EP0160279A2 - Improved grounding circuit for moving coil pickup cartridge - Google Patents

Abstract

A pickup cartridge of the moving coil type including a magnetic circuit having, in series, (a) an armature with which the coil is associated, (b) a pole-piece (c) a rear yoke, (d) a magnet, and (e) a front yoke. The improvement constitutes grounding magnetic circuit at either end part of the series magnetic circuit, the grounding point being on the front yoke farthest from the armature or on the surface of the armature.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention
• This invention relates to a moving coil pickup cartridge and, in particular, to the grounding of the magnetic circuit for such a cartridge.
2. Discussion of the Prior Art
• As shown in Fig.l, a moving coil type pickup cartridge may include an armature 3 having a generator coil 2 wound thereabout. The rear of a cantilever 1 is joined at the center of the armature, the cantilever having a stylus tip at its front end. A ring-shaped damper 5 is placed between armature 3 and a pole-piece 4 and the unit is held in place by a stopper 6 formed within the cantilever, a stopper 6' inserted and fixed in pole-piece 4, and suspension wire 7. The magnetic circuit for the cartridge is comprised of a magnet'8, a rear yoke 9, pole-piece 4, armature 3, and front yoke 10. Output voltage is induced in generator coil 2 by rotation of armature 3 during record reproduction, the coil output being applied to output terminals 11 comprising hot terminal H and ground terminal G. Since the space between the generator coil and armature is, in essence, insulated, the metal parts of the main structure including armature 3 must be electrostatically equipotential with generator coil 2 in order to eliminate capacitance and inductance generated in space. Consequently, measures have been taken to ground the magnetic circuit by connecting the ground line G of output terminals 11 to the rear end of pole-piece 4 or rear yoke 9 as shown in Fig.l. These measures have been taken to improve the reproduced sound quality response and the high frequency range.
SUMMARY OF THE INVENTION
• As a result of research regarding various connecting positions for the ground line, it has been discovered, in accordance with the present invention, that two types of grounding the magnetic circuit at a position substantially removed from the armature 3 or at a position of the armature 3 itself contributes most to improved sound quality. Preferably in case of the former the grounding should occur on the surface of front yoke 10 and, most preferably, at the end of the front yoke which is farthest removed from the armature, in case of the latter grounding should occur on the center part of the armature 3.
• Other objects and advantages of this invention will be apparent from a reading of the following specification and claims taken with the drawing.
BRIEF DESCRIPTION OF THE DRAWING
• Fig.l is a diagrammatic illustration in cross-section of a conventional pickup cartridge of the moving coil type in accordance with the prior art.
• Fig.2 and Fig.4 are diagrammatic illustrations in cross-section of a pickup cartridge of preferred embodiments in accordance with the invention.
• Fig.3 and Fig.5 are schematic diagrams for explaining the invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION
• Reference should be made to the drawing where like reference numerals refer to like parts.
• As shown in Fig.2, ground terminal G of output terminals 11 is connected to front yoke 10, which is the (7it;cuit component of the magnetic/farthest from the armature in the sequence of armature 3, pole-piece 4, rear yoke 9, and magnet 8. This is further illustrated in Fig.3. The magnetic circuit comprises in series connection, armature 3, pole-piece 4, rear yoke 9, magnet 8, and front yoke 10. Generator coil 2 is positioned in parallel with armature 3 and an electrostatic potential response having an uni-directionality becomes possible by grounding earth line 12 to the grounding position 13 of the series arranged elements 3, 4, 9, 8 and 10 in the magnetic circuit. As shown in Fig.4, grounding terminal G of output terminal 11 is connected to armature 3, which is another end component of the said series magnetic circuit. This is further illustrated in Fig.5. An electrostatic potential response having an uni-directionality becomes possible by grounding earth line 12' to the grounding position 13' of the series arranged elements 10, 8, 9, 4 and 3 in the magnetic circuit. In fact, it is most preferable to establish the ground at either end part of the series magnetic circuit, one is the remote end P of the front yoke, which is positioned at the point farthest from the armature in the magnetic circuit, as shown in Fig.2. Another is the armature itself as shown in Fig.4. The sound quality reproduced by the pickup cartridge of the present invention displays improved characteristics in the high frequency range, improved clarity in the midrange, and improved responses in the low range. Other improvements such as reduced play-back distortion were obtained.
• It is to be understood that the above detailed description of the various embodiments of the invention is provided by way of example only. Various details of design and construction may be modified without departing from the true spirit and scope of the invention as set forth in the appended claims.

Claims (3)

1. In a pickup cartridge of the moving coil type including a magnetic circuit having, in series, (a) an armature with which the coil is associated, (b) a pole-piece,(c) a rear yoke, (d) a magnet, and (e) a front yoke, the improvement of grounding magnetic circuit at either end part of said series magnetic circuit.

2. The improvement as in Claim 1 where said grounding point is at the point on the front yoke farthest removed from the armature.

3. The improvement as in Claim 1 where said grounding point is on the surface of the armature.

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