JPH11136060A - Sound volume control circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the deterioration of sound quality that is caused at a semiconductor switch part by deciding the sound volume according to the on/off actions of a semiconductor switch in a sound volume control mode and turning on a relay switch to bypass the semiconductor switch if the sound volume is not controlled for a prescribed time or longer. SOLUTION: The relay switches 61 to 63 are connected in parallel to the semiconductor switch of a gain switching circuit 53, e.g. between the collectors and emitters of transistors TR 54 to 56 and then turned on and off by a relay circuit 60 via the control signal that is sent from a controller 40. When the controller 40 decides that the position of a motor-driven volume 7 does not vary for a prescribed time, the switch 61 connected in parallel to the TR 54 that is currently turned on, for example, is turned off via the circuit 60. As a result, the TR 54 to which a signal is supplied is bypassed by the switch 61 and has no relation with a signal line.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a volume control circuit, and more particularly to a volume control circuit for controlling the volume of an audio signal.

[0002]

2. Description of the Related Art FIG. 5 is a circuit diagram of a power amplifier showing an example of a conventional volume control circuit. This power amplifier has a volume control function and a CD (compact disc)
Can be reproduced. In FIG. 5, 1 is a CD
CD reproducing means for reproducing a digital audio signal from a digital audio signal;
/ A conversion circuits 3 and 4 are first and second analog input terminals for inputting analog audio signals from an external analog audio source device, and 5 is an output of the D / A conversion circuit 2 and first and second analog inputs. A selector circuit for selecting a user-desired source from the inputs of the terminals 3 and 4, a loudness circuit 6 for increasing the reduction gain at the time of low volume with respect to the output of the selector circuit 5, and a loudness circuit 6 for output An electric volume control for adjusting the volume of an analog audio signal. For example, a variable resistor 8 that can continuously change the voltage division ratio by rotating a slider on a resistor formed in an arc shape is provided. doing. The slider is rotated by a motor controlled by a controller described later. Reference numeral 9 denotes a potentiometer that detects the volume position of the electric volume control 7 by detecting the rotational position of the slider. Reference numeral 100 denotes a power amplifier that amplifies the power of the analog audio signal whose volume has been adjusted by the electric volume control 7 and outputs the amplified signal to the speaker output terminal 11.

[0005] Reference numeral 12 denotes a changeover switch for selectively switching the output of the D / A conversion circuit 2 and the output of the electric volume control 7. Reference numeral 20 denotes a source / signal path selection operation, a variable volume operation, a loudness on / off operation, and a CD reproduction. PLAY ・
A key operation unit 40 for performing a STOP operation is a controller including a microcomputer or the like.
In accordance with the operation, the source selection control, the volume control, the loudness on / off control, the CD reproduction operation control, and the signal transmission path selection control of the CD reproduction output are performed.

In the power amplifier 100, reference numeral 51 denotes a differential amplifier, and the output of the changeover switch 12 is input to a + input terminal. A negative feedback signal formed by dividing the output of the differential amplifier 51 by a negative feedback circuit 52 is input to one input terminal of the differential amplifier 51. The negative feedback circuit 52 includes fixed resistors R1 and R2 connected in series between the output side of the differential amplifier 51 and the ground, and a gain switching circuit 53 connected in parallel to the resistor R2. Fixed resistors R1 and R2
Is connected to one input terminal of the differential amplifier 51.

The gain switching circuit 53 switches the plurality of switches to change the connection state of the plurality of fixed resistors, thereby changing the negative feedback rate and enabling the gain to be switched in a plurality of stages. Is a semiconductor switch 54 comprising a fixed resistor R3 and a transistor or the like.
Are connected in parallel with the resistor R2, the fixed resistor R4 and the semiconductor switch 55 are connected in series, and then the resistor R2 is connected.
2 and a fixed resistor R5 and a semiconductor switch 56.
Are connected in series and then connected in parallel with the resistor R2. The semiconductor switches 54, 55, and 56 are on / off controlled by a gain switching control signal from the controller 40.

When all of the semiconductor switches 54 to 56 are off, the power amplifier 100 has the minimum gain GMIN,
MIN = (R1 + R2) / R2. When all of the semiconductor switches 54 to 56 are turned on, R2 to R5 are in a parallel connection state, so that the gain is the maximum GMAX. When the semiconductor switches 54 and 55 are closed, R2 to R4 are in a parallel connection state. Decreases by g1 to G1,
When only the semiconductor switch 54 is turned on, R2 and R3 are connected in parallel, so that the gain further decreases by g2 to G2. When all of the semiconductor switches 54 to 56 are turned off, the gain further decreases by g3 to GMIN.
Here, it is assumed that R1 to R5 are set so that g1 = g2 = g3 = 20 dB.

The controller 40 performs CD playback operation control, source / signal path selection control, loudness on / off control, and volume control in accordance with key operations of the key operation unit 20. In the source / signal path selection control, when any one of the CD key 21, the C analog 1 key 22, and the analog 2 key 23 is pressed, the selector circuit 5 switches the CD, ANA,
1. The switch is switched to the corresponding position in the ANA 2, and the changeover switch 12 is switched to the b side so that the audio signal input to the power amplifier 10A passes through the path of the selector circuit 5, the loudness circuit 6, and the electric volume control 7. When the CD direct key 24 is pressed,
The changeover switch 12 is switched to the a side so that the output of the D / A conversion circuit 2 is directly input to the power amplifier 100 without passing through the paths of the selector circuit 5, the loudness circuit 6, and the electric volume control 7.

In the volume control, a volume up key 2
5. Every time the volume down key 26 is pressed, the volume is set by increasing or decreasing the volume data VD managed in the memory (not shown) in units of 1 dB in the range of 0 to -80 dB, and controlling the electric volume 7. Adjust the volume. When the changeover switch 12 is switched to the D / A conversion circuit 2 by pressing the CD direct key 24, the gain switching control for the gain switching circuit 53 and the variable attenuation control for the digital attenuator 50 are combined. And the power amplifier 100 has the maximum gain GMAX
0 dB with the minimum attenuation of the digital attenuator 50
With reference to the time, the signal level in the entire system is reduced just by the volume data VD, and the continuous volume control for the CD reproduction output is performed.

By the way, when the audio signal reproduced from the CD passes through the selector circuit 5, the loudness circuit 6, and the electric volume control 7, the S / N ratio is deteriorated. desirable.
Therefore, when the user presses the CD direct key 24, the controller 40 switches the changeover switch 12 to a side, and the signal path of the CD reproduction output is switched to the selector circuit 5,
CD bypassing the loudness circuit 6 and the electric volume control 7
The reproduction output is directly input to the power amplifier 100. Further, the digital attenuator 50 and the gain switching circuit 53 are controlled as a set to enable continuous volume adjustment.

When the changeover switch 12 is set to the "a" side, the controller 40 adjusts the gain of the power amplifier 100 and the digital attenuator 5 according to the volume change operation.
By variably controlling the attenuation amount of 0 appropriately,
The volume of the audio signal obtained from the CD reproducing means 1 having a built-in power amplifier can be continuously varied in units of 1 dB. Since high resistance is not included in the transmission system of the CD reproduction output, resistive noise does not increase, and the variable resistor 8
As described above, the noise does not increase due to the oxidation of the slider, so that a good S / N can be obtained. To reduce the volume, use power amplifier 1
By greatly reducing the gain of 00, the attenuation of the digital attenuator 50 does not need to be so large, and the resolution does not significantly deteriorate as in the case of adjusting the volume only with the digital attenuator 50.

[0011]

However, in the above circuit, the switching circuit for changing the combination of the fixed resistors of the gain switching circuit 53 relating to the volume adjustment is provided with transistors and the like in consideration of shock noise and switching speed. Semiconductor switches 54 to 56 have been used. However, if an active element such as a semiconductor switch is present at a location related to the signal line, the sound quality may be degraded.

It is an object of the present invention to provide a volume control circuit which can reduce sound quality deterioration.

[0013]

According to a first aspect of the present invention, there is provided a volume control circuit for controlling a volume by switching a combination of a plurality of fixed resistors by on / off control of at least one semiconductor switch. In a sound volume adjusting circuit having a sound volume adjusting unit, a relay switch connected in parallel to the at least one semiconductor switch, a judging means for judging whether or not the sound volume adjusting operation has been performed for a predetermined time or more, and a judgment result of the judging means. Control means for turning on the relay switch corresponding to the at least one semiconductor switch during the on-operation from off to on when the volume adjustment operation has not been performed for a predetermined time or more.

Thus, during the volume adjustment operation, the volume is determined according to the ON / OFF of the semiconductor switch. When the volume adjustment operation is not performed for a predetermined time or more, the relay switch is turned on to bypass the semiconductor switch. The sound quality deterioration due to is reduced.

According to a second aspect of the present invention, in the volume adjusting circuit according to the first aspect, the control means switches the relay switch when the volume adjusting operation is started. It is characterized by being turned off from on.

Thus, during the volume adjustment operation, since the relay switch is turned off, there is no influence on the volume adjustment.

[0017]

FIG. 1 is a circuit diagram of a power amplifier including a first embodiment of a volume control circuit according to the present invention.
In FIG. 1, the same components as those of the conventional circuit in FIG. In FIG. 1, the difference from the configuration of FIG.
3 semiconductor switches, for example, transistors 54 to 56
Are connected in parallel between C (collector) and E (emitter), and these switches are turned on / off by the relay circuit 60 by a control signal from the controller 40.

In the above configuration, the relay switch 61
3 to 63 operate according to the flowchart shown in FIG. 2, for example. That is, in FIG. 2, first, in step S1, the controller 40 determines whether or not the volume position of the electric volume control 7 has changed for a predetermined time (for example, several seconds). Is set so that among the transistors 54 to 56 in the gain switching circuit 53, a relay switch, for example, 61, which is connected in parallel with a transistor currently on, for example, 54, is turned on from off.
Switching control is performed via the relay circuit 60. Therefore, the transistor 54 to which a signal flows due to the ON operation
Is bypassed by the relay switch 61 and becomes irrelevant to the signal line, so that deterioration of sound quality is reduced.

Next, in S3, the controller 40 determines whether or not the volume position of the electric volume control 7 has been moved by the key operation of the volume up key 25 or the volume down key 26 of the key operation unit 20, and the answer is yes. If so, proceed to S4. In S4, the controller 40 controls the switching via the relay circuit 60 so that all the relay switches connected in parallel to the transistors 54 to 56 in the gain switching circuit 53 are turned off. For example, the relay switch 61 turned on from off in S2 described above turns off from on in S4.

As described above, at the time of volume adjustment, when the volume is fixed and the user listens to music, the relay switch is turned on and the effect of the semiconductor switch is eliminated, so that the sound quality is improved.

[0021]

FIG. 3 is a circuit diagram of a power amplifier including a second embodiment of the volume control circuit according to the present invention. In FIG. 3, the same components as those in FIG. 1 are denoted by the same reference numerals. First, the configuration of the power amplifier will be described. In FIG. 1, the gain of the power amplifier 10 can be changed stepwise, whereas in FIG. 3, the gain of the power amplifier is fixed and the analog attenuator 70
Is provided so that the amount of attenuation can be switched stepwise. 10A is a power amplifier having a fixed gain, 70 is an analog attenuator provided between the changeover switch 12 and the power amplifier 10A, and switches a plurality of semiconductor switches, for example, transistors 72 and 73, to connect a plurality of fixed resistors. Is changed, the voltage division ratio with respect to the output of the D / A conversion circuit 2 is changed, and the amount of attenuation can be switched to a plurality of stages. Here, for example, the amount of attenuation can be switched in four stages. Assuming that the variable step of the attenuation in the digital attenuator 50 is kdB and the variable width is (nk) dB (n is an integer), the attenuation switching width between the stages of the analog attenuator 60 is (nk) dB. .

Of the analog attenuator 70, R6 to R
Reference numeral 9 denotes a fixed resistor. The output side of the changeover switch 12 is connected to the terminal a of the switch 71, and is also connected to the terminal b via the fixed resistor R6. Switch 71
Is connected to the power amplifier 10A. A fixed resistor R7 is connected between the terminal b of the switch 71 and the ground. The fixed resistor R8 and the transistor 72 are connected in series and then connected in parallel with the fixed resistor R7. The fixed resistor R9 and the transistor 73 are connected in series and then connected in parallel with the fixed resistor R7. The transistors 72 and 73 are opened and closed by an attenuation amount switching control of the controller 40 described later. The connection state of the fixed resistors R6 to R9 is changed by switching between the open and closed states of the transistors 72 and 73, and the voltage division ratio (attenuation amount) to the output of the D / A conversion circuit 2 is changed.
Is switched step by step.

In the volume control, the controller 40 controls the volume control each time the volume up key 25 and the volume down key 26 are pressed.
Volume data VD managed by a memory not shown
Set the volume by increasing or decreasing by 1dB in the range of -80dB,
The electric volume 7 is controlled and adjusted to the set volume.
When the changeover switch 12 is switched to the D / A conversion circuit 2 due to the pressing of the CD direct key 24, the attenuation amount switching control for the analog attenuator 70 and the attenuation amount variable control for the digital attenuator 50 are combined. And the analog attenuator 70
Both the digital attenuator 50 and the digital attenuator 50 perform continuous volume control with respect to the CD reproduction output by lowering the signal level just by the volume data VD with reference to the time when the attenuation amount is the minimum of 0 dB. The other components are exactly the same as those in FIG.

The control process of the controller 40 in FIG. 3 is substantially the same as the process by the controller 40 in FIG. 1 except that instead of performing the gain switching control on the power amplifier 10, the analog attenuator 70 is attenuated. The only difference is that the amount switching control is not performed. If the power amplifier 10 shown in FIG.

Since the attenuation of the analog attenuator 70 is determined by the resistance ratio of the fixed resistors R6, R7, R8, R9, it is not necessary to use a high resistance. Therefore, the resistance noise can be reduced by using a fixed resistor R6 having a small resistance value. In the CD direct mode, a slider such as the variable resistor 8 of the electric volume control 7 on the signal transmission system can be used. Good S / N can be obtained because no noise increase due to oxidation occurs. Since the bit length of the digital audio signal output from the digital attenuator 50 is constant regardless of the amount of attenuation in the digital attenuator 50, the volume of 0 to -80 dB is obtained only by the attenuation in the digital attenuator 50 without using the analog attenuator 70. If an attempt is made to adjust the resolution, the resolution becomes poor at low volume and the quantization noise increases. However, since the attenuation in the digital attenuator 50 is within -20 dB, the resolution deteriorates even at low volume. Never.

Next, the volume control circuit of the present invention in FIG. 3 will be described in detail. In FIG. 3, relay switches 64 and 65 are connected in parallel between a semiconductor switch of an analog attenuator 70 related to volume adjustment, for example, between C (collector) and E (emitter) of transistors 72 and 73. Is turned on / off by the relay circuit 60 by the control signal of

In the above configuration, the relay switch 64
And 65 operate according to the flowchart shown in FIG. 2 as described with respect to FIG. That is, if the volume position of the electric volume control 7 has not changed for a predetermined time (for example, several seconds), the process proceeds to S2, and the controller 4
0 indicates that the relay circuit 60 is turned on from off to on, for example, a relay switch, for example 64, connected in parallel with the transistor currently on, for example 72, of the transistors 72 and 73 in the analog attenuator 70. The switching control is performed via. Therefore, the transistor 72 to which a signal flows due to the ON operation is bypassed by the relay switch 64 and becomes irrelevant to the signal line, so that deterioration of sound quality is reduced.

When the volume position of the electric volume control 7 moves, the relay circuit 6 is turned off so that all the relay switches connected in parallel to the transistors 72 and 73 in the analog attenuator 70 are turned off.
Switching control is performed via 0. For example, the relay switch 64 turned on from the off state as described above turns off from the on state here.

As described above, when the volume is adjusted and the volume position is determined and the user listens to music, the relay switch is turned on and the effect of the semiconductor switch is eliminated, so that the sound quality is improved.

Next, FIG. 4 is a circuit diagram of a power amplifier including a third embodiment of the volume control circuit according to the present invention. The configuration of the power amplifier of FIG. 4 is as follows. In the embodiment of FIG. 3 described above, the analog attenuator 70 is interposed between the changeover switch 12 and the power amplifier 10A. However, in FIG. 4, the D / A conversion circuit 2 and the changeover switch 1 are connected.
2 and can be made to function exactly as in the case of FIG. However, in the case of FIG. 4, the processing for returning the source / signal path selection mode from the CD direct mode to the other mode is performed by the controller 4.
It is only necessary to control the digital attenuator 50 to 0 dB, which is the minimum attenuation, so that the same volume is reproduced before and after switching the changeover switch 12 from a to b, and after switching to the b side, Maximum volume is 0
It is possible to increase to dB.

Further, since the volume control circuit of the present invention in FIG. 4 is completely the same as that in FIG. 3, detailed description thereof will be omitted. However, in FIG. In the listening state, the relay switch is turned on, so that the effect of the semiconductor switch is eliminated, and the sound quality is improved.

[0032]

According to the present invention, deterioration of sound quality due to a semiconductor switch can be reduced, and sound quality is improved.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a power amplifier including a first embodiment of a volume adjustment circuit according to the present invention.

FIG. 2 is a flowchart illustrating a volume adjustment operation in the figure.

FIG. 3 is a circuit diagram of a power amplifier including a second embodiment of the volume adjustment circuit according to the present invention.

FIG. 4 is a circuit diagram of a power amplifier including a third embodiment of the volume adjustment circuit according to the present invention.

FIG. 5 is a circuit diagram of a power amplifier including an example of a conventional volume control circuit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 CD reproduction means 2 D / A conversion circuit 3 1st analog input terminal 4 2nd analog input terminal 5 Selector circuit 6 Loudness circuit 7 Electric volume control 8 Variable resistor 9 Potentiometer 10A Power amplifier 12 Changeover switch 20 Key operation part 40 Controller 50 Digital attenuator 54 Semiconductor switch 55 Semiconductor switch 56 Semiconductor switch 60 Relay circuit 61 Relay switch 62 Relay switch 63 Relay switch 64 Relay switch 65 Relay switch 70 Analog attenuator 72 Semiconductor switch 73 Semiconductor switch

Claims (2)

[Claims] 1. A volume control circuit having a volume control unit for controlling a volume by switching a combination of a plurality of fixed resistors by ON / OFF control of at least one semiconductor switch, wherein the relay is connected in parallel to the at least one semiconductor switch. A switch; a determining means for determining whether or not the volume adjustment operation has been performed for a predetermined time or more; if the volume adjustment operation has not been performed for a predetermined time or more based on the determination result of the determination means, Control means for turning on or off the relay switch corresponding to one of the semiconductor switches. 2. The volume control circuit according to claim 1, wherein
The control means turns off the relay switch from on to off when the volume adjustment operation is started.