JP2001196867A - Audio signal input circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve a problem that a conventional digital mixer with an insertion jack has had difficulty of preventing the S/N from being deteriorated for the adjustment of a signal level when an effecter is connected or not through the plugging a plug to the jack. SOLUTION: A 2nd amplifier 20 is connected to a microphone terminal 1 via a 1st amplifier 2. An operational amplifier is adopted for the 2nd amplifier 20. When a plug 8 is not plugged into a jack 3a, an output of the 2nd amplifier 20 is fed to an LPF 5 while bypassing an attenuation circuit 4 by using a terminal 22 of the jack 3a. When the plug 8 is plugged into the jack 3a, the plug 8 separates terminals 21, 22 to cut off a bypass circuit. Thus, the attenuation circuit 4 to attenuate an output level of the effecter 9 can easily by removed from a signal transmission line when the plug is not plugged in.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an audio signal input circuit suitable for a digital audio mixer having an insertion jack for selectively connecting an external circuit such as an effector.

[0002]

2. Description of the Related Art As shown in FIG. 1, a conventional digital audio mixer comprises a microphone input connector 1;
A microphone amplifier 2, an insertion jack 3,
It comprises an attenuation circuit 4, a low-pass filter or LPF 5, an analog-to-digital converter or ADC 6, and a digital signal processing circuit for a mixer or DSP 7. A microphone is connected to the microphone input connector 1 to input an audio signal. Microphone amplifier 2 connected to connector 1
Amplifies the input audio signal. The microphone amplifier 2 has a variable resistor 2a for gain adjustment. Therefore, the gain of the microphone amplifier 2 can be arbitrarily adjusted.

An insertion jack 3 provided at the output stage of the microphone amplifier 2 is for selectively connecting an effector 9 as an external circuit by inserting a plug 8 here. An auxiliary terminal 11 consisting of a fixed contact which comes into contact with the first chip terminal 10 when the plug 8 is not inserted and comes into non-contact with the first chip terminal 10 when the plug 8 is inserted;
It comprises a second chip terminal 12 made of a contact spring and a sleeve terminal 13. The first and second chip terminals 1
0 and 12 can also be referred to as first and second plug connection terminals. When the plug 8 is not inserted, the first chip terminal 10 is in contact with the auxiliary terminal 11. Plug 8
Is inserted into the jack 3, the first terminal 8 of the plug 8
a contacts the first chip terminal 10 of the jack 3, and the second terminal 8 b of the plug 8 contacts the second chip terminal 12 of the jack 3. At this time, the first chip terminal 10 of the jack 3 is separated from the auxiliary terminal 11. Accordingly, when the chip 8 is inserted, the microphone amplifier 2, the first chip terminal 10, the first terminal 8a, the effector 9, the second terminal 8b, the second chip terminal 12, the attenuation circuit 4, the LPF
5, a circuit of the ADC 6 and the DSP 7 is formed.

[0004] The effector 9 is a well-known circuit for applying an effect process such as reverb, chorus, etc. to an audio signal. The output reference level of the effector 9 in this example is +4
dBu.

[0005] The attenuation circuit 4 connected to the auxiliary terminal 11 and the second chip terminal 12 of the jack 3 comprises resistors R3 and R4. When the effector 9 is connected, the attenuating circuit 4 reduces the output level of the effector 9 of +4 dBu to the input reference level of the ADC 6, which is lower than this, about -13 dBu. That is, the attenuating circuit 4 attenuates the output reference level +4 dBu of the effector 9 by 17 dB to make the input reference level of the ADC 6 -13 dBu. Note that the dBu is 0.776 Vrms at 0 dBu.
Is a well-known unit.

The ADC 6 connected to the attenuation circuit 4 via the LPF 5 for noise removal converts an audio signal into a digital signal and supplies the digital signal to a DSP 7 as a digital mixer.

[0007]

In FIG. 1, the attenuation circuit 4 provided in consideration of the insertion of the effector 9 is provided.
Since the connection is made even when the effector 9 is not inserted, the microphone amplifier 2 is connected when the effector 9 is not inserted.
Therefore, it is necessary to further amplify the gain which is originally required by +17 dB. For example, in consideration of amplifying a microphone input of −60 dBu when the effector 9 is not inserted, the gain of the microphone amplifier 2 is 47 dB in order to match the input reference level of −13 dBu of the ADC 6 as is clear from FIG. Although good, in consideration of the insertion of the effector 9, the microphone amplifier 2 amplifies the signal by 64 dB to +4 dBu, and then attenuates the signal to -13 dBu by the attenuation circuit 4. When the microphone amplifier 2 is configured to amplify the signal by 64 dB, the SN ratio is deteriorated. In general, it is desirable to amplify the signal by about 40 to 50 dB by the microphone amplifier 2. If the signal is amplified to 64 dB at once, distortion increases, which is not desirable for audio signals.

An object of the present invention is to provide an audio signal input circuit capable of performing a good gain adjustment.

[0009]

SUMMARY OF THE INVENTION In order to solve the above problems and to achieve the above object, the present invention provides a first amplifier for amplifying an audio signal and a second amplifier connected to the first amplifier. And a first plug connection terminal for connecting the second amplifier to a terminal on the input side of the plug, and an output side of the plug for receiving a plug connected to an external circuit. A jack having a second plug connection terminal for connecting to the first terminal and at least one auxiliary terminal interlocked with the insertion of the plug, and an attenuation connected to the second plug connection terminal of the jack. Wherein the auxiliary terminal outputs the output of the second amplifier without attenuation by the attenuation circuit when the plug is in a non-inserted state with respect to the jack; When the plug is in the inserted state, the output of the external circuit inserted through the jack to the output stage of the second amplifier is output with the attenuation of the attenuation circuit. The present invention relates to an audio signal input circuit characterized in that:

A gain setting circuit for the second amplifier is provided so that the gain can be set without inserting a plug.
It is desirable to switch according to insertion. Claim 3
As shown in FIGS. 10 and 10, only the first amplifier can be used when the plug is not inserted, and the first and second amplifiers can be used when the plug is inserted. It is desirable that the damping circuit be a voltage dividing circuit of two resistors R3 and R4. Further, it is desirable to provide first and second auxiliary terminals 22 and 23 as auxiliary terminals of the jack. Further, a third gain setting resistor R5 can be provided for gain switching. Claims 7 and 9
As shown in (1), a short-circuit protection resistor and a coupling capacitor can be provided. As shown in claim 8, first, second, third and fourth auxiliary terminals 32, 33, 3 as auxiliary terminals.
5, 36 can be provided.

[0011]

According to the present invention, the attenuation operation by the attenuation circuit does not occur when the plug is not inserted, so that the gain of the first and second amplifiers or the first amplifier is not changed when the plug is not inserted. It is no longer necessary to significantly increase
It is possible to improve the ratio and the waveform distortion. Further, even if the external circuit requires a high level when the plug is inserted, the signal is amplified by the two amplifiers, so that it is not necessary to greatly increase the gain of one amplifier, which is advantageous in terms of the SN ratio and distortion. . According to the second aspect of the present invention, the gain of the second amplifier is switched in conjunction with the insertion of the plug, so that the optimum gain can be easily obtained. According to the fifth to tenth aspects of the present invention, since the switching of the gain and the switching of the operation of the attenuation circuit are performed using the auxiliary terminal of the jack, this can be easily achieved with a simple configuration. According to the seventh and eighth aspects of the present invention, short-circuit protection and DC removal can be performed.

[0012]

Embodiments and Examples Next, embodiments and examples of the present invention will be described with reference to FIGS. However, in FIGS. 3 to 9, substantially the same parts as those in FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted. 3 to 9, the same parts are denoted by the same reference numerals, and will be described in detail on one side, and detailed description on the other side will be omitted.

[0013]

First Embodiment A digital audio mixer according to a first embodiment shown in FIG. 3 has a microphone input connector 1, a first amplifier 2 as a microphone amplifier, an attenuation circuit 4, an LPF 5, an ADC 6 as in FIG. , DSP 7, plug 8 and effector 9 as well as an improved insertion
It has a jack 3a, a second amplifier 20, and gain setting resistors R1 and R2. In FIG. 3, the microphone connector 1 to the LPF 5 function as an audio signal input circuit of the ADC 6.

The insertion jack 3a includes a first chip terminal 21 made of a contact spring, a first auxiliary terminal 22 made of a fixed contact selectively contacting the first chip terminal 21, and a fixed contact. Second auxiliary terminal 23
, A second chip terminal 24 made of a contact spring, and a sleeve terminal 25 connected to the ground. The first chip terminal 21 is connected to the second amplifier 20, and the first auxiliary terminal 22 is connected to the interconnection point 26 of the resistors R3 and R4 of the attenuation circuit 4 to form a bypass, and the second auxiliary terminal 22 is connected to the second amplifier 20. The terminal 23 is connected to the negative input terminal of the second amplifier 20,
The second chip terminal 24 is connected to the resistor R3. Note that the first and second chip terminals 21 and 24 can also be referred to as first and second connector connection terminals. When the plug 8 is not inserted into the jack 3a, as shown in FIG. 3, the first chip terminal 21 contacts the first auxiliary terminal 22 for forming a bypass, and the second chip terminal 24 is connected to the second auxiliary terminal 22. It contacts the terminal 23. When the plug 8 is inserted into the jack 3a, the first chip terminal 21
, And the second chip terminal 24 is connected to the plug 8.
, And the first and second chip terminals 21 and 24 are separated from the first and second auxiliary terminals 22 and 23. The sleeve terminal 25 is connected to the ground terminal 8c of the plug 8.

The second amplifier 20 composed of a differential amplifier, ie, an operational amplifier, can also be called a gain adjustment amplifier. This positive input terminal is connected to the output terminal of the microphone amplifier, ie, the first amplifier 2. . Therefore, the second amplifier 20 functions as a non-inverting amplifier. To configure the gain setting circuit of the second amplifier 20, a first resistor R1 is connected between the negative input terminal of the second amplifier 20 and the ground.
Is connected, and a second resistor R2 for feedback is connected between the output terminal and the negative input terminal of the second amplifier 20. The third resistor R3 of the attenuation circuit 4 is used for adjusting the gain of the second amplifier 20. Therefore, the second auxiliary terminal 23 can be called a gain switching terminal. The fourth resistor R4 of the attenuation circuit 4 is connected between the interconnection point 26 and the ground. LPF 5 is connected to interconnection point 26.

As shown in FIG. 3, the plug 8 is a jack 3a.
Is not inserted into the second amplifier 20, the output terminal of the second amplifier 20 is connected to the first chip terminal 21, the first auxiliary terminal 22 for bypass formation, the interconnection point 26, and the ADF via the LPF 5.
Connected to C6. The third resistor R3 is a circuit composed of a first chip terminal 21, a first auxiliary terminal 22, a third resistor R3, a second chip terminal 24, and a second auxiliary terminal 23 for gain switching. 2 connected in parallel to two resistors R2. Therefore, the gain of the second amplifier 20 is [(R2 R
3) / {R1 (R2 + R3)}] + 1. Since the output of the second amplifier 20 having such a gain is directly supplied to the LPF 5 via the interconnection point 26, no attenuation operation occurs in the attenuation circuit 4. As a result, in order to set the input signal level of −60 dBu supplied from the microphone connector 1 to the input reference level of −13 dBu of the ADC 6, both the first amplifier 2 and the second amplifier 20 require 47 dB.
What is necessary is just to amplify by dB. For this reason, the gain of the first and second amplifiers 2 and 20 can be significantly reduced compared to the conventional 64 dB, so that the SN ratio and the waveform can be improved.

In FIG. 3, when the plug 8 is inserted into the jack 3a, the first chip terminal 21
, And the second chip terminal 24 is connected to the second terminal 8 b of the plug 8. At the same time,
The first and second chip terminals 21 and 24 are separated from the first and second auxiliary terminals 22 and 23, and the third resistor R3 of the attenuation circuit 4 is disconnected from the second amplifier 20. As a result, when the plug 8 is inserted into the jack 3a, as shown in FIG.
, The bypass of the attenuation circuit 4 is cut off, and the gain of the second amplifier 20 is switched. That is, in FIG. 4, the first amplifier 2, the second amplifier 20, the first chip terminal 21, the first terminal 8a of the plug 8, the effector 9, the second terminal 8b of the plug 8,
A circuit composed of the chip terminal 24, the attenuation circuit 4, the LPF 5, the ADC 6, and the DSP 7 is established, and the attenuation circuit 4 operates effectively similarly to the attenuation circuit 4 of FIG.

When the plug is inserted, the gain of the second amplifier 20 is (R2 / R1) +1. Also, the attenuation circuit 4
Is R4 / (R3 + R4), and 17d
B is set to be attenuated. In this embodiment, the amplification factor of the first amplifier 2 as a microphone amplifier is set to a maximum of 45 dB. When the plug 8 is not inserted into the jack 3a, the gain of the second amplifier 20 as the gain adjusting amplifier is set to 6 dB, and when the plug 8 is inserted into the jack 3a, the gain is set to 20 dB. Have been. Accordingly, by setting the amplification factor of the first amplifier 2 to 44 dB when the plug 8 is inserted, the total amplification factor of the first and second amplifiers 2 and 20 becomes 64 dB, which is − 6
The input signal at the level of 0 dBu can be amplified by the first and second amplifiers 2 and 20 to the signal of the level of +4 dBu required by the effector 9. Also, plug 8
Is not inserted into the jack, the first amplifier 2
Is adjusted to 41 dB, and the first and second gains are adjusted.
By setting the total gain of the amplifiers 2 and 20 to 47 dB, the input signal of the level of −60 dBu can be set to the input reference level of the ADC 6 of −13 dBu.

As is apparent from the above description, according to the present embodiment, the second terminal is formed by using the auxiliary terminals 22 and 23 of the jack 3a.
The switching of the gain of the amplifier 20 and the switching of the attenuation operation of the attenuation circuit 4 are performed. When the plug 8 is not inserted, the attenuation by the attenuation circuit 4 is stopped, and the first and second amplifiers 2 and 20 having a relatively low gain are used. Since the signal level (-13 dBu) required by the ADC 6 is obtained, the SN ratio and the waveform distortion are improved. Further, even when the plug 8 is inserted, the first and second amplifiers 2 and 20 amplify 64 dB in total without performing 64 dB amplification with one amplifier.
Can be obtained in a state with little distortion. The auxiliary terminal 2 of the jack 3a
Since the switching of the gain of the amplifier 20 and the switching of the attenuation circuit 4 are performed using the switches 2 and 23, these switchings can be easily performed. That is, since the gain is automatically switched by inserting and removing the plug 8, the operation of switching the gain by the variable resistor 2a becomes unnecessary. Switching between gain and attenuation is performed by the auxiliary terminal 22 of the jack 3a,
23, the switching can be performed with a simple configuration. Note that, in addition to the first and second chip terminals 21 and 24, the first and second auxiliary terminals 22, 2
The provision of 3 is easily achieved by a well-known jack configuration in which each terminal 21 to 25 is supported by an insulator. Further, since the resistor R3 of the attenuation circuit 4 is also used as the feedback resistor of the second amplifier 20, the circuit configuration can be simplified.

[0020]

Second Embodiment An audio mixer according to a second embodiment shown in FIG. 5 is constructed by adding fifth and sixth resistors R5 and R5 to the circuit shown in FIG.
R6 and first and second coupling capacitors C1 and C2 each composed of an electrolytic capacitor are added, and the other components are the same as those shown in FIG.

In FIG. 5, a fifth resistor R5 as a third gain setting resistor is connected between the negative input terminal of the second amplifier 20 and the second auxiliary terminal 23 of the jack 3a. First coupling capacitor C connected in series with each other
The first and sixth resistors R6 are connected between the output terminal of the second amplifier 20 and the first chip terminal 21. The second coupling capacitor C2 is connected between the interconnection point 26 of the third and fourth resistors R3 and R4, that is, between the output terminal of the attenuation circuit 4 and the LPF 5. The fifth resistor R5 contributes to the gain setting of the second amplifier 20, the sixth resistor R6 contributes to preventing the output stage of the second operational amplifier 20 from being short-circuited, and the first and second coupling capacitors C1 and C2. Contributes to DC component removal.

As an example of the circuit constant of each part in FIG.
Is 10 kΩ, R2 is 150 kΩ, R3 is 9.1 kΩ, R
4 is 1.5 kΩ, R5 is 3.9 kΩ, R6 is 100Ω,
C1 and C2 are each 10 μF.

In FIG. 5, when the plug 8 is not inserted into the jack 3a, a series circuit of a third resistor R3, a fifth resistor R5, and a sixth resistor R6 is provided for the second resistor R2. They are connected in parallel via a coupling capacitor C1.
Therefore, the gain of the second amplifier 20 is a value obtained by replacing R3 in the gain equation in the circuit of FIG. 3 with R3 + R5 + R6. In FIG. 5, when the plug 8 is inserted into the jack 3a, the first and second chip terminals 21, 24 are separated from the first and second auxiliary terminals 22, 23, so that the fifth resistor R5 is connected to the second resistor R5. It is disconnected from the amplifier 20. The audio mixer of FIG. 5 has the same effect as that of the first embodiment in addition to the effect of short-circuit protection by the sixth resistor R6 and the effect of improving the degree of freedom in gain adjustment by the fifth resistor R5. .

[0024]

Third Embodiment An audio mixer according to a third embodiment shown in FIG. 6 is obtained by transforming the jack 3a of the mixer of the first embodiment shown in FIG. 3 into a completely independent jack 3b. Others are substantially the same as those in FIG.

The jack 3b shown in FIG. 6 includes a first chip terminal 31 composed of a metal contact spring, a first auxiliary terminal 32 composed of fixed contacts for gain switching, and a first chip terminal 31 when the plug 8 is inserted. Insulating protrusion 3 pressed by
3a made of a metal spring having a tip at its tip.
When the plug 8 is not inserted, the second auxiliary terminal 33 is in contact with the first auxiliary terminal 32, is separated from the first auxiliary terminal 32 when the plug 8 is inserted, and the second chip terminal 3 made of a metal contact spring.
4, a third auxiliary terminal 35 for forming a bypass formed of a fixed contact, and a metal spring having at its tip an insulating protrusion 36a pressed by the second chip terminal 34 when the plug 8 is inserted. When the plug 8 is not inserted, the third auxiliary terminal 35 contacts the third auxiliary terminal 35 and is separated from the third auxiliary terminal 35 at the place where the plug 8 is inserted, and the sleeve terminal 37 connected to the ground. Become. Note that each terminal 3
1 to 37 are supported by an insulator similarly to a well-known jack.

The first chip terminal 31 is connected to the output terminal of the second operational amplifier 20. Second auxiliary terminal 33
Is connected to the negative input terminal of the second operational amplifier 20 via the fifth resistor R5. The first auxiliary terminal 32 is connected to the output terminal of the second amplifier 20. The second chip terminal 34 is connected to the third resistor R3 of the attenuation circuit 4. The fourth auxiliary terminal 36 bypasses the attenuation circuit 4 and
Connected to PF5. The third auxiliary terminal 35 is connected to the output terminal of the second amplifier 20. Note that the first and second auxiliary terminals 32 and 33 are gain switching terminals,
The fourth auxiliary terminals 35 and 36 can also be referred to as bypass forming terminals.

In FIG. 6, when the plug 8 is not inserted into the jack 3b, the circuit of FIG. 6 is established, and the fifth resistor R5 is connected in parallel with the second resistor R2. Second amplifier 20
Output terminals are a third auxiliary terminal 35 and a fourth auxiliary terminal 36.
Is connected to the LPF 5 via the. As a result, the gain of the second amplifier 20 is [(R2 R5) / {R1 (R2 + R5)}] + 1. Further, the formation of the bypass (side path) by the third and fourth auxiliary terminals 35 and 36 makes the attenuation circuit 4 independent of signal transmission. Therefore, when the plug 8 is not inserted, the second
The gain of the amplifier 20 can be set independently of the attenuation circuit 4, and the degree of freedom in this setting is increased.

When the plug 8 is inserted in the circuit of FIG. 6, the first terminal 8a of the plug 8 contacts and presses the first chip terminal 31 of the jack 3b, and at the same time, the second terminal
Contacts the second chip terminal 34 and presses it. As a result, the second and fourth auxiliary terminals 33, 3
6 is pressed by the first and second chip terminals 31, 34,
It is separated from the first and third auxiliary terminals 32 and 35. Thereby, as shown in FIG. 7, the second amplifier 20, the first chip terminal 31, the first terminal 8a, the effector 9, the second terminal 8b, the second chip terminal 34, the attenuation circuit 4, the LPF
5, a circuit of the ADC 6 and the DSP 7 is formed. When the plug is inserted, the gain of the amplifier 20 is switched by the separation of the first and second auxiliary terminals 32 and 33, and (R2
/ R1) +1. In addition, the third and fourth auxiliary terminals 3
By the separation of 5, 36, the bypass is released or cut off,
The damping circuit 4 functions effectively, and this damping rate is R4 / (R3
+ R4).

The third embodiment has the same effect as the first embodiment, and also has an effect that the degree of freedom in gain setting is high.

[0030]

Fourth Embodiment An audio mixer according to a fourth embodiment shown in FIG. 8 includes a sixth resistor R in the circuit shown in FIG.
6, except that the first and second coupling capacitors C1 and C2 are added. In FIG. 8, a series circuit of the first coupling capacitor C1 and the sixth resistor R6 is connected between the output terminal of the second amplifier 20 and the first chip terminal 31. The second coupling capacitor C2 is connected between the attenuation circuit 4 and the LPF 5.
The sixth resistor R6 contributes to the prevention of short circuit similarly to the circuit of FIG. 5, and the first and second coupling capacitors contribute to the elimination of the DC component.

As an example of the constant of each part in FIG.
0 kΩ, R2 is 150 kΩ, R3 is 18 kΩ, and R4 is 3 kΩ.
kΩ, R5 is 13 kΩ, R6 is 100Ω, C1 and C2
Is 10 μF. In the circuit of FIG. 8, when the plug 8 is not inserted, the sixth resistor R6 is disconnected from the second amplifier 20, so that the gain becomes completely irrelevant.

[0032]

Fifth Embodiment An audio mixer according to a fifth embodiment shown in FIG. 9 corresponds to a modification of the mixer according to the third embodiment shown in FIG. Of the amplifier 20 is not inserted into the signal transmission path. The jack 3c in FIG. 9 is obtained by omitting the third and fourth auxiliary terminals 35 and 36 from the jack 3b in FIG.
Other than the above, it has first and second chip terminals 31 and 34, which operate in the same manner as the jack 3b of FIG. 6, first and second auxiliary terminals 32 and 33 for forming a bypass, and a sleeve terminal 37. 9, the first chip terminal 31 is connected to the second amplifier 20, and the second auxiliary terminal 33 is connected to the LPF5.
, The first auxiliary terminal 32 is connected to the first amplifier 2, and the second chip terminal 34 is connected to the attenuation circuit 4. A plug 8 has an effector 9 connected to this jack 3c.
Is inserted with When the plug 8 is inserted into the jack 3c, the first and second terminals 8a, 8b of the plug 8 come into contact with the first and second chip terminals 31, 34, and the second auxiliary terminal 33 becomes the first auxiliary terminal 33. And the bypass is cut off at the same time as the effector 9 is inserted.

In FIG. 9, when the plug is not inserted, the first
Amplifier 2, bypass first auxiliary terminal 32, bypass second auxiliary terminal 33, LPF5, ADC6, DS
The circuit of P7 is formed. This circuit is the second amplifier 20
And a circuit unrelated to the attenuation circuit 4. Therefore, -60d
ADC 13 requires Bu input signal level of -13 dB
To make the level u, the signal level is increased by 47 dB by the first amplifier 2.

When the plug is inserted, the second auxiliary terminal 33 for bypass is separated from the first auxiliary terminal 32, the bypass is cut off, and the first amplifier 2, the second amplifier 20 and the first
, A first terminal 8a of the plug 8, an effector 9, a second terminal 8b, a second chip terminal 34, an attenuation circuit 4, an LPF 5, an ADC 6, and a DSP 7 are formed. In this case, the gain of the first amplifier 2 is 47 dB, which is the same as when the plug is not inserted, and the gain of the second amplifier 20 is 17 dB. As a result, the input signal at the level of −60 dBu can be increased by 64 dB by the first and second amplifiers 2 and 20 to +4 dBu required by the effector 9.

The embodiment shown in FIG. 9 has the same effect as the third embodiment, and furthermore, the gain when the plug is not inserted can be determined only by the first amplifier 2, and the gain adjustment becomes easy. Has an effect.

[0036]

[Sixth Embodiment] The audio / video converter of the sixth embodiment shown in FIG.
The mixer corresponds to a modification of a part of the mixer of the third embodiment of FIG. 6, and is configured so that the second amplifier 20 is not inserted into the signal transmission path when the plug 8 is not inserted. The jack 3d of FIG. 10 is obtained by omitting the first and second auxiliary terminals 32 and 33 from the jack 3b of FIG. 6, and the other is a first operation that operates similarly to the jack 3b of FIG.
And second chip terminals 31 and 34, third and fourth auxiliary terminals 35 and 36 for forming a bypass, and a sleeve terminal 37. The third and fourth auxiliary terminals 35, 3 in FIG.
6 has the same function as the first and second auxiliary terminals 32 and 33 in FIG. 6, and thus can be referred to as first and second auxiliary terminals. In FIG. 10, the first chip terminal 31 is connected to the second amplifier 20, and the fourth auxiliary terminal 36 is
The third auxiliary terminal 35 is connected to the first amplifier 2, and the second chip terminal 34 is connected to the attenuation circuit 4. A plug 8 is inserted into the jack 3d with an effector 9. Plug 8 is 3d jack
, The first and second terminals 8 a of the plug 8,
8b contacts the first and second chip terminals 31, 34,
Further, the fourth auxiliary terminal 36 is separated from the third auxiliary terminal 35, and the bypass is cut off at the same time when the effector 9 is inserted.

In FIG. 10, when the plug is not inserted, the first amplifier 2, the third auxiliary terminal 35 for bypass, the fourth auxiliary terminal 36 for bypass, the LPF 5, the ADC 6, the D
The circuit of SP7 is formed. This circuit is the second amplifier 2
0 and a circuit unrelated to the attenuation circuit 4. Therefore, -60
ADC 6 requests input signal level of dBu -13d
To achieve the Bu level, the first amplifier 2 increases the signal level by 47 dB.

When the plug is inserted, the fourth auxiliary terminal 36 for bypass is separated from the third auxiliary terminal 35, the bypass is cut off, and the first amplifier 2, the second amplifier 20, and the first
, A first terminal 8a of the plug 8, an effector 9, a second terminal 8b, a second chip terminal 34, an attenuation circuit 4, an LPF 5, an ADC 6, and a DSP 7 are formed. In this case, the gain of the first amplifier 2 is 47 dB, which is the same as when the plug is not inserted, and the gain of the second amplifier 20 is 17 dB. As a result, the input signal at the level of −60 dBu can be increased by 64 dB by the first and second amplifiers 2 and 20 to +4 dBu required by the effector 9.

The embodiment of FIG. 10 has the same effects as the third embodiment, and also determines the gain when the plug is not inserted by only the first amplifier 2 as in the fifth embodiment of FIG. This has the effect that gain adjustment is facilitated.

[0040]

[Modifications] The present invention is not limited to the above-described embodiment, and for example, the following modifications are possible. (1) An audio signal other than a microphone can be input. (2) The types of the jacks 3a to 3c and the plug 8 can be changed. (3) An external circuit other than the effector 9 can be inserted. (4) In FIG. 5, a circuit for connecting the first auxiliary terminal 22 and the second plug connection terminal 24 is provided.
Can be made independent of the gain setting of the second amplifier 20.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a conventional audio mixer.

FIG. 2 is a diagram showing a level of an input signal, a reference level of an effector, and a reference level of an ADC in the circuit of FIG. 1;

FIG. 3 is a block diagram showing an audio mixer of the first embodiment.

FIG. 4 is a block diagram showing an electric circuit when a plug of the mixer of FIG. 3 is inserted.

FIG. 5 is a block diagram illustrating an audio mixer according to a second embodiment.

FIG. 6 is a block diagram illustrating an audio mixer according to a third embodiment.

FIG. 7 is a block diagram showing an electric circuit when the plug of the mixer of FIG. 6 is inserted.

FIG. 8 is a block diagram illustrating an audio mixer according to a fourth embodiment.

FIG. 9 is a block diagram illustrating an audio mixer according to a fifth embodiment.

FIG. 10 is a block diagram illustrating an audio mixer according to a sixth embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Microphone connector 2 1st amplifier 3-3c jack 4 Attenuation circuit 5 LPF 6 ADC 7 DSP 8 Plug 9 Effector 20 2nd amplifier

Claims (10)

[Claims] A first amplifier for amplifying an audio signal; a second amplifier connected to the first amplifier; and a plug connected to an external circuit; A first plug connection terminal for connecting a second amplifier to an input terminal of the plug and a second plug connection terminal for connection to an output terminal of the plug are interlocked with insertion of the plug. A jack having at least one auxiliary terminal; and an attenuation circuit connected to the second plug connection terminal of the jack, wherein the auxiliary terminal does not have the plug inserted into the jack. When in the state, the second
The output of the amplifier is output without attenuation by the attenuation circuit, and when the plug is in the inserted state with respect to the jack, the output stage of the second amplifier is inserted through the jack. An audio signal input circuit formed so as to output an output of an external circuit with the attenuation of the attenuation circuit. 2. A first amplifier for amplifying an audio signal, a second amplifier connected to the first amplifier, and a plug connected to an external circuit, wherein the first amplifier receives a plug connected to an external circuit. A first plug connection terminal for connecting a second amplifier to an input terminal of the plug and a second plug connection terminal for connection to an output terminal of the plug are interlocked with insertion of the plug. A jack having at least one auxiliary terminal; an attenuation circuit connected to the second plug connection terminal of the jack; and a gain setting circuit of the second amplifier, wherein the auxiliary terminal includes: When the plug is not inserted into the jack, the gain setting circuit is connected to the second amplifier so that the gain of the second amplifier becomes a first value, and the second amplifier is connected to the second amplifier. The output of the form a bypass for transmitting not accompanied attenuation by the attenuating circuit,
The connection of the gain setting circuit to the second amplifier such that the gain of the second amplifier is a second value greater than the first value when the plug is in the inserted state with respect to the jack. And the output of the external circuit inserted into the output stage of the second amplifier via the jack is output with the attenuation of the attenuation circuit. An audio signal input circuit, characterized in that: 3. A first amplifier for amplifying an audio signal, a second amplifier connected to the first amplifier, and a plug connected to an external circuit, wherein the first amplifier receives a plug connected to an external circuit. A first plug connection terminal for connecting a second amplifier to an input terminal of the plug and a second plug connection terminal for connection to an output terminal of the plug are interlocked with insertion of the plug. A jack having at least one auxiliary terminal; and an attenuation circuit connected to the second plug connection terminal of the jack, wherein the plug is not inserted into the jack. When in the state, a bypass is formed for transmitting the output of the first amplifier without passing through the second amplifier and the attenuation circuit, and the plug is inserted into the jack. The case that an audio signal input circuit, characterized in that it is formed so as to release the bypass. 4. The damping circuit comprises a series circuit of first and second damping resistors (R3, R4), one end of the series circuit is connected to the second plug connection terminal, and The other end is connected to the ground, and is formed so as to obtain an attenuation output from an interconnection point (26) of the first and second attenuation resistors (R3, R4). 4. The audio signal input circuit according to 2 or 3. 5. The attenuation circuit comprises a series circuit of first and second attenuation resistors (R3, R4), one end of the series circuit is connected to the second plug connection terminal, and The other end is connected to the ground, and is formed so as to obtain an attenuation output from an interconnection point (26) of the first and second attenuation resistors (R3, R4). The second amplifier is an operational amplifier (20). And the positive input terminal of the operational amplifier (20) is connected to the first amplifier (1).
2), the output terminal of the operational amplifier (20) is connected to the first plug connection terminal (21), and the gain setting circuit connects first and second gain setting resistors (R1, R2). And the first damping resistor (R
3) is also used for gain setting, and the first gain setting resistor (R1) is connected to the operational amplifier (2).
0) and the ground, and the second gain setting resistor (R2) is connected to the operational amplifier (2).
0) and the negative input terminal, and a first and a second auxiliary terminal (22, 2) as the auxiliary terminal.
3), wherein the first auxiliary terminal (22) is connected to the interconnection point (26) of the attenuation circuit (4), and the first plug connection terminal (22) when the plug is not inserted. 21), and is formed so as to be in a non-contact state with the first plug connection terminal (21) when the plug is in the inserted state. The second auxiliary terminal (23) is provided with the operational amplifier (2).
0) and is in contact with the second plug connection terminal (24) when the plug is not inserted, and contacts the second plug connection terminal (2) when the plug is inserted.
The audio signal input circuit according to claim 2, wherein the audio signal input circuit is formed so as to be in a non-contact state with respect to (4). 6. A gain setting resistor (R5) connected between a negative input terminal of the operational amplifier (20) and the second auxiliary terminal (23). The audio signal input circuit according to claim 5. 7. A series connection of a first coupling capacitor (C1) and a short-circuit protection resistor (R6) between the output terminal of the operational amplifier (20) and the first plug connection terminal (21). A circuit is connected.
Or the audio signal input circuit according to 6. 8. The attenuation circuit comprises a series circuit of first and second attenuation resistors (R3, R4), one end of the series circuit is connected to the second plug connection terminal, and The other end is connected to the ground, and is formed so as to obtain an attenuation output from an interconnection point (26) of the first and second attenuation resistors (R3, R4). The second amplifier is an operational amplifier (20). A positive input terminal of the operational amplifier (20) is connected to the first amplifier (2), an output terminal of the operational amplifier (20) is connected to the first plug connection terminal (31), and the gain is The setting circuit has first, second and third gain setting resistors (R1, R2, R5), and the first gain setting resistor (R1) is connected to a negative input terminal of the operational amplifier (20) and ground. And the second gay A resistor for setting gain (R2) is connected between the output terminal of the operational amplifier (20) and the negative input terminal, and one end of the third resistor for setting gain (R5) is connected to the negative input of the operational amplifier (20). A first, second, third, and fourth auxiliary terminal (32, 33, 35, 36) as the auxiliary terminal, wherein the first auxiliary terminal (32) is connected to the operational amplifier (20). )
The second auxiliary terminal (33) is connected to the other end of the third gain setting resistor (R5) and the first auxiliary terminal (33) when the plug is not inserted. 32) is formed so as to be in contact with the first auxiliary terminal (32) when the plug is in the inserted state, and the third auxiliary terminal (35) is connected to the operational amplifier (20).
The fourth auxiliary terminal (36) is connected to the output side of the attenuation circuit (4), and contacts the third auxiliary terminal (35) when the plug is not inserted, 3. The audio signal input circuit according to claim 2, wherein the audio signal input circuit is formed so as not to be in contact with the third auxiliary terminal when the plug is inserted. 9. A series connection of a first coupling capacitor (C1) and a short-circuit protection resistor (R6) between an output terminal of the operational amplifier (20) and the first plug connection terminal (31). A circuit is connected, and a second coupling capacitor (C2) is connected to an interconnection point (26) of the first and second attenuation resistors (R3, R4), and the fourth auxiliary terminal (36) is connected. 9. The audio signal input circuit according to claim 8, wherein the signal is connected to an output side of the second coupling capacitor. 10. The attenuation circuit comprises a series circuit of first and second attenuation resistors (R3, R4), one end of the series circuit is connected to the second plug connection terminal, and The other end is connected to ground, and the first and second
The second amplifier is an operational amplifier (20), and a positive input terminal of the operational amplifier (20) is configured to obtain an attenuation output from an interconnection point (26) of the attenuation resistors (R3, R4). The first amplifier (2) is connected, the output terminal of the operational amplifier (20) is connected to the first plug connection terminal (31), and the gain setting circuit is provided with first and second gain setting resistors ( R1, R2), the first gain setting resistor (R1) is connected between a negative input terminal of the operational amplifier (20) and ground, and the second gain setting resistor (R2) A first and second auxiliary terminal (32 or 35, 33 or 36) connected as an auxiliary terminal between the output terminal of the operational amplifier (20) and the negative input terminal; Terminal (32 or 35) The second auxiliary terminal (33 or 36) is connected to the output side of the attenuation circuit (4) and is connected to the first auxiliary terminal (32) when the plug is not inserted. 4. The audio signal according to claim 3, wherein the audio signal is formed so as to be in contact with the first auxiliary terminal (32 or 35) when the plug is in the inserted state. Input circuit.