JP2006304281A - Volume-adjusting device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a volume-adjusting device which can inhibit tone quality impairment in about 1/2 attenuation area, using a simple configuration. <P>SOLUTION: It provide a volume-adjusting device which can be suppressed with simple configuration for tone quality deterioration in 1/2 attenuation region. An input audio signal is decayed by a reducing transformer 11, and input into a variable resistor 13 via a change-over switch 12. In the variable resistor 13, a reduced audio signal which is input from the reducing transformer 11, is further attenuated. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

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

  An audio device inputs an audio signal of 2 Hz to 100 kHz (usually 20 Hz to 20 kHz) from a source device (for example, a recording medium for broadcasting, a CD including a super audio, a tape, etc.) as a signal source, and amplifies the preceding stage. A preamplifier to perform, a power amplifier (or main amplifier) that amplifies the audio signal amplified in the previous stage, and an electroacoustic device (for example, a speaker) that is driven by the power amplified audio signal. While also serving as a volume control device for controlling the amplification degree, a volume control device may be inserted next to the preamplifier.

  Conventionally, such a volume adjusting device is configured using a variable resistor, thereby adjusting the attenuation of the audio signal.

  FIG. 25 shows a conventional volume control device VC20 for audio equipment.

The volume control device VC20 includes an input terminal Ti of the audio signal from the source device SA or preamplifier PA is input, the potential to ground line G of the input terminal Ti, that is, the variable resistance of the potentiometer for dividing the input voltage e _IN a vessel 1, the potential to ground line G of the variable resistor 1 of the slider 1a, as an output voltage e _O, constructed and an output terminal to for outputting to the next stage of the main amplifier MA. Input voltage e _IN is divided by the voltage dividing resistors R1, R2 of the variable resistor 1, since the divided voltage _{e IN · R2 / (R1 +} R2) becomes the output voltage _{e O,} audio signal, the Minutes, attenuated, and corresponding volume adjustments are made.

  The output terminal To is connected to the control terminal of the amplification element constituting the main amplifier MA, for example, the grid terminal g of the three-station vacuum tube TR in FIG. 27, and its floating input capacitance, for example, the plate p and the grid g of the vacuum tube TR. And the capacitance Cpg between the grid g and the cathode k are superimposed. These capacitors Cpg and Cgk constitute an output impedance Zo of the variable resistor 1 and a low-pass filter to bring about an attenuation action in the high sound range. In particular, the capacitor Cpg is multiplied by the voltage gain of the amplifying element by the Miller effect. Therefore, the impact is great.

  If the voltage gain is A, the equivalent input capacitance Ci is Ci = Cgk + (A + 1) Cpg, and the cutoff frequency fc of the low-pass filter is fc = 1 / (2πZoCi). This means that the high cut-off frequency is the lowest when the attenuation ATT = 6 dB.

  FIG. 27 shows the relationship between the attenuation level ATT of the volume adjusting device VC20 and the output impedance Zo, and FIG. 28 shows the relationship between the attenuation level ATT of the volume adjusting device VC20 and the cutoff frequency fc of the high-frequency attenuation filter due to the stray capacitance Ci. .

  The voltage dividing resistors R1 and R2 of the variable resistor 1 have a constant sum and an inversely proportional product. Therefore, when R1 = R2, that is, when the attenuation ATT is ½ (= −6 dB), the output impedance Zo becomes the maximum, and as the attenuation ATT becomes far from ½ (= −6 dB), the impedance When Zo decreases and the maximum or minimum volume is reached, Zo becomes the minimum (0Ω).

  The output impedance Zo is low in the attenuation region close to the maximum volume or the minimum volume. However, in the vicinity of 1/2 attenuation, the output impedance Zo increases, and is formed by the parallel combined resistance of the voltage dividing resistors R1 and R2 and the stray capacitance from the output side of the volume adjusting device VC20 to the input side of the amplification element of the main amplifier MA. The cut-off frequency fc of the high-frequency attenuating filter is lowered, and when the audio signal passes there, the sound quality deteriorates.

Therefore, Patent Document 1 discloses a volume adjusting device using a step-down transformer instead of a variable resistor.
FIG. 26 shows a volume control device VC21 using a conventional step-down transformer 61. FIG. The same elements as those in FIG. 25 are denoted by the same reference numerals.

  In the volume adjusting device VC21, n step-down transformers 2 connected to an input terminal Ti are provided with n intermediate taps 2-1 to 2-n, and n switching contacts 3 connected one-to-one with these taps. By selecting an appropriate intermediate tap 2-i (i ≦ i ≦ n) using the selector switch 3 having −1 to 3-n, a signal attenuated according to the position of the tap 2-i is obtained. The signal is output from the output terminal To.

  Since the signal attenuation by the step-down transformer 2 is based on magnetic coupling, the sound volume adjustment device VC21 does not show any deterioration in sound quality in the vicinity of ½ attenuation.

  The volume adjusting device VC21 requires a number of intermediate taps 2-1 to 2-n satisfying the maximum attenuation width and a desired resolution, and a corresponding number of switch contacts 3-1 to 3-n. Becomes complicated. For example, in order to secure an attenuation width of 60 dB with a resolution of 2 dB, as many as 30 intermediate taps and switch contacts are required.

  The present invention has been made in view of the above points, and an object of the present invention is to provide a volume adjusting device capable of suppressing deterioration in sound quality in an attenuation region in the vicinity of ½ with a simple configuration.

  To achieve the above object, a volume control apparatus according to a first aspect of the present invention acquires a corresponding audio signal by selecting a transformer to which an audio signal is input from a signal source and an intermediate tap of the transformer. And a resistance attenuator for attenuating the audio signal input from the signal acquisition unit.

  To achieve the above object, a volume control device according to a second aspect of the present invention is the volume control device according to the first aspect, wherein the transformer attenuates an audio signal input from the signal source. The step-down transformer includes a plurality of intermediate taps having different attenuation degrees, and the signal acquisition unit selects the intermediate tap among the plurality of intermediate taps.

  To achieve the above object, a volume control device according to a third aspect of the present invention is the volume control device according to the first aspect, wherein the transformer is a winding to which an audio signal is input from the signal source. The intermediate tap is provided on the winding.

  In order to achieve the above object, a volume control device according to a fourth aspect of the present invention is the volume control device according to the first aspect, wherein the transformer is a primary volume in which an audio signal is input from the signal source. And a secondary winding provided with the intermediate tap.

  In order to achieve the above object, a volume adjustment device according to a fifth aspect of the present invention is the volume adjustment device according to the second aspect, wherein the signal acquisition unit is configured to switch the plurality of intermediate taps. An intermediate tap selection unit that selects an intermediate tap and a signal output unit that outputs an audio signal input to the resistance attenuator.

  In order to achieve the above object, a volume adjustment device according to a sixth aspect of the present invention is the volume adjustment device according to the fifth aspect, wherein the intermediate tap selection unit is different among the plurality of intermediate taps. A plurality of select switches for selecting intermediate taps, and the signal output unit inputs an audio signal including a difference between the audio signals acquired by the plurality of select switches to the resistance attenuator;

  In order to achieve the above object, a volume control device according to a seventh aspect of the present invention is the volume control device according to the fifth aspect, wherein the signal output unit receives a signal input to the resistance attenuator. An amplifier for amplification is provided.

  In order to achieve the above object, a volume control device according to an eighth aspect of the present invention is the volume control device according to the second aspect, wherein the resistance attenuator is continuously variable connected to the signal acquisition unit. A resistor is provided.

  In order to achieve the above object, a volume adjustment device according to a ninth aspect of the present invention is the volume adjustment device according to the eighth aspect, wherein the signal acquisition unit is connected to each of the plurality of intermediate taps. The resistance attenuator is connected to the continuous variable resistor connected to the output end of the first changeover switch and to the output end of the first changeover switch. A second changeover switch having a plurality of switch contacts and a switch contact connected to the sliding portion of the continuous variable resistor, and the second changeover switch is interlocked with the first changeover switch. .

  In order to achieve the above object, a volume adjustment device according to a tenth aspect of the present invention is the volume adjustment device according to the second aspect, wherein the signal acquisition unit is connected to the plurality of intermediate taps. A first plurality of switch contacts, the resistance attenuator being connected to one of the first plurality of switch contacts and a node between the plurality of fixed resistors; A second plurality of switch contacts connected; and a selector switch capable of selecting the first plurality of switch contacts and the second plurality of switch contacts.

  In order to achieve the above object, a volume control device according to an eleventh aspect of the present invention is the volume control device according to the tenth aspect, wherein the first fixed resistor is connected to the plurality of serial fixed resistors. One of the plurality of switch contacts is connected to an intermediate tap having the greatest attenuation among the plurality of intermediate taps.

  In order to achieve the above object, a volume adjustment device according to a twelfth aspect of the present invention is the volume adjustment device according to the second aspect, wherein the signal acquisition unit is connected to the plurality of intermediate taps. The resistance attenuator includes a first changeover switch connected to one of the first plurality of switch contacts, and a second selectable by the first changeover switch. A plurality of switch contacts, a plurality of fixed voltage dividing circuits respectively connected to the second plurality of switch contacts, and a third plurality of switch contacts connected to output ends of the plurality of fixed voltage dividing circuits. , And a second changeover switch capable of selecting the first plurality of switch contacts and the third plurality of switch contacts.

  In order to achieve the above object, a volume adjusting apparatus according to a thirteenth aspect of the present invention includes a plurality of intermediate taps for attenuating an input audio signal and outputting the audio signal corresponding to each attenuation level. A transformer, a changeover switch for selecting one of the plurality of intermediate taps according to an operation, and an output side of the changeover switch, and continuously changing the audio signal by changing a resistance value according to the operation And a variable resistor that attenuates and outputs.

  In order to achieve the above object, a volume adjusting apparatus according to a fourteenth aspect of the present invention includes a plurality of intermediate taps for attenuating an input audio signal and outputting the audio signal corresponding to each degree of attenuation. A transformer, a changeover switch for selecting one of the plurality of intermediate taps according to an operation, an amplifier connected to the output side of the changeover switch, for amplifying the audio signal, and connected to the output side of the amplifier And a variable resistor for continuously attenuating and outputting the audio signal according to a change in resistance value according to an operation.

  In order to achieve the above object, a volume control apparatus according to a fifteenth aspect of the present invention includes a plurality of intermediate taps for attenuating an input audio signal and outputting the audio signal corresponding to each attenuation level. A transformer, a first changeover switch for selecting one of the plurality of intermediate taps according to an operation, and a second changeover switch for selecting one of the plurality of intermediate taps according to an operation; The one input terminal is connected to the output side of the first changeover switch, the other input terminal is connected to the output side of the second changeover switch, and the audio signal is continuously transmitted by changing the resistance value according to the operation. And a variable resistor that attenuates and outputs.

  In order to achieve the above object, a volume adjusting apparatus according to a sixteenth aspect of the present invention includes a plurality of intermediate taps for attenuating an input audio signal and outputting the audio signal corresponding to each attenuation level. A transformer, a first changeover switch for selecting one of the plurality of intermediate taps according to an operation, and an output side of the first changeover switch are connected. A variable resistor that continuously attenuates and outputs an audio signal, and is connected to the output side of the first changeover switch and the variable resistor, and operates in conjunction with the first changeover switch according to an operation. A second changeover switch, wherein the second changeover switch has an intermediate tap at which the attenuation of the audio signal is maximized. -Option was only outputs the output signal of the variable resistor time, outputs the output signal of the first changeover switch when said first changeover switch selects the other intermediate taps.

  In order to achieve the above object, a volume adjusting apparatus according to a seventeenth aspect of the present invention includes a plurality of intermediate taps for attenuating an input audio signal and outputting the audio signal corresponding to each attenuation level. A transformer, a first changeover switch for selecting one of the plurality of intermediate taps according to an operation, an amplifier connected to the output side of the first changeover switch for amplifying the audio signal, and Connected to the output side of the amplifier and connected to the output side of the variable resistor for continuously attenuating and outputting the audio signal according to the change of the resistance value according to the operation, the first changeover switch and the variable resistor And a second changeover switch that operates in conjunction with the first changeover switch in response to an operation, wherein the second changeover switch includes the first changeover switch. The output signal of the variable resistor is output only when the changeover switch selects the intermediate tap that maximizes the attenuation of the audio signal, and when the first changeover switch selects another intermediate tap, the amplifier The output signal is output.

  In order to achieve the above object, a volume control apparatus according to an eighteenth aspect of the present invention includes a plurality of intermediate taps for attenuating an input audio signal and outputting the audio signal corresponding to each attenuation level. A switching resistor having an input terminal connected to a transformer and an intermediate tap that maximizes the attenuation of the audio signal, and having a plurality of output terminals that attenuate and output the audio signal input from the intermediate tap in stages And a selector switch for selecting one of the plurality of intermediate taps and the plurality of output terminals of the switchable resistor according to an operation.

  In order to achieve the above object, a volume control device according to a nineteenth aspect of the present invention is the volume control device according to any one of the thirteenth to eighteenth aspects, wherein the step-down transformer is a primary This is a step-down transformer with a secondary independent winding structure.

  The volume control apparatus according to any one of the first to twelfth aspects of the present invention acquires a highly attenuated audio signal input from a signal source to a transformer by a signal acquisition unit, and the audio input from the signal acquisition unit. Since the signal is attenuated by the resistance attenuator, it is not necessary to use the resistance attenuator in the ½ attenuation region, and sound quality deterioration in the vicinity of the ½ attenuation region can be suppressed with a simple configuration.

  A volume adjusting apparatus according to any of the thirteenth to nineteenth aspects of the present invention includes a step-down transformer that steps down an input audio signal and a variable resistor that continuously attenuates the signal stepped down by the step-down transformer. Therefore, in the high attenuation region, if the signal highly attenuated by the step-down transformer is output to the variable resistance type attenuator, it is not necessary to use the variable resistor in the 1/2 attenuation region. 2 It is possible to suppress deterioration in sound quality in the vicinity of the attenuation region.

  Hereinafter, a volume control device according to the best mode for carrying out the present invention will be described in detail with reference to the accompanying drawings. In the drawings, the same elements are denoted by the same reference numerals.

(First embodiment)
First, a volume control device VC1 according to a first embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a circuit diagram of the volume control device VC1, FIG. 2 is an output level diagram of the volume control device VC1, FIG. 3 is a photograph showing the main part of the volume control device VC1, and FIGS. 11 is a characteristic diagram of FIG.

  The volume adjusting device VC1 includes a step-down transformer 11 that steps down and attenuates an audio signal input from a signal source (source device or preamplifier) (not shown), and a plurality of (in this example, five) attenuations of the transformer 11 are different. By selecting one of the intermediate taps 11a, 11b, 11c, 11d, and 11e, a signal acquisition unit SAC that acquires a corresponding audio signal, and resistance attenuation that attenuates the audio signal input from the signal acquisition unit SAC Device RAT.

The step-down transformer 11 has a winding 11f to which an audio signal is input from a signal source, and intermediate taps 11a to 11e are provided in the winding 11f. This step-down transformer has ATT (attenuation) vsf (frequency) characteristics shown in FIG. 4, THD (total harmonic distortion) vsse _IN (input voltage) characteristics shown in FIG. 5, and Zin (input impedance) shown in FIG. vs f (frequency) characteristics.

  The signal acquisition unit SAC outputs the audio signal input to the resistance attenuator RAT from the changeover switch 12 as the intermediate tap selection unit TS that selects the intermediate tap by switching the intermediate taps 11a to 11d. And a signal output unit SO.

  The resistance attenuator RAT includes a continuously variable resistor 13 connected to the signal acquisition unit SAC.

  That is, as shown in FIG. 1, the volume control device VC1 includes a step-down transformer 11 having a plurality of intermediate taps 11a to 11e for stepping down an input audio signal, and switch terminals 12a to 12d. The change-over switch 12 for selecting one of 11d and the variable resistor 13 connected to the output terminal 12e of the change-over switch 12 and continuously attenuating and outputting the audio signal are provided.

  The intermediate taps 11a to 11d have different attenuations and are connected to the terminals 12a to 12d of the changeover switch 12. The variable resistor 13 has a sliding portion 13a, and performs voltage division with the resistor R1 between the sliding portion 13a and the terminal 12e and the remaining resistor R2.

  When an audio signal is input to the volume control device VC1, the voltage is stepped down by the step-down transformer 11. The stepped down audio signal is output from the intermediate tap to the variable resistor 13 via the changeover switch 12. For example, when the terminals 12b and 12e of the changeover switch 12 are connected, a signal is output from the intermediate tap 11b to the variable resistor 13 via the terminals 12b and 12e.

  The signal input to the variable resistor 13 is divided and attenuated by R1 and R2, and is output from the sliding portion 13a.

  FIG. 2 shows the output level of the volume adjusting device VC1 when the step-down step of the intermediate taps 11a to 11d is 10 dB. For example, when the terminals 12b and 12e of the changeover switch 12 are connected and the intermediate tap 11b is selected, the audio signal is stepped down by -10 dB by the step-down transformer 11, and the stepped-down signal is further attenuated by the variable resistor 13. The The attenuation in the variable resistor 13 can be continuously changed.

  According to the volume control device VC1, by outputting the signal attenuated by the step-down transformer 11 to the variable resistor 13 in the ½ attenuation region, the variable resistor 13 can be used in the region where the attenuation is small. At this time, since R1 of the variable resistor 13 is relatively small, the parallel combined resistance of the resistor R1 and the resistor R2 is reduced, and deterioration of sound quality can be avoided. Further, since the output impedance of the step-down transformer 11 is lowered, the resistance value of the variable resistor itself can be lowered, and higher sound quality can be maintained.

  Since the attenuation amount can be continuously changed by the variable resistor 13, it is not necessary to provide a large number of intermediate taps unlike the volume adjusting device VC21, and it can be constructed economically.

  Although the intermediate tap in FIG. 2 has been described with a step of 10 dB, it is ideal that the intermediate tap has a step of 6 dB or less. However, it is practically sufficient to provide up to −60 dB in 20 dB steps. In this case, the number of intermediate taps can be four.

(Second Embodiment)
Next, a volume control device VC2 according to a second embodiment of the present invention will be described with reference to FIG. FIG. 7 is a circuit diagram of the volume adjusting device VC2.

  The volume adjusting device VC2 includes a step-down transformer 11 that steps down and attenuates an audio signal input from a signal source (not shown), and a plurality (five in this example) of intermediate taps 11a and 11b having different attenuation degrees. , 11c, 11d, and 11e, a signal acquisition unit SAC that acquires a corresponding audio signal and a resistance attenuator RAT that attenuates the audio signal input from the signal acquisition unit SAC.

  The step-down transformer 11 has a winding 11f to which an audio signal is input from a signal source, and intermediate taps 11a to 11e are provided in the winding 11f.

  The signal acquisition unit SAC amplifies the changeover switch 12 serving as the intermediate tap selection unit TS that selects the intermediate tap by switching the intermediate taps 11a to 11d, and the output of the changeover switch 12, and is input to the resistance attenuator RAT. And an amplifier 15 as a signal output unit SO that outputs an audio signal.

  The resistance attenuator RAT includes a continuously variable resistor 13 connected to the signal acquisition unit SAC.

  That is, in the volume adjusting device VC2, in addition to the configuration of the volume adjusting device VC1, an amplifier 15 is connected to the output side of the changeover switch 12 that selects the intermediate taps 11a to 11d of the step-down transformer 11, and the output side of the amplifier 15 is a variable resistor. Connected to the vessel 13. The amplifier 15 has an input impedance sufficiently higher (10 times or more) than the output impedance of the step-down transformer 11, does not affect the output of the step-down transformer 11, and can output the variable resistor 13 sufficiently ( Current and voltage) and sufficiently low (less than 1/10) output impedance with respect to the variable resistor 13.

  In the volume adjusting device VC2, the signal current flowing from the intermediate taps 11a to 11d into the amplifier 15 is reduced, and the sound quality is further improved as compared with the volume adjusting device VC1. Moreover, since a variable resistor having a low resistance value can be used as the variable resistor 13, the impedance at the output end can be lowered, and the cut-off frequency of the high-frequency attenuation filter composed of the stray capacitance can be further increased. Improvements in characteristic sound quality can be expected.

(Third embodiment)
Next, a volume adjusting device VC3 according to a third embodiment of the present invention will be described with reference to FIGS. FIG. 8 is a circuit diagram of the volume adjusting device VC3, and FIG. 9 is an output level diagram of the volume adjusting device VC3.

  The volume control device VC3 includes a step-down transformer 11 that steps down and attenuates an audio signal input from a signal source (not shown), and a plurality of (in this example, five) intermediate taps 11a and 11b having different degrees of attenuation. , 11c, 11d, and 11e, a signal acquisition unit SAC that acquires a corresponding audio signal and a resistance attenuator RAT that attenuates the audio signal input from the signal acquisition unit SAC.

  The step-down transformer 11 has a winding 11f to which an audio signal is input from a signal source, and intermediate taps 11a to 11e are provided in the winding 11f.

  The signal acquisition unit SAC outputs an audio signal input to the resistance attenuator RAT from the intermediate tap selection unit TS that selects the intermediate tap by switching the intermediate taps 11a to 11e, and the intermediate tap selection unit TS. And an output unit SO.

  The intermediate tap selection unit TS includes a plurality of (two in this example) select switches for selecting different intermediate taps among the intermediate taps 11a to 11e, that is, changeover switches 12 and 17 interlocking with each other, and a signal output unit The SO inputs an audio signal composed of a difference between the audio signals acquired by the changeover switches 12 and 17 to the resistance attenuator RAT.

  The resistance attenuator RAT includes a continuously variable resistor 13 connected to the signal acquisition unit SAC.

  That is, as shown in FIG. 8, the volume adjusting device VC3 includes a step-down transformer 11 having a plurality of intermediate taps 11a to 11e for attenuating an input audio signal, and switch terminals 12a to 12d, and the intermediate taps 11a to 11a. The selector switch 12 for selecting one of 11d and switch terminals 17a to 17d, and the selector switch 17 for selecting one of the intermediate taps 11b to 11e and the output terminal 12e of the selector switch 12 And the other input terminal is connected to the output terminal 17e of the changeover switch 17, and includes a variable resistor 13 that continuously attenuates and outputs the audio signal.

  The intermediate taps 11a to 11e have different attenuations, of which the taps 11a to 11d are connected to the terminals 12a to 12d of the changeover switch 12, and the taps 11b to 11e are connected to the terminals 17a to 17d of the changeover switch 17. Is done. The changeover switch 12 and the changeover switch 17 are linked so that the intermediate tap selected by the changeover switch 17 is one step below the intermediate tap selected by the changeover switch 12. The variable resistor 13 has a sliding portion 13a, and the resistance between the sliding portion 13a and the terminal 12e is represented by R1, and the resistance of the remaining portion is represented by R2.

  In the volume adjusting device VC3, the input audio signal is stepped down by the step-down transformer 11, and the stepped-down audio signal is output from the intermediate tap to the variable resistor 13 via the changeover switch 12 and the changeover switch 17.

  For example, when the terminals 12b and 12e of the changeover switch 12 are connected and the terminals 17b and 17e of the changeover switch 17 are connected, the terminals 17b and 17e are connected from the intermediate tap 11b through the terminals 12b and 12e and from the intermediate tap 11c. A signal is output to the variable resistor 13 via

  The signal input to the variable resistor 13 is divided and attenuated by the voltage dividing resistors R1 and R2, and is output from the sliding portion 13a.

  FIG. 9 shows the output level of the volume control device VC3 when the attenuation of the intermediate taps 11a to 11e is 10 dB steps. For example, when the terminals 12b and 12e of the changeover switch 12 are connected and the terminals 17b and 17e of the changeover switch 17 are connected, a signal stepped down by −10 dB by the step-down transformer 11 is output to the terminal 12e. The signal that is stepped down by −20 dB is output to the terminal 17e. In the variable resistor 13, the level difference between the terminal 12e and the terminal 17e can be continuously changed.

  Since the volume adjusting device VC3 uses the variable resistor 13 in each step of the attenuation range of the step-down transformer 11, it can be used in a region where the attenuation of the variable resistor 13 is small. Since R1 of the variable resistor 13 is relatively small, the parallel combined resistance of the resistor R1 and the resistor R2 is also reduced, and deterioration of sound quality can be avoided. Further, since the output impedance of the step-down transformer can be used in a small state, the resistance of the variable resistor 13 can be a smaller one, and further sound quality deterioration can be prevented.

(Fourth embodiment)
Next, a volume adjustment device VC4 according to a fourth embodiment of the present invention will be described with reference to FIGS. 10 is a circuit diagram of the volume adjusting device VC4, FIG. 11 is an output level diagram of the volume adjusting device VC4, and FIG. 12 is a user interface of the volume adjusting device VC4.

  The volume adjusting device VC4 includes a step-down transformer 11 that steps down and attenuates an audio signal input from a signal source (not shown), and a plurality (five in this example) of intermediate taps 11a and 11b having different attenuation degrees. , 11c, 11d, and 11e, a signal acquisition unit SAC that acquires a corresponding audio signal and a resistance attenuator RAT that attenuates the audio signal input from the signal acquisition unit SAC.

  The step-down transformer 11 has a winding 11f to which an audio signal is input from a signal source, and intermediate taps 11a to 11e are provided in the winding 11f.

  The signal acquisition unit SAC selects an intermediate tap by switching between the intermediate taps 11a to 11d, and a signal output that outputs an audio signal input to the resistance attenuator RAT from the intermediate tap selection unit TS. Part SO.

  The intermediate tap selection unit TS includes a change-over switch 12 that selects one of the intermediate taps 11a to 11d.

  The resistance attenuator RAT is used to select a continuous variable resistor 13 connected to the signal output unit SO, a plurality of terminals 41a, 1b, 41dc connected to the signal output unit SO, and an intermediate tap of the intermediate tap selection unit TS. In conjunction with this, there is provided a changeover switch 41 as a terminal selection unit TMS for selecting a changeover between the output terminal 41d of the continuous variable resistor 13 and the plurality of terminals 41a to 41c.

  That is, as shown in FIG. 10, the volume adjusting device VC4 is configured by connecting a changeover switch 41 to the configuration of the volume adjusting device VC1. The terminals 41a to 41c of the selector switch 41 are connected to the output terminal 12e of the selector switch 12, and the terminal 41d is connected to the sliding portion 13a. The changeover switch 41 is linked to the changeover switch 12, and when the terminals 12a and 12e are connected, the terminals 41a and 41e are connected. When the terminals 12b and 12e are connected, the terminals 41b and 41e are connected. When the terminals 12c and 12e are connected, the terminals 41c and 41e are connected. When the terminals 12d and 12e are connected, the terminals 41d and 41e are connected.

  Therefore, when the switch terminals 41 a to 41 c of the changeover switch 41 and the output terminal 41 e are connected, signals are directly output from the intermediate taps 11 a to 11 c of the step-down transformer 11.

  When the terminals 41d and 41e of the changeover switch 41 are connected, the signal is output from the variable resistor 13 and can be continuously attenuated to −∞ dB.

  FIG. 11 shows an output level diagram of the volume adjusting device VC4 when the attenuation of the intermediate taps 11a to 11d is changed in 10 dB steps.

  When the switch terminals 41a to 41c of the changeover switch 41 are selected, signals are directly output from the intermediate taps 11a to 11c of the step-down transformer 11, so that the attenuation changes step by step, and the changeover switch When the switch terminal 41d of 41 is selected, a signal is output from the variable resistor 13, so that it can be attenuated continuously.

  The change-over switches 12 and 41 and the variable resistor 13 are operated using the user interface shown in FIG. For example, when the selector switch operating knob 42 is set to the position a, the terminal 12a and the terminal 41a are selected. When the selector switch operation knob 42 is set to the position d, the terminal 12d and the terminal 41d are selected. Only at this time, the volume can be adjusted using the variable resistor operation knob 43.

  When the switch terminals 41a to 41c of the changeover switch 41 and the output terminal 41e are connected, the volume adjusting device VC4 outputs a signal directly from the intermediate taps 11a to 11c of the step-down transformer 11, so that the signal is It is possible to avoid deterioration in sound quality due to passing through the variable resistor 13.

(Fifth embodiment)
Next, a volume control device VC5 according to a fifth embodiment of the present invention will be described with reference to FIG. FIG. 13 is a circuit diagram of the volume adjusting device VC5.

  The volume adjusting device VC5 includes a step-down transformer 11 that steps down and attenuates an audio signal input from a signal source (not shown), and a plurality (five in this example) of intermediate taps 11a and 11b having different attenuation degrees. , 11c, 11d, and 11e, a signal acquisition unit SAC that acquires a corresponding audio signal and a resistance attenuator RAT that attenuates the audio signal input from the signal acquisition unit SAC.

  The step-down transformer 11 has a winding 11f to which an audio signal is input from a signal source, and intermediate taps 11a to 11e are provided in the winding 11f.

  The signal acquisition unit SAC selects an intermediate tap by switching between the intermediate taps 11a to 11d, and a signal output that outputs an audio signal input to the resistance attenuator RAT from the intermediate tap selection unit TS. Part SO.

  The intermediate tap selection unit TS includes a changeover switch 12 that selects one of the intermediate taps 11 a to 11 e, and the signal output unit SO includes an amplifier 15.

  The resistance attenuator RAT includes a continuous variable resistor 13 connected to the signal output unit SO, a plurality of switch terminals 41a, 41b, 41dc connected to the signal output unit SO, and selection of an intermediate tap of the intermediate tap selection unit TS. In conjunction with this, there is provided a changeover switch 41 as a terminal selection unit TMS for selecting a changeover between the output terminal 41d of the continuous variable resistor 13 and the plurality of switch terminals 41a to 41c.

  That is, in the volume adjusting device VC5, as shown in FIG. 13, in addition to the configuration of the volume adjusting device VC4, an amplifier 15 is connected to the output side of the changeover switch 12 that selects the intermediate taps 11a to 11d of the step-down transformer 11. The output side of the amplifier 15 is connected in parallel to the variable resistor 13 and the changeover switch 41. The amplifier 15 has an input impedance sufficiently higher (10 times or more) than the output impedance of the step-down transformer 11, does not affect the output of the step-down transformer 11, and can output the variable resistor 13 sufficiently ( Current and voltage) and sufficiently low (less than 1/10) output impedance with respect to the variable resistor 13.

  The volume adjusting device VC5 has less signal current flowing from the intermediate taps 11a to 11d to the amplifier 15, and the sound quality is further improved as compared with the volume adjusting device VC4. Further, the resistance of the variable resistor 13 can be set low, and the characteristics and sound quality are improved.

(Sixth embodiment)
Next, a volume adjustment device VC6 according to a sixth embodiment of the present invention will be described with reference to FIGS. FIG. 14 is a circuit diagram of the volume adjusting device VC6, and FIG. 15 is a user interface of the volume adjusting device VC6.

  The volume adjusting device VC6 includes a step-down transformer 51 that steps down and attenuates an audio signal input from a signal source (not shown), and n intermediate taps 51-1, 51-2, 51 with different degrees of attenuation of the transformer 51. -3. . . , 51- (n-1), 51-n, the signal acquisition unit SAC that acquires the corresponding audio signal and the audio signal input from the signal acquisition unit SAC are attenuated. And a resistance attenuator RAT.

  The step-down transformer 51 has a winding 51f to which an audio signal is input from a signal source, and the intermediate taps 51-1 to 51-n are provided in the winding 51f.

  The signal acquisition unit SAC includes n switch contacts 53-1, 53-2, 53-3,... Connected to the n intermediate taps 51-1 to 51-n. . . , 53- (n-1), 53-n.

  The resistance attenuator RAT includes a switchable resistor 52 including m fixed resistors connected in series to one of the n switch contacts 53-1 to 53-n, and m fixed resistors. M switch contacts 52-1, 52-2,... Connected to the node between the resistors. . . , 52-m, and a selector switch 53 having a selector capable of selecting the n switch contacts 53-1 to 53-n and the m switch contacts 52-1 to 52-m.

  One of the switch contacts 53-n to which the m series fixed resistors are connected is connected to the intermediate tap 51-n having the highest attenuation among the n intermediate taps 51-1 to 51-n. Has been.

  That is, the volume control device VC6 includes a step-down transformer 51 having n intermediate taps 51-1 to 51-n for attenuating an input audio signal, and m fixed resistors connected in series with each other. The switchable resistor 52 having m switch terminals 52-1 to 52-m from which the audio signal input from the intermediate tap 51-n having the maximum degree is attenuated and output in stages, and the intermediate taps 51-1 to 51-n. A switch 53 having a selector capable of selecting one of n switch terminals 53-1 to 53-n connected to 51-n and the m switch terminals 52-1 to 52-m. Prepare.

  In the volume adjusting device VC6, the input audio signal is stepped down by the step-down transformer 51. The stepped-down audio signal is output via terminals 53-1 to 53-n of the changeover switch 53 connected to the intermediate taps 51-1 to 51-n.

  When obtaining an attenuation level exceeding the attenuation level (for example, −20 dB) of the intermediate tap 51-n, the audio signal is further attenuated by the switching resistor 52, and also serves as an output terminal of the switching resistor 52 in the switching switch 53. It is output via the switch terminals 52-1 to 52-m.

  The volume control device VC6 includes only the changeover switch operation knob 54 shown in FIG. 15 as a user interface, and the convenience of operation is improved compared to the user interface shown in FIG.

(Seventh embodiment)
Next, a volume adjustment device VC7 according to a seventh embodiment of the present invention will be described with reference to FIG. FIG. 16 is a circuit diagram of the main part of the volume control device VC7.

  As shown in FIG. 16, the volume control device VC7 is different from the first to sixth embodiments VC1 to VC6 in that a step-down transformer 61 having a primary and secondary independent winding structure is used. In the transformer 61, a primary winding 61a to which an audio signal is input from an input terminal Ti and a secondary winding 61b provided with an intermediate tap connected to the signal acquisition unit SAC are wound around a core 61c. As a result, the interference is reduced and the sound quality is further improved.

  The transformer 61 may be a step-up transformer. In particular, if the amplifier installed in the front stage of the volume control device VC7 has a sufficient output current capacity, the sound quality can be further improved by using a step-up transformer having a low input impedance.

  In order to improve the performance of the transformer 61, the material of the core 61c may be permalloy or sen alloy. The structure of the transformer 61 is ideally a toroidal shape, but a cut core shape can provide good performance.

  Also in the first to sixth embodiments, a step-down transformer 61 having a primary and secondary independent winding structure can be used instead of the step-down transformer described above.

(Eighth embodiment)
Next, a volume adjustment device VC8 according to an eighth embodiment of the present invention will be described with reference to FIGS. FIG. 17 is a circuit diagram of the volume adjusting device VC8, and FIG. 18 is a photograph of the volume adjusting device VC8.

  Volume control device VC8: Steps down the audio signal input from a plurality of signal sources (for example, REC, TAPE, LINEIN1 to 4) via direct input terminal DIRECT or input selector IS and input terminal Ti. A step-down transformer 81 that attenuates; n (n = 11 in this example) intermediate taps 81-1, 81-2,. . . , 81- (n-1), 81-n, n switch contacts 82-1, 82-2,. . . , 82- (n−1), 82-n, and by selecting one of them, a signal acquisition unit SAC that acquires a corresponding audio signal; audio input from the signal acquisition unit SAC And a resistance attenuator RAT for attenuating the signal.

  This resistance attenuator RAT is: an input side switch contact selector TS connected to a switch contact 82-n having the maximum attenuation (−20 dB) among the n switch contacts 82-1 to 82-n; N + m (in this example, n + m = 11 + 35 = 46) switch contacts 83-1, 83-2,. . . , 83-(n + m), except for the first n-1 dummy, m + 1 (m + 1 = 35 + 1 = 36 in this example) switch contacts 83-n, 83- (n + 1),. . . , 83- (n + m); and these m + 1 switch contacts 83-n,. . . , 83-(n + m) and the ground line G, respectively, m + 1 resistor circuits 84-0, 84-1,. . . , 84- (m−1), 84-m. Among these m + 1 resistor circuits, the first resistor circuit 84-0 is composed of a fixed resistor R2, and the following m-1 resistor circuits 84-1 to 84- (m-1) use fixed resistors R1 and R2. The last resistor circuit 84-m is composed of a fixed resistor R1.

  The resistance attenuator RAT further includes: voltage dividing output terminals of m−1 resistor circuits 84-1 to 84- (m−1) configured as fixed voltage dividing circuits among the m + 1 resistor circuits, and A total of m switch contacts 82- (n + 1), 82- (n + 2),... Connected to the ground terminal of the last resistor circuit 84-m. . . 82- (n + m); n switch contacts 82-1 to 82-n and m switch contacts 82- (n + 1) to 82- (n + m) of the signal acquisition unit SAC can be selected. , And an output side switch contact selector RS capable of selecting n + m switch contacts 82-1 to 82- (n + m) in total, and this selector RS is connected to the output terminal To.

  That is, the volume adjusting device VC8 includes: a step-down transformer 81 having n intermediate taps 81-1 to 81-n that perform stepwise attenuation in an attenuation range of −0d to −20 dB; and an annular shape as shown in FIG. A switch 82 having n + m switch contacts 82-1 to 82- (n + m) and selectors RS arranged therein; and n + m switch contacts 83-1 to 83- (n + m) also arranged in an annular shape And a selector switch 83 having a selector TS of the step-down transformer 81. Further, stepwise attenuation is performed in the attenuation range of -21 dB to -80 dB by using the step-down transformer 81 in series with the maximum attenuation (-20 dB) intermediate tap 81-n. m-1 fixed voltage dividing circuits 84-1 to 84- (m-1) and R1Ω to 0Ω fixed voltage dividing circuit 84-m corresponding to −∽dB attenuation are arranged in parallel. The damping resistance group 84 is provided.

  Therefore, the output terminal To receives the audio signal appropriately attenuated by the transformer 81 and / or the resistor group 84, and this audio signal is connected to the output line directly from the terminal To via the output terminal DIRECT or the output selector OS. The signal is output to the terminal LINE OUTPUT-1 and / or LINE OUTPUT-2.

Table 1 shows the specifications of the winding 81f of the step-down transformer 81 of the eighth embodiment VC8. This table can also be applied to the step-down transformers of other embodiments.

  Similarly to the first to sixth embodiments VC1 to VC6, the step-down transformer 81 has a configuration in which intermediate taps 81-1 to 81-n are provided in a winding to which an audio signal is input from the input selector IS. However, according to the seventh embodiment VC7, an intermediate tap may be provided in the secondary winding of the transformer in which the audio signal from the signal source is input to the primary winding.

(Ninth embodiment)
Next, an audio system including a volume control device VC9 according to a ninth embodiment of the present invention will be described with reference to FIGS. 19 is a perspective view seen from the back side of the audio system, and FIG. 20 is a perspective view seen from the front side of the system.

  The volume control device VC9 may be any of the volume control devices VC1 to VC8, and is manufactured as a single unit in a predetermined size.

  In the audio system, a CD player SA, a preamplifier PA, a main amplifier MA, a pair of speakers SP, and a pair of speakers SP, which are unitized in a size corresponding to the volume adjusting device VC9, and the volume adjusting device VC9 are connected as illustrated. Configured.

  Note that each of the volume control devices VC-1 to VC-8 according to the first to eighth embodiments may be unitized together with the preamplifier or the main amplifier, or an amplifier including appropriate related devices. You may comprise as a unit. According to this, a good level balance can be realized, the number of wirings is reduced, the stray capacitance is also reduced, and deterioration of sound quality can be minimized. A specific example is shown below.

(Tenth embodiment)
A volume control device VC10 according to a tenth embodiment of the present invention will be described with reference to FIGS. FIG. 21 is a block diagram of the volume control device VC10, and FIG. 22 is a front view of the volume control device VC10.

  The volume adjusting device VC10 is configured as a unit including an equalizer, an input selector IS, a preamplifier PA, and a main amplifier MA. VR is a volume control knob.

(Eleventh embodiment)
A volume control device VC11 according to an eleventh embodiment of the present invention will be described with reference to FIGS. FIG. 23 is a block diagram of the volume adjusting device VC11, and FIG. 24 is a front view of the volume adjusting device VC11.

  The volume adjusting device VC11 further includes an output selector OS as compared with the volume adjusting device VC10.

  As is apparent from the above description, according to each embodiment of the present invention, a highly attenuated audio signal input from a signal source to a transformer is acquired by a signal acquisition unit, and the audio signal input from the signal acquisition unit Is attenuated by the resistance attenuator, it is not necessary to use the resistance attenuator in the ½ attenuation region, and sound quality deterioration in the vicinity of the ½ attenuation region can be suppressed with a simple configuration.

  In addition, it has a step-down transformer that steps down the input audio signal and a variable resistor that continuously attenuates the signal stepped down by the step-down transformer. If output to the resistance type attenuator, it is not necessary to use the variable resistor in the ½ attenuation region, and sound quality deterioration in the vicinity of the ½ attenuation region can be suppressed with a simple configuration.

  It should be noted that the above description of the embodiment is not a limitative description but merely an example, and those skilled in the art will understand that various modifications can be made within the scope of the claims.

  For example, if the resistance on the high potential side is set to Ra and the resistance on the low potential side from the sliding contact of the resistive voltage divider is Rb, the voltage gain (attenuation) is given by Rb / (Ra + Rb), and the output impedance is Since it is given by RaxRb / (Ra + Rb), the following configuration can be adopted for the volume adjuster VC6 according to the sixth embodiment and the resistance attenuator RAT of the volume adjuster VC8 according to the eighth embodiment.

  Regarding the switchable resistor 52 of the volume control device VC6, when the resistance value of the i-th fixed resistor connected to the i (1 ≦ i ≦ m) -th switch terminal 52-i is represented by Ri, i approaches m. The resistance value is set so that Ri decreases as the time increases. This facilitates equalization of the attenuation step width of the series resistance group.

  Further, regarding the attenuation resistor group 84 of the volume control device VC8, i is set to m while the sum of the resistances R1 and R2 of the fixed voltage dividing circuit 84-i (1 ≦ i ≦ m) is kept almost constant regardless of i. The resistance value is set so that R1 increases as it approaches (thus, R2 decreases).

Specifically, the specification values in Table 2 are given to the volume adjustment circuit (FIG. 29) of the volume adjustment device VC8.

  According to this, since the parallel resistance is switched, the signal does not pass through a large number of fixed resistances, and there is little deterioration in sound quality, so that not only high sound quality can be obtained, but also the attenuation step of the parallel resistance group Equalizing the width is easy.

FIG. 1 is a circuit diagram of a volume control device according to a first embodiment of the present invention. FIG. 2 is an output level diagram of the volume control device of FIG. FIG. 3 is a photograph showing the main part of the volume control device of FIG. FIG. 4 is a characteristic diagram of the step-down transformer of the volume control device of FIG. FIG. 5 is a characteristic diagram of the step-down transformer of the volume control device of FIG. FIG. 6 is a characteristic diagram of the step-down transformer of the volume control device of FIG. FIG. 7 is a circuit diagram of a volume control apparatus according to the second embodiment of the present invention. FIG. 8 is a circuit diagram of a volume control apparatus according to the third embodiment of the present invention. FIG. 9 is an output level diagram of the volume control device of FIG. FIG. 10 is a circuit diagram of a volume adjusting apparatus according to the fourth embodiment of the present invention. FIG. 11 is an output level diagram of the volume control device of FIG. FIG. 12 shows a user interface of the volume control device of FIG. FIG. 13 is a circuit diagram of a volume control apparatus according to the fifth embodiment of the present invention. FIG. 14 is a circuit diagram of a volume control apparatus according to the sixth embodiment of the present invention. FIG. 15 shows a user interface of the volume control device of FIG. FIG. 16 is a circuit diagram of a volume adjusting apparatus according to the seventh embodiment of the present invention. FIG. 17 is a circuit diagram of a volume control apparatus according to the eighth embodiment of the present invention. FIG. 18 is a photograph of the volume control device of FIG. FIG. 19 is a perspective view seen from the back side of an audio system including a volume control device according to a ninth embodiment of the present invention. 20 is a perspective view seen from the front side of the audio system of FIG. FIG. 21 is a block diagram of a volume control apparatus according to the tenth embodiment of the present invention. FIG. 22 is a front view of the volume control device of FIG. FIG. 23 is a block diagram of a volume control apparatus according to the eleventh embodiment of the present invention. FIG. 24 is a front view of the volume control device of FIG. FIG. 25 is a circuit diagram of a conventional volume control device for audio equipment. FIG. 26 is a circuit diagram of a volume adjusting device using a conventional step-down transformer. FIG. 27 is a graph showing the relationship between the attenuation and the output impedance of the volume control device of FIG. FIG. 28 is a graph showing the relationship between the degree of attenuation of the volume control device of FIG. 25 and the cutoff frequency of the high-frequency attenuation filter due to stray capacitance. FIG. 29 is a circuit diagram of a volume adjustment circuit of the volume adjustment apparatus of FIG.

Explanation of symbols

VC1, VC2, VC3, VC4, VC5, VC6, VC7, VC8, VC9, VC10, VC11 Volume control device Ti input terminal To output terminal 11, 51, 61, 81 Transformer as step-down transformer,
11a to 11e, 51-1 to 51-n, 81-1 to 81-n Intermediate tap SAC signal acquisition unit RAT Resistance attenuator 11f, 51f, 81f Winding 61a Primary winding 61b Secondary winding TS Intermediate tap selection unit SO signal output unit 12, 17, 41, 53, 82, 83 change-over switch 15 amplifier 13 variable resistors as continuous variable resistors 12a-12d, 17a-17d, 41a-41d, 52-1-52-m, 53 -1 to 53-n, 82-1 to 82- (n + m), 83-1 to 83- (n + m) Switch contact 12e, 17e, 41e Output terminal 13a Sliding part 52 Switchable resistor 84 Damping resistor group 84- 1-84-m Fixed Voltage Divider 11 Step-down Transformer 12 Changeover Switch 11a-11e Intermediate Tap 15 Amplifier 52 Switchable Resistor

Claims (19)

A transformer to which an audio signal is input from a signal source;
A signal acquisition unit for acquiring a corresponding audio signal by selecting an intermediate tap of the transformer;
A volume control device comprising: a resistance attenuator that attenuates an audio signal input from the signal acquisition unit. The transformer includes a step-down transformer that attenuates an audio signal input from the signal source. The step-down transformer includes a plurality of intermediate taps having different attenuation degrees, and the signal acquisition unit selects the intermediate taps from the plurality of intermediate taps. The volume control apparatus of Claim 1 performed in a tap. The volume control device according to claim 1, wherein the transformer has a winding to which an audio signal is input from the signal source, and the intermediate tap is provided in the winding. The volume control device according to claim 1, wherein the transformer includes a primary winding to which an audio signal is input from the signal source and a secondary winding provided with the intermediate tap. The signal acquisition unit includes: an intermediate tap selection unit that selects the intermediate tap by switching the plurality of intermediate taps; and a signal output unit that outputs an audio signal input to the resistance attenuator. The volume control apparatus of description. The intermediate tap selection unit has a plurality of select switches for selecting different intermediate taps from the plurality of intermediate taps, and the signal output unit is an audio comprising a difference between audio signals acquired by the plurality of select switches. The volume control apparatus according to claim 5, wherein a signal is input to the resistance attenuator. The volume control apparatus according to claim 5, wherein the signal output unit includes an amplifier that amplifies a signal input to the resistance attenuator. The volume control device according to claim 2, wherein the resistance attenuator includes a continuously variable resistor connected to the signal acquisition unit. The signal acquisition unit includes a first changeover switch having a switch contact connected to each of the plurality of intermediate taps,
The resistance attenuator is
The continuously variable resistor connected to the output terminal of the first changeover switch;
A second changeover switch having a plurality of switch contacts connected to the output end of the first changeover switch and a switch contact connected to the sliding portion of the continuous variable resistor;
The volume control device according to claim 8, wherein the second changeover switch is interlocked with the first changeover switch. The signal acquisition unit includes a first plurality of switch contacts connected to the plurality of intermediate taps,
The resistance attenuator is
A plurality of serial fixed resistors connected to one of the first plurality of switch contacts;
A second plurality of switch contacts connected to a node between the plurality of fixed resistors;
The volume control apparatus according to claim 2, further comprising: a changeover switch capable of selecting the first plurality of switch contacts and the second plurality of switch contacts.   The one of the first plurality of switch contacts to which the plurality of series fixed resistors are connected is connected to an intermediate tap having the greatest attenuation among the plurality of intermediate taps. Volume control device. The signal acquisition unit includes a first plurality of switch contacts connected to the plurality of intermediate taps,
The resistance attenuator is
A first changeover switch connected to one of the first plurality of switch contacts;
A second plurality of switch contacts selectable by the first changeover switch;
A plurality of fixed voltage dividing circuits respectively connected to the second plurality of switch contacts;
A third plurality of switch contacts connected to the output ends of the plurality of fixed voltage divider circuits;
The volume control device according to claim 2, further comprising: a second changeover switch capable of selecting the first plurality of switch contacts and the third plurality of switch contacts. A step-down transformer having a plurality of intermediate taps for attenuating an input audio signal and outputting the audio signal corresponding to each attenuation;
A changeover switch for selecting one of the plurality of intermediate taps according to an operation;
A volume control device comprising: a variable resistor connected to an output side of the changeover switch and continuously attenuating and outputting the audio signal by a change in resistance value according to an operation. A step-down transformer having a plurality of intermediate taps for attenuating an input audio signal and outputting the audio signal corresponding to each attenuation;
A changeover switch for selecting one of the plurality of intermediate taps according to an operation;
An amplifier connected to the output side of the selector switch for amplifying the audio signal;
A volume control device comprising: a variable resistor connected to an output side of the amplifier and continuously attenuating and outputting the audio signal by a change in resistance value according to an operation. A step-down transformer having a plurality of intermediate taps for attenuating an input audio signal and outputting the audio signal corresponding to each attenuation;
A first changeover switch for selecting one of the plurality of intermediate taps according to an operation;
A second changeover switch for selecting one of the plurality of intermediate taps according to an operation;
One input end is connected to the output side of the first changeover switch, and the other input end is connected to the output side of the second changeover switch. The audio signal is continuously transmitted by a change in resistance value according to the operation. And a variable resistor that attenuates and outputs the sound. A step-down transformer having a plurality of intermediate taps for attenuating an input audio signal and outputting the audio signal corresponding to each attenuation;
A first changeover switch for selecting one of the plurality of intermediate taps according to an operation;
A variable resistor connected to the output side of the first changeover switch and continuously attenuating and outputting the audio signal by a change in resistance value according to the operation;
A second changeover switch connected to the output side of the first changeover switch and the variable resistor and operating in conjunction with the first changeover switch according to an operation;
The second changeover switch outputs the output signal of the variable resistor only when the first changeover switch selects an intermediate tap that maximizes the attenuation of the audio signal, and the first changeover switch A volume control device for outputting an output signal of the first changeover switch when another intermediate tap is selected. A step-down transformer having a plurality of intermediate taps for attenuating an input audio signal and outputting the audio signal corresponding to each attenuation;
A first changeover switch for selecting one of the plurality of intermediate taps according to an operation;
An amplifier connected to the output side of the first changeover switch for amplifying the audio signal;
A variable resistor connected to the output side of the amplifier and continuously attenuating and outputting the audio signal by a change in resistance value according to the operation;
A second changeover switch connected to the output side of the first changeover switch and the variable resistor and operating in conjunction with the first changeover switch according to an operation;
The second changeover switch outputs the output signal of the variable resistor only when the first changeover switch selects an intermediate tap that maximizes the attenuation of the audio signal, and the first changeover switch A volume adjusting device that outputs an output signal of the amplifier when another intermediate tap is selected. A step-down transformer having a plurality of intermediate taps for attenuating an input audio signal and outputting the audio signal corresponding to each attenuation;
A switchable resistor having a plurality of output terminals for connecting the input terminal to an intermediate tap that maximizes the attenuation of the audio signal, and attenuating and outputting the audio signal input from the intermediate tap in stages.
A volume control device comprising: a switch for selecting one of the plurality of intermediate taps and the plurality of output terminals of the switchable resistor according to an operation.   The volume control device according to any one of claims 13 to 18, wherein the step-down transformer is a step-down transformer having a primary and secondary independent winding structure.