US3051495A - Pick-up comprising two or more needles the holders of which are externally damped - Google Patents

Description

Aug. 28, 1962 N. WITTENBERG PICK-UP COMPRISING TWO OR MORE NEEDLES THE HOLDERS OF WHICH ARE EXTERNALLY DAMPED Filed Sept. 1, 1954 INVENTOR G RW N E E W G E% T United States Patent 9 3,051,495 PICK-UP COMPRISING TWO OR MORE NEEDLES THE HOLDERS OF WHICH ARE EXTERNALLY DAMPED Nico Wittenherg, Eindhoven, Netherlands, assignor, by

mesne assignments, to North American Philips Company, Inc., New York, N.Y., a corporation of Delaware Filed Sept. 1, 1954, Ser. No. 453,529 Claims priority, application Netherlands Sept. 17, 1953 1 Claim. (Cl. 274-37) The invention relates to pick-ups comprising two or more scanning needles, for example for use with normal and micro-groove disc records, which can be alternately made operative or inoperative and are each secured to a resilient needle holder, the said needle holders being connected via an armature to a common transducing element, while undesired movements of the needle holders are externally damped, for according to the invention it has been found that a needle holder which is inoperative during operation of the pick-up and consequently is connected to the entire system as a body supported at one end may be set into resonance due to the fact that the natural frequency of this body is attained. Owing to the fact that at this frequency energy is absorbed this will result in a comparatively sharp fall in the frequency curve of the pick-up, which is detrimental to a faithful reproduction of the vibrations required to be scanned by the pick-up. In order to substantially avoid this phenomenon it is already known to damp the resilient needle holder externally in that this part is connected to the pick-up housing via a body made of damping material, with the result that the amplitudes of any resonance vibrations which may occur are greatly reduced. Since the inoperative needle holders have to be clamped in such a manner in all the playing positions of the pick-up, the operative needle holder will also be provided with such a body. The provision of a damping member results in the introduction of an additional rigidity of the needle holder with respect to the system. The rigidity of the needle holder with respect to the pick-up housing inter alia determine-s the force necessarily required to be exerted sideways on the needle in order to obtain a predetermined deflection of the needle. In playing a record this force must be kept within a certain limit since by exceeding this limit the needle is likely to leave the groove along one of its walls under the action of the said force. This will be counteracted by the weight of the pick-up by which the needle is urged against one or both of the walls of the groove. Owing to the introduction of a greater rigidity by the provision in known manner of a damping member between the needle holder and the pick-up housing an equal deflection of the needle will require a greater force which, if the pick-up is likely to be forced from the groove, will have to be compensated for by a greater weight of the pick-up, which again results in greater wear of the needle and the disc record.

In order to avoid this disadvantage, in a pick-up according to the invention external damping is obtained by the provision of a member made of damping material and arranged between the resilient needle holder and the armature. According to the invention it has been found that in the case of a crystal pick-up, with which the invention is preferably used, the total rigidity of the needle with respect to the pick-up housing substantially consists of the sum of the rigidities of the resilient needle holder, of the armature and of the crystal about its torsion axis. Since, as is required for a satisfactory operation of the pick-up, the first-mentioned two rigidities are great as compared with the last-mentioned rigidity, the introduction of the new rigidity of the damping member will not Patented Aug. 28, 1962 ICC result in an important increase of the total rigidity, since the greatest rigidity only is increased by the parallel connection of the rigidity of the damping material and the smallest rigidity, by which the obtained amplitude is substantially determined, remains constant. Consequently the force required to cause a pre-determined sideways deflection of the needle will also remain substantially constant in spite of the provision of the damping material, while the above described resonance phenomenon will no longer exert a detrimental influence.

A satisfactory structural solution consists in that that part of the armature to which the damping member is secured consists of an extension substantially extending.

in the direction of the resilient needle holder.

The invention will now be described with reference to the accompanying drawing, in which one embodiment thereof is shown by way of example, and in which FIG. 1 is a cross-sectional view of a crystal pick-up according to the invention, and

FIG. 2 is a front elevation in which the front face of the pick-up housing has been cut away.

In the figures 1 designates the housing of a crystal pick-up comprising two scanning needles 2 and 3 the first of which is in position and the second is out of position for engaging the grooves of a record. The two needles, for example sapphires, are secured to resilient needle holders, as is shown with respect to the scanning needle 2 secured to a needle holder 4. The needle holder is in turn connected through an armature 5 to a crystal 6 which supports both armatures. The crystal is clamped in the housing 1 at 7 and can be twisted by the armature 5 about axis 8 of a shaft journaled in the housing at 9 and 10. The rigidity of the entire pick-up system consists of the torsional rigidity of the crystal about the shaft 8 and the rigidities of the armature 5 and of the needle holder, the two latter rigidities substantially exceeding the first mentioned rigidity. According to the invention the movement of the needle holder is externally damped by the provision of damping members 11 and 12 arranged between the resilient needle holders and the armatures 5 and 15. The parts of the armatures to which the damping members 11 and 12 are secured consist of extensions 13 and 14 extending substantially in the direction of the resilient needle holders. The rigidities caused by the damping members 11 and 12 are only parallel to the larger rigidities of the resilient needle holders, with the result that the smallest rigidity about the torsion shaft 8 remains constant, while any resonance of the free needle 3 which may occur is counteracted by the damping material.

What is claimed is:

A pick-up comprising at least two resilient needle holders, a scanning needle mounted in each needle holder and alternately operable, a common transducing element, a separate armature for connecting each needle holder to said common transducing element, each of said armatures having an extension extending in a direction substantially parallel to the longitudinal axis of said needle holder, and a damping member arranged between each resilient needle holder and the extension of its corresponding armature and extending substantially perpendicular to the latter.

References Cited in the file of this patent UNITED STATES PATENTS 2,554,209 Miner et al May 22, 1951 2,586,362 Martin Feb. 19, 1952 2,601,126 Palo et al June 17, 1952 2,639,156 Ward May 19, 1953 2,658,763 Roys Nov. 10, 1953

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