Improvements to magnet and cartridge assembly for a turntable

Abstract

A cartridge 30 for an audio turntable (fig 1) comprises a plurality of electromagnetic wound coils 42, 44, 46, 48, located on respective, spaced apart, bars to position the same to define therebetween a field in which a magnet 38 is positioned. Relative movement between the said magnet and coils is possible in response to movement of the stylus 26 to create a variation in an electrical current which is subsequently translated into an audio signal. The magnet is at least partially formed of neodymium and may be provided in the form of an elongate rod located in a port at an end of the cantilevered body 32. The invention also relates to audio apparatus including the magnet and an apparatus and a method for magnetising the magnet to a sufficient value (up to 5 Tesla) to be effective in use.

Description

The invention to which the application relates is to a magnet and a cartridge assembly for use as part of an audio turntable and with the aim of improving the performance of the cartridge with respect to comparative conventional cartridges and hence improve the audio quality. The invention is particularly, although not necessarily exclusively, related to a cartridge of a type known as a Moving Magnet cartridge which is provided as a substantially integral unit for attachment to an arm at a first end and the arm, in turn, is mounted, at or adjacent to the opposing end from the cartridge, to the turntable base and adjacent to a platter on which a record, such as an album, is placed to as to be rotated when the platter is driven to rotate by a drive motor and belt located in the base. Turntable apparatus of this type are well known and the pick up or transfer and the audio from the album into a form for the generation of audio via a connected amplifier and speakers typically utilises relative movement between a configuration of metal wound coils, and a magnet which is mounted in a field or space defined by the coils and the magnet forms or is part of a member on which a stylus, such as for example, a diamond stylus, is mounted. The diamond stylus is provided to move along the groove on the record and react to changes in the groove which represent different audio sounds and which are translated to relative movement between the coils and the magnet. The relative position creates an electrical current and the relative movement causes change in the current and the current is transferred and variations in the current are translated into audio generated via the amplifier and speaker. There are several different types of cartridge arrangement, another of which is a movable coil arrangement in which the coils move relevant to the fixed position magnet. The movable magnet cartridge arrangement has the magnet positioned on a cantilevered member on which the stylus is also mounted and the cantilevered arrangement of the member means that variations in the position of the stylus, change the position of the member and in turn, the position of the magnet with respect to the coils which are provided in a fixed position on bars with typically four bars being provided, each of which has a coil wound thereon and the magnet is located within a field between the said coils. Conventionally, the movable magnet cartridges use conventional magnets with a relatively weak magnetic strength. As a result of this the gap between the magnet and the respective coils, is required to be as small as possible in order to improve the detection of what are relatively dimensionally small variations in the movement of the magnet, and hence change of current, in order to provide the required quality of audio reproduction. However, this tn turn, provides problems in terms of the tolerance of the manufacture of the coils and the positioning of the magnet as any offset or incorrect positioning of the magnet at the time of manufacture or indeed subsequently during use of the apparatus, with respect to the coils can result in a relatively large impact on the audio quality. As such, at present, considerable time is taken to check the relative positions and, if necessary adjust tire components such as the winding of the coils, the formation of the bars on which the coils are wound and / or the positioning of the magnet at the manufacturing stage. Furthermore, the need to provide these coils in a relatively close position with regard to the magnet, typically means that the bars on which the coils are mounted, are required to be bent in order to provide the relatively close positioning which in turn, further increases the complexity of manufacture of the same. It is also conventionally the case that the cartridge body is formed from a plurality of components which are joined together to form the cartridge and, furthermore, in order to correctly position and retain the respective components with regard to the body, metal inserts are typically required to be inserted into the plastics material body in order to provide sufficiently secure and accurate positioning of those components during use. It is found that the provision of these inserts and relative movement between the parts which form the body of the cartridge can, in turn, cause inconsistencies, and adversely affect, the performance of the cartridge and the audio reproduction. A further problem is that the magnets which have conventionally been used, are believed to be of the highest magnetic strength possible, despite the problems which the use of the same can cause and, until now, no alternative magnet or magnet arrangement has been utilised. An aim of the present invention is to provide improvements to a cartridge for an audio turntable, and typically a cartridge of the type known as a movable magnet cartridge and which allows improvements in the manufacturing of the cartridge and the quality of the audio reproduction. In a first aspect of the invention there is provided a cartridge for an audio turntable, said cartridge including a plurality of electromagnetic wound coils, located on respective bars to position the same so as to define therebetween a field in which a magnet is positioned such that relative movement is possible between the said magnet and coils so as to create a variation in an electrical current which is translated into an audio signal and wherein said magnet is at least partially formed of neodymium. In one embodiment, the said cartridge is of the Movable Magnet cartridge type in which the magnet is mounted towards one end of a cantilevered member and, at the opposing end, there is provided a stylus which can be moved to locate and move along the groove of a record and so detect and follow variations in said groove. In one embodiment the said member is mounted in a cantilevered manner in a body of the cartridge such that the variations which are detected by the stylus are transferred via the movement of the member and hence magnet and so alter the position of the magnet in the field defined by said coils. In one embodiment, the said magnet is exposed at the external surface of the member. In one embodiment the magnet is provided in the form of an elongate rod which is typically located in an open port provided at said end of the cantilever member. In one embodiment, the said magnet is magnetised using a magnetic field strength of up to 5 Tesla by placing the same within magnetising apparatus. In one embodiment, prior to placing the magnet into the magnetising apparatus, the said magnet is placed, with a plurality of further magnets, into a jig and said jig is in turn located in the magnetising apparatus. It is found that this allows the magnetisation of a plurality of said magnets at the same time in a uniform manner and therefore represents a cost effective and economical way to operate the magnetising apparatus and hence achieve the magnetisation of a plurality of said magnets for use with the apparatus. In one embodiment, the magnets and members to which the same are adhered, are placed into the said jig. Typically said magnets are provided in an equally spaced arrangement around a circular path within the jig and located within a housing, the said housing including an external part which is movable between a substantially sealed position for use during the magnetisation of the magnets and an open position which allows the loading and removal of said magnet assemblies. In one embodiment, the said jig, once formed, includes a plurality of interlocked parts. In a further aspect of the invention there is provided An audio apparatus, said audio apparatus comprising a base, a rotatable platter, a motor and drive assembly to rotate the platter, an arm located on said base at or adjacent to one end, and, at the opposing end, a cartridge is located thereon, said cartridge including a body, a plurality of electromagnetic coils which define a field and in which is located at least one end of a cantilevered member which includes a magnet and at the opposing end a stylus is located and wherein said magnet is magnetised using magnetic field strength of up to 5 Tesla. Typically the magnet is formed of neodymium material. Typically, the said magnet has an N (Mega Gauss Oresteds (MGOe)) rating of 55 and preferably? is provided in an uncoated condition. In one embodiment the magnet is formed by sintering of powder into dimensions required to allow the same to be fitted to the said cantilever member. Typically, as a result of increasing the magnetic field strength the criticality of the relative dimensions between the magnet and coils is reduced in terms of the quality of audio so that the relevance of any inconsistencies in the positioning of the magnet with regard to the field and the coils, is less significant and therefore reduces the time, checks and / or adjustment required to check each product at the time of manufacture and / or increases the quality of the apparatus and audio reproduction. In one embodiment, the number of turns or windings for each of the coils, may be significantly reduced in comparison to conventional apparatus without affecting the quality of the audio reproduction in comparison to conventional apparatus. In one embodiment the windings in the coil may be in the region of 1200-1300 windings which is approximately 2 / 3 of that of the conventional coil. In one embodiment the body of the cartridge is formed from polyphenylene sulfide (PPS) which is an organic polymer consisting of aromatic rings linked by sulfides. In one embodiment the cartridge includes inserts that allow the location of the cartridge with the arm and the inserts are located in threaded apertures formed directly in the PPS body thus removing the need for an insert to be added for fixing of the inserts. In a further aspect of the invention, there is provided apparatus for magnetising magnets for use in an audio cartridge, said apparatus including a jig with a first part including a plurality of location means at spaced apart intervals, said jig further including a guide part and a sheath housing is provided to be selectively movable along and with respect to said guide means between a loading and unloading position in which said magnets can be placed into and removed from said location means, and a closed position to form a closed housing in which the said magnets are located during magnetisation with the jig placed in magnetising apparatus. Typically said sheath can be engaged so as to be retained in either, and typically both the loading / unloading position and the closed position. In a further aspect of the invention, there is provided a method of magnetising magnets for use in an audio cartridge, said method comprising the steps of providing a jig including a plurality of location means, each of said location means provided to receive and locate a magnet or a member including a magnet, moving a sheath housing into position so as to enclose said magnets within the closed jig and placing said jig into said magnetising apparatus and operating the same to magnetise the magnets of each of the members within the said housing. In one embodiment, the jig includes a gripping part which allows the jig to be gripped during use in the magnetising apparatus and during transport. Specific embodiments of the invention are now described with reference to the accompanying drawings wherein: Figure 1 illustrates a turntable apparatus in accordance with one embodiment of the invention in a schematic manner. Figures 2 and b illustrate perspective views of a cartridge assembly in accordance with one embodiment of the invention. Figures 3a and b illustrate an embodiment of a member for use with a cartridge of the type shown in figure 2 in accordance with one embodiment of the invention. Figures 4a-c illustrate views of a jig in accordance with one embodiment of the invention. Referring firstly to Figure 1, there is illustrated, for the purposes of understanding the current invention, a turntable apparatus 2 within which the invention can be incorporated. The apparatus includes a base 4, feet 6 on the underside of the base which serve to locate the base on a support surface such as a table or stand when in use. Mounted within the base 4 is a drive assembly of a conventional form typically comprising a motor and a drive belt which is rotated by the motor, and which is also engaged to rotate a platter 14 about axis pin 10. The top surface of the platter receives thereon a record 16 which rotates along with the platter. In order to allow audio to be created from the record, the apparatus further includes a pick up or tone arm 18 which is provided on a mounting bracket 20 to the base 4 and which can be selectively pivotably moved about axis 22 between a storage position at one side of the platter and a position overlying the platter and hence record 16 and the arm is lowered and raised as indicated by arrow 24 and, when lowered, a stylus 26 positioned at a free end 28 of the arm is brought into contact with the groove on the record. The stylus 26 is provided as part of a cartridge 30 and a form of which in accordance with the invention is shown in Figures 2a and b. The stylus 26 detects alterations in the groove of the record, typically the depth of the same, to be detected and, these alterations are in turn electrically transmitted to an amplifier and in turn speakers which allow audio to be generated to the user and hence the audio represented by the record groove, to be reproduced to the user. The invention is particularly related to the provision of the cartridge 30 and in which the stylus is attached to a member 32 and the member 32 is mounted in a cantilever arrangement so as to be relatively movable with respect to the body 34 in reaction to the variations in the groove detected by the stylus. The member is also provided with, at the end 36 opposing the stylus 26, a magnet 38. The member 32 is shown in more detail in Figures 3a and b and it will be appreciated that once the stylus 26 is in position and attached and the magnet 38 is attached to the end 36 of the member 32 a substantially unitary and integral member is formed. In one embodiment the magnet is provided as a rod which is inserted into an open port located at the end 36 with the member, at least at this portion provided in a tubular form so that the magnet can be located and gripped therein. The member is located on the body 34 of the cartridge so that the magnet 38 is located within a field 40 in the body, with the field defined by the position of bars around which wire is wound to form an electromagnetic coil. In this embodiment four coils are provided 42, 44,46,48 are provided and they respectively define the corners of the field 40. The coils are held in a fixed position in the body via supports 50,52 and due to the plastics material used to form the body, can be directly engaged with the plastics material and hence alter the position of the member in said field. The cantilevered member 32 allows movement to be transferred intermediate the ends of the member 32 so that the magnet 38 position relative to the coils m the field 40 alters when the stylus position is affected by the record groove and so alters the particular current which is transmitted from the cartridge via electrical contacts 54. In accordance with the invention, the magnet 38 is formed of neodymium material, typically by sintering and is preferably uncoated. The magnet, once formed, is magnetised using a field strength of up to a value of 5 Tesla which is a relatively high magnetic strength. The provision of this relatively high magnetic strength means that the effect of a change in position of the member 32 and hence change of position of the magnet 38 in said field 40 is more pronounced and is detected more clearly and reliably. In order to be able to magnetise the magnet 38 to the sufficient magnetic strength, magnetisation apparatus is required to be used into which the magnets are placed and, while this would be a prohibitively expensive process for magnetisation of one magnet at a time, this problem has been overcome in the current invention by allowing a plurality of magnets to be magnetised simultaneously and uniformly by the magnetising apparatus so that the magnets can be magnetised in batches up to the required relatively high magnetic strength and hence reduce the cost of magnetisation per magnet in comparison to conventional approaches. This is achieved in accordance with one embodiment of the invention utilising a jig apparatus in which a plurality of said members can be securely held and positioned so as to allow the uniform magnetisation of the same. An embodiment of a suitable jig is shown tn Figures la c with the jig shown in a loading / unloading position in Figure 4a, an in use position in Figure 4b and the first part with locating means of the jig shown in more detail in Figure 4c. Turning firstly to Figure 4a there is shown the jig 56 with a first part 58 in which there is provided a series of location means for the members 32 with the magnet 38 and one of the members is shown in position. The first part 58 is located to a guide part 60 which extends along longitudinal axis 62 to a gripping part 64. Also provided is sheath portion 66 which is slidable along said guide part and along the axis 62 between a loading / unloading position as shown in Figure 4a and in use position as shown in Figure 4b and in which position the members 32 are located within the sheath and hence within a closed housing and in which position the jig 56 can be moved into the magnetisation apparatus and the magnets of the respective members 32 magnetised to the required value. Typically the guide part 60 includes engagement formations which locate with formations on the interior of the sheath to allow guided movement of the sheath between the respective positions and also the selective retention of the sheath in one or both of the positions. The gripping part 64 enables improved handling of the jig manually and / or by automated apparatus and may take a different from to that shown. The number of locations means 66 for the respective members 32 and / or the number of members positioned on the jig at an instance of use can be selected for specific batch sizes and / or economic benefit but in this embodiment the location means are provided a series of equally spaced ports which pass into the first part 58 of the jig and which are spaced around, in this example concentric rings of location means 68, 70 as illustrated in Figure 4c and in which a number of members 38 are shown in located positions. It should be appreciated that different versions of the cartridge can be provided and all incorporate the inventive aspects of this application. For example, there may be differences in the cantilever and / or stylus having different types and profiles of diamonds whilst the body, coils, and design of assembly all remain the same throughout. In one example, the cartridge may include an elliptical diamond shape stylus, another version may have a spherical diamond blank which is ground to a perfect elliptical shape stylus and another may include a fineline diamond profile stylus. In each case it will typically be possible for the cartridges to be assembled and formed independently of the remainder of the audio apparatus and then selected to be fitted to the arm at the time of assembly of the audio turntable and the cartridge may then be replaceable over time without affecting the other components of the turntable.

Claims

1. A cartridge for an audio turntable, said cartridge including a plurality of electromagnetic wound coils, located on respective bars to position the same so as to define therebetween a field in which a magnet is positioned such that relative movement is possible between the said magnet and coils so as to create a variation in an electrical current which is translated into an audio signal and wherein said magnet is at least partially formed of neodymium and the magnet is provided in the form of an elongate rod which is located in a port provided at an end of a cantilevered member.2.Apparatus according to claim 1 wherein the at the opposing end of said cantilevered member, there is provided a stylus provided to be located and move along the groove of a record mounted on a turntable and so detect and follow variations in said groove to generate said audio signal.3 .Apparatus according to claim 2 wherein the said cantilevered member is mounted on a body of the cartridge such that the variations detected by the stylus are transferred via the movement of the member and hence magnet and so alter the position of the magnet in the field defined by said electromagnetic wound coils.4.Apparatus according to any of the preceding claims wherein the said magnet is exposed at an external surface of the member.

5. Apparatus according to any of the preceding claims wherein said cartridge is of the movable magnet cartridge type.6.Apparatus according to any of the preceding claims wherein said apparatus includes a means for allowing the said magnet to be magnetised using a magnetic field strength of up to 5 Tesla by placing the same within magnetising apparatus.7.Apparatus according to claim 6 wherein the apparatus includes a jig in which a plurality of said magnets and said jig is placed into said magnetising apparatus, so as to provide magnetisation of a plurality of said magnets at the same time in a uniform manner.8.Apparatus according to claim 7 wherein the magnets and cantilevered members to which the same are adhered are placed into the said jig.

9. Apparatus according to any of the claims 7 or 8 wherein the magnets are provided in an equally spaced arrangement around a substantially circular path within the jig and located within a housing.

10. Apparatus according to claim 9 wherein the said housing includes an external part which is movable between a substantially sealed position for use during the magnetisation of the magnets and an open position which allows the loading and removal of said magnets.

11. Apparatus according to claim 10 wherein the said jig, once formed, includes a plurality of interlocked parts.

12. Apparatus according to any of the preceding claims wherein the magnet has an N rating of 55.

13. Apparatus according to any of the preceding claims wherein the magnet is provided in an uncoated condition.

14. Apparatus according to any of the preceding claims wherein the magnet is formed by sintering of powder into dimensions required to allow the same to be fitted to the said cantilevered member end.

15. Apparatus according to any of the preceding claims wherein the number of windings in each of said coils is in the range of 1200-1300.

16. Apparatus according to any of the preceding claims wherein the body of the cartridge is formed from polyphenylene sulfide which is an organic polymer consisting of aromatic rings linked by sulfides.

17. An audio apparatus, wherein said audio apparatus comprises a base, a rotatable platter, a motor and drive assembly to rotate the platter, an arm located on said base at or adjacent to one end, and, at the opposing end, a cartridge in a form as defined in any of claims 1-5 and claims 12-16 is located thereon.

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