GB2459273A

GB2459273A - Magnetic tone arm balance mechanism

Info

Publication number: GB2459273A
Application number: GB0806841A
Authority: GB
Inventors: Eric Leonard Vant
Original assignee: Individual
Current assignee: Individual
Priority date: 2008-04-15
Filing date: 2008-04-15
Publication date: 2009-10-21
Anticipated expiration: 2028-04-15
Also published as: GB0806841D0; GB2459273B

Abstract

A pivoted tone arm balance mechanism utilising repelling magnetic sources M1, M2 in place of a counterbalance weight to provide an adjustable arm torque to achieve a specified cartridge C stylus tracking force. Force is adjustable using screw S to adjust the distance between the magnets. Permanent or electromagnets may be used. Using magnets instead of a counterbalance weight reduces unwanted inertial forces when playing records with warps and groove path eccentricity. Also the tracking force dynamically increases to maintain stylus groove contact when the tone arm cartridge is raised above the horizontal playing position when a warped record grooved is traced.

Description

Tone Arm Balance Mechanism This invention relates to a tone arm balance mechanism.

In order to reproduce audio information recorded on a gramophone record, a cartridge cantilever (stylus) attached to a tone arm needs to accurately trace the playing groove whilst the record is rotated on a turntable. The stylus is designed to work at a specified tracking force (weight), which is less than the weight of the cartridge when fitted on the tone arm.

On a conventional pivoted tone arm, counterbalance weights are attached to the opposite end of the arm so that the applied torque about the pivot point produces a reduction of the effective mass of the cartridge to such a degree for the desired tracking force to be achieved. A normal stylus tracking force is in the region of 2 grammes and the counterbalance weights around 100 grammes.

However, physical factors related to both the record and turntable often result in playing groove path eccentricities and warps which affect the tone arm movement when traced by the stylus. The resultant oscillation of the arm can be in both vertical and horizontal planes and motion induced inertia is generated by reciprocative movement of the counterbalance weights.

The stylus, which is the only point of contact of the tone arm with the record, is subjected to these unwanted inertia forces and can generate spurious cartridge audio signals and lose tracking force weight with consequential degradation of audio reproduction.

To overcome these problematical inertia forces associated with a conventional pivoted tone arm counterbalance mechanism, the present invention proposes a pivoted tone arm balance mechanism utilising a magnetic force in place of counterbalance weights to apply an adjustable torque factor in a manner to achieve a specified cartridge stylus tracking force.

By utilising a repelling magnet force (flux) on a component part of the tone arm the resultant torque reaction produces a reduction in the effective mass of the tone arm cartridge to enable the required stylus tracking force to be set. The strength of the magnetic force (flux density) and the manner in which it is applied is variable so that any specified cartridge tracking force can be set.

The proposed invention mechanism also dynamically increases the effective mass (weight) of the tone arm cartridge when it is raised above the horizontal playing position when a warped record groove is traced by the stylus.

Superior audio reproduction is possible due to the improvements in stylus trace accuracy and a more constant tracking force due to the innovations of this invention.

An example of the invention will be described by referring to the accompanying diagrams and drawings, with reference being made to current practice balance mechanisms in order to clarify novelty features: Figure 1 shows a vector diagram of the applied forces for conventional tone arm balance mechanisms.

Figure 2 shows a vector diagram of the applied forces related to the balance mechanism of the present invention.

Figure 3 shows a general arrangement for a tone arm magnetic power source.

Figure 1, shows a conventional tone arm T mounted on a pivot P with a horizontal extension arm B. The required stylus tracking force G for the cartridge C is resultant from a torque reaction produced by an applied weight W on the arm B. It should be noted that the angular movement Y of the tone arm when a record groove warp is traced, moves the mass at W in a path arc subjected to gravitational forces that further aggravate the motion inertia problems related to counterbalance weights.

Figure 2, shows the present invention tone arm T mounted on a pivot P with a vertical extension arm L. The required tracking force G for the cartridge C is resultant from a torque reaction produced by a magnetic repelling force F on the arm L. It should be noted that the angular movement X of the tone arm when a record groove warp is traced, is not subject to gravitational forces in relation to the applied magnetic force.

The required magnetic repelling force (flux density) is produced by an arrangement of opposing magnetic poles (north against north or south against south) using permanent magnets. However, electromagnets could be substituted to achieve the same result in the subject invention balance mechanism. The opposing flux density force is relative to the proximity of the magnetic poles and increases as the gap decreases.

Figure 3, shows an example of a suitable arrangement using two neodymium disc magnets attached to the tone arm and the pivot fulcrum. Magnet Ml is a fixed magnet mounted on the tone arm extension L and magnet M2 is set on an adjustable screwed rod attached to the pivot fulcrum R. Magnetic flux density strength is relative to the proximity of the opposing magnetic poles, so that by adjusting the distance between them by the screw mechanism S of magnet M2, a variable flux density force can be achieved. The magnitude of the applied torque is adjusted to provide the required stylus tracking force for the cartridge C when the tone arm T is set in a horizontal plane parallel to the record playing surface. This ensures that when a record groove warp is encountered by the stylus, the effective mass of the cartridge increases to maintain stylus groove contact.

It can be readily seen from figure 3, that angular lifting movement of the tone arm T when a record groove warp is traced, will move the magnet Ml on arm L away from the adjustable magnet M2 with a resultant reduction of magnetic flux density force and also a consequent reduction of tone arm applied torque. Any reduction of the torque setting for the stylus tracking force will result in an increase of the effective mass of the cartridge and an increase of the stylus tracking force. This feature controls the inertia which tends to lift the stylus away from the record playing groove on the peak of a traversed groove warp and improves the stylus trace accuracy.

Claims

Claims 1. A pivoted tone arm balance mechanism utilising a magnetic force in place of counterbalance weights to apply an adjustable torque factor in a manner to achieve a specified cartridge stylus tracking force.
2. A pivoted tone arm balance mechanism according to claim 1, in which permanent magnets are used to create the applied torque.
3. A pivoted tone arm balance mechanism according to claim 1, in which electromagnets are used to create the applied torque.
4. A pivoted tone arm balance mechanism according to any of the preceding claims, in which two or more magnetic fields are used in a manner to achieve the required cartridge stylus tracking force.