Variable Resistance Device For An Electronic Musical Instrument

Abstract

A variable resistance device adapted for use in a portamento performance combined with an electronic musical instrument comprises a narrow base made of electrical insulating material, an elongated resistance element disposed on said base and used as an element for determining the oscillating frequency of a tone signal generator and a flexible sheetlike conductor arranged above said resistance element at a prescribed space from each other. When a finger depressing the conductor to bring it into contact with the resistance element is shifted in the longitudinal direction of the element, resistance prevailing between the conductor and one end of the element successively varies with the resultant continuous change in the oscillator frequency, thereby obtaining the portamento effect.

Description

The present invention relates to a variable resistance device adapted for use in a portamento performance in combination with an electronic musical instrument, for example, an electronic organ.

With the prior art electronic musical instrument, there was imitatingly obtained a portamento effect by the glissando performance in which the finger was slidingly moved on and along the keyboard in the direction in which the keys were arranged.

The portamento effect results from successive variations in the frequency of sound waves. Therefore, the portamento effect in the truest sense of the word can be realized, in the case of an electronic musical instrument, by forming a tone source circuit from a variable frequency oscillator and using a variable resistance device as an element for determining the frequency of said oscillator and successively varying the resistance of said device so as to obtain a continuously changing oscillating frequency.

A variable resistance device for generating such a portamento effect is required to be of such type as allows the player to vary the magnitude of resistance easily by a single hand, particularly in succession from any proper position of the resistance element, that is, from any proper level of resistance at which the desired portamento effect starting with a desired note can be produced.

Among the prior art variable resistance device is a type in which the magnitude of resistance is varied by moving a knob with a slider which can slide on the resistance element in close contact therewith. Where such variable resistance device is employed as a variable resistor for a variable frequency oscillator, it is impossible immediately to vary the magnitude of resistance in succession starting from a proper level for the desired portamento effect, because the slider always contacts the resistance element. In such case, therefore, the sliding knob has to be brought back to a proper position for said portamento effect, each time it is needed. Moreover, since the slider of said knob always contacts the resistance element as described above, the control of the oscillator requires an extra switching means other than said knob. Also use of such type of variable resistance device presents difficulties in allowing the player to make a portamento performance simply by one of his hands. There is presented in FIGS. 1A and 1B a prior art device which claims improvement in the aforementioned drawbacks.

There will now be described said prior art variable resistance device by reference to FIG. 1A. At the substantially central part of a narrow base 1 is formed an elongated resistance element 3 extending in the longitudinal direction of said base 1 with an electrical insulating material 2 interposed therebetween. To both sides of said base 1 are fixed narrow foamed resilient materials 4a and 4b. Further across said foamed resilient materials 4a =and 4b is stretched a flexible contact member 5. In this case, the foamed resilient materials 4a and 4b and element 3 are designed to have such a height that while there is not applied any external force on said flexible contact member 5, the element 3 and contact member 5 are not brought into mutual contact. Namely, the element 3 is so formed as to have a smaller height than the foamed resilient materials 4a and 4b.

There will now be described the flexible contact member 5 by reference to FIG. 1B. Reference characters 6a and 6b =denote coil springs. These coils 6a and 6b are forcefully expanded to allow a gap 9 between the respective turns. And in each of said gaps 9 is disposed a horizontal rod 7 consisting of a conductor. Above the horizontal rods 7 and inside of the coil springs 6a and 6b respectively are introduced vertical rods 8 a and 8b made of flexible material. When, thereafter, the force applied to the coil springs 6a and 6b is removed, said horizontal rods 7 and vertical rods 8a and 8b are coupled together by the compressive force of said coil springs 8a and 8b to form a flexible contact assembly 5. In this case, said horizontal rods 7 are covered with a sheet of flexible insulation film 10. When one of the horizontal rods 7 involved in said flexible contact assembly 5 is depressed, it is deformed as illustrated by a phantom line 11 to contact the resistance element 3. Accordingly, the resistance prevailing between said flexible contact assembly 5 and one end of the element 3 assumes a certain value. Where the finger slides on said plurality of horizontal rods 7 to depress them one after another, then the magnitude of resistance will vary in succession. Actually, however, when the flexible contact assembly 5 is depressed, the horizontal rods 7 involved therein are urged downward substantially at the same time to contact the element 3, because the horizontal rods 7 are very slender and the intervals therebetween are also very small.

Where such variable resistance device is used in producing a portamento effect, the horizontal rods 7 are not brought into contact with the element 3 until they are depressed by the finger. Under such condition, there prevails an infinite magnitude of resistance, preventing the oscillator from being operated. Accordingly, the above-mentioned prior art device indeed has the advantage of eliminating the necessity of using any additional switching means in controlling the oscillator and enabling the magnitude of resistance to be successively varied starting from any level required for the desired portamento performance. Nevertheless, such variable resistance device is of too much complicated arrangement for mass production.

If, in case the flexible contact assembly 5 is depressed by the finger, only those of the horizontal rods which occupy a smaller space than the width of said finger contact the resistance element, then there will not be raised any problem with said prior art variable resistance device for a portamento effect. In fact, however, there are occasions where other horizontal rods than those depressed by the finger are unnecessarily deformed by the coil springs to contact the resistance element. If such event happens it will be difficult to select a proper oscillating frequency accurately. Further, it sometimes occurs that even when the finger slides to depress the horizontal rods one after another the frequency of said oscillator does not always correspondingly vary in succession.

It is accordingly the object of the present invention to provide a variable resistance device adapted for use in a portamento performance combined with an electronic musical instrument, the device being of simple construction, excellently fits mass production, allows the player to operate it easily by one of his hands and enables the frequency of an oscillator to be accurately controlled.

According to a broad aspect of the present invention, there is provided a variable resistance device adapted for use in a portamento performance comprising a narrow base made of electrical insulating material, an elongated resistance element disposed at the substantially central part of said base in a manner to extend in its longitudinal direction, a flexible sheetlike contact member positioned above said element and having at least that part thereof facing said elongated element made of electrically conductive material and a means for supporting said contact member at both sides of said base with a prescribed interval allowed between said element and contact member in such a manner that while there is not applied an external force on said contact member, it is not brought into contact with said element.

The flexible sheetlike contact member of a variable resistance device according to the present invention has a conductor portion integrally formed therewith which is to be brought into contact with a resistance element, thus allowing the entire device to be easily assembled and manufactured at low cost. With this device, the flexible sheetlike contact member does not normally contact the resistance element, preventing an oscillator from being operated. Accordingly, the player need not be concerned with the control of the oscillator by using an extra switching means.

Further, the device of the present invention is of such arrangement that when the flexible sheetlike contact member is depressed by a finger only that part of said contact member thus depressed contacts the resistance element, permitting the accurate control of the oscillating frequency. Accordingly, if the position of the finger depressing the flexible contact member is discontinuously shifted, then there will be realized not only a portamento performance but also other musical scale performances.

This invention can be more fully understood from the following detailed description when taken in connection with reference to the accompanying drawings, in which:

FIG. 1A is a sectional view of a prior art variable resistance device for generation of a portamento effect;

FIG. 1B is a plan view of a flexible contact member used in the device of FIG. 1A;

FIG. 2A is an exploded perspective view of a variable resistance device according to a first embodiment of the invention;

FIG. 2B is a sectional view of the device of FIG. 2A in an operating condition;

FIG. 3A is a perspective view of a variable resistance device according to a second embodiment of the invention;

FIG. 3B is a perspective view of the flexible contact member used in the device of FIG. 3A;

FIG. 4 is a perspective view of a variable resistance device according to a third embodiment of the invention;

FIG. 5A is a perspective view of a variable resistance device according to a fourth embodiment of the invention;

FIGS. 5B to 5E are plan views of modifications from a flexible contact member used in the device of FIG. 5A;

FIG. 6A is a perspective view of a variable resistance device according to a fifth embodiment of the invention;

FIG. 6B is a sectional view of the device of FIG. 6A in an operating condition; and

FIG. 7 is a schematic circuit diagram of an electronic musical instrument involving a variable resistance device.

There will now be described by reference to FIGS. 2A and 2B a variable resistance device according to a first embodiment of the present invention. A base 21 involved in said variable resistance device is prepared from electrical insulating material such as wood or plastics and formed into an elongated rectangular strip. The base 21 has inclined planes 22 and 23 formed on its upper surface in a manner to extend in its longitudinal direction which descend from both lateral edges of the base 21 to its central part to define a depression 24. Further at the central part of said depression 24 is cut out a groove 25 extending in the longitudinal direction of the base 21. The base 21 also has two other inclined planes 26 and 27 formed on both lateral edges in a manner to extend in its longitudinal direction. These two other inclined planes descend in an opposite direction to the first mentioned two inclined planes 22 and 23 constituting said depression 24, namely, toward the lateral edges of the base 21. Into the groove 25 cut out at the central part of the base 21 is fitted a narrow thin platelike element 28 of electrical resistance material. Said element 28 may consist of a layer of carbon material coated on the upper surface of the base 21. In this case the aforesaid groove 25 will become unnecessary. Further to the upper side of the base 21 is attached a slitted metal plate 29 acting as a flexible contact member. Said slitted plate 29 is formed of a good conductor, for example, a flexible nickel silver plate about 0.1 to 0.2 mm. thick. This slitted plate 29 has a large number of slits 30 formed by photoetching or punching in a direction perpendicular to the length of the element 28 in a manner to have a greater length than the width of the base 21. The smaller the width of each of these slits, and the interval 31 therebetween, the more minutely can be varied successively the magnitude of resistance. Both width and interval are preferably about 0.5 to 0.1 mm.

Said slitted plate 29 has walls 32 and 33 formed along both lateral edges at a space substantially equal to the width of the base 21, in a manner to be bent downward at right angles to the top plane of said slitted plate 29. The slits 30 also extend far down into the walls 32 and 33. These walls 32 and 33 allow the slitted plate 29 to be fitted to the base 21. When the slitted plate 29 is fitted to the base 21 from its top as illustrated in FIG. 2B, said plate 29 is secured in place by the edge portions 34 and 35 defined by a group of inclined planes 22 and 26 and another group of inclined planes 23 and 27 respectively, in such a manner that said slitted plate 29 faces the element 28 at the bottom of said depression 24 normally at a small clearance.

When integrally assembled in the aforementioned manner, the base 21, element 28 and slitted plate 29 form an operating section for a portamento performance in combination with an electronic musical instrument, said assembly constitutes a kind of potentiometer serving as a fingerboard to be manipulated in playing music.

When the upper surface of the slitted plate 29 is depressed by a finger, the intervening portions 31 between the slits 30 are brought down to contact the resistance element 28. Since there are defined spaces 36 and 37, as shown in FIG. 2B, by the inclined planes 26 and 27 formed on both lateral edges of the base 21 with the walls of the slitted plate 29, the intervening portions 31 between the slits 30 of the slitted plate 29 are fully bent as illustrated by a phantom line 38 to contact the element 28. Further, the presence of said spaces 36 and 37 allows only those of the intervening portions 31 between the slits 30 which are depressed to be brought into contact with the resistance element 28. Accordingly, the resistance prevailing between the conductors 39 and 40 connected to one end of the resistance element 28 and slitted plate 29 respectively assumes a value corresponding to the position of the intervening portions 31 between the slits 30 of the slitted plate 29 which are brought into contact with the resistance element 28. Therefore, it will be apparent that when that part of the upper surface of the slitted plate 29 which is depressed by the finger is shifted in turn in the longitudinal direction of the element 28, the magnitude of resistance prevailing between said conductors 39 and 40 will successively vary.

When used as an element for determining the frequency of a variable frequency oscillator, the variable resistance device of the present invention having the aforementioned arrangement enables said oscillator frequency to be easily varied in proper sequence and in consequence a portamento effect to be easily realized. Further, said device does not allow the slitted plate 29 to contact the resistance element 28 unless the former is depressed, so that under such condition, there prevails infinite resistance between the conductors 39 and 40, bringing the oscillator to an inoperable state.

A portamento performing mechanism involving such a variable resistance device is generally operated by a finger, and accordingly the upper surface of the slitted plate 29 is shielded with a protective cover 41 which is pliant and little subject to expansion and contraction such as a piled cloth, then said portamento performance can be made smoothly.

There will now be briefly described by reference to FIG. 7 a form of variable frequency oscillator for portamento performance involving the aforementioned variable resistance device. The indicated oscillator is a Wien bridge oscillator. It comprises an amplifier 100 involving transistors Tr.sub.1 and Tr.sub.2, the circuits 111, 112, 113 and 114 of a frequency determining element connected parallel between the collector and emitter of said transistor Tr.sub.2, each of which consists of a series circuit involving a resistor and capacitor connected in series with a parallel circuit involving another resistor and capacitor and differs in phase shifting characteristics, emitter follower type impedance transducers 121, 122, 123 and 124, each of which is supplied with signals from the contact of the aforesaid series and parallel circuits involving resistors and capacitors, a resistance element 131 provided with a tap connected to the emitter of a transistor involved in each of said impedance transducers 121, 122, 123 and 124 and a conductor 132 constituted by the flexible contact member of said variable resistance device which is to be brought into contact with said resistance element 131. Said conductor is connected to the transistor Tr.sub.1 of said amplifier circuit through a separate capacitor, thereby forming a feedback circuit.

The aforesaid circuits 111, 112, 113 and 114 of a frequency determining element have frequencies which successively differ from each other as for example by one octave. Accordingly, frequency variation by 3 octaves is available in the embodiment shown in FIG. 7. Since there is not formed a feedback circuit unless the resistance element 131 and conductor 132 contact each other, it will be apparent that the aforementioned oscillator is not normally brought to an operable state. Where the conductor 132 contacts the element 131 between the taps of the element 131 connected to the emitter of each of the impedance transducer circuits 121 and 122, the oscillator oscillates at a frequency having a magnitude intermediate between those of the specific frequencies of the two circuits 111 and 112 of said frequency determining element which are located nearest to said contact point between the conductor 132 and element 131. Shifting of the contact point results in the sequential change of the oscillator frequency. Outputs from the oscillator are drawn out of the emitter of the transistor Tr.sub.2 involved in the amplifier 100 and supplied to a loudspeaker 143, if required, through a tone coloring circuit 141 and another amplifier 142. If the conductor plate 132 is intermittently depressed by the finger for contact with the resistance element 131, then there will be realized not only a portamento performance, but also other music scale performances.

The oscillator shown in FIG. 7 represents a sine wave generator involving a capacitor and resistor. However, the variable resistance device of the present invention is also applicable in varying the frequency of a square wave generator such as an astable multivibrator. In such case, there is connected a variable impedance element such as field effect transistor in series to the stationary resistor constituting an element for determining the frequency of said astable multivibrator. And there is impressed a prescribed DC voltage across both ends of the resistance element of the variable resistance device of the present invention, and the conductor facing the resistance element is connected to the gate electrode of said field effect transistor. Then said device acts as a voltage divider to supply the gate electrode of said field effect transistor with successively varying DC voltage with the resultant change in the impedance of said field effect transistor, causing the frequency of said astable multivibrator to be continuously altered. Also in this case, the oscillator remains inoperable, so long as the conductor does not contact the resistance element.

There will now be described by reference to FIGS. 3A and 3B a variable resistance device according to another embodiment of the invention. There is fixed an element 52 of electrical resistance material at the central part of the upper surface of a base 51 made of electrical insulating material such as wood or plastics in a manner to extend in the longitudinal direction of said base 51. To the upper surface of the base 51 on both lateral sides of the element 52 there are attached a pair of resilient members 53 and 54 made of foamed rubber or the like. In this case, said resilient members 53 and 54 are so formed as to have a greater height than the resistance element 52. There is also formed a flexible contact member 55 in a manner to be supported by both resilient members 53 and 54 with a clearance of about 1 to 2 mm. allowed between said contact member 55 and resistance element 52. Said flexible contact member 55 generally consists to a copper layer plated with a film of precious metal such as gold or silver and superposed on a substrate made of, for example, a mylar film. In said contact member 55 there are cut out a large number of slits 56 extending in the transversed direction, defining a large number of intervening portions 57 therebetween. Further, said contact member 55 is shielded with a protective cover 58 made of, for example, a piled cloth which is fixed to both lateral sides of the base 51. The variable resistance device of FIGS. 3A and 3B constructed as described above can be operated in the same manner as the device of the preceding embodiment. Thus when the flexible contact member 55 is depressed by the finger tip 59, only those of the intervening portions 57 between the slits 56 which are depressed contact the resistance element 52 due to the spring action of the resilient members 53 and 54.

In the embodiment shown in FIG. 3A, the resilient members 53 and 54 are mounted on the shoulder portions of the base 51 which are cut out to receive the members 53 and 54, but the present invention can of course be practised even when the resistance element 52 is fitted to the same plane of the base 51 as that to which the resilient members 53 and 54 are attached. However, if the resilient members 53 and 54 are fitted to the lower plane of the base 51 than that to which the resistance element 52 is attached, then there will be obtained a suitable spring constant. Accordingly, when the flexible contact member 55 is depressed by the finger, the resilient force of the resilient members 53 and 54 can be varied more suitably for a portamento performance than in the case where the element 52 and resilient members 53 and 54 are fitted on the same plane of the base 51 as described above. Further, the flexible contact member 55 may consist of not only said laminated plate, but also a thin metal plate slitted by punching or etching or a plastics film plated with a conductor layer.

There will now be described by reference to FIG. 4 a variable resistance device according to a third embodiment of the invention. On the upper surface of a base 61 made of electrical insulating material such as wood or plastics there is formed a depression 62 extending in the longitudinal direction of said base 61. Further at the central part of said depression 62 is cut out a groove 63 extending similarly in the longitudinal direction of said base 61. Into the groove 63 is fitted a narrow rectangular platelike element 64 of electrical resistance material. From above the base 61 is stretched a flexible contact member consisting of an elastic screen prepared from, for example, a netlike formation of nylon or polyester, in a manner to cover said depression and be supported on both lateral edges of the base 61. On that part of the underside of said screen 65 facing the resistance element 64 is mounted a conductor film 66 preferably 10 to 20 microns thick by bonding or vapor depositing a metal foil. The depth of the depression 62 of the base 61 and the thickness of the resistance element 64 are so chosen as to allow a clearance of about 1 to 2 mm. between the conductor film 66 and element 64.

With a variable resistance device of the aforementioned arrangement, when the screen 65 is depressed by the finger, it is locally brought into contact with the resistance element 64 due to its elasticity. The resistance prevailing between one end of the resistance element and a conductor wire (not shown) connected to the conductor film 66 assumes a certain value. The sliding of the finger along the resistance element 64 will successively vary said value. If, in this case, the upper surface of the screen 65 is shielded, where required, with a protective cover 67 such as piled cloth, then there will be smoothly realized a portamento performance.

There will now be described by reference to FIG. 5A a variable resistance device according to a fourth embodiment of the invention. On the upper surface of a base 71 made of, for example, wood or plastics, there is formed a depression 72. To the central part of said depression 72 is fitted a narrow rectangular element 73 of electrical resistance material extending in the longitudinal direction of the base 71. On both lateral edges of the base 71 is supported a thin conductor plate 74 acting as a flexible contact member in a manner to cover the element 73. In said thin conductor plate 74 are cut out a plurality of slits 75 by etching or punching in a length smaller than the width of the base 71. In this case, said slits 75 are formed in the transverse direction of said thin conductor plate 74 in a manner to occupy the major part of its width. Both ends of the slits are slightly inclined in a horizontal plane with respect to the transverse direction of said conductor plate 74 at the same angle. Accordingly, the intervening portions 76 between the slits 75 are shaped like said slits 75. Said intervening portions 76 between the slits 75 are bent near both ends thereof toward the same plane as that defined by the upper surface of the thin conductor plate 74. When, therefore, said intervening portions 76 are depressed by the finger, the bent parts cause the resultant moment to be applied downward and in consequence the intervening portions 76 to be depressed to contact the resistance element 73. In this case, only those of the intervening portions 76 which are depressed are brought into contact with the element 73 due to the presence of said bent parts. Accordingly, when the finger depressing the conductor plate 74 is gradually shifted as in the case of the variable resistance device in the preceding embodiments, then the magnitude of resistance prevailing between one end of the resistance element 73 and a conductor wire (not shown) connected to said conductor plate 74 will vary in succession. The width of said slits and intervening portions therebetween is preferably about 0.3 to 1 mm., although in FIG. 5A the width is shown in an enlarged scale. Further, if required, the upper surface of the thin conductor plate 74 acting as a flexible contact member is shielded with a protective cover 77, for example, a piled cloth as is practised in the variable resistance device of the foregoing embodiments.

FIG. 5A represents a case where the intervening portions 76 between the slits 75 are bent at both ends to the same side with respect to the transverse direction of the conductor plate 74. However, said intervening portions 76 may be bent only at one end as shown in FIG. 5B. Further, as shown in FIG. 5C, both ends of said intervening portions 76 may be bent to opposite sides with respect to the transverse direction of the conductor plate 74. When the outermost ends of the bent parts of the intervening portions between the slits shown in FIGS. 5A and 5C are further so bent as to have parallel parts with the central part of the intervening portion as illustrated in FIGS. 5D and 5E, then there will be obtained the same effect as realized by the preceding embodiments. In FIG. 5B to FIG. 5E, the widths of the slits and intervening portions are shown in an enlarged scale for the sake of clarity.

There will now be described by reference to FIG. 6A a variable resistance device according to a fifth embodiment of the invention. At the central part of the upper surface of a base 81 made of electrical insulating material such as wood or plastics there is formed a first depression 82 extending in the longitudinal direction of the base 81 and further on both lateral sides are formed second depressions 83 and 84 in parallel to said first depression in a manner similarly to extend in the longitudinal direction of said base 81. At the central part of said first depression 82 is fixed a narrow rectangular element 85 of electrical resistance material. On said base 81 is mounted a thin conductor metal plate 86 acting as a flexible contact member in a manner to cover said resistance element 85. In the thin conductor plate 86 there are cut out a plurality of slits 87 defining a plurality of intervening portions 88 therebetween. The width of said slits 87 and intervening portions 88 is preferably 0.3 to 1 mm., although in FIG. 6A the width is shown in an enlarged scale. Both ends of each of said intervening portions 88 are bent by a press or the like into depressions 89 and 90 having a semicircular cross section whose bottoms project to the same side. When said thin conductor plate 86 is mounted on the base 81, the semicircular bent ends 89 and 90 of said intervening portions 88 are disposed in the second depressions 83 and 84 respectively which are positioned adjacent to both sides of said first depression 82. Further, if necessary, the upper surface of the thin conductor plate 86 is shielded with a protective cover 91 as in the variable resistance device of the foregoing embodiments, said cover being fixed to both sidewalls of the base 81.

With the variable resistance device according to the embodiment of FIG. 6A, when the intervening portions 88 between the slits 87 are urged downward by the finger, said portions 88 are fully bent, as illustrated by the phantom line 92 of FIG. 6B, to contact the resistance element 85 in such a manner that said terminal semicircular depressed parts 89 and 90 are allowed to open slightly outward as shown in FIG. 6B. In this case, those of the intervening portions 88 which are not depressed are not subjected to any external force, so that they are prevented from contacting the resistance element 85. The resistance is successively varied in the same manner as in the preceding embodiments.

The aforementioned variable resistance device may be used alone with the arrangement indicated in FIG. 7 and also in conjunction with an electronic musical instrument such as the prior art electronic organ.

Claims

What is claimed is:

1. A variable resistance device for use in a portamento performance comprising

a narrow base made of electrical insulating material,

an elongated element of electrical resistance material disposed at the substantially central part of said base in a manner to extend in the longitudinal direction of said base so as to be used as an element for determining the frequency of signals sent forth by a tone signal generator,

a flexible sheetlike contact member disposed above said elongated element and having at least that part thereof facing said elongated element made of electrically conductive material,

means which, while there is not applied any external force to said contact member, cause said contact member to be supported on both lateral edges of said base with a prescribed clearance allowed between said contact member and said elongated element,

said base having a depression formed on its surface in which said element is to be disposed and separate inclined planes formed on both lateral edges of said base in a manner to extend in its longitudinal direction and to descend toward its lateral edge, and

said contact member is an electrically conductive metal plate having a plurality of slits so formed as to have a greater length than the width of said base and extend in the transverse direction thereof and to the lateral edges of the base.

2. The device according to claim 1 wherein said contact member is covered with a soft material little subject to expansion and contraction.

3. A variable resistance device for use in a portamento performance comprising

a narrow base made of electrical insulating material,

an elongated element of electrical resistance material disposed at the substantially central part of said base in a manner to extend in the longitudinal direction of said base so as to be used as an element for determining the frequency of signals sent forth by a tone signal generator,

a flexible sheetlike contact member disposed above said elongated element and having at least that part thereof facing said elongated element made of electrically conductive material,

means which, while there is not applied any external force to said contact member, cause said contact member to be supported on both lateral edges of said base with a prescribed clearance allowed between said contact member and said elongated element, and

said contact member consists of an electrically conductive metal plate having a large number of slits formed in its transverse direction and being supported by resilient members fixed on both lateral sides of the elongated element disposed on the surface of said base in a manner to extend in the longitudinal direction of said base with a prescribed clearance allowed between said contact member and said element.

4. The device according to claim 3 wherein said contact member is covered with a soft material little subject to expansion and contraction.

5. The device according to claim 3 wherein the plane of the base to which the element is fitted is positioned higher than that to which the resilient member is attached.

6. A variable resistance device for use in a portamento performance comprising

a narrow base made of electrical insulating material,

an elongated element of electrical resistance material disposed at the substantially central part of said base in a manner to extend in the longitudinal direction of said base so as to be used as an element for determining the frequency of signals sent forth by a tone signal generator,

a flexible sheetlike contact member disposed above said elongated element and having at least that part thereof facing said elongated element made of electrically conductive material,

means which, while there is not applied any external force to said contact member, cause said contact member to be supported on both lateral edges of said base with a prescribed clearance allowed between said contact member and said elongated element,

said base has a depression formed on its upper surface in a manner to extend in its longitudinal direction in which said element is to be disposed, and

said contact member has a large number of slits, at least one end of each of which is inclined in a horizontal plane with respect to the transverse direction of said base and the remainder part thereof is disposed parallel to the transverse direction of said base.

7. The device according to claim 6 wherein said contact member is covered with a soft material little subject to expansion and contraction.

8. The device according to claim 6 wherein both ends of said slits are inclined in a horizontal plane with respect to the transverse direction of the base to the same side at the same angle.

9. The device according to claim 8 wherein the outermost tip of the end of each of said slits which is inclined in a horizontal plane with respect to the transverse direction of the base further extends in the transverse direction of the base.

10. The device according to claim 6 wherein both ends of the slits are inclined in a horizontal plane with respect to the transverse direction of the base in opposite directions.

11. The device according to claim 10 wherein the outermost tip of the end of each of said slits which is inclined in a horizontal plane with respect to the transverse direction of the base further extends in the transverse direction of the base.

12. A variable resistance device for use in a portamento performance comprising

a narrow base made of electrical insulating material,

an elongated element of electrical resistance material disposed at the substantially central part of said base in a manner to extend in the longitudinal direction of said base so as to be used as an element for determining the frequency of signals sent forth by a tone signal generator,

a flexible sheetlike contact member disposed above said elongated element and having at least that part thereof facing said elongated element made of electrically conductive material,

means which, while there is not applied any external force to said contact member, cause said contact member to be supported on both lateral edges of said base with a prescribed clearance allowed between said contact member and said elongated element,

said base has a first depression formed at its central part in a manner to extend in its longitudinal direction in which said element is to be disposed and a pair of second depressions formed adjacent to both lateral sides of said first depression in a manner similarily to extend in the longitudinal direction thereof,

said contact member consists of a conductor plate having a large number of slits formed in the transverse direction of said conductor plate, defining a large number of intervening portions therebetween, and

each of said intervening portions between said slits has a pair of bent end portions having a semicircular cross section formed to the same side with respect to the upper surface of said conductor plate in such a manner that said bent end portions are located in said pair of second depressions respectively.

13. The device according to claim 12 wherein said contact member is covered with a soft material little subject to expansion and contraction.