US1756966A - Electromagnetic pick-up - Google Patents

Description

Ma3 '6,1930. MALDEN l 1,756,966

ELECTROMAGNETIC PICK-UP Filed Jan. 17, 1927 INVENT R Ratented May 6,1930

: UNITED STATES PATENT OFFICE mirror ALDEN, or srnmermnn, massacnusm'rs, ASSIGNOR To run ALDEN an'urac'runme comrnmr, or naocxroiv, massacnusnrcrs, A coaromrron or massacnusnrrs Application filed January 17 1 The main ob ect of my invention 1s to produce a devlce' or the'conversion of the me- 'chanical movement of a needle or stylus caused by the undulations ofthe grooves ofa 5 sound record into electrical pulsations of corresponding frequency and ainplitude'-such devises are frequently called magnetic pickups.

" Another object is to provide a device of the above descri tion in which the moving parts are light an therefore of little inertia and hence readily able to accurately follow the above describedhaving a short air-gap, hence undulations of the-record.

Another object isto producea device .as

a large percentage change of magnetic cirtivity.

cuit reluctance and thereforeof high sensi- Another object is to produce a magnetic pick-up which will operate on-the typeof record which produces movement in a plane view of still another embodiment.

. 1 In Fig. 1 thepole pieces 5 and 6 are secured in some convenient, manner to the ends of the'permanent magnet 7 On-these pole transverse tothe axis of the stylus or on a record which produces movement along said axis b merely'motating the reproducer into i pieces are mounted the bobbins or spools 8 and 9 which carry the windings 10 and 11,, which may be connected to the input of a .suitable' am lifier (not shown). The-arma-.

'ture12 is he d against the pole tip 13-,by means Oftllfl resilient washer 14 which is pressed uponby-the bar or strip 15. .This strip 15,

is provided with an aperture 16 of sufficient w si'z'eto afford adequate clearance for the stylus-holder 17., The stylus holder 17 is secured to the armature 12 at a point such as,

f18 close to the-point of contact with the pole tip 13. The po'sitionof the bar 15 is regu- 'Iated by thethumb screws 19and 20 whlch operate in the threaded bushings studs'21 and ner.

nnncrnomaeimric PICK-UP 1927. a Serial m. 161,620.

22. It will be seen that adi'ustment of the nut 20 will PI'OdIiICG a large 0 iange inthe air gap 23 between t e armature 1 2 and the pole gap can be left unc anged and the compres sion of the resilient washer 14 may be varied, thus afi'ectin the damping of the armature or reed .12. %t will be seen that the lateral motion of the stylus 25 will change the air gap 23, thus changing the magnetic circuit consisting of the permanent magnet7, the

pole iece 6, the armature 12, the air gap 23 and t e pole piece 5', thus producing voltages, substantially proportionate to this movement,

in the wlndings 10' and 11 which ma be amplified and reproducedin any suita le man- With :the more usual type of lateral cut record in which the music is recorded by radial changes of the needle path along the record, the section shown in Fig. 1 would be along the plane passing through the radii of the record, but if the reproducer is rotatedthrough 90 degrees so that the section shown is in a plane normal to a radii of the record, the hill and dale type of record will produce the desired movement of the armature.-

tip 24, while by ad'usting both nuts the air 4 .In Fig. 2 the armature 12 is secured in any suitable mannerdirectly to the pole piece 13 as by the screw 13. Two resilient damping bloc s and 31 are .placed on either side of the armature and are held between the annature and the spool head 32 and between the armature and the clamping bar 33, respectively. The knurled nut 34 is then used to regulate the size of the air gap'2 3. The mag-' netic system of the embodiment shown in Fig.

2 is similar to that of Fig. 1 and Fig. 3.

'In-Fig. 3 the stylus holder 17 carries a collar 40 which is] preferab made integral. This collar is supported In two yielding or. resilient washers .41 and-42. The washer 41 is'positioned on the adjusting bar 43 by the externally threaded ring whose interior threads engage the threads of the ring 44 serves to clamp the. washer 42 against the collar 49 of the stylus 17 The on is provided with an' aperture'46 of Sn cient size to allow adequate freedom of movement of the stylus holder 17 By rotat- 44. The cup 45 I ing the cup 45 the clamping action of the two resilient washers 41 and 42 upon the col-- lar may be varied, thus varying thedamping' action upon themoving parts. The relative clearance between the pole pieces 13 and 24: and. the armature 12 may also be regulated by the rotation of the knurledsheaded screws 47 and48.

In all three embodiments shown the stylus 25 is secured in .the stylus holder 17 by the thumb screw 49.

It has been foundthat the structures destgibed are highlyeflicient needing less amp fication for a given outputvolume than isusually considered necessary. By using but one air gap and having that adjustable so that it can be made smaller than would be manufacturablv practicable if made fixed, a large change of magnetic reluctance with extremely small movement is secured, which I believe accounts for thehigh sensitivity.

The simplicity and lightness of the moving parts, combined with the fact that these parts are yieldingly held in position, produces, extremely faithful reproduction and the natural period and harmonics of the armature do not cause the I corresponding frequencies to, be emphasized as often occurs ii other devices of this nature. I

It is also possible by varying both the air gap and the yieldingly compressive force, which holds the armature in position, to

change the characteristic of. the device sufliv armature near its the two spoles.

ciently to make it adjustable for a wide range of amplifiers, or other varying conditions.

It is not unusual in devices of this nature for the air gap to become clogged with fillings, dust or. other foreign material. With my construction the armature may be readily re- .moved and such material wiped from the armature and pole-tip. It is also extremely easy to replace the armature and stylus hold- .er in case it becomes bent, crystallized or otherwise injured.

Another novelfeature of my device is that the adjustment of the air. gap and damping may be. effected by means of the screws such .as 19,,20, 47 and 48 while a record is being played and can thus be adjusted with little difiiculty to maximum sensitivity or to suit the personal quality.

I claim:

1. A double pole magnet havin an armature pivotally supported by one 0 said poles normally out of engagement with the-other pole and a stylus directly attached to the pivoted end andbetween preferences of theuser as to 2. In a magnetic pick-up a bi-polarmagnetic system and having an armature in contact with one pole, a stylus carried by said armature, a damping member adjacent to said stylus, and common means for adjusting. the

damping member and the air gap, said means acting directly on said damping member.

3. A magnetic pick-up device comprising a magnet having pole pieces projecting from one side, an armature pivoted below one pole piece, a stylus carried by the armature, a

damping means 'for said armature, and a screw having an ad ustmg end vaccessible supported by one of said poles normally out v of engagement with the other pole, one ofsaid pole pieces, said armature having a stylus holder rigidly attached .to said armature at apoint on said armature between-"said pole pieces and at right angles to said armature.

5. A magnetic pick up having a magnetii: system consisting of a permanent magnet having two pole-pieces carrying windings, an armature pivotally supported by one of said poles normally out of engagement with the other pole,-and a stylus directly attached toand disposed at right angles to said armature and between said p'ole pieces so as to vary the reluctance of said magnetic system substantially in accordance with the variations of, a sound record, said armature be-= ing yieldingly supported against said con-,-

'tacting pole-piece.

6. A magnetic pick-up having a magnetic system consisting of a permanent magnet havarmature pivotally supported by one of said poles normally out of engagement with the other pole, and a stylus directly attached to with the type of sound record whose'varia-g tions are radial or with the type of sound record whose variations are parallel to its axis of rotation. v

MILTON ALDEN.

ing two pole pieces carrying windings, an

' and disposed at right angles to said armature

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