US2119584A

US2119584A - Pick-up device for electrical musical instruments

Info

Publication number: US2119584A
Application number: US53589A
Authority: US
Inventors: Armand F Knoblaugh
Original assignee: BALDWIN CO
Current assignee: BALDWIN Co
Priority date: 1935-12-09
Filing date: 1935-12-09
Publication date: 1938-06-07
Anticipated expiration: 1955-06-07

Description

June 1, 1938. A. F. KNOBLAUGH 9,

PICK-UP DEVICE FOR ELECTRICAL MUSICAL INSTRUMENTS Fi led Dec. 9,1935 2 sheets-sheet 1 y- Ftyz ////Zn.]3/Z /7.

[NVEJVTQR ATTX June 7, 1938. A. F. KNOBLAUGH PICK-UP DEVICE FOR ELECTRICAL MUSICAL INSTRUMENTS Filed Dec. 9, 1955 2 Shgets-Sheet 2 z f x #m f; M .J u/ w mm 7 x M MM f .g M F 8 p Patented June 7, 1938 UNITED STATES PATENT OFFICE PICK-UP DEVICE FOR ELECTRICAL MUSI- CAL INSTRUMENTS Armand F. Knoblaugh, Cincinnati, Ohio, assignor to The Baldwin Company} Cincinnati, Ohio Application December 9, 1935, Serial No. 53,589

5 Claims.

terial, the translation of the motion of the vi- The electromotive forces generated in an electromagnetic pick-up device of an electrical musical instrument employing tuned vibrators have been found to be very small. In order to hear these induced electrical vibrations reproduced as musical tones from a loudspeaker of conventional type, some form of amplification involving thermionic-vac'uum tubes is necessary.

In general, the supply of electrical power for an amplifier can be furnished most economically and conveniently when a commercial source of supply is used; batteries require frequent inspection and replacement and there are obvious disadvantages in the use of other types of purely local power sources.

In an electrical musical instrument for use in a home, there are often advantages in placing the amplifier and loudspeaker in the case or cabinet of the instrument groper. When this is done, however, the amplifier and speaker will have been placed rather near the pick-up device. Since commercial electric mains usually supply alternating current, the pick-up device will be exposed to stray alternating electric and magnetic fields, due mainly to the leakage flux from the amplifier power transformer, to a lesser degree to flux from the choke coils of the amplifier filter system and from the loudspeaker field coil (in which structures .there are usually some residual alter: nating currents flowing) and from any other sources in the vicinity. These stray fields act upon the pick-up device to produce an alternating electromotive force, which is amplified and reproduced as an objectionable hum.

The eifect'of the stray electric fields can be reduced satisfactorily by an electrostatic shield enclosing the pick-up structure. Magnetic shielding, however, has not been found to be so eifec tive, and is not convenient to employ in my invention, as will be obvious in my future description. Therefore, another principle must be used to minimize the eifect of the stray magnetic fields; theemployment of this principle is. the main object of this invention. This and other objects which will be evident to those reading this specification,

I shall now explain and shall describe my invention in detail.

In the drawings which form a part hereof:

Fig. l is a side view of the form on and in which are placed the elements of the pick-up device to be described.

Fig. 2 is a plan view of the assembled structure,

showing in proximity the tuned vibrators, exem- I plarily indicated here as tuned strings.

Fig. 3 is a side view, showing the adjacent. strings, in section.

\ Fig. 4 is a cross-section taken on A-B of Fig. 2

Figs. 5- and 6 are wiring diagrams, showing two schematic arrangements for connecting the device to an amplifier.

Fig. 7 is a partial wiring diagram of anamplifier.

In making a pick-up device in accordance with my invention, holders l, 2 and 3, of insulating material and having in each a central lengthwise slot, are properly spaced on two insulating strips 4 and 5, inserted and spaced apart in the slots of

holders

1, 2 and 3. At the ends of the strips 4 and 5 are inserted half-round pieces 6 and I, thus completing smooth forming surfaces.

In the space between the strips 4 and 5 and end pieces 6 and 1, two sets of

silicon steel 1aminations

8 and 9 are" fit tightly and spaced apart therein by an insulating, non-magnetic piece W.

In the space between holders; and 2, on the smooth surface formed by strips 4 and 5 and halfround pieces 6 and I, and around the laminated, steel core 8, is placed a coil H of fine, insulated copper wire. In a similar manner a coil H of the same kind of wire is placed in the space between

holders

2 and 3 on the surface formed by strips 4 and 5 and half-round pieces 5 and 'l, and

around the laminated steel core 9. The end wires 13 and ll of the coil II and the end,wires l5 and iii of the coil I2 may be conveniently attached to terminal posts set in an insulating plate,

the pitches of a musical scale and can be set in motion by the impact of hammers as is done in instruments of the piano type, or can be excited in any other well known manner.

The motions of the magnetized strings (and strings composed of the high carbon steel used for piano wire will retain their magnetism for a con siderable length of time) and the consequent motions of the flux from the magnetic poles on the strings, cyclically toward and away from the pickup device, induce corresponding electromotive forces in the coils H and I2 by electromagnetic induction, which can be amplified and reproduced as musical tones. It is to be noted particularly, in this respect, that essentially all of the induced electromotive forces are generated in the coil i2 which is nearer to the strings I'd (see Figs. 3 and f1) and that very little of the electromotive forces are generated in the farther coil Ii, because of its greater distance from the strings and the magnetic isolation effected by the nonmagnetic piece l0.

The principal object of my invention is the elimination of effects caused by stray magnetic accomplish by efiecting external to the amplifier the connection between the first choke coil 21 and terminals of wires I4 and i 6, the terminals of wires i3 and I5 becoming the output terminals of the device. The induction of electromotive forces by stray magnetic fields into coil I2 is then counterbalanced, part by part, by the induction of equal and opposite electromotive forces into coil I l, with the result that any reproduced extraneous noises, such as hum, are essentially eliminated.

The functioning of the device as a pick-up structure is not affected, however, as has been ex:

plained in the preceding paragraph. It is to be,

noted, in' this respect, that in practice, the crosssectional dimensions of the device (such as the dimensions of Fig. 4) would be small as compared with the distance from it to any source of stray I magnetic flux, but that these cross-sectional dimensions are large as compared with the distance from the strings to the device. The main object of my invention can be also accomplished by connecting the two coils in par allel in an opposite sense. This can be done by joining the terminals of wires l3 and ii to i'orm one output terminal and by joining the terminals of wires l4 and Hi to form the other output terminal of the device. I

In Fig. 7 is shown a partial wiring diagram of an amplifier. As the principles oi operation 01 this amplifier are well known to those acquainted with the art and will be understood on examining this specification, I shall not describe it in complete detail, except to note that it has input terminals I I and I9,

output terminals

20 and 2|, 8.

rectifier-filter system 22,

terminals

22 and 24 for supplying rectified current to a field coil 28 of a loudspeaker, and a terminal 26 which can be used (in conjunction with a return terminal such as I!) for supplying rectified current for magnetically charging the strings H, with the use of the device of this invention.

As it is necessary to supply current for magnetic charging only 'for short periods of time, I have arranged that this current be furnished by diverting, when necessary, a part of the output current or the rectifier-filter system 22. This I the second choke coil 28, of the system 22, by means or the terminal 26, attached to the output strings.

i ducted from the system 22 through the terminal 26, through coil 12 (the coil nearer to the strings) and through the return terminal II to furnish rectified current for magnetically charging the For quietness of operation during the charging process, the input terminals I2 and IQ of the amplifier are connected together by the switch 30.

By placing the switch 20 in the upward position,

terminals

28 and 29 are connected together, thus supplying rectified current to the amplifier,

and end wire I! of coil I l is connected to the input terminal l8, allowing the device to function as a pick-up structure in accordance with my invention, coils H and I2 being connected in a series arrangement, end wire l4 being permanently attached to end wire l6, as shown.

In Fig. 6 is shown another arrangement. when the singlepole-doublethrow switch 2| is placed in the upward position, "current is conducted from the system 22 through the terminal 28, through coils II and i2, and through the return terminal I9 to furnish charging current. By placing the switch 3| in the downward position the terminals 2G and 29 are connected together, supplying rectified current to the amplifier and allowing the structure to operate as a pick-up device in association with amplifying and reproducing 'means, the coils H and i2 being connected in a parallel arrangement, as shown. For simplicity. in Fig. 6, as also in Fig. 5, I have omitted. the terminal posts and plate shown in Figs. 2 and 3.

In series with the end wire'in, or Fig. 6, is an adjustable resistance 22, which can be used to compensate for any electrical unbalance in the construction and assembly of coils II and I2. With the use of the resistance 32 as shown and with the coils I l and I2 in a parallel arrangement it is not necessary that the coils be essentially identical. Coil ll may have more turns and a greater inductance than coil l2; the resistance 22 can be employed to compensate for any lack of proportionately greater resistance 01' coil Ii, and the device will function according to the teachings of my invention.

In Fig. 6 is shown a condenser 22. This serves to isolate the input system of the amplifier from the current of the magnetic charging process.

In both Figs. 5 and 6 are shown a switch 24, which can be used to short-circuit the output circuit of the amplifier, eliminating any of the reproduced noises caused by the operation of the switches 30 and II. Many modifications in the construction of the

switches

20, 3| and 24 are possible, the diagrammatic types shown being merely for clarity of description. One modification that I have found advantageous is operatively to link the switch I and switch 20 (or ii). Such linking insures that the switch 24 be closed preceding the operation of the switch II (or II) from the pick-upposition to the charsins p sition and that it be opened after the operation of the switch 20 (or 2!) from the charging position to the pick-up position.

An additional modification that 1 have found advantageous for quietness of operation pertains to the switch 30. This switch can be so constructed that in the operation from the pick-up position to the chargingposition, the following sequence is obtained: first, the input terminals 18 and it are connected together, then, the end wire I3 is disconnected from the input terminal l8, and

terminals

28 and 29 are disconnected, and finally, the terminal 26 is connected to coil l2. through the end wire "5. In the operation from the charging to the pick-up position, the reverse of the above sequence occurs.

Many'modifications may be made in structural A features and wiring arrangements and still come within the scope of my invention. What I claim as my invention is:

1. In a musical instrument, the combination of a plurality of tuned magnetized vibratile members arranged substantially in a plane and a pick up device for said members, said pick-up device including a frame work arranged transverse to said members, a coil of wire on said frame work in proximity to said members, a second coil of wire onsaid frame work and disposed between said first-mentioned coil and said members, the two said coils being electrically connected in phase opposition.

2. In a musical instrument, the combination of a series of tuned magnetized strings arranged substantially ina plane and a pick-up device for substantially in a plane and a pick-up device for said strings consisting of a framework in proximity and transverse to said strings, a coil of wireof substantially planar turns on-said framework in proximity and transverse to said strings, the planes of which turns are substantially parallel to the plane of said strings, a second'coil of wire of substantially planar turns on said framework transverse to said strings, the planes of said second turns being substantially parallel to those of said first turns, said second coll being located between said first coil and said strings, the two said coils being electrically connected in phase opposition.

4. In a musical instrument, the combination of a series of tuned vibratile magnetic members arranged substantially in a plane, means for magnetizing said members, and'a pick-up device for said members including a framework arranged transverse to said members, a coil of wire on said framework in proximity to said members, a second coil of wire on said framework and disposed between said first-mentioned coil and said members, the two said coils being electrically con- -nected whereby said second coil comprises a means for translating the motions of said members, a coil of wire on said framework in proximity to said members, a core of magnetic material encompassed by said coil, a second coil of wire on said framework and disposed between said first-mentioned coil and said members, a second core of magnetic material encompassed by said second coil, the two said coils being electrically connected whereby said second coil comprises a means for translating the motions of said members into electromotive forces and said first coil comprises a means for neutralizing any stray hum induced in said second coil.

\ ARMAND F. KNOBLAUGH.-