US3769869A

US3769869A - Electronic musical instrument keying assembly providing a minimum of electrical noise

Info

Publication number: US3769869A
Application number: US00247056A
Authority: US
Inventors: C Nelson
Original assignee: Opsonar Organ Corp
Current assignee: Opsonar Organ Corp
Priority date: 1972-04-24
Filing date: 1972-04-24
Publication date: 1973-11-06
Anticipated expiration: 1990-11-06
Also published as: CA981070A; DE7243122U; JPS4955318A; DE2257553A1; IT975817B; GB1367014A

Abstract

A switch for an electronic organ or other electronic instrument, which produces a minimum of electrical noise even when low level electrical signals pass through the switch for later high gain amplification. The switch includes a cylindrical wire connected to a tone generator, and a strip of conductive elastic material which can be deflected against the wire and that spreads onto the wire to gradually increase the contact area therewith and decrease the contact resistance. An electrically conductive lubricant is applied to the wire and elastic strip so that as the elastic material of the strip spreads under pressure, the spreading portions smoothly slide outwardly. An insulator strip is fastened to the elastic conductive strip, and another elastic conductive strip is fastened to the insulator and is grounded, to shield the first conductive strip from stray electrical currents.

Description

Unite States Patent Nelson, .11.

[ 1 Nov. 6, 1973 [75] Inventor: Carl S. Nelson, Jr., Los Angeles,

Calif.

[73] Assignee: Opsonar Organ Corporation, Bronx,

221 Filed: Apr. 24, 1972 21 Appl. No.: 247,056

[52] U.S. C1. 84/l.01, 84/DIG. 7, 200/159 B,

307/116, 340/365 R [51] Int. Cl. ..G10h l/00 [58] Field of Search 214/101, 1.04, 1.09,

84/1.l,1,27, DIG. 7, 423, 427, 433, 439, 440; 200/159 R, 159 A, 159 B; 338/69, 307/116;

3,626,350 12/1971 Suzuki et a1. 338/69 3,643,041 2/1972 Jackson 200/159 B 3,657,459 4/1972 Peterson et 211.. 84/1.0l 3,668,337 6/1972 Sinclair 200/159 B X 3,694,559 9/1972 Suzuki et al. 154/101 Primary Examiner-Richard B. Wilkinson Assistant Examiner-Stanley .1. Witkowski Attorney-Seymour A. Scholnick [57] ABSTRACT A switch for an electronic organ or other electronic instrument, which produces a minimum of electrical noise even when low level electrical signals pass through the switch for later high gain amplification. The switch includes a cylindrical wire connected to a tone generator, and a strip of conductive elastic material which can be deflected against the wire and that spreads onto the wire to gradually increase the contact area therewith and decrease the contact resistance. An electrically conductive lubricant is applied to the wire and elastic strip so that as the elastic material of the strip spreads under pressure, the spreading portions smoothly slide outwardly. An insulator strip is fastened to the elastic conductive strip, and another elastic conductive strip is fastened to the insulator and is grounded, to shield the first conductive strip from stray electrical currents.

5 Claims, 10 Drawing Figures PATENTED MIN 6 I975 SHEET 10F 3 ELECTRONIC MUSICAL INSTRUMENT KEYING ASSEMBLY PROVIDING A MINIMUM OF ELECTRICAL NOISE BACKGROUND OF THE INVENTION This invention relates to electrical musical instruments.

One type of electronic organ includes a series of signal sources, a high gain amplifier, and a keyboard that can be operated by a musician to selectively connect different signal sources to the amplifier. The signal sources, may generate only a very low level signal, so that if the keyboard switches generate even a low level of noise, the noise will be greatly amplified with the musical signals and will be noticeable in the organ output. Noises of the switch arise from several sources. One source of noise arises from the suddenness of electrical contact which can allow sudden discharges of currents and the creation of popping sounds. This can be minimized by utilizing an elastic resistive con tact member for gradually establishing contact. However, the contact area must increase very rapidly with slight increases in displacement of the operating key if the contact resistance is to quickly fall to a low level. Where a pair of flat contacts are utilized, one of them being an elastic resistive member deformable against the other, the contact area increases only gradually with pressure. Furthermore, as the elastic member is deformed against the other member, the spreading elastic material tends to stickand suddenly slip, so that the contact area may increase in increments and thereby create noise.

Another source of noise in keyboard switches arises from the pick-up of stray electrical signals. Such pickup can be minimized by positioning a grounded conductive plate near the switch to shield it from stray signals. However, if the moveable switch member mechanically vibrates relative to the grounded plate, and if they are at a different potential, then the variable capacitance creates microphonic noises'which may be heard in the organ output.

SUMMARY OF THE INVENTION In accordance with one embodiment of the present invention, an organ keyboard is provided for connecting signal sources to an amplifier in a manner that minimizes noise. The keyboard includes an insulator board that supports a row of cylindrical wires, and a strip of insulative spacer material extending over the row of wires and having windows leading to the wires. An elastic sandwich of strips extends above the spacer strip and can be deflected through the windows in the spacer strip to contact the cylindrical wires. The sandwich includes lower and upper strips of elastic conductive material separated by a middle strip of elastic insulative material. When a downward force is applied to the upper strip, a portion of the sandwich deflects so that the lower strip passes through a window in the spacer strip and into contact with one of the wires. Such downward forces are produced when a musician depresses a key of the keyboard to progressively flatten a leaf spring into the upper strip. The leaf spring progressively lays the lower strip onto the cylindrical wire. This results in a progressively greater contact area between the lower strip and the cylindrical wire.

Each of the wires is connected to a different signal source while the lower conductive strip of the sandwich is connected to the input of the high gain amplifier. The progressive laying down of the lower conductive strip on a wire produces a gradual decrease in contact resistance to minimize noise. The curvature of the round wire results in contact with the strip being reliably established over a small area of the wire, so there is a minimum of making and breaking of microscopic contact points as downward pressure on the strip increases. Both the lower elastic strip and the wire are coated with a conductive lubricant, so that spreading of the elastic strip onto the round wire occurs smoothly rather than in a rapid stick-and-slip manner that would create noise. Each of the signal sources has a grounded terminal and the upper conductive strip of the sandwich is also grounded. The upper sandwich strip shields the lower strip from stray currents. The fact that the upper and lower strips are fixed to an insulative strip between them means that they cannot vibrate relative to one another, and therefore noises that could be created by such relative movements do not arise.

The novel features of the invention are set forth with particularity in the appended claims. The invention will be best understood from the following description when read in conjunction with the accompanying drawmgs.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a partial sectional end view and partial schematic view of an organ constructed in accordance with the invention;

FIG. 2 is a partial perspective view of the keyboard apparatus of the organ in FIG. 1;

FIG. 3 is a partial sectional view of the keyboard of FIG. 1;

FIG. 4 is an enlarged view of a portion of the apparatus of FIG. 3;

FIG. 5 is a partial enlarged view taken on the line 5-5 of FIG. 4, showing the wire and lower strip thereof;

FIG. 6 is a partial perspective view of the apparatus of FIG. 5;

FIG. 7 is a plan view of the apparatus of FIG. 6;

FIGS. 8 and 9 are greatly enlarged views of the wire and lower strip. of FIG. 5, illustrating the manner in which contact is made; and

FIG. 10 is a partial perspective view of an organ chord section constructed in accordance with the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 illustrates an organ which includes a plurality of signal sources l0, 12 which can be connected through

switch portions

14, 16 of a keyboard assembly to an amplifier 18 whose output drives a loudspeaker 20. The

signal sources

10, 12 generate a very low level tone or other signal which is highly amplified by the amplifier 18, so that any noise generated at the switch portions l4, 16 will be highly amplified. The switch arrangement is constructed to minimize the generation of noise as each switch portion is closed and also to minimize the pick-up of stray electrical current.

The switch arrangement includes a row of cylindrical electrical rods or wires such as

wires

22, 24 that are connected to the tone generators l0, 12. A contact strip 26 of highly elastic and particularly electrically conductive material is positioned above the row of

wires

22, 24, and is connected by a conductor 28 to the input of the amplifier 18. When the contact strip 26 is downwardly deflected into contact with one of the wires, as shown for the wire 22, signals from the tone generator can pass from the wire 22 to the contact strip 26 and to the amplifier 18 for amplification and feeding to the loudspeaker 20. The row of

wires

22, 24 is supported on a support board 28' of insulative material. The contact strip 26 is normally spaced from the wires by a spacer strip 30 which has windows 32 through which portions of the contact strip 26 can be deflected. Deflection of the contact strip is accomplished when a musician depresses a key 34 with his finger.

The contact strip 26 is part of a sandwich 36 which includes a shielding strip 38 constructed of elastic and electrically conductive material, and which also includes a central strip 40 constructed of elastic insulative material. The insulator strip 40 is fixed facewise to the two

conductive strips

26, 38, so that all portions of the sandwich deflect together. The shielding strip 38 is connected by a grounding wire 42 to ground potential, and serves to isolate the contact strip 26 from stray electrical currents.

As shown in FIGS. 3 and 4, each key 34 is pivotally mounted on a pivot bar 43 that lies on the support board 28'. A leaf spring 45 has a rearward end portion fixed to the key 34 and an opposite forward end portion biased downwardly against the shielding strip 38. The shielding strip is mounted on a locater strip 49, and the forward end portion of the spring normally bears against the region of the shielding strip that lies over the locater strip. As a musician depresses the forward portion 34F of the key, the spring progressively flattens against the shielding strip, causing it to progressively lay down the contact strip 26 onto the wire 22. Thus, after a large downward key movement, the spring may have the configuration indicated at 45A whkle the contract strip may be moved down to the position 26A against the wire 22.

When the contact strip 26 is deflected and first begins to contact the wire 22, there is only a small area of contact between the strip of wire. The strip 26 is constructed of a material of moderate resistance, or in other words only partial conductivity, so that a small area of contact results in a high contact resistance. As the strip 26 continues to be downwardly deflected, it deforms over the wire so that a larger area of the contact strip touches the wire to provide a relatively low resistance contact. The high initial contact resistance eliminates much of the popping sound that can occur when a low resistance contact is suddenly established between elements that may be at different potentials. The fact that the contact area rapidly increases with even a small additional deformation of the contact strip 26, means that a low resistance contact is quickly established that permits most of the signal from the signal source to flow to the amplifier. When a musician quickly depresses a key 34 with enough pressure to deflect the contact strip 26 far enough to touch a wire 22, be generally has applied enough force to assure the quick establishment of low resistance through the switch.

FIG. 6 illustrates the situation as the contact strip is rolled or progressively layed down onto the wire 22. The initial contact point is at 5] while additional contact points rearwardly of italong the length of the wire are added, such as the point 53. All of these points lie substantially at the top of the wire along the imaginary 7 the wire 22, due to the contact strip being progressively laid down, as well as along the width of the wire due to the contact strip being deformed slightly by the higher pressure near the original contact point 51. There is only a moderate increase in pressure around the original contact point 51, so that the rubber-like material of the contact strip is not mashed which would greatly shorten its useful life.

It has been found that lower noise is produced by utilizing a wire 22 or other contact member which has a rounded upper surface, than one which has a flat upper surface. It is believed that this is due to a reduction in the making and breaking of microscopic contact points. FIGS. 8 and 9 illustrate the condition which is believed to exist near the initial contact point 51. The lower surface of the contact strip 26 is wavy rather than straight, and it changes shape as the pressure on it changes. FIG. 9 shows the strip 26 when contact is first established between it and the wire 22, at the point 51. If the wire 22 had a flat upper surface, then the initial contact point might instead be at another point 61 which is below the level of point 51 (indicated by the imaginary horizontal line 59 which passes through point 51). FIG. 9 shows the strip 26 after additional downward pressure is applied to the strip, which can cause local skewing and deformation of the strip. If the wire 22 had a flat upper surface, then such skewing and deformation of the strip cause point 61 to lift off the flat surface and cause contact to be established at another lower point 63. Such breaking and making of contact results in noise.

In the case of the rounded wire 22, additional pressure merely increases the contact area around the initial contact point 51, because slight changes in the orientation and shape of the contact strip 26 are not enough to lower the

points

61 and 63 into contact with the wire. Once a substantial area of contact is established around the point 51, the contact resistance is low enough that any microscopic contacting and breaking of contact has no noticeable effect. Thus, it is believed that the rounded wire 22 provides lower noise because it assures spreading of contact area around the initial contact point. Of course, it is necessary that the strip 26 does not slide relative to the wire 22 after initial contact is established. This is assured by the mounting of the strip 26 on the elastic shielding strip 38. Regardless of the way in which this is accomplsihed, however,

the rounded wire has been found to lower the noise as contact begins. It should be noted that the wire 22 has an elongated contact portion (where it engages the strip 26) which is convex in only one plane, that being the plane which is perpendicular to its length.

As described above, the contact strip spreads largely sidewardly onto the wire 22, as pressure increases at the locations where it has already touched the wire. The elastic material of the contact strip 26 may have a relatively high coefficient of friction, so that there may be a tendency for the material to repeatedly stick and slip as it spreads out along-the wire. Such rapid sticking and slipping, which may be referred to as stician, can create noticeable noise. To minimize the creation of such noise, a conductive lubricant indicated at 48 and 50 in FIG. 5 is coated on the wire 22 and on the lower surface of the contact strip 26. The contact strip 26 may be constructed of a variety of materials such as silicone rubber impregnated with carbon particles, and the

lubricant

48, 50 may be an extremely fine powered graphite.

The shielding effect provided by the grounded shielding strip 38 could be provided by a simple plate of conductive material rigidly mountedon the organ near the contact strip 26. However, if the contact strip 26 were to vibrate, then a signal would be generated due to such vibrations and it would be fed to the amplifier 18. Such a signal would arise because the contact strip 26 normally has a voltage above ground potential, in those cases where the signal sources l0, l2 generate tones with D C components. A signal source which includes a photo-cell that senses light passing through an optical track is one example of such a source. In such an organ, the contact strip 26 quickly attains the average D C potential created by the signal source and is maintained at that potential by a coupling capacitor 51. In the present keyboard arrangement, extraneous sounds are not created by vibrations of the contact strip 26 relative to the shielding strip 38, because these two strips are fastened together and cannot move relative to each other. The insulator strip is fixed facewise to both of the

strips

26, 38 to prevent any relative movement of them apartand together. The insulator strip 40 may be constructed of rubberized electrical tape commonly used in wrapping wires, but with adhesive on both faces. The shielding strip 38 may be constructed in the same manner as the contact strip 26, as of silicone rubber impregnated with carbon particles. The spacer strip 30, which has the windows 32 through which portions of the contact strip 26 can pass, can be formed of fish paper insulation or a variety of other materials. The use of numerous windows in a single strip facilitates construction of the switch assembly. The sandwich 36 can be maintained in a taut condition in extension over the spacer strip 30.

A main purpose of the shielding strip 38 is to intercept electromagnetic waves from the environment that might otherwise be picked up by the contact strip 26 and be fed to the amplifier. A consequence (which may be unwanted) of the closeness of the

strips

26, 38 is that a high capacitance existsbetween them. Any variation in the separation of the strips 26, 38' would result in a variation in capacitance, and if the

strips

26, 38 are initially at a different DC potential then the change in capacitance tends to cause a change in voltage. This would cause a current flow from the contact strip 26 to the amplifier. If the strip 26 vibrates, but the shielding strip 38 is stationary, then a rapid change in voltage on the strip 26 can occur, which results in a signal being fed to the amplifier 18. This phenomenon is often referred to as microphonics. The present switch construction avoids microphonics by preventing relative movement of the

strips

26, 38, while still permitting deformation of the strip 26. The strip 26 may vibrate, but it is everywhere spaced from the shielding strip 38 by a constant distance equal to the thickness of the insulating central strip 40.

The switch construction can be utilized in a variety of keying arrangements. FIG. 10 illustrates a portion of a switch arrangement with button type keys 70, that is suitable for the chord portion of an organ. Each key or button is slideably mounted in a pair of

plates

72, 74 and bears against a tab 76 formed in a plate 78 of spring material. A grounding strip 80 carries a narrow insulator strip 82 and a narrow contact strip 84. Regions of the contact strip 84 can pass down through windows 86 in a spacer strip 88 to contact cylindrical conductors 90. The conductors 90 are mounted on a circuit board 92 that has conductive ribbons which connect the wires to signal sources.

Thus, the invention provides a switch arrangement which is economical to produce, and which minimizes the creation of noise in an organ that has signal sources of low output. Contact noise is minimized by utilizing

wires

22, 24 of stiff material such as brass, and with a convex surface for receiving a deformable contact strip 26. The contact strip 26 is constructed of highly elastic material which is much more easily deformed than the material of the

wires

22, 24, and the area of contact of the strip 26 with the wires increases in a stable manner that minimizes noise when it is progressively pressed against them. The use of a conductive lubricant on the wires and contact strip minimizes stician as the material of the contact strip spreads out on the wire, thereby minimizing this source of noise. The contact strip is shielded from stray currents by a shielding strip 38 that is also constructed of elastic material, and which is fastened to an insulator that is fastened to the contact strip. The shielding and contact strips therefore cannot vibrate relative to one another, so that microphonic noise is minimized. Of course the insulating strip and shielding strips can be formed as films instead of relatively thick sheets.

Although particular embodiments of the invention have been described and illustrated herein, it is recognized that modifications and variations may readily occur to those skilled in the art and, consequently, it is intended that the claims be interpreted to cover such modifications and equivalents.

What is claimed is:

1. In an electronic musical instrument which includes a manually operable switch for connecting an amplifier input to a signal source that has first and second terminals, and in which the switch includes a first sheet-like switch member that is easily deformable into contact with another switch element, and in which the first sheet-like switch member is connected to the amplifier while the switch element is connected to the second terminal of the signal source, the improvement comprising:

a second sheet-like member of easily deformable insulative material fixed facewise to said first sheetlike switch member and a third sheet-like shielding member of easily deformable electrically conductive material fixed facewise to said second sheetlike member on a face thereof opposite said sheetlike switch member; and

means coupled to said third sheet-like shielding member and to said first signal source terminal for preventing rapid changes in their potential with respect to each other, whereby to prevent vibration of the first switch member with respect to its shield.

2. The improvement described in claim 1 wherein:

said musical instrument includes a plurality of additional switch elements arranged in a row; and

said first sheet-like switch member and said second and third sheet-like members are of elastomeric material and are held in a taut condition in extension along said row of switch elements.

3. The improvement described in claim 1 wherein:

said means for preventing rapid changes in potential connects said shielding member and said first source terminal together to maintain them at the same potential.

4. An electronic musical instruement switch comprising:

a support;

an electrically conductive member mounted on said support, said member having a convex contact portion facing away from said support;

a contact strip of electrically conductive and easily stretched and deformed elastic material;

means for supporting said contact strip in a taut condition so itis spaced from said convex contact portion but can be deflected against it;

manually operable means for deforming said contact strip against said convex contact portion;

a strip of elastic insulative material fixed facewise to a face of said contact strip which lies opposite the face thereof which is nearest said conductive membet;

a second strip of elastic electrically conductive material fixed facewise to a face of said strip of insulative material which is opposite said first named strip of conductive material;

a signal generator having a grounded first terminal and having a second terminal coupled to said conductive member;

an amplifier;

means for coupling the input of said amplifier to said first named strip of conductive material, and

means for grounding said second strip of conductive material.

5. An electronic musical instrument switch comprising:

a support;

an electrically conductive contact member mounted on said support;

a sandwich which includes a first strip of elastic conductive material, a second strip of elastic insulative material disposed facewise against said first strip, and a third strip of elastic conductive material disposed facewise against said second strip on a face thereof which is opposite said first strip, the opposite faces of said second strip respectively fixed to said first and third strips to maintain said first and third strips at a constant distance;

means for supporting said sandwich so that said first strip thereof is spaced from said contact member but can deflect against it;

manually operable key means for selectively pressing against said third strip to cause said first strip to deflect against said contact member;

a signal source having first and second terminals;

means for coupling said second terminal of said signal source to said contact member;

an amplifier;

means for coupling the input of said amplifier to said first strip of said sandwich; and

means electrically coupled to said first terminal of said signal generator and said third strip of said sandwich for maintaining said first terminal at a constant potential with respect to said third strip.

Claims

1. In an electronic musical instrument which includes a manually operable switch for connecting an amplifier input to a signal source that has first and second terminals, and in which the switch includes a first sheet-like switch member that is easily deformable into contact with another switch element, and in which the first sheet-like switch member is connected to the amplifier while the switch element is connected to the second terminal of the signal source, the improvement comprising: a second sheet-like member of easily deformable insulative material fixed facewise to said first sheet-like switch member and a third sheet-like shielding member of easily deformable electrically conductive material fixed facewise to said second sheet-like member on a face thereof opposite said sheet-like switch member; and means coupled to said third sheet-like shielding member and to said first signal source terminal for preventing rapid changes in their potential with respect to each other, whereby to prevent vibration of the first switch member with respect to its shield.

2. The improvement described in claim 1 wherein: said musical instrument includes a plurality of additional switch elements arranged in a row; and said first sheet-like switch member and said second and third sheet-like members are of elastomeric material and are held in a taut condition in extension along said row of switch elements.

3. The improvement described in claim 1 wherein: said means for preventing rapid changes in potential connects said shielding member and said first source terminal together to maintain them at the same potential.

4. An electronic musical instruement switch comprising: a support; an electrically conductive member mounted on said support, said member having a convex contact portion facing away from said support; a contact strip of electrically conductive and easily stretched and deformed elastic material; means for supporting said contact strip in a taut condition so it is spaced from said convex contact portion but can be deflected against it; manually operable means for deforming said contact strip against said convex contact portion; a strip of elastic insulative material fixed facewise to a face of said contact strip which lies opposite the face thereof which is nearest said conductive member; a second strip of elastic electrically conductive material fixed facewise to a face of said strip of insulative material which is opposite said first named strip of conductive material; a signal generator having a grounded first terminal and having a second terminal coupled to said conductive member; an amplifier; means for coupling the input of said amPlifier to said first named strip of conductive material, and means for grounding said second strip of conductive material.

5. An electronic musical instrument switch comprising: a support; an electrically conductive contact member mounted on said support; a sandwich which includes a first strip of elastic conductive material, a second strip of elastic insulative material disposed facewise against said first strip, and a third strip of elastic conductive material disposed facewise against said second strip on a face thereof which is opposite said first strip, the opposite faces of said second strip respectively fixed to said first and third strips to maintain said first and third strips at a constant distance; means for supporting said sandwich so that said first strip thereof is spaced from said contact member but can deflect against it; manually operable key means for selectively pressing against said third strip to cause said first strip to deflect against said contact member; a signal source having first and second terminals; means for coupling said second terminal of said signal source to said contact member; an amplifier; means for coupling the input of said amplifier to said first strip of said sandwich; and means electrically coupled to said first terminal of said signal generator and said third strip of said sandwich for maintaining said first terminal at a constant potential with respect to said third strip.