US3154701A - Pickup for musical instruments - Google Patents

Description

Oct. 27, 1964 c, EVANS 3,154,701

PICKUP FOR MUSICAL INSTRUMENTS Filed May 28, 1962 INVENTOR cm u/vcsr RICHARD El /1N8 Evan, Dam Elli/ cf United States Patent 3,154,701 PICKUP FOR MUSICAL INSTRUMENTS Chauncey Richard Evans, Kalamazoo, Mich, assignor to AftuIlJg (lilorporation, Salt Lake City, Utah, a corporation 0 ta Filed May 28, 1962, Ser. No. 197,963 4 Claims. (Q1. 3109.6)

This invention relates to pickups for musical instruments, and more particularly, to piezoelectric pickup units for converting mechanical vibrations generated in musical instruments into electrical signals that may be supplied to amplifiers and loudspeakers. Although certain features of the invention may be applied in various musical instruments, it will be convenient to describe the invention in connection with electric guitar apparatus. Having gained an understanding of this form of the invention, persons skilled in the art will appreciate the manner in which the principles of the invention may be applied in other instruments.

Although the use of piezoelectric transducers in pickups for musical instruments has been suggested heretofore, the actual structures proposed have been deficient in some respects. For example, difiiculties have been experienced in establishing adequate electrical connections between the transducers and the lead wires for conducting the signals to an amplifier. Moreover, shielding has been a problem because the signals are applied to high impedance circuits where stray radiation effects may result in the production of noise components of substantial magnitude.

It is a general object of this invention to provide improved pickups of the piezoelectric type which can be manufactured economically and which will give satisfactory service under the environmental conditions encountered in the use of musical instruments. Other objects and advantages of the invention wil become apparent as the description proceeds.

A pickup in accordance with a preferred embodiment of the invention is made up of a plurality of transducer units supported on a base or platform unit. Each transducer unit includes a hollow, tunnel-shaped, piezoelectric body having inner and outer surfaces which are coated with conductive material to form the terminals of the transducer. The outer conductive coating normally is grounded, and the inner coating carries the electrical signal which is to be amplified and used in the production of music.

The connection to the inner signal-carrying terminal of each transducer is provided by a lead wire carried by a preformed shoe. The shoe conforms in shape to the inner surface of the transducer, and the lead wire passes through the shoe and has a splayed end which may be brought into contact with the inner terminal of the transducer when the shoe is pressed into place. A suitable non-conductive adhesive secures the shoe to the transducer body and serves to hold the lead wire in contact with the inner terminal.

The platform unit of the assembly is provided with electrically conductive coatings also. These coatings are so arranged as to provide electrical connections with the coatings on the outer surfaces of the transducer units when the parts are brought into their final positions. Means are provided for grounding the coatings on the platform unit and the outer surfaces of the transducer units so as to shield the inner terminals and lead wires of the assembly against stray radiation.

A more complete understanding of the invention will be gained from a consideration of the following detailed description of the embodiment illustrated in the accompanying drawings in which:

FIGURE 1 is a partial perspective view of an electric 3,154,701 Patented Oct. 27, 1964 guitar embodying pickup apparatus constructed in accordance with the invention;

FIGURE 2 is a plan view of a bridge assembly for the guitar of FIGURE 1; and

FIGURE 3 is an enlarged cross-sectional view taken along the line 3-3 of FIGURE 2.

The guitar illustrated in FIGURE 1 is of the classic type. It includes a guitar body 2 which may be of conventional construction. Strings 4 are mounted on the guitar in the usual manner, the means for securing the lower ends of the strings 4 being illustrated diagrammatically at 6 in FIGURE 1. The strings 4 are tensioned and, just forwardly of the means 6, they pass over a bridge assembly designated generally by the reference numeral 8.

The bridge assembly 8 includes a plurality of piezoelectric transducer units 10 supported by a platform or base unit 12 which is mounted on the instrument body 2. When the strings 4 are vibrated, the transducer units 10 are stressed so as to generate electrical signals correspond ing to the vibrations of the strings 4. These signals are transmitted through suitable leads to cable means 14 connected to a conventional amplifier and loudspeaker system (not illustrated). The cable means 14 preferably is a coaxial cable having an active signal-carrying core and a grounded conductor insulated from and disposed in surrounding relationship with respect to the core.

Each of the transducer units It is adapted to cooperate with one of the strings 4. To this end, the upper surface of each is provided with a string-receiving notch or groove 16 terminating at its forward end in an abrupt shoulder 18. When a string 4 is disposed within the groove 16 of a transducer unit 10, the shoulder 18 serves to define the end of the vibrating length of that string.

Each of the transducer units 10 includes as its active component a hollow, tunnel-shaped, generally semi-cylindrical body 2 of material capable of generating electrical signals in response to pressure variations. Polarized ceramic materials such as barium 'titanate have been found to be suitable for this purpose. The terminals for the unit are provided by coatings 22 and 24 of conductive material, such as silver, disposed respectively on the inner and outer surfaces of the body 20. These coatings 22 and 24 are applied in such a way as to leave the end faces 26 of the legs of the ceramic body 20 bare. Hence, there is no electrical path from the interior coating 22 to the outer coating 24.

After the coatings 22 and 24 have been applied to the ceramic body 20, a thin preformed covering member or shoe 28 of fiber glass or other suitable insulating material is brought into position and secured to both the inner surface bearing coating 22 and to the end faces 26 of the legs of the body 20'. A non-conducting cement or adhesive 30, such as an epoxy resin, is admirably suited for this purpose.

Prior to the attachment of shoe 28 to the transducer body 20, a lead wire or pigtail 32 is inserted through a small opening at the top of the shoe 28, and the upper end 34 of the lead wire 32 is splayed out over the topmost portion of the shoe. The adhesive 30 normally is applied to the coating 22 and to the end faces 26 of the legs of the ceramic body 2. Then when the shoe 28 is pressed into place, the splayed end 34 of the lead wire 32 is brought into contact with the conductive coating 22 to establish a good electrical connection. The splayed end 34 is held securely by the adhesive 36) and by the shoe 28. This type of assembly provides assurance that the electrical connections will remain in good condition over long periods of active service.

The portions of the shoe 28 that underlie the legs of the ceramic body 2 provide flat surfaces which enhance the positional stabilityof the unit. This feature is of considerable importance in some instances where the manufacturing operations involved in forming the ceramic bodies do not give these bodies perfectly flat bearing faces and where, in the absence of the shoes 28, rocking might result.

After a shoe 28 has been cemented in place, a transducer unit may be completed by applying to the bottoms of the legs a conductive coating 36 of a material such as silver. This coating is applied in such a way as to form a continuation of the coating 24 on the outer surface of the ceramic body 20. It will be noted from FIGURE 3 that the coating 36 is insulated from the coating 22 on the inner surface of the ceramic body by the fiber-glass shoe 28.

The platform or base unit 12 is formed of a body of plastic 13 provided with a plurality of conical openings 38 in its upper surface, with the openings 38 being so arranged that each of the transducer units 10 may overlie one of these openings. With this arrangement, the lead wire 32 from a transducer unitlil may be passed down wardly through one of the openings 38 for connection to the signal-carrying conductor in the cable 14 leading from the pickup to an amplifier.

Referring to FIGURES 2 and 3, it will be observed that the transducer units 10 need not be in exact alignment longitudinally of the base unit 12. Thelead wires 32 normally are slack as they pass through the openings 38, so that the transducer units 10 may be moved slightly relative to the platform unit 12 when the musician desires to make small adjustments in the vibrating lengths of the strings 4 of the guitar. Such fine adjustments are of some importance to classic guitar artists.

The interior of the platform unit 12 is provided with a longitudinal groove or channel 40 and with a transverse groove 42. The cable 14 enters the longitudinal groove 40 at one end of the assembly, and the lead wires 32 from the transducer units 10 enter the groove 40 through the openings 38. The lateral groove'42 provides a channel for a ground wire 44 connected at one end to the ground conductor in the cable 14 and connected at the other end to an electrically conductive coating 46 on the exterior surface of the platform unit 12. An epoxy resin 48 may be employed to fill the groove 42 after the lead 44 has been brought into place.

The coating 46 is applied to the plastic body 13 in such a Way as to cover all of the exposed surfaces except those located at the bottom of the base unit. Spraying techniques have been found suitable. If the coating 46 is applied in such a way as to enter the openings 38 at the top of the plastic body 13, these openings should be reamed or otherwise treated to remove the electrically conductive material therefrom or to interrupt all possible electrical paths between the walls of these openings and the coating 46. Then when the lead wires 32 are brought down through the openings 38 there is no danger that these lead wires will be in electrical communication with the coating 46 on the exterior surface of the platform unit 12.

After the transducer units 10 and the cable 14 have been brought into position with respect to the platform unit 12 and the leads 32 have been connected together and to the core of the cable 14, the bottom surface of the platform unit 12 may be finished. The bottom of the plastic body 13 has secured thereto by a suitable non-conductive cement 50 a sheet of paper or other non-conducting material 52. This provides a smooth bottom surface for the assembly, and the bottom surface then may be coated with a polyester resin 54 for protecting the paper 52 and a conductive coating 56 may be applied'over theentire bottom of the device.

The coatings 46 and 56 are in electrical contact with each other and the coating 46 is in electrical contact with the coating 24 on the exterior surface of the transducer units 10. Since the coating 46 is grounded through the lead 44, it will be apparent that the assembly provides highly efficient shielding for the electrical components within the interior of the assembly. In this connection it will be observed also that the plastic body 13 which forms the base of the assembly is provided with end walls 58 and 69 which extend upwardly to levels above the tops of the inner terminals of the transducer units. The coating 46 covers these end walls also so as to provide protection against the entrance of radiation through the ends of the transducer units. The arrangement is such that the grounded shielding means substantially surrounds the signal-carrying components, and there is very little chance of stray radiationaifecting the electrical signals-appearing on the internal terminals 22 of the transducer unit or on the lead wires 32 that carry these signals to the'cable 14.

Although a single embodiment of the invention has been illustrated and described in detail, various changes and modifications will suggest themselves to persons skilledin the art. It is intended, therefore, that the foregoing description be considered as exemplary only and that the scope of the invention be ascertained from the following claims.

I claim: a

1. A pickup for converting mechanical vibrations in a musical instrument into electrical oscillations comprising a piezoelectric transducer of generally semi-cylindrical shape having an inner surface and an outer surface and having electrically conductive material on said surfaces, a thin shoe of electrically insulating material conforming in contour to the inner surface of said transducer and being adhesively secured thereto, and a lead wire'passing through said shoe and having an end portion held in conducting relation with said electrically conductive material on said inner surface.

' 2. A pickup for converting mechanical vibrations in a musical instrument into electrical oscillations comprising a hollow piezoelectric transducer body of generally semi-. cylindrical shape having a-pair of legs, said transducer body having an inner and an outer surface and electrically conductive coatings on said surfaces, a thin fiber glass shoe conforming in contour to said inner surface and to the end surfaces of said legs of said transducer body and being adhesively secured to said body, and a lead wire passing through said shoe and having an end portion held in-conducting relation with said electrically conductive coating on said inner surface.

3. A pickup for converting-mechanical vibrations in a musical instrument into electrical oscillations comprising a support member having an electrically conductive surface, a tunnel-shaped piezoelectric transducer having at least two legs supported on said'conductive surface of said support member, said transducer having inner and outer surfaces and electrically conductive coatings on such surfaces, a thin shoe of electrically insulating material conforming in contour to said inner surface and to the end surfaces of said legs and being adhesively secured thereto, an electrically conductive coating on the exposed surfaces of the portionsof said shoe at the ends of said legs, the last-mentioned coating being in electrical contact with both the coating on the outer surface of the transducer and said electrically conductive surface of said support member, a lead wire passing through saidshoe and having an end portion held in conducting relation with said electrically conductive coating on said inner surface, and means for grounding said electrically conductive surface of said support member.

4. A bridge for a string instrument comprising a base member having an elongated interior channel and a plurality of longitudinally spaced apart openings extending inwardly from the top of the base member to said channel, electrically conductive material on the bottom, side and top surfaces of said base member, a plurality of tunnel-shaped piezoelectric transducers overlying said openings and having legs supported 'by the top of said base member, electrically conductive material on the outer surface of each of said transducers in electrical contact With said electrically conductive material on the surfaces of said base member, electrically conductive material on the inner surface of each of said transducers, and a plurality of electrical leads each being connected at one end to the conductive material on the inner surface of a transducer and passing downwardly through the opening therebeneath into said channel in said base.

References Cited in the file of this patent

Claims (1)

1. A PICKUP FOR CONVERTING MECHANICAL VIBRATIONS IN A MUSICAL INSTRUMENT INTO ELECTRICAL OSCILLATIONS COMPRISING A PIEZOELECTRIC TRANSDUCER OF GENERALLY SEMI-CYLINDRICAL SHAPE HAVING AN INNER SURFACE AND AN OUTER SURFACE AND HAVING ELECTRICALLY CONDUCTIVE MATERIAL ON SAID SURFACES, A THIN SHOE OF ELECTRICALLY INSULATING MATERIAL CONFORMING IN CONTOUR TO THE INNER SURFACE OF SAID TRANSDUCER AND BEING ADHESIVELY SECURED THERETO, AND A LEAD WIRE PASSING THROUGH SAID SHOE AND HAVING AN END PORTION HELD IN CONDUCTING RELATION WITH SAID ELECTRICALLY CONDUCTIVE MATERIAL ON SAID INNER SURFACE.

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