GB2114800A - Tone arm - Google Patents

Abstract

A tone arm comprises a carriage 1 holding a pickup head 2, a cylindrical guide 3 extending through an opening in the carriage 1 and arranged parallel to the radius of reproduction of the record 11. The tone arm also has: a driving mechanism for rotation of the cylindrical guide 3 about the longitudinal axis thereof and a means for producing pressing force of the pickup head 2. The driving mechanism is a freely rotating roller 5 whose axle is connected by a flexible shaft 8 with the cylindrical guide 3 and which is arranged so that frictional contact with the record 11 can be effected. The tone arm can be used in vertical record playing systems. <IMAGE>

Description

SPECIFICATION Tone arm This invention relates to mechanical recording and acoustic reproduction and is intended for electric record players.

This invention has an object of providing a simplier tone arm.

The invention resides in that in a tone arm comprising a carriage holding a reproducing head, a cyclindrical guide extending through an opening in the carriage and arranged parallel to the record radius when said record is set on a rotational disc of the record player, a driving mechanism for rotation of the cylindrical guide around the longitudinal axis thereof and a means for producing pressing force of a pickup head, according to the invention, the driving mechanism is made as a freely rotating roller whose axle of rotation is connected by a flexible shaft with the end of the cylindrical guide and which is arranged so that frictional contact with the record can be effected.

The means for producing pressing force should be preferably made as a magnetic pair comprising a supporting slide which is a rod of soft magnetic material and arranged parallel to the cylindrical guide, and a permanent magnet mounted on the carriage.

The tone arm proposed herein is simple because a complicated driving mechanism of the electric motor is replaced by a passive roller.

Furthermore, the tone arm is characterized by high fidelity of acoustic reproduction and can be used in record playing devices featuring both horizontal and vertical record positioning devices.

The invention will be now described in greater detail with reference with the accompanying drawings, wherein, in accordance with the invention: Fig. 1 shows a top view of a tone arm featuring a means for producing pressing force for the pickup head, made as a magnetic pair; Fig. 2 shows that the view of Fig. 1, wherein the pressing force producing means has an additional support roller.

A tone arm comprises a carriage 1 (Fig. 1) holding a pickup head 2. The carriage 1 can travel along a cylindrical guide way 3 running parallel to the reproduction radius, secured in rotational supports in a frame 4 and extending through an opening in the carriage 1. A roller 5 is secured on an axle 6 arranged for free rotation on a brace 7 hinged to the frame 4. The roller 5 and the axis 0, of rotation of the brace 7 lie in one plane. The end of the cylindrical guide 3 and the axle 6 of the roller 5 are connected by a flexible shaft 8. A means for producing of pressing force for the head 2 is made as a magnetic pair composed of a slide 9 which is a rod of a soft magnetic material and a permanent magnet 10 mounted on the carriage 1 so it can interact with the support slide 9. The slide 9 is secured in the frame 4 parallel to the cylindrical guide 3. The permanent magnet 10 and the slide 9 are arranged in different planes at different distances from a record 11.

As the tone arm is placed on the rotating record 1 the roller 5 comes into frictional contact with the record 11 in the zone of a label 1 2. The roller 5 is acted upon by the tangential motive force of the record 11 and the thrust directed to the axis of rotation of the brace 7 (point O, in Fig. 1). A component of the motive force, perpendicular to the axle 6 of the roller 5 sets the roller 5 into rotation, whereas the component parallel to the axle 6 produces torque with respect to the axis 0, of the brace 7 and the brace 7 is turned and the roller 5 occupies a position where the side force is equal to zero, in other words when the tangential motive force of the record 11 and the thrust lie on one line and act in opposite directions. The torque of the roller 5 is transmitted via the axle 6 and the flexible shaft 8 to the cylindrical guide 3. The stylus of the pickup head 2 is shifted by the groove of the record 11 and travels along the radius thereof. The carriage 1 slides along the guide 3.

The magnetic force pressing the permanent magnet 10 and the slide 9 together produces the torque of the carriage 1 in the direction around the cylindrical guide 3. The pickup head is pressed against the record and the carriage 1 is stable when playing vertically arranged records (wallhanged record players).

An embodiment of the tone arm illustrated in Fig. 2, unlike that of Fig. 1, has a means for producing pressing force of the pickup head 2, which is made as a strip 1 3 rigidly secured in the frame 4 parallel to the cylindrical guide 3 and an additional freely rotating roller 14 turning on an axle 1 5 secured in the carriage 1 which can roll along the strip 1 3.

The tone arm of Fig. 2 operates similar to that of Fig. 1, except that, when the carriage 1 travels along the cylindrical guide 3, the roller 14 rolls along the strip 1 3 providing the required pressing force and stable position of the pickup head 2.

The proposed tone arm is much simplier than the known ones. The known RCA tone arm comprises a drive motor which is complicated in design and in manufacture. The proposed tone arm has a passive element instead of an active one, and that is the roller 5 which is in friction contact with the record 11 being played.

The proposed tone arm has some additional advantages in comparison with the known ones.

The motor in the known tone arm is one more source of vibrations. The motor is a high-speed one, as a rule. The vibrations of the motor are transmitted to the pickup head through the guide-rail whereto the shaft of the motor is rigidly secured and through the plate of the record player whereon the micromotor is mounted. At high rotational speed the noise falls within the sound range. Some special protection means are introduced. Like vibroinsulation of the motor and the plate. In the proposed tone arm the roller 5 is frictionally connected with the record 11, the frequency of rotation never exceeds 1 00 rpm, vibration noise is outside the reproducible frequencies (lower than 5 hz). The roller, consequently, brings no additional vibrations in. Furthermore, the proposed tone arm, unlike the known ones, can be used for playing vertically arranged records. The roller 5 is pressed against the record 1 1 sufficiently strongly as to keep the record 11 on the disc axle. The required force for the pickup stylus is furnished by the additional slideway 9. The tone arm is reliable in operation. The roller 5 can be made of plastic (polyurethane, for example) which is wear resistant and has low residual deformation or permanent set.

A prototype tone arm had the following characteristics (embodiment of Fig. 1): roller 5: - diameter 20 mm, material polyurethane, flexible shaft 8: - steel spring, diameter 4mm, iength 60 mm.

cylindrical guide 3: rod of structural steel 10, magnet made of barium ferrite.

The tone arm was tested in a record player having vertical position of the record with the following results: - detonation coefficient less than 0.15%; - pressing force of pickup less than 40 mN; - relative rumble level (without weighting) not worse than 31 dB.

Claims (3)

1. A tone arm comprising a carriage holding a pickup head, a cylindrical guide extending through an opening in the carriage and arranged parallel to the radius of the record in the position when said record is placed on the rotational disc of the record player, a driving mechanism for rotation of the cylindrical guide about the longitudinal axis thereof and a means for producing pressing force of the pickup head, wherein the driving mechanism is made as a freely rotating roller whose axle is connected by a flexible shaft to the end of the cylindrical guide and which is arranged so frictional contact with the record can be achieved.

2. A tone arm as claimed in Claim 1, wherein the means for producing pressing force is made as a magnetic pair comprising a support slide which is a rod made of soft magnetic material and arranged parallel to the cylindrical guide and a permanent magnetic mounted on the carriage.

3. A tone arm made substantially as described hereinabove in preceding claims and in the accompanying drawings.