GB2115970A - A gramophone pick-up assembly - Google Patents

Abstract

A gramophone pick-up assembly (10) comprising a pair of articulated arms (18, 19), a base plate assembly (13, 15, 16, 17), for mounting the arm (18) on a turntable deck (11) for pivotal movement relative thereto, the other arm (19) carrying a cartridge (26) having a record-tracking stylus. A curved channelled guide member (22), and a guide pin (Figure 3, not shown), cause the arm (19) to follow the curvature of guide member (22) during play thus to ensure that the centre line of the stylus maintains a tangent to the record groove at the point of contact therewith throughout play. This overcomes the phenomenon known as "lateral tracking error". The head assembly comprising the guide pin allows pivotting of head shell 25 to compensate eccentricity, and rising and falling according to record warp. <IMAGE>

Description

SPECIFICATION A gramophone pick-up assembly This invention concerns a gramophone pick-up assembly to be mounted on a turntable deck.

Much advanced technology is employed in the design and manufacture of modern record playing equipment in an attempt to reproduce, as closely as possible, the originally recorded sound. Original recordings are made on a master disc using a cutting stylus which is mounted to be capable of oscillation from side to side and to lie with its longitudinal access or centre line always at a tangent to the groove being cut.

For the avoidance of uncertainty, the term "the centre line of the stylus" shall be construed herein as the longitudinal access of the stylus with respect to the transverse oscillatory movement thereof to produce the recorded sound.

Absolute fidelity of reproduction is possible only if the stylus used in the pick-arm of the reproducing equipment is arranged in a similar manner. In some conventional equipment where the pick-up is of fixed length and is pivotally attached at a fixed position to the turntable deck, the stylus at the free end of the pick-up arm thus describes a fixed arc about the pivotal axis of the arm. Therefore the centre line of the stylus cannot maintain alignment with a tangent to the groove as it tracks across the record and there arises a phenomenon known as "lateral tracking error" which may be defined as the angular difference between the centre line of the stylus (or of the pick-up cartridge carrying same) and a line drawn at right angles to the record radius at the point of the stylus contact on the record.

An object of the present invention is to provide an improved technique for overcoming lateral tracking error employing means simple in construction and of low mass.

According to the present invention, there is provided a gramophone pick-up assembly comprising a pair of articulated arms, means for mounting one of said arms on a turntable deck for pivotal movement relative thereto, the other of said arms carrying a record-tracking stylus, a curved guide member adapted to be mounted in a fixed disposition relative to the deck, and means on said other arm for maintaining engagement with the guide member as the stylus tracks across a record during play such that the stylus is constrained to described an arc complementary to the curvature of the guide member.

Preferably the guide member is attached to means for elevating same relative to the turntable deck thus to enable the stylus to be raised and lowered with respect to a record. In this case, in the raised position the guide member is pivotable about a vertical axis relative to the turntable deck so that it may be moved aside together with said other arm to enable a record to be placed on the turntable and removed therefrom.

An embodiment of the invention will now be decribed, by way of example only, with reference to the accompanying drawings in which: Figure 1 is a plan view of a turntable deck with turntable, having mounted thereon a pick-up assembly made in accordance with the invention; Figure 2 is an enlarged fragmentary plan view of part of the assembly illustrated in Figure 1; and Figure 3 is a part-sectional side elevation of the part illustrated in Figure 2.

Referring now to the drawings the assembly generally indicated at 10 is mounted on a turntable deck 11 in a position radially displaced from the circumference of a turntable 12 thereon.

A base piate 13 permanently fixed by screws 14 to the deck 11 supports a fixed member having a first limb 15 extending therefrom and carrying an upstanding pillar 16 on which is pivotally mounted about a vertical axis at 17, a first arm 18 being one of a pair of articulated arms 18,19. The pivot point 17 is preferably in the form of an upstanding bearing pin giving point contact with the underside of the arm 18. An adjustable balance weight 20 is attached to one end of the arm 18, and further adjustable balance weights 20a and 20b are mounted each side of the weight 20 so that the arm 18 is balanced about its longitudinal and transverse axes at the pivot point.For user convenience, a small circular spirit level will be provided in the arm 18 immediately above the pivot point 17 so that the whole arm assembly can be balanced.

A second limb 21 of the fixed member attached to the base plate 13, extends in a direction generally opposite to that of the limb 15 and supports at its free end, a curved guide member 22 having a channel 23 extending longitudinally therein. The arm 19 which carries a balance weight 24 is mounted about vertical and horizontal pivotal axes at the end of the arm 18 remote from the counterweight 20. The end of the arm 19 remote from the weight 24 carries a head shell 25 on which is mounted a cartridge 26 carrying a stylus 27.

As can be seen from Figure 1 the head shell 25 extends beyond and above the curved guide member 22. Rotatably connected near the free end of the head shell 25 by means of a swivel pin 28, is a small flat member 29 having therein between the swivel pin 28 and the inner free end of the member an aperture 30. A guide pin 31, preferably of a low friction material, and of a diameter only slightly less than that of the apertures 30 passes through the member 29 to rest in the channel 23 of the guide member 22. The pin 31 also lies within an aperture 32 in the head shell 25, this aperture being of greater diameter than the aperture 30.

The guide member 22 is located by means of a vertical pin 33 in the free end region of the limb 21.

The pin 33 is fixed with respect to the guide member 22, and a control member 34 is rotatable to raise and lower the guide member 22 relative to the limb 21.

An assembly such as a rack and pinion disposed between the member 34 and the pin 33 is provided to produce the necessary elevation. Additionally, when the guide member 22 is lowered thus to allow the member 29 and the arm 19 to descend such that the stylus 27 can engage the groove of a record on the turntable 12, the pin 33 is prevented from rotation so that the guide member 22 maintains a fixed disposition. However, when the guide member 22 is raised by the control member 34, the pin 33 and thus the guide member 22 are free to rotate and move clear of the turntable 12 to provide access thereto.

In use, the guide member 22 and arm 19 are manoeuvred to a position in which the stylus is above the edge region of the record whereupon the control member 34 is operated to lower the stylus into tracking engagement with the record groove. As the stylus tracks across the record towards the centre, so the pin 31 is constrained to follow the channel 23 thus producing a component of forwards movement of the stylus away from the fixed base plate 13. In this way, as dictated by the curvature of the channel 23, the longitudinal axis of the stylus maintains a tangent to the record groove at the point of contact therewith throughout play.

Compensation for any eccentricity in the record groove is provided by pivotal movement of the head shell 25 relative to the member 29 which in turn is permitted by the free lateral movement of the pin 31 within the aperture 32. Also, if the record should be warped the stylus and the head shell are free to rise and fall since the pin 31 resting in the channel 23 is freely located in the aperture 30 of the member 29.

It will be appreciated that the materials of which the guide member 22, head shell 25, pin 28, member 29 and pin 31 are constructed are chosen for minimum frictional engagement between these va rious parts which are in sliding contact during play.

However, the surface characteristics of the base and/or walls of the channel 23 may be selected to control the movement of the arm assembly to an extent which will prevent the stylus from skating across the record.

New claims or amendments to claims filed on 13 May 1983 New or amended claims:

Claims (9)

1. A gramophone pick-up assembly comprising a pair of articulated arms, means for mounting one of said arms on a turntable deck for pivotal movement relative thereto, the other of said arms carrying a record-tracking stylus, a curved guide member adapted to be mounted in a fixed disposition relative to the deck, and means on said other arm for maintaining engagement with the guide member as the stylus tracks across a record during play such that the stylus is constrained to follow a path complementary to the curvature of the guide member.

2. A gramophone pick-up assembly according to Claim 1, wherein the guide member is attached to means for elevating same relative to the turntable deckthusto enable the stylus to be raised and lowered with respect to a record on the turntable.

3. A gramophone pick-up assembly according to Claim 2, wherein said guide member, in its raised position, is pivotable about a vertical axis so that it can be moved from said fixed disposition to enable a record to be placed on the turntable or removed therefrom.

4. A gramophone pick-up assembly according to any preceding claim, wherein said guide member includes a channel extending throughout its effective length, and wherein an upstanding guide pin passes freely through an aperture in said other arm and rests in the base of the channel so that it is free to move along the latter during play.

5. A gramophone pick-up assembly according to any preceding claim, wherein the stylus is mounted on said other arm at a position between the first arm and said means for maintaining engagement of said other arm with the guide member.

6. A gramophone pick-up assembly according to Claim 1, wherein said means for mounting said one arm on the turntable deck for pivotal movement relative thereto, comprises an upstanding bearing pin giving point contact with the underside of said arm, there being balance weights connected respectively to said articulated arms thus to balance the latter relative to said bearing pin whilst enabling the stylus on said other arm, to descend into playing contact on a record.

7. A gramophone pick-up assembly according to Claim 4, including means pivotally connected to said other arm and having an aperture through which said guide pin passes to rest in the channel of said guide member, the size of said aperture being only slightly greater than that of said guide pin, said aperture being generally co-axial with a further aperture of greater size within said other arm, and through which said guide pin also passes.

8. A gramophone pick-up assembly according to Claim 4 or Claim 7, wherein said guide pin is of a material providing minimal frictional engagement with said other arm.

9. A gramophone pick-up assembly according to any preceding claim, wherein the curvature of said pick-up arm is such that, during play, the stylus moves with a component of forwards movement away from the pivotal connection of said one arm with the turntable deck, whereby the centre line of the stylus maintained a tangent to the record groove at the point of contact therewith during play.