Abstract:
The present invention is directed to a stringed, musical instrument where the instrument strings are grounded by a string ground circuit, and wherein the string ground circuit includes a circuit breaker having a current path that defines a portion of the string ground circuit between the strings and a ground.

Description:
FIELD OF THE INVENTION 
   The present invention is directed to a ground path for a musical instrument, and more particularly to a ground path having a circuit breaker for an electric musical instrument. 
   BACKGROUND OF THE INVENTION 
   Professional and amateur musicians often employ stringed instruments that are fitted with pickups, i.e., devices that allow the instruments to be electrically connected to an amplifier. However, the use of electric amplifiers and other peripheral equipment, such as microphones, creates a risk of electrical shock, which in some cases may be lethal. 
   The threat of electrical shock may arise through various types of electrical malfunction such as: 1) an electrical failure in the musician&#39;s equipment; 2) improper wiring of the power circuit to which the musician&#39;s equipment is attached; and/or 3) an electrical failure of peripheral equipment. One example of the first type of malfunction occurs when a guitarist&#39;s amplifier induces a high voltage to the ground side of the guitar output jack. An example of the second type of malfunction is improper wiring of a three-pronged electrical wall socket such as where the “earth” ground is not connected and the “neutral” and “hot” sides of the outlet are reversed, thereby resulting in a high voltage being applied to the “neutral” lead. An example of the third type of malfunction occurs when the musician&#39;s equipment is functioning properly while connected to properly wired wall sockets, but other equipment, such as a microphone, is improperly grounded. 
   Often in electric instruments, an earth ground is provided, such as through an amplifier. The earth ground reduces the amount of audible noise by providing a pathway for any induced noise to drain from the instruments circuitry. However, in some cases the earth ground is not present or is insufficient. A common way to provide noise reduction in instruments where the earth ground is lacking has been to provide the “grounded effect” by including a “string” ground. 
   String grounds are commonly used in electric guitar circuitry. A string ground generally includes a conductive path between the strings to the ground output or ground plane of the guitar circuitry. In the most common string ground configuration, the metal guitar strings touch a metal bridge and a wire that is connected between the metal bridge and the outside casing of a volume potentiometer or shielding inside the guitar. Although such a design provides a reduction in noise it also creates the mechanism, which in conjunction with any one of the previously mentioned malfunctions, may result in the musician being electrically shocked. 
   Suggestions for minimizing the risk of electrical shock have included checking the power outlets to which all of the musician&#39;s equipment, as well as any peripheral equipment, is connected with an outlet tester. However, such a practice may not always be feasible. Testing every outlet may be extremely time consuming and it may not be allowed where the sockets are used to power equipment not controlled by the musician. 
   The use of Ground Fault Circuit Interruptor (GFCI) extension cords has also been suggested as a practice that can reduce the risk of electrical shock. The practice includes plugging electrical equipment into a GFCI extension cord and plugging the extension cord into a wall socket. Such a circuit will trip, or open, if a certain threshold leakage current is detected. However, such a practice has various disadvantages. First, any GFCI extension cord must be tested prior to each use to assure that it is functioning properly. Next, a large number of the devices may be required for productions utilizing many pieces of equipment, which may result in the technique being prohibitively expensive. Additionally, to thoroughly utilize the technique a GFCI device must be used with any equipment that the musician will contact, including peripheral equipment not owned by the musician. 
   Various alterations to electrical musical instrument, such as guitars, have also been suggested to reduce the risk of electrical shock. For example, removing the string ground has been recommended. However, such an alteration also removes the noise reduction benefits provided by the ground. 
   Another suggested alteration requires placing a capacitor and a resistor in parallel within the string ground path. However, the alteration does not prevent a shock from occurring, but it may, if the capacitance and resistance are sufficient, prevent the shock from being lethal. In fact, the alteration does not provide a strict maximum current limit, but rather reduces the current level. As a result, even after the current has been reduced by such a device, the reduced current may still be lethal. 
   In view of the above, there exists a need for a musical instrument featuring a string ground path that is configured to reduce the risk of electrical shock. 
   SUMMARY OF THE INVENTION 
   In view of the foregoing, it is an object of the present invention to provide a musical instrument featuring a string ground circuit having a circuit breaker. 
   It is another object of the invention to provide a musical instrument featuring a string ground circuit that includes a replaceable fuse that is rated to open the string ground circuit upon application of a non-lethal current. 
   It is another object of the invention to provide a string ground circuit including a circuit breaker that may be incorporated into a guitar as a retrofit or during initial construction. 
   One aspect of the invention involves a musical instrument string ground circuit that includes a circuit breaker. The circuit breaker is configured to open the string ground circuit upon application of a current having a magnitude that is greater than a predetermined current limit. 
   In the preferred embodiment of the invention, a musical instrument includes electrically conductive strings and a string ground circuit that extends between the strings and a ground connector. The string ground circuit includes a circuit breaker that prohibits the flow of current through the string ground circuit that has a magnitude above a predetermined current limit. The circuit breaker is a fuse that includes a fuse socket and a removable fuse. 
   These and other features and advantages of the present invention will be appreciated from review of the following detailed description of the invention, along with the accompanying figures in which like reference numerals refer to like parts throughout. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is perspective view of a musical instrument including a string ground circuit having a circuit breaker, in accordance with the principles of the present invention; 
       FIG. 2  is a bottom view of a top plate of a body portion of the musical instrument of  FIG. 1  showing a string ground circuit with a circuit breaker, in accordance with the principles of the present invention; 
       FIG. 3  is an enlarged detail view of a portion A, shown in  FIG. 2 , of the musical instrument of  FIG. 1  showing a string ground with a circuit breaker, in accordance with the principles of the present invention; 
       FIG. 4  is a cross-sectional view of a portion of the musical instrument of  FIG. 1  taken along line B-B of  FIG. 3 ; 
       FIG. 5  is a cross-sectional view of a portion of the musical instrument of  FIG. 1  taken along line C-C of  FIG. 3 ; 
       FIG. 6  is perspective view of a musical instrument including a string ground circuit having a circuit breaker, according to another embodiment of the present invention; 
       FIG. 7  is a cut-away view of the back side of the front of the body portion of the musical instrument of  FIG. 6 ; 
       FIG. 8  is an enlarged detail view of a portion D, shown in  FIG. 7 , of the musical instrument of  FIG. 6  showing a string ground circuit with a circuit breaker, in accordance with the principles of the present invention; and 
       FIG. 9  is a perspective view of an alternative embodiment of the present invention. 
   

   DETAILED DESCRIPTION 
   In the following paragraphs, the present invention will be described in detail by way of example with reference to the attached drawings. Throughout this description, the preferred embodiment and examples shown should be considered as exemplars, rather than as limitations on the present invention. As used herein, the “present invention” refers to any one of the embodiments of the invention described herein, and any equivalents. Furthermore, reference to various feature(s) of the “present invention” throughout this document does not mean that all claimed embodiments or methods must include the referenced feature(s). 
   When a musician encounters an electrically charged instrument, or piece of peripheral equipment, through one of the previously mentioned electrical malfunctions, the musician&#39;s body may become part of the path of least electrical resistance for high current. If so, high magnitude current may pass through the string ground circuit and the musician. The present invention provides a musical instrument featuring a string ground circuit having a circuit breaker that provides a musician protection from electrical shock. 
   A musical instrument  10 , which may be a guitar as illustrated in  FIG. 1 , generally includes a head  11 , a body portion  12 , a neck portion  13  that extends between head  11  and body portion  12 , and a plurality of strings  14 . A plurality of tuning heads  15  are mounted on head  11  and a first end of each string  14  is wrapped around a portion of a respective tuning head  15  so that when the opposite ends of strings  14  are fixedly coupled to body portion  12 . Actuation of tuning heads  15 , for example by rotation, may be used to adjust the tension in strings  14 . 
   Body portion  12  may be hollow, as shown, or solid. Body portion  12  generally includes atop plate  21 , or soundboard, a bridge plate  22 , a bottom plate  23  and side walls  24 . In the illustrated embodiment, side walls  24  are coupled to each of top plate  21  and bottom plate  23  along the periphery of each and extend between top plate  21  and bottom plate  23  to form a cavity. Bridge plate  22  is coupled to a top surface of top plate  21  and provides string mounting features so that an end of each string  14  may be fixedly coupled to body portion  12 . It shall be appreciated that body portion  12  may also include any number of braces, linings, channels and/or tail blocks located anywhere on or within body portion  12  as shown in  FIG. 2  and as would be recognized in the art. 
   As mentioned above, neck portion  13  extends between head  11  and body portion  12 . Neck portion  13  generally includes an elongated neck member  16 , a nut  17 , a fretboard  19  and a plurality of frets  20 . A first end of neck member  16  is fixed to head  11 , while a second end of neck member  16  is fixed to body portion  12 . Neck member  16  may be fixed to head  11  and body portion  12  by any method known in the art, such as mechanical fasteners (e.g., screws, bolts) and/or adhesives. Neck member  16  may be constructed from wood, plastic, metal or a combination thereof as would be appreciated by a person having ordinary skill in the art. 
   Nut  17  is coupled to neck member  16  at the first end of neck portion  13  adjacent to head  11 . Nut  17  may be a block having any cross-sectional shape constructed from plastic, metal, ivory, wood or any other material known in the art. Nut  17  may also include grooves (not shown) for receiving and orienting strings  14 . Nut  17  may be fixedly coupled to neck member  16 , such as by mechanical fasteners and/or adhesives, or nut  17  may be held in place against neck member  16  by strings  14 . 
   Fretboard  19  may be coupled to a top surface of neck member  16 . Fretboard  19  is generally a thin elongated member. Fretboard  19  may extend from nut  17  toward body portion  12 . Fretboard  19  overlays neck member  16  and a portion of top plate  21  of body portion  12 . Fretboard  19  may be constructed from wood, plastic, metal or any combination thereof and fretboard  19  may further include decorative features, such as inlays. Fretboard  19  may be fixed to neck member  16  by mechanical fasteners and/or adhesives or by any other attachment technique known in the art. 
   Frets  20  are fixedly coupled to fretboard  19 . Frets  20  generally extend laterally across fretboard  19  and above the top surface of fretboard  19 . Frets  20  may be made of metal, plastic, wood or any other material known in the art and they may be fixed to fretboard  19  by inserting a portion of each fret  20  into a slit, or channel, machined in fretboard  19 . Furthermore, frets  20  may also, or alternatively, be coupled to fretboard using mechanical fasteners and/or adhesives. 
   A first end of each string  14  is wrapped around a portion of a respective tuning head  15 . Each string  14  is drawn over nut  17 , along and spaced above fretboard  19  and frets  20 , over a saddle  32  and fixedly coupled to body portion  12 , as described below. As is well known in the art, actuation of tuning heads  15 , for example by rotation, may be used to adjust the tension in strings  14 . Strings  14  are conductive and may be constructed from steel, brass or any other material known in the art. 
   As shown in  FIGS. 4 and 5 , a ball end  27  on an end of each string  14  is inserted through a bridge aperture  28  and held in place by a bridge pin  29 . Bridge aperture  28  extend from the environment through bridge plate  22 , top plate  21 , a pin plate  30  and a ground plate  31  and into the cavity defined by body portion  12 . 
   Ground plate  31  is affixed to a bottom surface of pin plate  30  so that each of a plurality of ground plate apertures  35  define a lower portion of bridge apertures  28 . Ground plate  31  and pin plate  30  may be coupled by an adhesive or any type of fastener known in the art. Ground plate  31  includes a bottom conductive layer  34 , a top conductive layer  33  and ground plate apertures  35 . Preferably conductive layers  33  and  34  are separated by a nonconductive layer  40 . Ground plate  31  may be constructed from materials such as paper-phenolic, or glass-epoxy materials or plastics such as polyamide or polystyrene. Each of the conductive layers may be created as a surface coating or a laminate layer and the conductive material of layers  33  and  34  may be copper, tin, brass, silver, nickel or any other conductive material known in the art. According to further embodiments of the invention, ground plate  31  may be replaced by one or more jumper wires (not shown). 
   As shown in  FIGS. 3 and 4 , bottom surface coating  34  of ground plate  31  is preferably discontinuous, such that there is a gap  41 , and thereby ensuring that there is no direct electrical conduction between a first portion  36  and a second portion  37  of conductive layer  34 . According to an aspect of the invention, a circuit breaker  38  is connected in series between first portion  36  and second portion  37 . As used herein, “circuit breaker” is any device, active or passive, that is capable of creating an open circuit when it is subjected to a predetermined threshold electrical current value. In the illustrated embodiment, circuit breaker  38  comprises a passive device such as a fuse. Upon application of a current greater than a predetermined limit, the circuit breaker transforms from a closed circuit configuration to an open circuit configuration that prevents current flow therethrough. 
   Circuit breaker  38  may comprise a micro-type fuse plugged into a fuse socket that is electrically coupled in series between first portion  36  and second portion  37  of conductive layer  34 . For example, circuit breaker  38  may be a replaceable micro-type fuse, such as a Micro Very Fast-Acting Subminiature Plug-In Fuse manufactured by Littlefuse, Inc. of Des Plaines, Ill. Circuit breaker  38  may be coupled to first and second portions  36  and  37  of conductive layer  34  by soldering, welding or any other electrically conductive fixation technique known in the art. 
   In accordance with the principles of the invention, circuit breaker  38  is selected so that it creates an open circuit before a lethal current is able to pass through the string ground circuit and the musician. As shall be appreciated, the threshold current rating, or current limit, of circuit breaker  38  is selected so that circuit breaker  38  will trip (i.e., create an open circuit) prior to a lethal current passing through the string ground circuit. For circuit breaker  38 , it is desirable that the threshold current value is in the range of 1-30 milliamps (mA). Preferably, the threshold value is in the range of approximately 1-7 mA, and most preferably about 5 mA. 
   It shall further be appreciated that although circuit breaker  38  is shown directly coupled to ground plate, the circuit breaker may be placed anywhere within the string ground circuit. One such embodiment is shown in  FIG. 9 . In this embodiment, ground plate  131  is shown. Ground wire  137  is soldered or otherwise electrically connected to ground plate  131 . Ground wire  137  is also electrically connected in series to circuit breaker  138  which in turn is electrically connected to ground wire  139 . 
   With further reference to  FIG. 4 , ground wire  39  is preferably electrically coupled to second portion  37  of conductive layer  34 , or directly to circuit breaker  38 , to provide a conductive path from circuit breaker  38  to a ground connector (not shown), such as a jack plate. The ground connector may be any structure that is used to electrically couple the electronics of the instrument to an earth ground provided through an amplifier. For example, the instrument&#39;s circuitry may include a ground circuit that is electrically coupled (sometimes through the housing of a volume potentiometer) to an external jack plate mounted directly on the instrument body. 
   The jack plate is preferably coupled to a ground wire in a chord extending to the amplifier, whereas the ground connector is preferably mounted directly to the body portion of the instrument. According to additional embodiments of the invention, the ground connector may be indirectly mounted to the body portion. For example, the ground connector may comprise an audio jack attached to the end of a wire pigtail that extends from any portion of the instrument. Ground wire  39  may be any conductive wire that is directly connected to one or both of second portion  37  and circuit breaker  38  using any electrically conductive fixation technique known in the art, such as soldering. 
   Each string  14  and/or ball end  27  is installed so that it is placed in contact with conductive layer  34  of ground plate  31 , as shown in  FIG. 5 . During installation of a string  14 , ball end  27  is inserted through bridge aperture  28  and into the cavity defined by body portion  12 . String  14  is then gently pulled while bridge pin  29  is pressed into bridge aperture  28 . A properly installed bridge pin  29  wedges the respective string  14  against the sidewall of aperture  28  while ball end  27  is held in contact with a first portion  36  of conductive layer  34  of ground plate  31 . The interaction between ball end  27  and conductive layer  34  provides conduction between string  14  and ground plate  31 . As described above, the interfaces between remaining components in the string ground circuit are created using known electrically conductive fixation techniques, such as soldering. 
   It shall be appreciated that the string ground circuit path extends between strings  14  and the ground connector, through at least strings  14 , circuit breaker  38  and the ground connector. As previously mentioned and shown, the string ground circuit path may also include additional conductive members such as ball ends, a ground plate and/or the housing of a volume potentiometer. 
   Referring to  FIGS. 6-8 , a musical instrument  50  is constructed with a head  51 , a body portion  52 , a neck portion  53  and a plurality of strings  54 . With the exception of body portion  52  and the configuration of strings  54 , the structural components of musical instrument  50  are generally functionally identical to the corresponding parts described above with respect to the instrument  10  of  FIGS. 1-5 , and therefore will not be described in further detail. 
   Body portion  52  of musical instrument  50  is solid and may include cavities that house circuitry for the pickups as well as volume and tone controls. Strings  54  may be coupled to body portion  52  through a tremolo  55 , rather than a stationary bridge. Tremolo  55  is constructed from metal and functions as a ground plate such that a separate ground plate is not needed. 
   As depicted in  FIG. 6 , strings  54  are suspended between tremolo  55  and a nut on neck portion  53 . Referring to  FIG. 8 , the ball ends  57  of the strings  54  prevents the strings  54  from slipping through tremolo apertures  58 . Strings  54  and ball ends  57  are electrically conductive and the contact between ball ends  57  and tremolo  55  provide electrical conduction between strings  54  and tremolo. 
   According to an aspect of the invention, circuit breaker  59  is electrically coupled to, and interposed between, tremolo  55  and a ground wire  60  that extends to a ground connector (not shown) to create a string ground. Similar to the previously described embodiments, ground connector may be a jack plate that is mounted directly on body portion  52  or it may be electrically coupled to a wire extending from instrument  50 . 
   According to a preferred implementation of the invention, the musical instrument comprises an acoustic guitar that includes pickups for transforming the motion of strings  14  into electric signals. However, as would be appreciated by those of ordinary skill in the art, the principles described herein may be applied to any additional musical instruments utilizing conductive strings and pickups, such as including electric guitars, mandolins, basses, violins and cellos, without departing from the scope of the present invention. 
   It shall be appreciated that an existing string ground circuit in an instrument may be modified, or retrofitted, to include a circuit breaker in accordance with the present invention. Furthermore, a string ground circuit with a circuit breaker may be added to an existing instrument or built into an instrument during initial manufacturing. 
   Furthermore, the string ground circuit of the present invention may be configured so that the circuit breaker may be easily replaced without requiring the assistance of a technician. Additionally, the circuit breaker of the present invention may be placed anywhere in the string ground circuit and anywhere that allows easy access for replacement. Furthermore, the circuit breaker of the present invention may be resettable so that rather than requiring replacement it may be reset to return the circuit breaker to a closed circuit configuration. 
   It shall further be appreciated that the string ground circuit of the present invention may be used in any instrument that employs conductive strings, regardless of the number of strings, and it may be used in conjunction with any type or combination of pickups, such as electromagnetic and/or piezoelectric pickups. In addition, it shall be appreciated that the string ground circuit may also provide a visual or audible indication of the activation of the circuit breaker. In other words, the musician may be alerted when the circuit breaker is tripped, or transformed from the closed configuration to the open configuration. 
   One skilled in the art will appreciate that the present invention can be practiced by other than the various embodiments and preferred embodiments, which are presented in this description for purposes of illustration and not of limitation, and the present invention is limited only by the claims that follow. It is noted that equivalents for the particular embodiments discussed in this description may practice the invention as well.