US3535968A

US3535968A - Adjustable electromagnetic pick-up for stringed musical instruments

Info

Publication number: US3535968A
Application number: US815612A
Authority: US
Inventors: James H Rickard
Original assignee: Kaman Corp
Current assignee: Kaman Corp
Priority date: 1969-04-14
Filing date: 1969-04-14
Publication date: 1970-10-27
Anticipated expiration: 1987-10-27

Description

United States Patent Inventor James H. Rickard Harwinton, Connecticut Appl. No. 815,612

Filed April 14, 1969 Patented Oct. 27, 1970 Assignee Kaman Corporation Bloomfield, Connecticut a corporation of Connecticut ADJUSTABLE ELECTROMAGNETIC PICK-UP FOR STRINGED MUSICAL [56] References Cited UNITED STATES PATENTS 1 2,612,072 9/1952 De Armond 84/1. 15 2,612,541 9/1952 De Armond 84/1.15X

Primary Examiner-W. E. Ray Attorney-Mc Corrnick, Paulding & Huber ABSTRACT: An electrical pickup for stringed musical instruments includes a plurality of magnetic cores adapted to be placed near the strings so that the vibration of a string induces a varying flux through its associated core. A generating winding surrounds all of the cores and has electrical signals induced therein by the varying fluxes through the various cores. The cores are adjustable to vary the spacing between them and the strings and a case providing a magnetic shield surroundsthe coil and cores. The construction of the adjustment means and of the case is such as to prevent the production of extraneous circulating currents opposing the flux variations, and to also allow the generating coil to be positioned in very close proximity to the magnet cores, thereby enhancing the signal produced by the generating coil.

Patented Oct. 27, 1970 Sheet INVENIOR. JAMES H. RIGKARD 4% ATTORNEYS ADJUSTABLE ELECTROMAGNETIC PICK-UP FOR STRINGED MUSICAL INSTRUMENTS BACKGROUND OF THE INVENTION This invention relates to transducers, commonly referred to as electrical pickups, for use with stringed musical instru ments, such as guitars, banjos and-the like for converting the vibrations of the instrument strings into electrical signals which may be amplified and played back through a speaker or speaker system to produce an amplified version of the sound produced by the vibrating strings. More particularly, the invention relates to an electrical pickup of the type employing a plurality of permanent magnet cores, one for each string or set of strings, surrounded by a common generating coil.

The general object of this invention is to provide an improved electrical pickup of the foregoing character and more particularly to provide such a pickup which is of simple construction, convenient to use, easy to adjust and which is capable of producing an output signal of increased intensity in comparison to other such devices presently available so as to require a lesser degree of amplification to produce a given intensity of sound from the associated speaker or speaker system.

SUMMARY OF THE INVENTION The invention resides in an electrical pickup for stringed musical instruments such as guitars, banjos and the like and consists of a plurality of permanent magnet cores which are normally of such a number as to provide one such core for each string of the instrument. The cores are received in a nonmagnetic, electrically nonconductive supporting body, located below the strings, which also supports a common generating winding surrounding all of the cores. The cores project upwardly so as to have their upper ends positioned close to the associated strings and when a string vibrates a varying flux is produced through the associated core and induces a corresponding signal in the generating coil. The lower ends of the cores project through and beyond the bottom of the support body and each includes a radially extending nonmagnetic adjustment arm fixed thereto which extends beyond the outer edge of the coil. A nonmagnetic adjustment screw engagable with the support body and the adjustment arm is also located beyond the outer edge of the coil thereby allowing the coil to pass in close proximity to the magnet cores without the interposition of any part of the adjustment means. An electrically conductive case forming an electric shield surrounds a major portion of the generating coil and has upper and lower openings through which the upper and lower ends of the magnet cores pass. A gap in this case extending from the upper opening to the bottom opening provides a nonconductive zone in the case so as to present an open circuit to electrical currents which would otherwise circulate through the case about the axis of the generating coil and oppose the varying flux passing through the magnet cores, thereby making a greater degree of flux change available for generating an output signal in the generating coil and increasing the intensity of such signal.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a guitar utilizing two electrical pickups embodying this invention.

FIG. 2 is a perspective view of one of the electrical pickups of the FIG. 1 guitar.

FIG. 3 is another perspective view of the electrical pickup of FIG. 2, but taken at a different angle.

FIG. 4 is still another perspective view of the pickup of FIG. 2, but taken at still another angle.

FIG. 5 is an enlarged top view of the pickup of FIG. 2.

FIG. 6 is a transverse sectional view taken on the line 6-6 of FIG. 5.

FIG. 7 is a view partly in section and partly in elevation taken on the line 7-7 of FIG. 5.

DESCRIPTION THE PREFERRED EMBODIMENTS Turning to the drawings, FIG. 1 illustrates, by way of-an example, a guitar 10 having two electrical pickups l2 and 14 embodying this invention. Both of the pickups 12 and 14 are mounted in openings formed in the top of the guitar body and are located below its strings l6, 16. The pickup 12 is located near the lower end of the finger board 18 of the guitar and is intended to pick up the fundamental and, lower harmonics of the string vibrations. The pickup 14, on the other hand, is located near the bridge 20 and is intended to pick up the higher harmonics of the string vibrations. Although desirable for best performance, it is not, however, entirely necessary to have two pickups on the guitar and in some cases guitars and other instruments may be made including only one such pickup.

As explained in more detail hereinafter, and still referring to FIG. 1, each of the pickups l2 and 14 includes a plurality of

permanent magnet cores

22, 22 each of which is associated with a respective one of the strings l6, 16, there being six strings in the illustrated guitar and a corresponding set of six

cores

22, 22 in each of the pickups. In some cases, such as twelve stringed guitars, mandolins and other instruments using closely spaced pairs of strings tuned in unison, a single core 22 may sometimes be used with each such pair of strings, but even in these instruments it is usually desirable to have a separate core 22 for each string.

The two electrical pickups l2 and 14 of FIG. I are identical to each other except for pole spacing and, for the purpose of illustration, FIGS. 2 to 7 show the detailed construction of one of these units which may be taken to be the upper unit 12. Turning to FIGS. 2 to 7, the pickup 12 there shown comprises a base or support body 24 which is made of a nonmagnetic and electrically nonconductive material such as plastic. The support body 24 may be made as a unitary piece, but preferably and as shown best in FIGS. 6 and 7, for ease of manufacture is made in two parts, these parts being a molded upper part 26 and a bottom plate 28. The support body 24 includes a longitudinally extending central portion 30 provided with a plurality of openings 32, 32 which pass therethrough from the top surface 34 of the body to the bottom surface 36. Each of the holes 32 in turn slidably receives a generally cylindrical permanent magnet core 22 made of alnico or the like and having an upper end portion which normally projects upwardly beyond the top surface 34 and a lower end portion which normally projects downwardly beyond the bottom surface 36.

The support body, as best shown in FIG. 6 also includes, on either side of the central portion 30, an upper flange 38 and a lower flange 40, the lower flange 40 in the illustrated case being formed by the bottom plate 28. The top and bottom flanges 38 and 40 are spaced from one another axially of the

magnet cores

22, 22 and receive therebetween a generating winding 42 consisting of many turns of fine wire wound around the central portion 30 so as to surround in common all of the

magnetic cores

22, 22, the shape of the central portion 30 giving the coil an elongated configuration with one elongated portion located on one side of the central portion and another elongated portion located on the other side of the central portion.

Each of the

magnetic cores

22, 22 of the pickup 12 is adjustable along its axis relative to the support body 24 independently of the other coresto vary the spacing between its upper end face and the associated string 16. As a means for accomplishing this adjustment, each magnet core 22 has an adjustment arm 44 of nonmagnetic material fixed to its lower end portion. The arm44 extends radially of the associated core 22 to one side of the center portion 30 of the support body and to apoint spaced beyond the outer edge 46 of the adjacent elongated portion of the coil 40, as shown best in FIG. 6. On this same side of the central portion 30 the upper flange 38 and bottom flange40 of the support member also extend beyond the outer edge 46 of the coil and for each adjustment arm 44 include an opening 48 in the upper flange and an aligned opening 50 in the bottom flange. The two openings 48 and 50 associated with each adjustment arm 44 receive an adjusting screw 52 which is threadably connected with the outer end of the adjustment arm 44. The upper opening 48 is counterbored to receive the head of the screw and to provide a bearing surface for engaging its undersurface. A helical compression spring 54 of nonmagnetic material is received on the screw 52 I and is positioned with its upper end in engagement with the top flange 38 and with itslower end inengagement with the adjustment arm 44, the spring 54 and screw 52 passing loosely through the bottom opening 50. The spring 54, therefore, urges the adjustment arm 44 and attached core 22 downwardly relative to the support body 24 and by turning the screw by means of a tool placed in the slot of its head, the adjustment ann may be moved to different axial positions relative to the screw to change the position of the core relative to the support body and to theassociated string.

Before dismissing consideration of the adjustment means, it should be noted that the arrangement of the various parts of the adjustment mechanism as shown in FIGS. 6 and 7 allows the adjusting screw 52 and the spring 54 to be located beyond the outer edge of the generating coil 42 and allows the generating coil to be located in very close proximity to the

magnet cores

22, 22 thereby providing the closest possible flux linkage between the coil and the varying flux passing through the cores. Also, the springs 54, 54 are received on the screws 52, 52, rather than on the

cores

22, 22 and, therefore, have no influence on the flux. If the springs were placed on the

magnet cores

22, 22, they could act as shorting windings providing a path for electrical currents opposing the flux changes occurring in the magnet cores.

Surrounding the major portion of the support body 24 of the pickup 12 is a case 56 of electrically conductive nonmagnetic material which in addition to its serving as a mechanical housing or cover, also serves to provide an electric shield which shields the coil 42 against stray electric fields in the air which would otherwise be picked up and produce hum or other noise in the speakers. In the illustrated case, the case 56 is made of two parts comprising a generally cup-shaped upper member 58 and a bottom plate 60 both of which are preferably made of brass. As shown in FIGS. 3 and 4, the bottom plate 60 fits within the lower edge of the cup-shaped upper member 54 and is fixed thereto by solder applied at various points along the adjoining edges of the two parts as indicated at 62, 62 in FIGS. 3 and 4. At each end of the pickup the bottom plate 60 projects beyond the adjacent edge of the member 58 and is apertured to provide

mounting ears

64, 64.

The case 56 adjacent the upper surface 34 of the support member 24 includes a relatively large opening 66 generally centered with the axis of the generating coil 42 and through which opening the upper ends of the

magnet cores

22, 22 project. Likewise, the bottom of the case 56 includes a relatively large bottom opening 70, but smaller than the top opening 66, also generally aligned with the axis of the coil and through which the lower end portions of the

cores

22, 22 project. Other

smaller openings

72, 72 are also formed in the bottom of the case for accommodating the adjustment screws 52, 52 and their associated springs 54, 54 and in the upper surface of the case other small openings 74, 74 are provided in registration with the heads of the adjustment screws to allow access to such heads by a screwdriver for rotating the same when making an adjustment.

In considering the case 56, it should be noted that it constitutes a piece of electrically conductive material surrounding the axis of the coil 42 and the

magnet cores

22, 22, and, there fore, if it were a continuous piece of material it would provide a closed circuit for circulating electrical currents opposing the variations in flux passing through the

cores

22, 22. In order to prevent such circulating currents and to thereby increase the intensity of the output signal produced by the generating coil,

the case 56 at one point there along includes a nonconductive zone extending from its upper opening 66 to its lower opening 70. In the illustrated case, this nonconductive zone is formed by a gap 76 in the case, including both the top part 58 and bottom plate 60 thereof, extending from-the top opening 66 to the bottom opening 70. This gap 76, therefore, presents an open circuit to electrical currents which would otherwise circulate about the axis of the coil and around the

magnetic cores

22, 22 and, as explained, permits greater variations in the flux through the magnet cores and as a result of this provides a greater intensity of output signal from the generating coil.

Iclaim:

1. A pickup for stringed musical instruments, said pickup comprising a support body of nonmagnetic and electrically nonconductive material having a top surface and a bottom surface and a longitudinally extending portion provided with a plurality of longitudinally spaced r: parallel holes extending therethrough from said top surface to said bottom surface, a plurality of permanent magnet cores each received in a respective one of said holes, a generating coil wound around said longitudinally extending body portion with its axis generally parallel to said holes so as to surround saidplurality of permanent magnet cores, and a shielding case of electrically conductive material surrounding said support body and said coil, said case having a top opening generally centered with the axis of said coil and a bottom opening also generally centered with the axis of said coil, arid said case further having at one point there along a nonconductive zone extending from the edge of said upper opening to the edge of said lower opening so as to present an open circuit for electrical currents which would otherwise circulate through said case about the axis of said coil.

2. A pickup for stringed musical instruments as defined in claim 1 further characterized by said permanent magnet cores each having a top end portion extending above said top surface and a bottom end portion extending below 'said bottom surface, said upper opening of said case receiving and surrounding said upper end portions of said magnetic cores and said lower openings of said case receiving and surrounding said lower end portions of said cores.

3. A pickup for stringed musicalinstruments as defined in claim 1 further characterized by said nonconductive zone of said case being defined by a gap in the material of said case which gap extends from the edge of said upper opening to the edge of said lower opening. I

4. A pickup for stringed musicalinstruments as defined in claim I further characterized by each of said permanent magnet cores being slidably received in its respective hole of said support body, and an adjustment means associated with each of said cores for adjusting the same along its axis relative to said body to vary the amount by which the upper end thereof projects beyond said upper surface of said body.

5. A pickup for stringed musical instruments as defined in claim 4 further characterized by said adjustment means for each of said cores comprising an arm attached to the lower end portion of said core beyond said support body and coil and extending radially to a point beyond the outer edge of said coil, and an adjustment screw carried by said support body and threadably engaged with said arm, said screw being located beyond said outer edge of said coil.

6. A pickup for stringed musical instruments as defined in claim 5 further characterized by said support body including axially spaced, generally radially extending upper and lower flanges between which said generating coil is received, said generating coil including two elongated portions each extending along one side of said longitudinal portion 'of said support body, said upper and lower flangesof said support body along One of said elongated portions extending radially outwardly beyond said coil portion, and having axially aligned openings for receiving said adjustment screw, said opening in the upper flange including a seat for engagement with the head of said adjustment screw and said adjustment screw passing loosely through the opening in said bottom flange, and a helical spring received on said screw and working between said arm and said support body for urging said screw and said magnetic core downwardly relative to said support body.

7. A pickup for stringed musical instruments as defined in claim 6 further characterized by said spring passing loosely through said opening in said bottom flange and engaging said upper flange.

8. A pickup for stringed musical instruments as defined in claim 7 further characterized by each of said openings in said upper flange being recessed to receive the head of the associated adjustment screw and said case including a portion which adjacent said top surface of said support body extends generally over the area of said upper flange containing said adjustment screw openings, said case portion including individual openings each aligned with a respective one of said screws for providing access to the associated screw head for adjustment purposes.

9. A pickup for stringed musical instruments, said pickup comprising a support body of nonmagnetic and electrically nonconductive material having a top surface and a bottom surface and a longitudinally extending portion provided with a plurality of longitudinally spaced parallel holes extending therethrough from said top surface to said bottom surface, a plurality of permanent magnet cores each slidably received in a respective one of said holes and having a top end portion extending above said top surface and a bottom end portion extending below said bottom surface, a generating coil wound around said longitudinally extending body portion with its axis generally parallel to said holes therein so as to surround said plurality of permanent magnet cores, a shielding case of electrically conductive material surrounding said support body and said coil, said case having a top opening through which said top end portions of said magnetic cores extend and a bottom opening through which said bottom end portions of said magnetic cores extend, and a plurality of means each associated with a respective one of said cores for adjusting the associated core along its axis relative to said support body to vary the extent by which its upper end portion projects above said top surface of said support body, each of said adjustment means including an adjustment arm of nonmagnetic material fixed to the lower end portion of the associated magnetic core below said case and extending radially of said core to a point located beyond the outer edge of said generating coil, and an adjustment screw located beyond said outer edge of said generating coil and engaged with said support body and said adjustment arm for moving said adjustment arm relative to said body.

10. A pickup for stringed musical instruments as defined in claim 9 further characterized by said support body including axially spaced, generally radially extending'upper and lower flanges between which said generating coil is received, said generating coil including two elongated portions each extending along one side of said longitudinal portion of said support body, said upper and lower flanges of said support body along one of said elongated portions extending radially outwardly beyond said coil portion and having axially aligned openings for receiving said adjustment screw, said opening in the upper flange including a seat for engagement with the head of said adjustment screw and said adjustment screw passing loosely through the openings in said bottom flange, and a helical spring received on said screw and working between said arm and support body for urging said screw and said magnetic core downwardly relative to said support body.

11. A pickup for stringed musical instruments as defined in claim 10 further characterized by said spring passing loosely through said opening in said bottom flange and engaging said upper flange.

12. A pickup for stringed musical instruments as defined in claim 11 further characterized by each of said openings in said upper flange being recessed to receive the head of the associated adjustment screw, and said case including a portion which adjacent said top surface of said support body extends generally over the area of said upper flange containing said adjustment screw openings. said case portion including individual openings each aligned with a respective one of said screws for providing access to the associated screw head for adjustment purposes.