GB2107913A

GB2107913A - Record playing turntable units

Info

Publication number: GB2107913A
Application number: GB08224539A
Authority: GB
Inventors: J A Michell
Original assignee: MICHELL ENGINEERING Ltd J
Current assignee: MICHELL ENGINEERING Ltd J
Priority date: 1981-08-27
Filing date: 1982-08-26
Publication date: 1983-05-05
Also published as: GB2107913B

Abstract

A record playing turntable unit has a base 1 resiliently supporting a chassis 4 via three spring support/damper means 5 spaced 120 DEG about the central turntable axis with bearings rotatably supporting turntable 9. The chassis on the undersurface is balanced dynamically and statically using three masses one of which is a notional mass effectively positioned at an extension 10 and coincident with the centre of mass of the playing arm assembly 12. In use a weight 18 is selected which totals with the playing arm assembly 12, the notional mass thus maintaining balance. <IMAGE>

Description

SPECIFICATION Improvements in record playing turntable units This invention relates to improvements in record playing turntable units, especially high quality transcription decks employing peripheral drive of the turntable through a belt. It is known to mount the chassis of such units on a base through spring means with the motor drive being separately mounted on the base. This reduces noise and vibration from the motor. With known units three or more spring mountings are used which are adjusted according to the mass which is effective at each mounting point. If the playing arm or head is changed then the mass of the unit changes as well as the balance.

An object of this invention is to provide a record playing turntable unit wherein static and dynamic balance can be achieved and maintained whilst still providing for interchangeable arms and even the provision of two arms if required.

According to this invention there is provided a record playing turntable unit comprising:~ (a) a chassis with means spaced around the periphery thereof for resiliently mounting same to a base, and having a central bearing assembly.

(b) a turntable rotatably carried by the bearing assembly and positioned above the base, (c) a playing arm carried by pivotal support means secured to a lateral extension of the chassis, and (d) a motor drive for mounting on the base and driving the turntable through a belt, the unit being characterised by the chassis being statically and dynamically balanced by masses disposed symmetrically around the periphery, one mass being positioned at the lateral extension.

The chassis is thereby arranged to be in balance as far as rotational moments are concerned about the central axis through the turntable axis, and also as far as static balance is concerned radially about said axis. Thus the resilient mounting of the chassis is effected through equal forces on the mounting means, for example cone springs. The balance is effected using a notional mass at the lateral extension which represents the heaviest playing arm assembly required in use. For any given playing arm an adaptor plate may be provided which, in mass, totals with the arm, said notional mass thus ensuring maintenance of the mass balance in the chassis for any mass of arm by a simple adaptor means.

Preferably the chassis is generally of circular planform with the lateral extension lying on one radial, two masses being provided on the periphery of the chassis and centered on two further radials, the radials being mutually spaced by 1200 of arc. The chassis conveniently comprises an annular rim with the bearing supported by radial spokes, the rim including three 1200 spaced base mounting means and heavy metal, for example lead, balance masses.

The overall mass of the chassis can thus always be made the same simply and regardless of the actual mass of the arm assembly used.

In a preferred embodiment a second lateral arm mounting extension is provided positioned radially outwardly of one mass. If a second arm is required then same can be mounted in this position and the original mass removed; the total second arm mass is then made up to maintain balance.

A second aspect of this invention provides for damping masses to be mounted on the underside of the turntable between the turntable and chassis, said masses being arranged to damp any turntable resonances and to balance same statically and dynamically.

One embodiment according to this invention is shown by way of example in the accompanying drawings. In the drawings:~ Figure 1 shows a perspective view of a turntable unit from one side, Figure 2 shows a perspective view of the unit from the other side, and Figure 3 shows an underneath plan view of the chassis.

Referring to Figures 1 and 2 of the drawings, the record playing turntable unit has a base 1 with a rear apron 2 to which a dust cover is hingedly secured at 3 (the cover is not shown). A chassis 4 is mounted on the base 1 through three cone shaped springs located by studs on the base and received in cylindrical housings 5 upstanding from the peripheral rim 6 of the chassis. The springs form a resilient damped three point support system.

The chassis rim 6 is of an annular form and three equi-spaced spokes 7 (Figure 3) support a central bearing assembly 8 rotatably carrying the turntable 9. The chassis has two laterally extending annular shaped support flanges 10 and 1 the one 10 supporting the playing arm assembly 12, the other 1 1 being functionally unused but conveniently embracing a motor 13. The motor is actually mounted on the base 1 with no connection to the chassis. A belt passes around the motor pulley 14 and drives the periphery of the turntable by through engagement with a groove 15.

The underside of the chassis carries two fixed masses 16 and 17 which, together with a third mass on the support 10, is set to statically and dynamically balance the chassis. Thus the chassis is balanced about the three mountings 5 in a radial sense.

The third mass is a notional one and represents the heaviest pick-up arm assembly likely to be used. The pick-up arm assembly 12 shown is of less mass and to maintain balance and adaptor plate 18 is included so that the total arm plus adaptor mass equals the notional mass. Thus balance is maintained.

If the arm assembly is changed then all that is required is a new, or additional, plate 18 to bring the mass again to the national value. The adaptor plate 18 is conveniently mounted on three pillars 19 to the flange 10.

A second arm assembly can be mounted on flange 1 in which case the motor 13 is removed to a different position on the base 1. For this mass 16 is removed and again an adaptor plate is used to being the second arm up to the required mass to maintain complete balance.

The turntable 9 is provided with distributed depending masses 9a to damp resonances and effect balance.

Claims

1. A record playing turntable unit comprising:~ (a) a chassis with means spaced around the periphery thereof for resiliently mounting same to a base, and having a central bearing assembly, (b) a turntable rotatably carried by the bearing assembly and positioned above the base, (c) a playing arm carried by support means secured to a lateral extension of the chassis, and (d) a motor drive for mounting on the base and driving the turntable through a belt, the unit being characterised by the chassis being statically and dynamically balanced by masses disposed symmetrically around the periphery, the centre of mass of one mass being positioned at the lateral extension coincident with the centre of mass of the playing arm, said mass in addition with the mass of the playing arm being that value which achieves balance of the chassis.

2. A turntable unit as claimed in Claim 1, wherein the chassis is in balance as far as rotational moments are concerned about the central axis through the turntable axis, and also as far as static balance is concerned radially about said axis.

3. A turntable unit as claimed in Claim 1 or 2, wherein the said one mass is detachable and mounted beneath the vertical pivot assembly of the playing arm, the mass being selected in combination with the mass of the playing arm assembly mounted thereon, to total the notional value of mass which effects balance.

4. A turntable unit as claimed in any preceding Claim, wherein the chassis is generally of circular planform with the lateral extension lying on one radial, two masses being provided on the periphery of the chassis and centred on two further radials, the radials being mutually spaced by 1200 of arc.

5. A turntable unit as claimed in any preceding Claim, wherein the chassis comprises an annular rim with the bearing supported by radial spokes, the rim including three 1200 spaced base mounting means and a heavy dense metal, for example lead, as balance masses.

6. A turntable unit as claimed in any preceding Claim, wherein a second lateral playing arm mounting extension is provided positioned radially outwardly of another mass, with a second playing arm mounted the original mass is removed and the total mass removed is made by the second playing arm and a further mass to maintain balance.

7. A turntable unit as claimed in any preceding Claim, wherein damping masses are mounted on the underside of the turntable between the turntable and chassis, said masses being arranged to damp any turntable resonances and to balance same statically and dynamically.

8. A turntable unit as herein described or exemplified or as illustrated in the drawings.