US 3322875 A
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Description (OCR text may contain errors)
y 30, 1 v J. 5. ROLL ETAL 3,322,875
HARMoNicA Eync'momc AMPLIFICATION Filed Oct. 9, 1964 INVENTORS (Jo/ml 4. Have BY dom/ 6. ROLL United States Patent ABSTRACT OF THE DISCLOSURE The following specification describes a simple technique for providing electronic amplification of the output of a musical instrument and in particular a harmonica. A capacitor plate is mounted on the inside of the harmonica cover and is insulated from the harmonica cover so as to avoid any shock hazard to the user. The capacitor plate is mounted opposite from and facing the reeds in the harmonica. The reeds are all electrically grounded and function electrically as the second plate of a capacitor. As the reeds vibrate to produce the normal acoustical output, the capacitance of the capacitor correspondingly varies. This variation in capacitance is employed in connection with an amplification network to provide an amplified electronic output.
This invention relates in general to the amplification of a musical instrument output and more particularly to a capacitor transducer technique for amplifying the output of a musical instrument having a vibrating reed in which the reed is employed as one of the plates of the capacitor.
There are a number of systems known for amplifying the output of a musical instrument. Most of these systems are cumbersome and expensive. Because the system of this invention is simple and require-s little added weight or equipment on the instrument being played, it has particular applicability to a harmonica and will be described in connection with a harmonica embodiment.
- It is a major purpose of this invention to provide a means for amplifying the output of a musical instrument without making the instrument more cumbersome to play.
It is another purpose of this invention to provide a means for reproducing the output of a musical instrument while retaining the timbre of the instrument.
It is a related purpose of this invention to provide a means for reproducing the output of a musical instrument without omitting or distorting the harmonics and subharmonics of the n'otesbeing played.
It is a further purpose of this invention to devise a means to amplify the output of a musical instrument without requiring redesign of the basic elements of the musical instrument.
In brief, this invention employs a capacitor which has its capacitance varied to provide the electrical signal that can then be amplified by electronic means. The capacitor is formed of one plate added to the harmonica and of a second plate consisting of the reeds in the harmonica. As the reeds vibrate, producing the normal acoustical output, the capacitance of the capacitor varies. In this fashion .there is generated a varying electrical parameter (the capacitance) which is adapted to electronic amplification. Unlike the capacitor microphoneand other acoustical pickup devices, this invention provides an electrical signal generated by the vibrating of the reed and not from the acoustical signal which is concurrently produced by the reed. The transducer is a mechanical to electrical one rather than an acoustical to electrical one. Thus one of the capacitor plates is the vibrating reeds (which reeds also directly provide an acoustic output). The other plate is an added plate spaced from and facing the reed and is preferably insulated from the covers and body of the instru- Patented May 30, 1967 ment. A DC. voltage of appropriate magnitude (250 volts in one harmonica embodiment) is applied across the capacitor thus formed. The reed side of the capacitor is kept at ground potential for the safety of the user. By employing the entire reed as one side of the capacitor, the maxi mum change in capacitance on playing is obtained so that the output signal, small as it may be with this technique, is nonetheless sufliciently large to provide a usable signal.
As the capacitance varies, the DC. voltage is modulated thereby providing a signal. The signal is fed through a coaxial cable directly to a very high gain first stage of an electronic amplification system. Because the electronic amplification system is separate from the instrument being played, the only weight added to the equipment is the capacitor employed, a small coaxial terminal, and the negilible eifect of a small coaxial cable to the amplification equipment.
In this extremely simple fashion, a negligible weight is added to the instrument so that the person who is playing the instrument is in no sense encumbered. Furthermore, the added capacitor plate can uually be added without a redesign of the basic elements and body of the musical instrument so that the parts and assembly techniques presently employed can continue to be employed. Equally important, the reproduction includes harmonics and subharmonics with a minimum of distortion.
Other features and purposes of this invention will become apparent from a consideration of the following detailed description and drawings, in which:
FIG. 1 is a schematic illustration of the device of this invention in a harmonica embodiment;
FIG. 2 is a perspective view of a harmonica incorporating this invention; and
FIG. 3 is a cross-section along the plane 33 of FIG. 2 showing the relationship between the reeds and the added capacitor plate.
As may be seen from the figures, a harmonica 10 of standard design may be readily adapted to this invention. The arrangement involves two units, one being a harmonica 10 which has been modified in accordance with the teaching. of this invention, and the second being an amplifier unit 12. The harmonica 10 and amplifier 12 are interconnected by a coaxial cable 14, which cable 14 is conveniently made detachable from the harmonica 10 by means of a coaxial plug connector 16 mounted on the body 26 of the harmonica 10.
It is convenient to mount the capacitor plate 18 being added inside the covers 20. The plate 18, covered on both 0 sides by insulation 22, may be mounted flush against the inside surface of the covers 20 separated from the normally metallic covers 20 only by one of the two insulating bands 22.
The insulation 22 may be any flexible insulating material such as an insulating tape or an epoxy layer which may be spread on from a liquid form. The particular insulation employed is not important as long as it can withstand the 250 volts which will be placed on the plate 18.
The particular type of harmonica 10 which is illustrated in the figures is a chromatic harmonica with reeds 24 on both sides of the body 26. Because it is a chromatic harmonica, a standard chromatic push-button 28 is shown. The body 26 of the harmonica 10 has two metal side plates 30 to which the metallic reeds 24 are attached. Thus it is convenient to tie the ground of the coaxial terminal 16 directly to the metal side plates 30. Because each metal reed 24 is directly connected to one of the two metal side plates 30, each reed is thereby eifectively grounded. The center lead 14a of the coaxial cable 14 is connected to the plates 18 and thereby places 250 volts, from a battery 32 in the amplifier unit 12, on the plates 18.
this capacitor pick-up technique is quite low. A mu of 1 25,000 through a two stage pre-amplifier employing a 12AX7 dual triode has been incorporated in one embodiment and found satisfactory.
The fact that the entire reed 24 is employed to create the capacitance variation results in an electrical signal of usual magnitude. In addition the use of the reed 24 as the varying electrical element means that the electrical signal generated is a direct analog to the musical signal being played. Further, the acoustical isolation of the reeds 24 means that the electrical signal generated is substantially free of environmental noise.
Piezoelectric microphone type of pick-ups have been employed on many musical instruments in order to provide the signal for an amplifier. However these pick-ups have the serious disadvantage that they do not properly pick up all of the harmonics generated. There is generally a distortion of one form or the other depending upon such matters as the location of the pick up. An acoustical pick-up was tried on a harmonica and it was found that the harmonics were distorted. The high frequency harmonics were inadequately picked up when the base reed was being blown and the lower frequency subharmonics were inadequately picked up when the higher frequency reeds were being played.
One of the more significant contributions of this in- Vention is that such pick-up distortion is avoided. The capacitance variation between the plate 18 and the reed 24 faithfully reproduces the sound generated. This is particularly important when the reed is driven hard since significant harmonics are then generated. By using the vibration of the very element (the reed 24) that produces the musical sound to produce an electrical signal, it becomes possible to achieve a high degree of accurate reproduction.
In addition, such a construction minimizes the additional material or equipment that must be added to the musical instrument thereby providing an instrument having exactly the same dimensional and weight characteristics with which the player is familiar.
This invention has been described in detail in connection with a harmonica embodiment for which the invention is particularly adapted to be used. It would, however, be possible to employ the invention in connection with other musical instruments and in particular in connection with those musical instruments in which a reed is employed to generate the musical sound. In certain musical instruments having reeds, the reed itself is not a metallic item and would have to be coated with a metal film in order to permit the reed to serve as one plate of a capacitor.
Thus it will be understood that this invention may be modified and adapted to different instruments. Accordingly, it shall be understood that all such modifications as fall within the scope of the invention also fall within the scope of the following claims.
What is claimed is:
1. In a harmonica having reeds, the improvement which adapts said harmonica to electronic amplification, comprising:
a capacitor plate mounted on said harmonica spaced from and facing said reeds to form a capacitor between said plate and said reeds, said capacitor plate being electrically insulated from said reeds,
whereby the vibration of said reeds will vary the capacitance of said capacitor thereby providing a varying electrical parameter which is adapted to electronic amplification.
2. In a harmonica having reeds mounted on a side plate and having a cover, the improvement which adapts said harmonica to electronic amplification, comprising:
a capacitor plate mounted along the inside of said cover spaced from the facing said reeds, said plate being electrically insulated from said cover, and
means to convey as an electrical signal the variation in capacitance between said capacitor plate and said reeds when said reeds vibrate,
whereby the vibration of said reeds provides an electrical signal adapted to electronic amplification.
3. In a harmonica having reeds mounted on a side plate and having a cover, the improvement which adapts said harmonica to electronic amplification, comprising:
a capacitor plate mounted along the inside of said cover spaced from and facing said reeds, said plate being electrically insulated from said cover, and
means for grounding said side plate and for applyin g a DC. voltage to said capacitor plate,
whereby the vibration of said reeds will modulate said DC. voltage thereby providing :an electrical signal adapted to electronic amplification.
References Cited UNITED STATES PATENTS 2,901,936 9/1959 Scherer et al. 841.14 X
ARTHUR GAUSS, Primary Examiner.
D. D. FORRER, Assistant Examiner.