounded state. On the other hand, when the microphone plug 1000 is inserted into the insertion slot 101A as shown in FIG. 4B, the sleeve of the plug 1000 comes into contact with the insertion slot 101A and is grounded via the terminal T1 '. Also, the chip of the plug 1000 comes into contact with the electrode 102A and the connection between the electrode 102A and the switch electrode 103A is disconnected, so that the audio signal supplied from the chip of the plug 1000 is input to the first stage amplifier 200A via the terminal T2 ′. Will be.

  Here, since there is an input noise level in the first stage amplifier 200A, noise is generated in the output of the first stage amplifier 200A even if the microphone plug 1000 is not connected. These noises are output as larger noises added by the adding unit 50A. The input noise levels of the first stage amplifier 200A in each input stage 10A-1, 10A-2,..., 10A-n are N1, N2,..., Nn, respectively, and the gains are G1, G2,. Then, the output noise level Vn output from the adder 50A is as shown in the following expression (1) in consideration of averaging due to the phase shift.

  If all the first stage amplifiers 200A have the same input noise level and gain (input noise level N = N1, N2,..., Nn, gain G = G1, G2,..., Gn), the output The noise level Vn is expressed as in equation (2).

Therefore, for example, if the input noise level is N = 1 μV, the gain is G = 100 times, and the number of input stages 10A is n = 4, the output noise level Vn is as large as 200 μV. For example, Patent Document 1 discloses a technique for reducing the noise level in a single input stage.
Japanese Patent Laid-Open No. 5-89591

  In such various noise level reductions, the configuration is often complicated, and many have led to an increase in cost.

  The present invention has been made in view of the above circumstances, and an audio signal addition that can reduce the overall noise level even if it has a large number of terminals so that a large number of microphone plugs can be inserted. An object is to provide an apparatus.

In order to solve the above problems, the present invention provides a plurality of input terminals to which a supply terminal for supplying an audio signal is connected, and amplification means provided corresponding to each of the plurality of input terminals, comprising an operational amplifier, The non-inverting amplifier circuit includes a ground resistor provided between an inverting input terminal and a ground terminal of the operational amplifier, and a feedback resistor provided between the output terminal and the inverting input terminal of the operational amplifier. a plurality of amplifying means for amplifying at each preset gain an audio signal supplied to the terminal, and adding means for adding each of the audio signals amplified by said plurality of amplifying means, said supply terminal is connected If not a gain set in the amplifier means corresponding to Kino input terminal this increases the resistance between the ground terminal and the inverting input terminal Accordingly, a gain reducing means for reducing a first switch provided between the ground resistor and the ground terminal, when the supply terminal is connected to said input terminal, in contact with the supply terminal And an electrode for inputting an output signal from the supply terminal to the non-inverting input terminal of the operational amplifier, and a second switch for electrically connecting the electrode to the ground terminal when the electrode is not in contact with the supply terminal. And the electrode is sandwiched between the first switch and the second switch to disconnect the first switch when the supply terminal is not connected to the input terminal, and the second switch It is arranged at a position to conduct, and when the supply terminal is connected to the input terminal, it is pushed by the supply terminal to approach the first switch, and the second switch Moving away from the switch, causes conduct the first switch by moving the first switch via an insulator, characterized by comprising a gain reducing means for cutting the second switch audio A signal adder is provided.

In another preferred aspect, when the first switch is disconnected in the gain reducing means, the switch electrode on the ground resistance side of the first switch has a resistance value higher than that of the ground resistance. It is a large resistor and is electrically connected to the other end of the resistor whose one end is grounded .

  ADVANTAGE OF THE INVENTION According to this invention, even if it has many terminals so that the plug of many microphones can be inserted, the audio signal addition apparatus which can reduce the whole noise level can be provided.

  Hereinafter, an embodiment of the present invention will be described.

<Embodiment>
FIG. 1 is an explanatory diagram showing a configuration of an audio signal adding device 1 according to an embodiment of the present invention. The audio signal adding apparatus 1 has n input terminals into which microphone plugs are inserted. As shown in FIG. 1, a plurality of input stages 10-1, 10-2,. 10-n (hereinafter simply referred to as input stage 10 if not distinguished from each other). In addition, an adder 50 that adds and outputs the audio signals output from each input stage 10 is provided.

  Each input stage 10 includes an input unit 100 having terminals T1, T2,..., T5, an operational amplifier 201, a feedback resistor R2, and a ground resistor R1. Terminals T1, T3, and T4 are connected to a ground terminal.

  An output signal from the terminal T2 of the input unit 100 is input to the non-inverting input terminal of the operational amplifier 201, and a feedback resistor R2 is provided between the output terminal and the inverting input terminal. Further, a ground resistor R1 is provided between the inverting input terminal and the terminal T5. The output signal from the operational amplifier 201 is input to the adder 50.

  Next, the input unit 100 of each input stage 10 will be described with reference to FIG. 2A and 2B are explanatory diagrams of the configuration of the input unit 100. FIG. 2A shows a case where the microphone plug 1000 is not inserted, and FIG. 2B shows a case where the plug 1000 is inserted. It is a figure which shows the state of.

  The input unit 100 includes an insertion port 101 into which a microphone plug 1000 is inserted, an electrode 102, and switch electrodes 103, 104, and 105, which are electrically connected to terminals T1, T2, T3, T4, and T5, respectively. Yes. An insulator 104a is provided between the switch electrode 104 and the electrode 102 so as not to be electrically connected. However, the switch electrode 104 and the electrode 102 are configured to maintain a physical contact state. When the electrode 102 is moved, the switch electrode 104 is also moved.

  As shown in FIG. 2A, when the microphone plug 1000 is not inserted, the electrode 102 and the switch electrode 103 are electrically connected, and the terminal T2 and the terminal T3 are electrically connected. Further, since the switch electrode 104 and the switch electrode 105 are not in contact with each other, they are electrically disconnected, and the terminals T4 and T5 are not electrically connected.

  Accordingly, since the terminal T5 is not grounded, the grounding resistor R1 is not grounded, and the operational amplifier 201 and the feedback resistor R2 function as an amplifier circuit having a gain of 1.

  On the other hand, as shown in FIG. 2B, when the microphone plug 1000 is inserted, the sleeve of the microphone plug 1000 comes into contact with the insertion port 101 and is grounded through the terminal T1. The tip of the microphone plug 1000 is in contact with the electrode 102. On the other hand, when the electrode 102 moves, the connection between the electrode 102 and the switch electrode 103 is disconnected, the terminal T3 and the terminal T2 are not conducted, and the terminal T2 is not grounded. A signal is supplied.

  Further, the switch electrode 104 is moved by the movement of the electrode 102, the switch electrode 104 and the switch electrode 105 are electrically connected, and the terminal T4 and the terminal T5 are electrically connected. Therefore, since the terminal T5 is grounded, one end of the grounding resistor R1 on the terminal T5 side is grounded, and the operational amplifier 201, the feedback resistor R2, and the grounding resistor R1 are (R1 + R2) / R1 times (simply described as R1, R2). In this case, the resistance values of the grounding resistor R1 and the feedback resistor R2 are shown. This corresponds to the first stage amplifier in the conventional example.

  In the above configuration, the switch electrodes 104 and 105 function as a determination unit that determines whether or not the microphone plug 1000 is inserted depending on the connection relationship. Further, when the microphone plug 1000 is inserted, the switch electrodes 104 and 105 have a gain of (R1 + R2) / R1 times set in the non-inverting amplifier circuit when the microphone plug 1000 is not inserted. It also functions as a gain reduction means for reducing the gain to 1 time.

  As described above, when the plug 1000 of the microphone is inserted, the audio signal supplied from the microphone is amplified by (R1 + R2) / R1 times. However, when the plug 1000 is not inserted, the audio signal is multiplied by 1. It becomes amplification. Therefore, in the input stage 10 in which the microphone plug 1000 is not inserted, the input noise is not amplified and output to the adder 50.

  Therefore, the output noise level Vn of the audio signal adding device 1 in this embodiment is that the input noise level of the amplifier circuit in each input stage 10 is N and the gain is G (“1” when the microphone plug 1000 is not inserted). Then, when the microphone plug 1000 is inserted into the input terminals of the m input stages 10 out of the n input stages 10, the following expression (3) is obtained.

  Here, since G >> 1 in general, the output noise level Vn is approximately expressed by Expression (4).

  Therefore, the comparison of the output noise level Vn between the audio signal adding apparatus 1 in the embodiment of the present invention and the audio signal adding apparatus 1A in the conventional example is performed. Here, it is assumed that there are five microphone input terminals (input stages 10, 10A) (n = 5), the input noise level is N = 0.7 μV, and the gain is 30 dB (G = 31.6). .

  In this case, the output noise level Vn of the audio signal adding apparatus 1A in the conventional example is 49.5 μV when applied to the above equation (2). This output noise level Vn occurs at a minimum regardless of how many microphones are used. On the other hand, the output noise level Vn of the audio signal adding device 1 in the embodiment of the present invention is 22.1 μV if only one microphone is used, and 31.3 μV if only one microphone is used, when applied to the above equation (4). If 3 lines are used, 38.3 μV, if 4 lines, 44.2 μV, if 5 lines, 49.5 μV.

  Therefore, in the audio signal adding apparatus 1 according to the embodiment of the present invention, when the microphone plug 1000 is not inserted, the gain of the amplifier circuit in the input stage 10 is reduced from (R1 + R2) / R1 times to 1 time. Therefore, the more input terminals into which the microphone plug 1000 is not inserted, the more the output noise level Vn can be reduced and the S / N ratio of the audio signal can be improved. In addition, since such a configuration can be realized by a mechanical structure, it can be realized at a low cost.

  As mentioned above, although embodiment of this invention was described, this invention can be implemented in various aspects as follows.

<Modification 1>
In the above-described embodiment, the ground resistor R1 is configured not to be grounded in the input stage where the microphone plug 1000 is not inserted. However, between the inverting input terminal of the operational amplifier and the ground resistor R1. May be configured to be cut. In this case, for example, the ground resistor R1 may be provided between the portion where the switch electrode 104 and the switch electrode 105 are in contact with the ground terminal.

<Modification 2>
In the embodiment described above, in the input stage where the microphone plug 1000 is not inserted, the ground resistor R1 is not grounded, so that the resistance value of the ground resistor R1 is substantially infinite. In this state, the gain of the amplifier circuit is reduced to 1 time. On the other hand, if the gain of the amplifier circuit is reduced by increasing the resistance value of the grounding resistor R1, the output noise level Vn can be reduced, so that the microphone plug 1000 is inserted. In the absence, the resistance value of the grounding resistor R1 may be changed.

  In this case, when the switch electrode 104 and the switch electrode 105 are not in contact with each other, the switch electrode 105 may be electrically connected to the other end of the resistor whose one end is grounded.

<Modification 3>
In the embodiment described above, the determination as to whether or not the microphone plug 1000 is inserted and the reduction of the gain of the amplifier circuit are performed with a mechanical configuration, but the configuration is not limited to such a configuration and is shown in FIG. The audio signal adding device 1a having such a configuration may be used. The configuration shown in FIG. 3 will be described below. FIG. 3 is an explanatory diagram showing the configuration of the audio signal adding device 1a according to this modification.

  The input unit 100a is inserted with a microphone plug 1000 and outputs an audio signal supplied from the chip to the variable amplifier circuit 202a. The input unit 100a is provided with detection means for detecting whether or not a microphone plug 1000 is inserted. For example, the detection unit may detect whether the input unit 100 in the embodiment is electrically connected to the terminal T4 and the terminal T5, or may be detected based on a signal level of an optical sensor, a pressure sensor, an audio signal, or the like. Good.

  The variable amplifier circuit 202a amplifies the input audio signal with a set gain and outputs the amplified audio signal to the adder 50a. The gain setting is controlled by the determination unit 110a. The determination unit 110a determines whether or not the microphone plug 1000 is inserted from the detection result of the detection means, and controls the gain of the variable amplifier circuit 202a based on the determination result. Specifically, when the determination unit 110a determines that the microphone plug 1000 is not inserted, the determination unit 110a performs control so as to reduce the gain set in the variable amplifier circuit 202a, compared to the determination that the microphone plug 1000 is inserted. To do. In this way, the gain of the variable amplifier circuit 202a can be reduced when the microphone plug 1000 is not inserted. Note that the gain set in the variable amplifier circuit 202a when the microphone plug 1000 is inserted may be changeable by an operator (not shown).

<Modification 4>
The audio signal addition device 1 in the above-described embodiment can be used by being incorporated in various devices, and is preferably used for, for example, a mixer, an amplifier, or the like.

It is explanatory drawing which shows the structure of the audio signal addition apparatus which concerns on embodiment. It is explanatory drawing which shows the structure of the input part which concerns on embodiment. It is explanatory drawing which shows the structure of the audio signal addition apparatus which concerns on the modification 3. It is explanatory drawing which shows the structure of the audio signal addition apparatus which concerns on a prior art example.

Explanation of symbols

1, 1a, 1A... Audio signal adding device 10, 10-1, 10-2, ..., 10-n, 10a, 10a-1, 10a-2, ..., 10a-n, 10A, 10A -1, 10A-2,..., 10A-n ... input stage, 50, 50a, 50A ... adder, 100, 100a, 100A ... input unit, 101, 101A ... insertion port, 102, 102A ... electrode, 103 , 103A, 104, 105 ... switch electrode, 104a ... insulator, 110a ... determination unit, 200A ... first stage amplifier, 201 ... op amp, 202a ... variable amplifier circuit, 1000 ... plug

Claims (2)

A plurality of input terminals to which supply terminals for supplying audio signals are connected;
Amplifying means provided corresponding to each of the plurality of input terminals, the operational amplifier, a ground resistor provided between the inverting input terminal of the operational amplifier and the ground terminal, and the output terminal of the operational amplifier and the inverting input A plurality of amplifying means for amplifying the audio signals supplied to the plurality of input terminals with a preset gain by a non-inverting amplifier circuit having a feedback resistor provided between the terminals ;
Adding means for adding each of the audio signals amplified by the plurality of amplifying means;
By the supply terminal increases the resistance value between the connection is set the gain to the amplifier means corresponding to the not do when Kino input terminal and the inverting input terminal the ground terminal, the gain reducing means for reducing Because
A first switch provided between the ground terminal and the ground resistor;
When the supply terminal is connected to the input terminal, an electrode that contacts the supply terminal and inputs an output signal from the supply terminal to the non-inverting input terminal of the operational amplifier;
A second switch for conducting the electrode to a ground terminal when the electrode is not in contact with the supply terminal;
The electrode is sandwiched between the first switch and the second switch so that the first switch is disconnected and the second switch is turned on when the supply terminal is not connected to the input terminal. When the supply terminal is connected to the input terminal, it is pushed by the supply terminal to move closer to the first switch and move away from the second switch, An audio signal adding device comprising: a gain reducing unit that moves the first switch through to make the first switch conductive and disconnects the second switch . In the gain reduction means, when the first switch is in a disconnected state, the switch electrode on the ground resistance side of the first switch is a resistor having a resistance value larger than the ground resistance and one end is grounded. The audio signal adding device according to claim 1, wherein the audio signal adding device is electrically connected to the other end of the resistor .

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