US2275309A - Reproducer for electric phonographs - Google Patents

Description

March 3, 1942. L, D, NORTON 2,275,309

REPRODUCER FOR ELECTRIC PHONOGRAPHS Filed Aug. 5, 1940 INVENTOR Leland D. Il/orion $1 Mag 1M0 v ATTOR Patented 3, 1942 i REPRODUCER FOR ELECTRIC PHONOGRAPHS Leland D. Norton, Bridgeport, Conn.,-

assignor to Dictaphone Corporation, New York, 'N. Y., a corporation of New York Application August 3, 1940, Serial No. 350,568 2 Claims. (01. 119-10041) This invention relates to electric phonographs, dictating machines, and the like, and more particularly to such machines of the transcribing type and to reproducers for use with such machines.

One difficulty frequently operation of electric sound reproducing machines is that the sound reproducing or pickup unit, in addition to picking up the sound from the record groove, also picks up considerable noise,

encountered the stylus 26, is encased in a supporting arm 28 which i in turn is suitably mounted on the carriage III by means of a gimbal-type pivot'structure, generally usually termed hum, from stray electrical fields in the neighborhood of the machine. Such stray electrical fields are frequently developed by the apparatus customarily used in electric phonographs, such as driving motors, power transformers, choke coils, and other electromagnetic devices, and these stray fields are particularly disadvantageous when the electrical phonograph is operated from an A. C. power supply.

It is an object of this invention to provide an electrical reproducer for use in electric phonographs in which the deleterious efiect of stray electric fields is minimized or eliminated.

It is a further obiectof this invention to provide means adapted to cooperate with electric re-' producers to overcome the effects of stray fields, and thereby to eliminate undesirable noise efiects in the output of the phonograph.

These and other apparent objects and advantages of this invention are obtained by the'means described in the following specification and may be more readily understood by reference to the accompanying drawing, in which:

Figure 1 is a side elevation, partly in section, of a portion of an electric phonograph including an electromagnetic reproducer unit;

Figure 2 is a plan view of the electromagnetic reproducer unit shown in Figure 1, taken on line 2-2;

Figure 3is a side elevation, partly insection, of a portion of an, electric phonograph showing another embodiment of the invention; and

Figure 4 shows schematicaly suitable electrical connections for the apparatus shown in Figures 1 and 2. v

The phonographic machine, shown in Figures 1 and 2 for the purpose of illustrating the invention, is a transcribing machine having a carriage 10 mounted on guide rods l2 and I4 supported on frames l6 and I8, respectively, attached to a base 20. A mandrel 22, adapted to support a sound record blank 24, is suitably rotatably mounted above the base parallel to the guide rods l2 and H. An electromagnetic reproducer indicated at 2 9.-

The pivot structure 28 may be of any suitable type which permits motion of the reproducer unit toward and away from the record 24 by rotation of the arm 28 about a substantially horizontal axis 30, and one which further permits limited rotation in a horizontal plane about a substantially vertical axis 32 to permit the stylus 26 freely to track the record sound groove when the machine is conditioned for reproducing. This I pivotal mounting structure 29 may also be provided with an arrangement to limit the oscilla tory motion about the vertical axis 32 during those periods when the machine is not conditioned for reproducing. Suitable apparatus for accomplishing all of these functions is illustrated in U. S. Patent 2,152,440 to Leland D. Norton and is not further described herein, because this apparatus per se does not form a portion of the present invention.

unit. generally indicated at 25, having a vibratory a. spring tween the feed screw-34 The reproducer support arm 28 is provided with a counterweight 2'! mounted on the other side of the pivotal axis 38 from the reproducer 25 to partially counterbalance the pressure exerted on the record 25 by the stylus 26 due to the weight of the reproducer 25 alone.

manually operable lever 42 is provided for temporarily disengaging the feed nut 36 'from the feed screw 38 and for lifting the stylus" from the surface of the record 24 when it is desired to move the reproducer25 to some other portion of the record.

Thereproducer unit 25 may be any suitable I sound translating device, such, for example, as

that shown in the co-pendingapplication Serial No. 263,229 filed by Leland D. Norton. As mayv be more easily seen in the enlarged section shown in Figure 2, this device comprises a C-shaped magnetic circuit structure M in which the tips 40, supplies the driving connection be and the carriage In. A

of the c form the pole tips 48 of the magnet. Two pickup coils 48 surround the pole tips 46 and a resilient armature supportingmember 50 supports an armature member 52 carrying the stylus 26 between the pole tips 46, substantially as shown. It is to be understood that this electromagnetic reproducer device does not per se form a portion of the present invention, and might be any suitable reproducer unit having operating coils corresponding to the coils 48.

In a phonograph instrument of the type just described, the driving motor, amplifier transformers, chokes, etc., are frequently mounted in the proximity of the electromagnetic reproducer 25, usually beneath the base 20. Thus the pickup coils 48 of the reproducer 25 usually are cut by stray fields from these elements andthus transient voltages are developed in these coils.

These transient voltages, as well as the sound signals developed. by the reproducer unit, are amplified and produce undesirable noises in the output of the phonograph. When the apparatus is operated on an A. C. power supply, the stray field is usually a 60-cycle field or the equivalent,- so that the transient voltages developed in the pickup coils 48 by this stray field usually manivided with means for moving the combined recorder-reproducer unit, generally indicated at 60, which is provided with a recording stylus 62 and a reproducing stylus 64, into'either its recording or reproducing positions by means of a lever 85 associated with the carriage l0 and the carriage guide I 4. The dual purpose electromagnetic translating device 60, which is provided with only one pickup coil 68, is mounted on one end of a lever secured to the carriage III by means of a suitable pivotal arrangement 29, in the manfest themselves as a -cycle hum in the output of the phonograph.

In accordance with the present invention, in order to counteract this stray field effect and eliminate the hum from the phonograph output, a compensating coil is provided, mounted near the pickup coil of the reproducer. This coil is given electrical characteristics similar to those of the pickup coil of the reproducer, it isconnected oppositely in series with the pickup coil, and it is mounted as close to the reproducer pickup coil as possible and is moved therewith so as to be subject to substantially the same stray field efi'ects. Thus, the parasitic voltages developed in this compensating coil due to the stray fields, are substantially equal and opposite to the voltages produced by the stray fields in the pickup coil. If the particular electromagnetic translating unit being used is provided with more than one pickup coil, then a plurality of compensating coils may be used, if desired, each one corresponding to a particular pickup coil of the translating device. In accordance with the preferred embodiment of the present invention, a. compensating coil is provided for each pickup coil in the reproducer unit, and this compensating coil is given electrical characteristics substantially the same as those oiits corresponding pickup coil. Each compensating coil is mounted as closely as possible to its corresponding pickup coil, and it preferably lies in the plane of its pickup coil with its axis parallel to the axis of the pickup coil. However, it is positioned so that its winding runs in the opposite direction to the winding of the pickup coil, and it is connected in series with the pickup coil.

In the present embodiment of the invention, as shown in Figure 2, the reproducer unit 25 is provided with two pickup coils 48, and two compensating coils 54 are mounted on a bracket 55 extending rearwardly from the frame supporting the magnetic structure 44. These coils 54 are connected in an opposed manner in series with the pickup coils 48, as shown in Figure 4.

With this arrangement, the parasitic voltages developed in the pickup coils 48 due to stray fields are canceled out because equal and opponer above described. However, in this embodiment a compensating coil I2, having electrical characteristics similar to those of the pickup coil 68, is positioned on the lever II on the other side of the pivotal axis 30 from the translating unit to in approximately the same plane as pickup coil 68 and with its axis approximately parallel to that of pickup coil 88. With this arrangement, the compensating coil 12 not only is eifective in eliminating the hum picked up by the pickup coil 68, but, in addition, the weight of this coil 12 is used as a counterweight to counterbalance the weight of the translating device 68 to effectively replace the counterweight 2'! shown in Figure 1.

As many possible embodiments may be made of the above invention without departing from the scope thereof, it is to be understood that all mat- 'site voltages are developed in the corresponding ter herein set forth or shown in the accompanying drawing is to be interpreted as illustrative and not in a limiting sense.

I claim:

1. In an electric phonograph adapted for use with cylindrical records of the "hill and dale type, the combination or, a base plate, a mandrel mounted above and parallel to said base plate and adapted to support and drive a cylindrical record surface, a carriage guide rod mounted above said base plate and parallel to the axis of said mandrel, a carriage member slidably mounted on said guide rod and adapted to be moved longitudinally along said mandrel, a support member pivotally mounted on said carriage member for movement about an axis parallel to the axis of said mandrel, an electromagnetic translating device having an operating coil and adapted to coact with a hill and dale" type record groove mounted on one end of said support lever for movement toward and away from a record surface on said mandrel, and a hum compensating coil mounted on the other end of said support lever on the opposite side of its pivotal mounting from said sound translating device and at approximately the same distance above said base plate as the operating coil of said translating device whereby said compensating coil partially counterbalances the weight of said translating device while traveling in the same direction with said translating device along said record surface in a path parallel to the axis of said mandrel and always at approximately the same distance as the operating coil of said translating device from sources of stray electric fields beneath said base plate.

2. In an electric sound reproducing machine aa' maoa adapted to reproduce cylindrical wax records of aroma-record on said mandrel, and a hum com I the hill and dale" type, the combination of, af' base, a cylindrical mandrel mounted above and: v

with its axis parallel to said base and designed to support and drive a cylindrical record, carriage guide rods mounted above said base parallel to the axis of said mandrel, a carriage slidably mounted on said guide rods, means moving said support lever for movement toward and away 5 perisating coil mounted on the other end 01' said pickup support lever on the opposite side of its pivotal mounting from said picku with its axis a parallel to the axis of said pickup coil and at apcoil partially counterbalances the Weight of saidpickup while traveling in the same direction with said pickup along said record in a path parallel to said base and the axis of said mandrel and always at approximately the same'distance as the pickup from sources of stray electric fields be-

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