US1831589A - Magnetic pickup - Google Patents

Description

Nov. 10, 1931. R. T. CLOUD MAGNETIC PlCKUP Filed Dec. 4, 1950 N59 oscillatory armature 16 having a clampin Patented Nov. 10, 1931 UNITED STATES MAGN TIC PICKUP These improvements relate to magnetic pickups, namely devices for translating varying mechanica vibrations into. correspondingly varying electrical impulses. Such a device used with a phonograph. disc modulates a current in accordance with the variations in the sound track. I

The object of this invention is to produce better results through the avoidance of variations extraneous to those desired to be reproduced. 7 In the accompanying drawings Figure 1 1s a top view of a magnetic pickup in accordance with the present invention;

Fig. 2 is a side elevation of the same; Fig. 3 is an enlarged fragmentary sectional view on the line 33 of either Fig. '1 or Fig. 2; Fig. 4 is a bottom view of the armature with the torsion rod secured thereto; and

Fi 5 is a side view of the armature show ing urther how the torsion rod is secured thereto.

Nearly all of the construction details shown 5 in the drawings are old and well-known. That is to say, it is old to provide a base as carrying the permanent magnet 11, the two electro- magnet voice coils 12 and 13 having the poles 14 and 15 respectively, the

member 17 for the needle or stylus 18, with Z torsion rod 20 secured midway between the ends of the armature and transversely thereof, as b crimping metalparts 21 tightly upon the ro 20, with clamplng means as 22 and 23 held by screws 24 upon the frame 25 for holding the ends of the torsion rod 20 tightly upon the frame.

The armature 16 is thus, according to old i practice, mounted intermediate its end to oscillate in front of the magnet poles 14 and 15 and against the torsional resistance developed in the straight, elongated, slender, spring steel rod or wire 20, which is held rigidly to the armature from side to side thereof and also rigidly at its end portions to relatively fixed supporting means; The oscillations are in parallel planes at right angles to the axis of the torsion rod and in di- 7150 rections toward and from the magnet poles 14 Application filed December 4, 1930. Serial No. 499,899.

and '15, one end portion of the armature moving toward one pole whilethe opposite end portion moves away from the other pole, and

eling in the sound track of the record (not shown). The armature is therefore mechanically oscillated inthe fields of thepoles 1 1 p and 15 against the torsion of rod 20.

In an effort to discover the cause of cer- PATENT OFFICEI" RAYMOND T. CLOUD, OF CHICAGO, ILLINOIS tain undesirable results in the reproduction I found that since this torsion rod is quite slender and the armature is carried (in the olderpractice) onlyby the torsion rod supported at its ends portions, and at places remote from the armature (necessaryto provide the desired torsion) the armature has motions in practice which are not purely oscillatory on the true axis of the torsion rod.. I found further that these extraneous motions of the armature have a decidedly deleterious efl'ect upon the results.

These oscillatory movements are exceedingly light. The Whole theory of th 1 -51 strument is based on slight and almost immeasurable variations in the armature move- 'ments.

positioned as closely aspossible to the arma'- ture itself. I prefer also to support the torsion rod throughout its length between the armature and the places respectively where the ends of the rod are made fixed. This preferred construction contemplates that while under torsion the rod may have a tendency to 'bend slightly out of its true axis.

Turning to Fig. 2 it will be observed that I 'havecarried frame 25 upward at 30 and 31 to provide a pair of oppositely extending elongated rests or supporting elements. 7 They may be separate elements but are conveniently a part ofthat frame 25. These rest or supporting elements '30 and 31 extend in- 1 wardly to the'armature 16. They terminate at 30a and 31:; respectively at the sideedges 16a and 16b of the armature,"and they may 'ion be flared away slightly as shown to avoid friction with the armature while coming almost into contact with these armature sides. Between the ends 30a and 30?) the frame is recessed to accommodate the armature for free movement.

In the top surface of each of these supports and 31 I provide an elongated straight groove or recess marked 33 on one side and 34 on the other, and which may conveniently have a depth of say half the diameter of the cylindrical wire or torsion rod 20. The lateral extensions of the torsion rod rest fairly snugly in these grooves 33 and 34. The grooves extend under the clamping elements 22 and 23 so that when these clamps-are tightened down the torsion rodis clamped tightly at its opposite ends and lies perfectly straight in the grooves or recesses 33-and axial position. The result therefore is that the reproduction is not influenced by the extraneous conditions pointed out, but is in accor-dance with armature movements caused by variations in the sound track alone.

I contemplate as-being included in these improvements all such changes, variations and departures from what is thusspec-ifically .illustrated and described as fall within the scope of the appended claims.

I claim: ,1. In a magnetic pickup of the character described having a magnet, an armature .as-

sociated therewith and adapted to :be oscillated mechanically, and a substantially long, slender and straight torsion rod carried by the armature and extending therefrom substantially at right angles to theplane defining the opposite directions of armature oscillation, with means material-1y spaced from the armature for fixedly holding the torsion rod to develop torsion therein when the armature is oscillated,- the combination therewith of means for supporting the torsion rod adjacent to the armature to maintain the 'rod substantially straight .andtofmain the armature with a substantially eonstantaxi-s of ;,oscillation under normal conditions of operation.

2. The combination of clai-m l hereof in which said rod-supporting means include a supporting element having an elongated straight recess therein, the rod resting In .said

L3. The combination of claim 1 hereof in which said rod-supporting means include a part having a bearing for the rod substantially on the true axis of the rod, said hearing being closely adjacent to the armature.

4. The combination of claim 1 hereof in which said torsion rod extends laterally of he armature in opposite directions and said supporting means are partly on one side of the armature and partly on the other side thereof in the directions of the rod extensions.

5. The combination of claim 1 hereof in which there is a frame part of the device and said supporting means are integral with said frame part an'dth'ere is an elongated recess in said .frame part and in which recess said rod rests. r

' 6. In a magnetic pickup of the character described having a magnet, an armature associated therewith and adapted to be oscillated mechanically,and an elongated torsion member carried by the armature and extending therefrom substantially at right angles to the plane defining the opposite directions of armature oscillation, with means material-1y spaced from the armature for fixedly holding the torsion memberto develop torsion therein when the armature is oscillated, the combination therewith of means for supporting the torsion member adjacent to the armature to maintain the torsion member on a substantially straight axis and to maintain the armature with a substantially constant axisof .osci-l-lation under normal conditions of operation. H V

RAYMOND T. CLOUD.

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