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Eduard Marthaler

Paul Zwicky

The disclosed arrangement is for a short pickup arm used with a tangential scanning system. The arm is supported on a single jewel thrust bearing and held against sideways tilting by a pair of attracting magnets, one mounted on the arm above the bearing and the other fixed above the first. This permits the arm to move freely in a plane parallel to the record and in a plane perpendicular to the record and tangent to the grooves. The center of gravity of the arm is chosen to be on a line between the bearing point and the stylus point in order to minimize the effects of outside disturbances.

Bearing arrangement for a record player tonearm

The disclosed arrangement is of the type for a short tonearm which is guided over the record so that the tonearm remains tangential to the grooves of the record. The tonearm is balanced mechanically on a single point bearing, with the phono cartridge to one side and a counterweight to the other side of the bearing. A permanent magnet fixed to the top of the tonearm interacts with a stationary magnet closely spaced from it to hold the tonearm vertically. The tonearm magnet is a vertical, round, solid cylinder section, while the stationary magnet is a parallelepiped with facing width equal to the diameter of the facing tonearm magnet. This constrains the tonearm to prevent it from tipping to the side, while permitting rotation about the vertical axis and about a horizontal axis through the point bearing and perpendicular to the tangent to the record groove. The improvement comprises that the stationary magnet is provided with a winding. By control of a direct current in the winding, the tonearm can be raised and lowered and the stylus pressure controlled, even while the stylus is tracking in a groove. Futhermore, the tonearm can be magnetically preloaded, so that in the absence of current in the control winding, the tonearm raises to its rest position, thus preventing damage to the record. Various designs are described for determining the interaction of the movable and stationary magnets and the superimposed magnetic field of the control winding.

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Zurich, Switzerland

Eduard Marthaler