US2565512A - Tone control apparatus for electrical musical instruments - Google Patents

Description

1951 E. MEINEMA 2,565,512

H. TONE CONTROL APPARATUS FOR ELECTRICAL MUSICAL INSTRUMENTS Filed June 13, 1949 Herbe'rt Meinema Atty.

Patented Aug. 28, 1 951 TONE CONTROL APPARATUS FOR ELEC- TRICAL MUSICAL INSTRUMENTS Herbert E. Meinema, Chicago, Ill., assignor t Hammond Instrument Company, Chicago, 111., a corporation of Delaware Application June 13, 1949, Serial No. 98,684

6 Claims.

My invention relates generally to electrical musical instruments and more particularly to improved means for controlling the tone quality of an instrument of the electric organ type.

In electric organs constructed in the manner disclosed in the patent to Laurens Hammond No. 1,956,350, the selection of the quality of the tones produced is accomplished by individually controlling the amplitudes of the various partials. In said instrument, playing key operated switches connect the tone signal generators for the various partials respectively to bus-bars. The signals thus applied to the bus-bars are of substantially equal amplitude and the Signals on these busbars are transmitted to the output system through a transformer by selectively connecting the busbars to various taps on the input side of the transformer so as to regulate or predetermine the relative amplitudes of the partials. In said instrument these selective connections are made by means of drawbars which have spring contacts engageable with spaced collector bars. In this construction, when the drawbars are adjusted the contact With one of the collector bars is broken before contact was made with another. This results in the production of clicks and other undesired noises in the output system. It is therefore the object of my invention to provide an improved drawbar construction whereby the adjustment of the drawbars may be effected without introducing transients which might result in the production of noise in the output of the instrument.

A further object is to provide an improved drawbar construction whereby each drawbar is provided with a pair of spaced contacts which are connected by a resistor of low value, the contacts being spaced sufilciently apart relative to the spacing of the collector bars with which they contact that one of these contacts will at all times be in contact with one of the collector bars.

Other objects will appear from the following description, reference being had to the accompanying drawings in which:

Fig. l is a partly schematic view of the generating system of an electric organ, showing a*por tion of the drawbar assembly in fragmentary section;

Fig. 2 is a side elevational View of the drawbar assembly;

Fig. 3 is a fragmentary sectional view taken on line 33 of Fig. 1; and,

Fig. 4 is a bottom plan view of a portion of a drawbar contact mechanism which is shown in fundamental, the second, third, and fourth harmonics of the note Al (110.000 c. p. s.), each of these generators comprising a tone wheel l0 having the required number of high points and driven at the speeds required to generate the frequencies of a 110, 220, 330, and 440 c. p. s., or frequencies very close to these values. Generators 34 and 46 are also utilized to supply the fundamental and second harmonic frequencies for the note A2 of having a fundamental frequency of 220 c. p. s. It will be understood that the generators 22, 34, 4|, and 46 are intended to be representative of approximately generators each supplying a substantially sine wave signal having a frequency required in the production of either the fundamental or one of the harmonic partials of the various notes of the musical scale Within the gamut of the instrument.

Each of the generators has a permanent magnet |2 provided with a wedge-shaped point l4 adjacent the periphery of the tone wheel. A pickup coil [6 is wound on each of the permanent magnets l2 and has one terminal grounded and the other connected through a capacitor IE to the ungrounded terminal of the primary winding of a transformer 20. The ungrounded terminals of the secondaries of these transformers are connected to switches 22 through parallel resistors 24, the impedance of these resistors being high with respect to the impedances of the generators to which they are connected.

The switches 22 are operable by the playing keys, such as the keys Al and A2, and are adapted to connect the generators to bus-bars 26. The connections between the generators and the switches 22 are such that, for example, the fundamental frequencies for the various tones will be impressed on the first (uppermost) bus-bar 26, the second harmonics will be impressed on the second bus-bar, etc.

The bus-bars 26 are connected respectively to drawbars 28 which are mounted for longitudinal sliding movement in a suitable drawbar housing 30 having vertical panels 32, of insulating material, which are suitably slotted to form guides for the drawbars.

The drawbars 28 have moulded plastic finger pieces 34 secured at their forward ends, while their rearward ends, which project from the back of the housing 30, are bent downwardly at an angle and have spring fingers 36 riveted thereto, each of these Spring fingers having a triangular end portion 38 which serves as a stop to limit the forward movement of the drawbar to which it is attached. The end portions 38 also serve as solderi'ng lugs for the flexible wires 40 by which the' drawbars are respectively connected to the busbars 26.

Each of the spring fingers 36 has a double contact assembly 42 secured at its free end. Each of these assemblies, as best shown in Figs. 3 and 4, comprises insulating sheet 44 and d of mica, or the like, which are secured to the spring finger by contact rivets 46, and 41. The rivet 46 extends through both sheets 44 and 35, through a small bracket 48, and through an enlarged hole 49 in the spring finger 36, and is thus electrically connected to the bracket 58 and insulated from the spring finger 36. The contact rivet 41 extends only through the insulating sheet 45 and the spring finger 36 and is thus electrically connected to the latter. The bracket 48 is located in proper position by a lug 5E) struck from the bracket and projecting through a suitably shaped opening 51 formed in the insulating sheet 44.

The spring finger has a pair of protecting flanges 52 and an offset ear 5d at its free end. A short length of wire 56, of a high resistance alloy, has its ends respectively welded to the bracket 43 and the ear 54. The effective resistance of this wire may be approximately 1 ohm.

The contact rivets it and Marc adapted to make electric contact with spaced collector bars 58 which are inlaid in an insulating sheet 66 secured within the housing 30. The bars 58 are so spaced with respect to the spacing of the contact rivets 46, ll that at least one of the latter will be held in electrical contact with one of the bars in every position to which the draw bar may be moved.

A tapered resistance element 622 is soldered to the bars 58, and is formed to provide progressively greater length portions thereof between the bars 58. The element 62 is a very thin sheet of a high resistance alloy and its shape and conformation are such that the resistance it provides between successive bars 58 increases substantially logarithmically from the rearmost to the foremost bar 58.

The rearmost bar 58 is connected to the grounded terminal of the primary winding 64 of an output transformer 35 while the foremost bar 58 is connected to the ungrounded terminal of this winding. The secondary 66 of transformer '65 is connected to a preamplifier 68, which may include a suitable expression or volume control device. The preamplifier is connected to a power amplifier it and the latter supplies a speaker 712. The resistance element 62 forms a voltage divider across the input terminals of the transformer 65, and thus the amplitude of the signal transmitted through the transformer is dependent upon which collector bar '58 is connected by the drawbar 28 to the bus-bar 26.

Due to the resiliency of the spring fingers, at least one of the contact rivets 46, i? is maintained in contact with one of the collector bars 58 at all times. When the contact rivets are in an intermediate position, in which they respectively contact adjacent bars 58, the resistance wire 56 is connected across such bars and thus the portion of the resistance element "62 between these bars is not short-circuited. Instead the resistance between the two bars is decreased but the resistance is nevertheless sufficient to prevent spurious signals to pass from one bus-bar to the other and to avoid serious alterations in the graduated resistances between the collector bars provided by the resistance element 62.

If the drawbars are shifted, even while a numtial transients will be produced because the signal is continuously transmitted to the output system through at least one of the collector bars 58. As the contacts of the drawbars are shifted from one collector bar to the next there is an intermediate position in which the signal is impressed on both collector bars, but due to the provision of the resistance 56 the transition is smooth and clickless. Mechanical noises due to shifting the drawbars are also substantially eliminated because it is not necessary that the drawbars be held in any definite positions, and the spring fingers 36 need not function as detents, as was necessary, or at least desirable, in prior constructions.

While I have shown and described a particular embodiment of my invention, it will be apparent to those skilled in the art that numerous modifications and variations may be made in the form and construction thereof, without departing from the more fundamental principles of the invention. I therefore desire, by the following claims, to include within the scope of my invention all such similar and modified forms of the apparatus disclosed, by which substantially the results of the invention may be obtained by substantially the same or equivalent means.

I claim:

1. A drawbar assembly for the tone quality control of an electrical musical instrument, comprising a plurality of spaced parallel collector bars, a plurality of manually operable drawbars insulated from the collector bars and movable transversely of the collector bars, a leaf spring secured to each drawbar, a pair of contactors mounted on each leaf spring for making sliding contact with the collector bars, said contactors being insulated from one another and spaced in the direction of movement of the drawbars a sufiicient distance to bridge the spaces between the collector bars, and a resistance element connected between the contactors of each pair.

2. A drawbar assembly for the tone quality control of an electrical musical instrument, comprising a plurality of spaced parallel collector bars, a plurality of manually operable drawbars insulated from the collector bars and movable transversely of the collector bars, a pair of contactors moved by each drawbar, resilient means to hold said contactors in position for making sliding contact with the collector bars, said contactors being insulated from one another and spaced in the direction of movement or" the drawbars a sufficient distance to bridge the spaces between the collector bars, and a resistance element connected between the contactors of each pair.

3. In a tone quality control apparatus for an electrical musical instrument in .which playing keys operate switches respectively to connect electric generators of the .partials of the tones to bus bars and in which an output system having a multi-tap coupling input impedance is employed, the combination of a plurality of manually adjustable control elements, a plurality of uniformly spaced collector bars respectively connected to the taps on the coupling impedance, a pair of contactors carried by each control element and cooperable with the collector bars, said contactors being spaced relative to the spacing of the collector bars so that one of the contactors of each pair will at all times be in contact with one of the collector bars, means respectively conber of the playing keys are depressed, no substan- 15 necting one contact on each control element to one of the bus bars, and a resistance interconnecting each pair of contactors.

4. In a tone quality control apparatus for an electrical musical instrument in which playing keys operate switches respectively to connect electric generators of the partials of the tones to bus bars and in which an output system is provided, the combination of a coupling input impedance, means to connect the coupling impedance with the input of the output system, said impedance having a plurality of taps, a plurality of manually adjustable control elements, a plurality of spaced collector bars respectively connected to the taps on said impedance, and contactors carried by the control elements and cooperable with the collector bars, said contactors being effective to bridge the spaces between adjacent collector bars so that at least one of the collector bars will at all times be in contact with the contactors, said contactors offering sufficient resistance, when bridging the space between adjacent collector bars, to prevent substantial shortcircuiting of the portion of the coupling impedance which is connected between such collector bars. and means for connecting the contactors respectively with the busbars.

5. An adjustable control apparatus for electrical musical instruments comprising, a plurality of spaced parallel collector bars, impedance means of graded low values respectively interconnecting said collector bars, a plurality of drawbars mounted adjacent one another for adjustable sliding movement in a direction perpendicular to the collector bars, a pair of contactors carried by each drawbar, resilient means urging the contactors toward the collector bars to make electrical contact therewith, the spacing of the contactors being such relative to the spacing of the collector bars that at least one contactor of each pair is at all times in contact with one of the collector bars, and impedances of low value respectively connecting the contactors of each pair.

6. In a tone quality control apparatus for an electrical musical instrument in which playing keys operate switches respectively to connect electric generators of the partials of the tones to bus bars and in which an output system is provided, the combination of a low value coupling input impedance, means to connect the coupling impedance with the input of the output system, said impedance having a plurality of taps, a plurality of manually adjustable control elements, a plurality of spaced collector bars respectively connected to the taps on said impedance, a contacting device carried by each of the control elements and cooperable with the collector bars, said devices being movable by the drawbars in a direction transverse to the collector bars, being of sufficient length in their direction of movement to bridge adjacent collector bars, and affording sufficient electrical resistance when bridging adjacent collector bars that the portion of the coupling impedance between such adjacent collector bars is not effectively shortcircuited, and means for connecting the contacting devices respectively with the bus-bars.

HERBERT E. MEINEMA.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,956,350 Hammond Apr. 24, 1934 2,254,366 Hammond Sept. 2, 1941

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