US2069313A - Electric pick-up utilizing piezoelectric crystals - Google Patents

Description

Feb. 2, 1937.

JQJ. HUGON ET AL ELECTRIC PICK-UP UTILIZING PIEZOELECTRIC CRYSTAL Filed April 28, 1933 ZSheets-Sheet 2 INVENTORS JEAN Huger; I Y SQUCARD ATTORNEY Patented Feb. 2, 1937 UNITED STATES PATET OFFICE ELECTRIC PICK-U1? UTILIZING PIEZO- ELECTRIC CRYSTALS Application April 28, 1933, Serial No. 668,404 In France April 30, 1932 5 Claims.

The present invention relates to an arrange-'- ment utilizing piezo-electric crystals and applications in particular for piezo-electric pick-up.

This invention is mainly concerned with pickups or electric phonographic plate reproducers based upon the piezo-electric principle. The necessary principle of such a pick-up resides in the following: The force produced by the action of the plate upon the contacting member (generally a needle) is applied after necessary mechanical transformation, to one or several crystal pieces of piezo-electric material which develop corresponding charges which when applied to a very high impedance produce a voltage sumcient to operate the grid and the tube of the first stage of an amplifier.

The electric pick--ups hitherto known and described in the prior art have all the characteristic provision according to which the arrangement of the needle of the member causing the pressure upon the piezo-electric crystal or crystals, and of the support are always of a practically rigid construction. This condition which is theoretically compatible with the execution of a correct pick-up as regards the electrical response, however it is not acceptable in View of the con servation of the plate.

The present invention is a remedy of this disadvantage and allows the execution of an absolutely practical piezo-electric pick-up. Furthermore, it provides means for raising the reproduction of needle vibrations very far, namely, beyond 10,000 periods, and the curve of reproduction plotted as a function of the frequency retains a perfect uniformity free of resonances. Finally the invention presents various accessory advantages as will be noted from the following description, in particular as regards its adaptation to pick-ups provided for lateral groove recorded discs as well. as for pick-ups destined for discs recorded by grooves of the hill and dale type.

The invention is primarily based upon the use of what is called a floating lever. This implies that the force exerted upon the piezo-electric crystal is transmitted by means of a lever constituted by the needle and (if provided) an armature or an electrode arrangement rigidly associated therewith, but this lever does not possess an axis in the mechanical sense of the word. The position of the point that transmits its force to the crystal has its central position fixed only by means of the relatively small reaction of an elastic mass as for instance of rubber, and also another point of the lever which preferably will be the point where the needle is fastened to the armature (if an armature is provided), has likewise its central position fixed by means of the elasticity of an elastic mass (rubber for example). The elastic masses thus employed however act not only by their elasticity but also by the con- 5 siderable damping which they procure.

The principal feature of the floating lever arrangement offers considerable advantages whose principles are enumerated in the following description:

(a) The needle remains yielding and follows large displacements at rapid frequency without carrying the total inert mass of the pick-up.

(b) At each frequency, the lever oscillates around an instantaneously rotating axis in a manner dependent on the frequency, on its mass and on its properties of inertia, and also elastic reactions exercised in the region of the axis and of the fixed point of the needle. These elastic reactions can be regulated in such manner that the charges developed upon the crystal furnish a suitable constant E. M. F. whatever the frequency of the disc to be recorded at constant speed, may be. This condition can not be obtained unless a floating lever arrangement is used.

(c) The crystal of piezo-electric material does no longer operate as a charge generator and its elasticity or compressibility does not play any part in the functioning of the apparatus contrary to what takes place in the other pick-ups as particularly in the pick-up of Rice according to French Patent No. 638,286 where, in order to cause the armature to become somewhat displaced, it is necessary to make the crystal of enormous dimensions so that its relative displacement A 1/1 remains small while A l is already of appreciable size. Since the piezoelectric action, measured by the amount of charges developed under a given force, depends only upon the force and not upon the surface on which this force is exerted, it is possible in pickups according to the invention to use crystals of any shape and in particular of very small dimen- The only requirement is that they are I 5 slons. suitably cut and that they are adaptable to armatures allowing the accumulation of the charges.

(d) The use of a small crystal as referred to therefore makes the problem of fabricating it, so as to ensure approximately identical crystals as far as their pieZo-electric properties are concerned, an extremely simple matter. The mechanical part or armature including the electrodes supplying the force to the crystal can as such be considerably reduced in size which is a favorable means as regards the extension of the reproduction into the high notes. Finally with the practically useful dimensions of the crystal, the armature may be entirely omitted and the floating lever arrangement being constituted by the needle only.

As additional feature, the invention'also consists of fixing in the space an axis or an equivalent device whereby one point of the lever is formed by the needle and the armature while this lever is no longer a floating lever in the sense of the preceding explanation, and further the additional feature of the invention consists of simultaneously ensuring the flexibility desired for the displacements of the needle by interposing between the piezo-electric crystal covered by its armature and the rigid members operating it, an elastic mass for instance of rubber. Thus the elasticity of the arrangement is obtained without the need, as in the case of the pick-up of Rice in French Patent No. 638,286, of providing enormous crystals. The crystal can also be directly supported by the rigid part by which it is operated provided that the crystal is fastened upon the support of the pick-up by means of the elastic mass, but this arrangement, which augments the inertia of'the movable parts, is less favorable for the production of the high sounding notes.

The present invention will be more readily understood with reference to the attached'drawings which represent in a non-limiting manner by way of example various modes of embodiment.

Fig; 1- shows aplan view of a pick-up arrangemen with a needle and separate armature.

Fig. 1A is a side view of Fig. 1.

Fig. 2 shows a plan View of a pick-up arrangement similar to Fig. 1 except that the arrangement is without an armature.

Fig. 2A is a side view of Fig. 2.

Fig. 2B is a sectional view of Fig. 2. V

Fig. 3A shows a perspective View of the lower portion of the pick-up arrangement including the needle retaining elements.

Fig. 3B is a perspective view of another embodiment of the lower portion of the pick-upassembly.

Fig. 4 is a sectional view of the pick-up device wherein two piezo-electric crystals are utilized.

Fig. 5 is a circuit diagram wherein the pick-up device as shown in Fig. 4 is employed in a pushpull arrangement.

Referring now to Figs. 1 and 1A, there is shown at I the groove of the disc illustrated by dotted lines, while 2 is the needle or pointer threaded in a holder 3 in which the same is clamped by a screw ZI having a knurled head, penetrating or engaging in the screw thread of member 4. A mass of rubber 6 surrounds the screw thread 4, the said mass itself being fixed to the support of the assembly 5, 5'. The holder 3 is supported upon rubber elements 8, 8'. Each of these elements bear upon the electrodes 9 or 9' respectively, the electrodes themselves being in contact with the crystal I or III upon the other side of which is the. second electrodes II or II' respectively, which comes to bear upon an insulating member I21or. I2 which is integral with the support. The entire assembly or lever arrangement is fixed upon the platelike members 22 and 23 andis secured thereto by screws 24 and 24'.

Referring. now to Figs. 2, 2A and 23, there is shown an arrangement without an armature or holder, the pointer only constituting the floating lever arrangement. The needle 2 is shown engaging in a groove of the member 3 and is clamped betweenthe elements indicated at I3 and I4 which preferably are made of rubber possessing relatively great hardness and fixed to the support of the pick-up 22, or else of hardmetal such as steel, they being fixed to the support on an intermediary of some supple material. The upper end of the pointer acts upon the rubber 8, 8', 8" and 8". Following it is the electrode 9, the crystal I9, the electrode II, and insulating member I2 integral with the support. The means to change the pointer consists in this instance of unscrewing the screw 2 I, thereby causing members I3 and I4 to recede or separate from each other while the change is taking place. If the members I3 and I 4 present hard or sharp edges, the pointer is pivotedv as on a spindle.

Figures 3A and 3B show the view of the lower assembly of another embodiment whose essential feature may better be seen from the section Figure 4.. According to this embodiment there is no armature used and the needle only constitutes the floating lever. When in operating position, the needle 2 is tightened between the two rubber materials as at IS, IS which are separate from the support I5, I. Furthermore, the parts I5, I5 present two stops IT, IT between which and the needle the rubber is still more compressed so that it tends to direct the elastic forces to the regions A and B of the needle. It will be seen that at the height A, a crystal In is placed between the two electrodes or armatures 9 and II and which is operated by the needle through an intermediate rubber piece. The tongs provided at I8 and I8 as seen in Figures 3A and 3B allow the pieces I 5 and I5 to be pivoted around the axis I 9.

The parts I5 and I5 are held in operating position and are strongly pressed against each other by a powerful spring designated by 20 in Figures 3A and 3B.

In all of the described arrangements instead of using one crystal, several crystals may be used as shown in Fig. 4, particularly two which are preferably disposed at both sides of the floating lever in such a manner, that the'mechanical forces exerted upon one crystal are in opposite phase with those exerted upon the other crystal. Thus, if the crystals are disposed in an inverse sense with respect to their piezo-electric action, then the piezo-electric eifects are of the same sense and. the charges obtained will be combined instead of their destroying each other. This result can also be obtained with crystals similarly arranged but whose electrodes are connected inversely in parallel to each other.

Referring now to Figure 4 the second crystal 1 0' is interposed between the electrodes 9 and I I which are connected respectively to 9 and II. g It must be understood. that the devices shown in the Figures 1, 2, 3A, 3B can also comprise the as-' sembly of the two crystals in opposition and whose effects are added to each other.

It is furthermore of advantage to retain the two crystals in opposition in the electrical arrangement and to cause these to operate two identical tubes, whose grids are likewise excited in opposition, but whose plate circuit, being arranged in push-pull, may accordingly operate any kind of an ordinary amplifier (as for instance one with push-pull in each stage).

Figure 5 shows a circuit arrangement of this idea in which Ill, II! designate the crystals provided with the grounded electrodes II, II. The electrodes 9 and 9' operate the grids of the tubes I8, 53 and they are connected to a negative biasing voltage or directly to the cathodeacross a high resistance-22', 22' of for instance 5 megohms.

The push-pull transformer l9 serves for operating the amplifier 20 which supplies the loud speaker 2|. The arrangement of Figure 5 is adaptable to even more general applications than its use for the piezo-electric pick-ups.

This push-pull arrangement should always be a preferred embodiment since it allows to annul the effects of the plastic induction produced in the connecting wires of the tubes l8, 18'.

We claim:

1. A pick-up comprising a support, a rigid assembly comprising a needle whose end is adapted to track a phonograph disk, at least one piezoelectric crystal placed between two electrodes and disposed in the support, an elastic mass interposed between the crystal and the said rigid assembly, and an electric circuit connected with the electrodes of the crystal.

2. A pick-up comprising a support, a rigid assembly comprising a needle whose point is adapted to track a phonograph disk, at least one piezoelectric crystal disposed between two electrodes and arranged in the support, an elastic mass or medium interposed between the crystal and the said rigid assembly, another elastic mass interposed between the rigid assembly and the support, and an electric circuit connected with the electrodes of the crystal.

3. A pick-up comprising a support, a rigid assembly comprising a needle whose point is adapted to track a phonograph disk, at least one piezoelectric crystal disposed between two electrodes and arranged in the support, an elastic mass or medium interposed between the crystal and the said rigid assembly, another elastic mass interposed between the rigid assembly and the support, means designed to overcome or suppress the pressure exerted by the said elastic masses upon the rigid assembly with a View to liberating the latter, and an electric circuit connected with the electrodes of the crystal.

4. A pick-up comprising a support, a rigid assembly comprising a needle whose point is adapted to track a phonograph disk, two piezo-electric crystals each placed between two electrodes and arranged in the support upon either side of the rigid assembly, an elastic mass interposed. between the crystals and the said rigid assembly, and an electric circuit connected with the electrodes of the crystal.

5. A pick-up comprising a support, a rigid assembly comprising a needle whose point is adapted to track a phonograph disk, two piezo-electric crystals each placed between two electrodes and arranged in the support either side of the rigid assembly, an elastic mass interposed between the crystals and the said rigid assembly, and an electric circuit connected with the electrodes of the crystal, this circuit comprising an amplifying stage with two push-pull connected tubes, each of the said tubes being worked upon by a crystal corresponding thereto.

JEAN JACQUES HUGON. YVES ROCARD.

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