Patent Publication Number: US-2023144776-A1

Title: Systainer system for electric stringed instruments

Description:
FIELD OF THE INVENTION 
     This invention relates generally to electronic sustainers and, in particular, to a sustainer that may be added to an electronic guitar with minimal modification. 
     BACKGROUND OF THE INVENTION 
     A “sustainer” is a device that amplifies the string vibrations of a musical instrument to keep the strings vibrating after the instrument is played. The effect can be generated with an ordinary electric guitar if the instrument is played in close proximity to the speaker of an audio amplifier. The acoustic energy caused by the original notes is fed back to the strings through the speaker, prolonging the original vibrations. For this technique to be effective, however, the sound must be very loud. 
     To avoid such high levels of amplification, instead of bringing the instrument close to the amplifier, the speaker can instead be brought close to the strings of the instrument. In fact, some early systems used a loudspeaker mounted on the instrument in close proximity to the strings. As described in U.S. Pat. No. 4,245,540, the amplified signal from the pickup is passed to the loudspeaker, so that acoustic vibrations produced by the loudspeaker impinge directly upon the strings. 
     As the output of a loudspeaker can be difficult to control, more modern sustainers use electromechanical transducers instead of speakers, but the idea is nevertheless the same: the string vibrations are amplified and used to drive the transducer, which causes the strings to keep ringing. Now there are sustainer devices that are hand held by the performer, devices that attach to existing instruments, and devices integrated into factory models. But in each case, the solutions are unnecessarily complex and expensive and/or less effective or versatile than they could be. 
     SUMMARY OF THE INVENTION 
     This invention improves upon the existing art by providing a simple yet effective sustainer for electronic stringed instruments, notably electronic guitars. While the system may be factory installed, the system is readily incorporated into an existing instrument with minimal modification. 
     The sustainer system is ideally suited to an electric stringed instrument having a bridge pickup and a neck pickup. A driver assembly, disposed adjacent the neck pickup of the instrument, includes a plurality of electromagnetic transducers operative to induce vibrations in the strings. A battery-operated electronic amplifier has an input adapted for connection to the bridge pickup, and an output connected to the driver assembly, such that, when the instrument is played, string vibrations sensed by the bridge pickup are amplified by the electronic amplifier and used to drive the driver assembly, thereby sustaining the played string vibrations. 
     The driver assembly includes a housing configured to receive a row of magnetic pole pieces, each pole piece being supported below a respective one of the strings of the instrument, with a coil of wire wrapped around the housing and the magnetic pole pieces. The output of the electronic amplifier is connected to the coil of wire. 
     In the preferred embodiment, the driver assembly is disposed in a ring that surrounds the neck pickup of the instrument. The ring may include an ON/OFF switch that routes power from the battery to the electronic amplifier and simultaneously deactivates the bridge pickup in the ON position. The ring may further include a switch that reverses the flow of current through the coil of wire wrapped around the housing and the magnetic pole pieces. 
     The magnetic pole pieces are preferably threaded into the housing, enabling a user to adjusted the distance between the pole pieces and the strings. The magnetic pole pieces may be composed of a permanent magnet and a magnetizeable member. The ring may be provided in multiple sizes, including a smaller size configured to surround a single-coil pickup and a larger size configured to surround a double-coil hum-cancelling pickup. 
     The electronic amplifier is preferably an audio amplifier based upon a monolithic operational amplifier, and the amplifier and battery may be disposed in a compartment within the instrument, accessible through back panel, for example. 
     Different signal and power switching options are disclosed using toggle, blade or other types of switches, including 2-way configurations (to select either bridge or neck pickup), as well as 3-way configurations (to select bridge, bridge and neck, or neck only). In all embodiments, however, the sustainer amplifier circuit is powered only when the neck pickup is deselected. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a perspective view providing an overview of the invention; 
         FIG.  2 A  is an exploded view showing the driver removed from a ring surrounding the neck pickup; 
         FIG.  2 B  is an underside, perspective view of a sustainer ring with components installed but not yet mounted on an instrument; 
         FIG.  3    is a block diagram showing electrical connections and switching functionality; 
         FIG.  4 A  is an exploded view of an unassembled driver assembly; 
         FIG.  4 B  is an assembled view of a driver assembly; 
         FIG.  5    illustrates a magnetized driver pole assembly; 
         FIG.  6    is a schematic diagram of an amplifier circuit applicable to the invention; 
         FIG.  7    is a block diagram used to illustrate how different switches may be used to route power to a sustainer circuit; and 
         FIG.  8    depicts a further embodiment utilizing a multi-position pickup-selection switch eliminating the need for neck pickup deactivation on the sustainer ring. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Now making reference to the accompanying drawings,  FIG.  1    is a perspective view providing an overview of the invention installed on a 6-string electric guitar  102 , with the understanding that the invention is equally applicable to other types guitars and stringed instruments with more or fewer strings. In broad and general terms, an electrical signal from the bridge pickup  104  is amplified by an electronic circuit  106 , and the amplified signal is delivered to a driver  108  proximate to neck pickup  110 . As strings  112  connected to bridge  114  vibrate, the electronically amplified vibrations are delivered to driver  108 , sustaining the vibrations for an extended period of time, in some cases indefinitely depending upon the strength of the original vibrations and other factors. 
     While in  FIG.  1    the driver is shown proximate to a double-coil humbucker type pickup, the invention is equally applicable to single-coil pickups. In the preferred embodiments, the driver  108  forms part of a ring structure  116  that surrounds the neck pickup. A smaller ring  116  than the one shown would be used for single-coil pickups. The ring, which may be constructed from plastic, provides two switches, including an ON/OFF switch  118  and a phase-reversing switch  120 . While the phase reversal function may be eliminated, it is provided in the preferred embodiment for more versatile sound effects. Though not visible in  FIG.  1   , when the unit is turned ON, an LED  122  is illuminated. 
       FIG.  2 A  is an exploded view showing the driver  108  removed from ring  116  viewed from the backside of the ring. Both switches  118 ,  120  are double-pole, double-throw (DPDT) switches, the wiring of which is best seen in  FIG.  3   . ON/OFF switch  118  provides three functions. First, it routes power to the amplifier, and second, it provides power to the LED. But perhaps most importantly, in the ON position, power switch  118  disconnects the neck pickup. With the driver  108  being so close to the neck pickup, if the neck pickup remained ON during sustain the feedback would be too strong to provide reliable results. 
       FIG.  3    is a block diagram showing electrical connections and switching functionality. When power switch  118  is in the ON position, one pole of the switch disconnects the neck pickup from line  302  to other connections within the guitar to volume controls, etc. The other pole of the switch  118  connects power (V+) to amplifier  400  and LED  122  through current-limiting resistor  124 . Note that V+ in this case is derived from a battery disposed along with amplifier  400  in the electronic compartment of the instrument, typically accessible through an access panel on the back of the instrument. The battery may be any operative voltage depending upon the amplifier circuitry described below, such as 5, 9, 12, 15 volts, etc. 
     While the invention may come factory installed within an instrument, it may also be added to an existing instrument, in which case connections such as A and B in  FIG.  3    may be accomplished with soldering, alligator clips, or any other reliable technique. In switch  120 , both poles are used simultaneously, such that in the two settings the windings around driver  108  are reversed. Note that  FIG.  3    is not to scale, and various aspects of the system are simplified, including the windings around the pickups  110 ,  114  and driver  108 . 
       FIG.  6    is a schematic diagram of an amplifier circuit  400  applicable to the invention, with the understanding that while this configuration is operable, other amplifier circuits are possible. As such, the invention is not limited in terms of the specific amplifier arrangement used. In this embodiment, the amplifier  402  is a TDA7267 fully integrated 2-Watt monophonic amplifier using conventional peripheral resistors and capacitors for signal coupling, currently limiting, filtering and so forth. 
       FIGS.  4 A , B are detailed diagrams of a driver coil assembly applicable to the invention, including a housing  502  including a plurality of cavities  504  to receive pole assemblies depicted in  FIG.  5   . The housing  502  may be of any non-conductive material such as molded plastic. A driver coil  506  is wound around the housing  502 , resulting in the completed assembly of  FIG.  4 B . The coil  506  may comprise 50 to 70 turns of 32 AWG insulated copper wire to achieve an impedance of 8 ohms so as to be compatible with the amplifier circuit of  FIG.  6   . Other numbers of turns and different wire gauges are of course possible depending upon the circuitry ultimately implemented. 
       FIG.  5    illustrates a magnetized driver pole assembly  602 . Each one of the cavities  504  in  FIG.  4 A  would receive a separate one of the driver pole assemblies  602 . Each assembly preferably includes a strong, rare-earth magnet  604  and cylindrical screw  606 . Magnet  604  may, for example, comprise an N54 neodymium disc having a height of 1 mm and a diameter of 5 mm. The screw  606  may have a diameter of 6 mm and a height of 4 mm, resulting is an overall driver pole measuring 6 mm wide by 5 mm high. The screw would be constructed of a magnetizeable material such as iron, or a magnetizeable alloy. 
     Whereas the embodiments thus far described utilize DPDT switches, other types of switches my be used for different pickup selection options, but in all cases, as shown in  FIG.  7   , power is only routed to the sustainer circuit when the neck pickup is disabled (and the sustainer ring ON/OFF switch is in the ON position if a separate ON/OFF switch is provided). 
     As one example of a different pickup selection arrangement,  FIG.  8    illustrates power and signal routing associated with a multi-position pickup-selection switch, in this case a 3-way, 4-pole, ON/ON/ON toggle switch (for example, Part No. SWM43-17 from C&amp;K). It will be further appreciated by those of skill in the art that different-sized toggle switches may be used, including mini-toggle switches, as well as blade-type switches. Note that when such multi-position switches are implemented, the need for a separate ON/OFF switch on the sustainer ring may be obviated. 
     In all positions of  FIG.  8   , the bridge pickup signal to the sustainer circuit is always routed to the amplifier circuit regardless of whether the amplifier is powered on. In position  1 , only the bridge pickup is selected, and power is indeed routed to the amplifier, and sustainer functionality is activated. In positions  2 ,  3  however, the neck pickup is selected, and power to the amplifier is disabled, thereby defeating sustainer functionality.