Patent Publication Number: US-9418635-B1

Title: Retrofittable closed-loop heater system for mouthpiece of brass wind musical instrument

Description:
FIELD OF THE INVENTION 
     The invention relates to brass wind musical instruments that have metal mouthpieces and must be played at times in cold weather. More specifically, the invention relates to a retrofitable heater system to controllably and dynamically warm the mouthpiece of such an instrument, for the comfort of the musician playing the instrument in cold weather. 
     BACKGROUND OF THE INVENTION 
     Brass musical instruments include without limitation the bugle, trumpet, cornet, flugel horn, piccolo trumpet, French horn, trombone, baritone, euphonium, and tuba. Such instruments typically terminate in a hollow leadpipe, into which a metal mouthpiece is inserted. While playing the brass musical instrument, the musician&#39;s lips are pressed against the mouthpiece. Often such instruments must be played outdoors in cold or even freezing weather. For example, the musician and instrument might be part of a marching band that is called upon to play outdoors in all seasons, perhaps a military band that plays martial music at funerals in winter. Playing brass instruments in extremely cold temperatures is very uncomfortable to the musician. The lips may become so cold and numb while blowing into the metal mouthpiece as to interfere with good playing of the instrument, and may even suffer injury. 
     Attempts to insulate the musician&#39;s lips from the often freezing cold temperature of the instrument mouthpiece may include pre-heating the mouthpiece before it is inserted into the hollow projecting leadpipe portion of the instrument. However this is not always practical and once the mouthpiece is inserted into the leadpipe and the instrument is exposed to cold temperature, the mouthpiece temperature will drop to ambient temperature. Another remedy is to apply lip balm to the musician&#39;s lips, to provide a small measure of thermal insulation from the cold mouthpiece of the instrument. However the lip balm provides minimal thermal protection for the musician, and can wear away as the instrument is played. These are stop gap measures at best, and are not very effective for long durations of music playing in very cold temperatures. Some musicians use plastic mouthpieces to improve lip comfort in cold weather playing, but such mouthpieces degrade the quality of the music. 
     What is needed is a heater system for use with the metal mouthpiece of a brass wind music instrument. Such heater system should controllably warm the instrument mouthpiece at a temperature comfortable to the musician, and should maintain a musician determined temperature for hours, even it the instrument is played in extremely cold, varying ambient temperature. The heater system preferably should be entirely self-contained such that no external preheating is required, and should not require the use of chemical lip balms or the like. The heater system should be retrofittable to existing musical instruments and should be portable. Preferably such heater should allow the musician to vary the desired temperature of the instrument mouthpiece in closed-loop fashion, even while the instrument is being used, which desired temperature should then be maintained, even in changing ambient temperature. 
     The present invention provides such a heater system. 
     SUMMARY OF THE PRESENT INVENTION 
     The present invention provides a retrofittable removably attachable standalone heater system to controllably heat the mouthpiece of a brass musical instrument. The heater system, except for its battery power supply, preferably is disposed on a flexible printed circuit board that is curved to fit within a cylindrical housing that has an opening at each end. Preferably regions of the interior housing surface are made thermally insulating so that heat produced within by the heater system does not readily escape through the housing wall. The opening in the housing rear is sized to pass the diameter of the mouthpiece rear narrow end region, and the housing front diameter is sized to fit snugly about an enlarged first region of the mouthpiece. In use, the mouthpiece rear narrow end region is passed coaxially through the housing, from housing front to rear, and the housing is abutted against the enlarged first region of the mouthpiece. A portion of the mouthpiece rear narrow end that projects through the housing rear opening is slid coaxially into the musical instrument leadpipe. 
     During manufacture of the present invention, airspace within the housing that surrounds the heater system preferably is filled with a thermally conductive elastomer. The manufacturer can insert coaxially though the housing openings a duplicate of the mouthpiece for the instrument type and model with which the assembled heater system will be used, and then fill the airspace within the housing with the elastomer Alternatively, instead of using an actual mouthpiece, the manufacturer may use a cylindrical-shaped jig whose exterior diameter matches that of the mouthpiece with which the finished heater system will be used. With the jig in place, airspace within the housing is filled with elastomer. In either manufacturing step, the elastomer is allowed to cure, and will hold the printed circuit board and components thereon securely within the housing. 
     After curing is complete, the manufacturer slides the mouthpiece or jig forward, out of the housing front. The cylindrical housing now contains the heater system, and a cylindrical void, coaxial with the housing longitudinal axis, which void is surrounded by cured elastomer. As described below, when used with an instrument, the elastomer enhances transfer of heat from the heater system to exterior surface portions of the mouthpiece. In use, the rear narrow end region of the actual mouthpiece is inserted through the housing front, through the cylindrical void within, and through the housing rear opening. At least a portion of the mouthpiece narrow rear end that projects out from the housing rear is slid coaxially into the leadpipe attached to the musical instrument. An optional stop clamp is attached to the mouthpiece end portion adjacent the rear of the cylindrical housing the narrower mouthpiece region to prevent lateral movement of the heater housing toward the rear of the musical instrument. Such movement is undesired and could impair good bonding and good thermal conductivity between the elastomer surrounding the cylindrical void and the outer surface of the mouthpiece the elastomer contacts. The combination of an insulating housing interior surface, and the use of elastomer help promote efficient transfer of heat generated by the heater system to at least a portion of the outer surface of the instrument mouthpiece, with minimal loss of heat through the cylindrical housing outer surface. This efficiency can extend lifetime of the battery used to power the heating system. Once so mounted, it is preferred that the heater system remain on the mouthpiece indefinitely. 
     As noted, the cylindrical heater housing contains battery powered electronic circuitry, preferably disposed on a flexible printed circuit board curved to fit within the housing. The electronic circuitry includes a thermal sensor that is in close thermal proximity to the mouthpiece and to a heater element of resistance R, also disposed within the housing. The electronic circuitry creates and controls an electrical current i(t) that flows through heater element R, which radiates heat proportional to i(t) 2 ·R. It is this heat, conducted at least in part via the elastomer, that heats the mouthpiece. As noted, heat loss through the housing exterior surface preferably is reduced by thermally insulating the housing interior surface, especially if the housing material happens to be a good heat conductor, such as metal. 
     In a preferred embodiment, the electronic circuitry dynamically compares a first parameter proportional to desired mouthpiece temperature against a second parameter proportional to actual mouthpiece temperature. The first parameter is preferably a fixed reference signal, perhaps a voltage level. The second parameter a signal determined by the thermal sensor, whose resistance changes with sensed temperature. Overall magnitude of the second parameter preferably is controllable in part by the musician, for example by varying a resistance in series with the thermal sensor. In closed-loop fashion these two parameters are dynamically compared using, for example, a differential input operational amplifier. 
     If the sensed mouthpiece temperature is too low, the circuitry automatically increases magnitude of current i(t), which causes the heating element to radiate more i(t) 2 ·R heat, which further heats the mouthpiece. However, if sensed mouthpiece temperature is too high, the circuitry automatically causes the heating element to radiate less i(t) 2 ·R heat, which allows the mouthpiece to grow somewhat cooler. Preferably the heat radiator is a resistance R through which electrical current i(t) is controllably caused to pass or not pass. Magnitude of i(t) is determined by closed-loop positive feedback operation of the circuitry, which controls a transistor whose output current is i(t), and preferably is either a high maximum value or a zero minimum magnitude at any given time. The musician playing the instrument can adjust the desired temperature of the mouthpiece using a control knob or the like, preferably disposed on the heater housing, to vary the second parameter. Such adjustment may be made at any time. The preferably closed-loop operation advantageously reduces power consumption for the heat generating electronics, and also allows the musician to concentrate on playing music rather than on constantly readjusting heat generation in an open loop heater system. 
     Electrical operating power for the electronic circuitry is provided by at least one battery, preferably disposed in a detached power supply housing. The power supply housing preferably may be attached to the leadpipe of the instrument using Velcro® or the like, with operating power coupled from the power supply to the heater housing via an electrical cable. If desired, however, the battery could be disposed within the housing that contains the remainder of the heater system. 
     Brass musical instruments with which the invention may be used include without limitation the trumpet, cornet, flugel horn, piccolo trumpet, French horn, trombone, baritone, euphonium, and tuba. 
     Other features and advantages of the invention will appear from the following description in which the preferred embodiments have been set forth in detail, in conjunction with their accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  depicts a musician using a brass wind musical instrument, a trumpet, whose mouthpiece is equipped with a heater system, according to embodiments of the present invention; 
         FIG. 2  is a lengthwise cross-sectional side view of an exemplary closed-loop heater system for a brass wind musical instrument, according to embodiments of the present invention; and 
         FIG. 3  is an exemplary schematic of a closed-loop heater system for a brass wind musical instrument, according to embodiments of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       FIG. 1  depicts a heater system  10 , according to embodiments of the present invention, used to heat mouthpiece  20  of a brass wind musical instrument  30 , here a trumpet. It is understood that musician  40  presses lips  50  against metal mouthpiece  20  to play music with instrument  30 . Although  FIG. 1  depicts instrument  30  as being a trumpet, other brass wind musical instruments with which the present invention  10  may be used include, without limitation, a cornet, a flugelhorn, a piccolo trumpet, a French horn, a trombone, a baritone, a euphonium, and a tuba. Each of these instruments has a metal leadpipe  60  into which metal mouthpiece  20  is coaxially inserted during play or removed as desired. The problem common to these brass wind instruments is that metal is an excellent thermal conductor. Consequently, the musician&#39;s lips can become uncomfortably cold pressed against a metal mouthpiece when such instruments are played in extremely cold ambient temperature, outdoors in winter, for example. 
     As best seen in  FIG. 2 , mouthpiece  20  typically has a largest diameter Dm region  20 - 2  that faces the musician during play. Mouthpiece  20  further has an elongated end region  20 - 4  that extends rearward (right-to-left in  FIG. 2 ) several inches with outer diameter Do, and an intermediate necked-down transition region  20 - 6  between regions  20 - 2  and  20 - 4 . Most of heater system  10  preferably is disposed within a cylindrical housing  70  that fits coaxially about and in good thermal proximity to at least a portion of the external surface of necked down transition region  20 - 6  and elongated region  20 - 4  of mouthpiece  20 . As will be explained, heat generated within housing  70  by heater system warms surface region  20 - 8  and transition region  20 - 6 , and thus regions of metal mouthpiece  20  contacted by the musician&#39;s lips while playing the instrument. Note that when coaxially mounted, housing  70  shares a common longitudinal axis (AXIS) with leadpipe  60  and mouthpiece  20 . 
     Referring still to  FIG. 2 , cylindrical housing  70  has a front open first end  70 - 2  facing the musician, and a rear second end region  70 - 4  that has a central opening  70 - 6  of diameter D 2 . Diameter D 2  is sized to be slightly larger than the diameter of the elongated narrow region  20 - 4  of mouthpiece  20 , which must pass through central opening  70 - 6  in end region  70 - 4 . For ease of illustration, housing  70  is depicted as having a flat shaped second end region  70 - 4 . However if housing  70  is produced by drawing or molding, region  70 - 4  can be rounded, i.e., convex facing instrument  30 . 
     Housing  70  has outer diameter Do, inner diameter Di, and a housing wall thickness T, and housing length L 1 . Table 1 below sets forth exemplary dimensions for cylindrical housing  70  for various types of brass wind musical instruments  30 , with which embodiments of the present invention may be used. In preferred embodiments, cylindrical housing  70  is fabricated from a polished metal, brass for example, so as not to detract from the physical appearance of the musical instrument with which it is used. Battery housing  130  may be fabricated from similar material, for the same esthetic reason. 
     
       
         
           
               
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                 Musical Instrument  
                 Do (inches) 
                 D2 (inches) 
                 L1 (inches) 
               
               
                   
               
             
            
               
                 Trumpet, Bugle, Cornet, 
                 1.0 
                 0.5 
                 1.5 
               
               
                 Flugelhorn, Piccolo trumpet, 
                   
                   
                   
               
               
                 French Horn 
                   
                   
                   
               
               
                 Trombone, Baritone, 
                 1.5 
                 0.5 
                 1.5 
               
               
                 Euphonium 
                   
                   
                   
               
               
                 Tuba, Sousaphone 
                 1.6 
                 0.6 
                 2.0 
               
               
                   
               
            
           
         
       
     
     Typically housing  70  is made of metal, brass perhaps, although a molded plastic material may instead be used. Preferably the exterior surface of housing  70  is finished to match the color and finish appearance of instrument  30 , for aesthetic reasons. In embodiments for which material comprising housing  70  is a good thermal conductor, e.g., metal, preferably a layer of heat insulating foam tape  70 - 8  or the like is attached to the inner housing surface to enhance thermal insulation of the inner surface. As such, material  70 - 8  minimizes loss of element R heat generated within housing  70  through the exterior housing surface. This feature allows more heat to remain within the interior of housing  70  to warm mouthpiece exterior surface  20 - 8 , and thus metal mouthpiece  30 . This enhanced thermal efficiency advantageously reduces power demand on the heat generating electronics and the battery power supply, which allows battery B 1  to function longer before recharging or replacement. 
     Applicant has found that filling air space within cylindrical housing  70  with a heat conducting material  100 , shown as crosshatch in  FIG. 2 , during manufacture enhances good heat transfer from element R to mouthpiece  20 . Material  100  promotes thermal conductivity and enhanced thermal proximity between heat generating element R (or  80 ) and at least a portion of mouthpiece  20 , especially region  20 - 8 . An exemplary such heat conducting material  100  is silicon elastomer SS-2204 or SS-2005, available from Silicone Solutions of Cuyahoga Falls, Ohio 44224 
     In practice, during manufacture of the present invention, a substitute mouthpiece similar in dimension to mouthpiece  20  (see  FIG. 2  and Table 1, herein) with which the completed heater system will be used, or a mouthpiece jig, perhaps a cylinder of exterior dimension D 2 , is used. Before introducing elastomer  100 , the substitute mouthpiece or jig, preferably is coated with a mold release, and is then inserted coaxially through the housing front opening with a portion of the substitute mouthpiece or jig projecting out opening  70 - 6  in the housing rear, along a common longitudinal AXIS, as shown in  FIG. 2 . The airspace in the interior of housing  70  is now filled with elastomer  100 , and the substitute mouthpiece or jig is pushed into the housing (or vice versa) to emulate what is shown in  FIG. 2 . The elastomer is then allowed to cure, e.g., at room temperature for perhaps two hours. It is understood that element R, and electronic components comprising circuitry  90  and their curved PCB are already within housing  70 . Further, openings through the housing wall will have been drilled, as needed, to permit light from the LEDs, if used, to be seen, and to pass the shaft of potentiometer R 1  so that a knob, ADJ, can be connected to the external, distal, shaft end; see  FIG. 2 . One role of elastomer  100  is to secure curved PCB and the components thereon securely within the housing interior. The other role is of course to enhance good transfer of heat generated within the housing interior to the exterior surface regions of mouthpiece  20  that in practice will be contacted by the cured elastomer. 
     Once the elastomer has cured, the manufacturer will carefully slide the substitute mouthpiece or jig out of the housing. Using  FIG. 2  as an analogy, the substitute mouthpiece or jig would be slid out in a left-to-right direction. The use of a mold release pre-curing can facilitate easier removal of the substitute mouthpiece or jig without damage to the cured elastomer. At this juncture, housing  70  has the PCB and components within, anchored by the cured elastomer. Controls such as the ADJ knob on the shaft of potentiometer R 1 , LEDs, etc. will protrude through the housing wall, as shown in  FIG. 2 . Extending along the longitudinal AXIS of housing  70  will be a cylindrical void that was previously occupied by the region of the substitute mouthpiece or jig that was surrounded by elastomer. The manufacturer has a completed heater assembly that can be marketed for use with a specific type mouthpiece that is used on specific model instruments. Thus, it will be appreciated that the present invention is retrofittable and may be used with existing musical instruments lacking a mouthpiece heating capability. 
     The musician buying the completed heater system suitable for the brass wind instrument in question will carefully insert the actual mouthpiece  20  for instrument  30  into the housing, inserting right-to-left, referring to  FIG. 2 . Mouthpiece elongated narrow end region  20 - 4  is first inserted through the large opening at the front of housing  70 , into the cylindrical void defined by the absence of elastomer  100  within the housing, and then out through opening then slid through housing  70 , and back into leadpipe  60 , (slid right-to-left) in  FIG. 2 , coaxially along the common longitudinal axis (AXIS). The larger Do diameter opening of cylindrical housing  70  is abutted against the inner portion adjacent largest mouthpiece diameter Dm region  20 - 2 . The elastomer binds and seems to form annular rings that secure the elastomer to at least portions of surface region  20 - 8  of mouthpiece  20 . 
     Optionally a small tube of thermal grease such as is available from vendors like Radio Shack®, Amazon®, and the like can be provided with the present invention. Such thermal grease commonly is used to enhance heat transfer between transistors and their heatsinks, and computer processor chips and their heatsinks. A similar function will occur here. A small dab of thermal grease can be spread on the exterior mouthpiece surface that will be contacted by the cured elastomer  100 , to enhance heat transfer between the elastomer and the relevant mouthpiece surface regions 
     A spring-loaded or other clamp  120  is then attached to region  20 - 4  of the mouthpiece, adjacent housing end  70 - 4 , to retard lateral movement of housing  70  rearward (right-to-left in  FIG. 2 ) along the mouthpiece. Such lateral movement could disadvantageously degrade quality of the physical binding between elastomer  100  and at least surface region  20 - 8  of the mouthpiece, and thus degrade efficient transfer of generated heat to mouthpiece  20 . 
     Housing  70  (with electronic components within) can remain on mouthpiece  20  for a long time, e.g., several years, especially as the weight of housing  70  and components within is relatively nil, and preferably the housing exterior matches the finish of instrument  30 . Repeatedly removing and reinserting mouthpiece  20  from or through housing  70  would break the desired good thermal seal between mouthpiece surface region  20 - 8  and the cured elastomer material  100 . It is understood that a good thermal seal promotes more efficient thermal transfer and heat generated within the housing to the mouthpiece, which efficiency can extend lifetime of the battery used to power the electronics within housing  70 . 
     As will now be described, ohmic heat electrically generated within housing  70  by system  10  controllably heats mouthpiece  20  for the comfort of musician  40 . Ohmic heat refers to heat generated and radiated by controllably passing electrical current i(t) through a resistive heater element  80  having resistance R, perhaps a length of Nichrome wire or at least one resistor. Radiated ohmic heat is conducted to at least portions of the mouthpiece and is what controllably elevates and maintains temperature of mouthpiece at a desired temperature set by musician  40 , e.g., by using the ADJ knob to vary effective resistance of potentiometer R 1 . 
     As also shown in  FIG. 2 , system  10  includes a portable power supply, preferably at least one battery B 1  disposed within power supply housing  130 , and accessible via housing door  130 - 2 . DC operative power from B 1  is coupled electrically via cable  140  to circuitry components comprising circuitry  90  (see  FIG. 3 ) within housing  70 . Power supply housing  130  may be removably attached to leadpipe  30  of instrument  30  using a Velcro® strap  150  or the like. Of course if housing  70  were suitably enlarged, battery B 1  could be disposed within the housing, thus obviating the need for a separate battery supply housing  130 . 
     Referring now to  FIG. 3 , an exemplary electronic implementation of system  10  is shown as comprising an ohmic heat generating element  80  (also denoted R), electronic circuitry components, collectively circuitry  90 , mounted on a flexible curved printed circuit board (PCB), and a power source  110 . Heating element  80 , or R, has resistance R, and is disposed in close physical and thermal proximity to at least a portion of mouthpiece  20 , e.g., surface region  20 - 8 . Responsive to current flow i(t) from circuitry  90 , which is powered from power source  110 , resistive heater element R radiates heat (shown as waves denoted HEAT) proportional to i(t) 2 ·R to controllably warm at least a portion of mouthpiece  20 . In one embodiment R was about 2Ω and was implemented using a coiled length of several inches of 30 gauge Nichrome wire, wound within cylindrical housing  70 , with windings spaced to occupy much of housing length L 1 . In another embodiment, R was implemented using several 0.5Ω resistors whose series-connected resistance was about 2Ω. The resistors may be surface mounted components, and in any event are mounted on a curved flexible printed circuit board PCB and preferably spaced to occupy most of the internal length of housing  70 , to more uniformly radiate heat across mouthpiece region  20 - 8 . It will be appreciated that the outer surface of mouthpiece  20  is itself cylindrical, and that use of a curved PCB within cylindrical housing  70  enables the heat generating components, a length of Nichrome wire, and/or a series of spaced-apart resistors, to be disposed spaced-apart cylindrically, which improves efficiency of heat transfer from R to the outer surface of mouthpiece  20 . More efficient heat transfer from heat generator  80  (or R) enables a single battery B 1  to power circuitry  90  to warm mouthpiece  20  for more hours of continuous use in inclement weather than would otherwise be possible. The electronic components comprising circuitry  90  may be implemented using surface mount devices (SMD), for ease of circuit layout on the PCB. 
     In  FIG. 3 , power supply  110  provides DC voltage VCC and preferably includes at least one lithium ion type 18650 3.7 V battery B 1 . Two such batteries B 1 , B 2  are shown in  FIG. 3  with series diodes D 1 , D 2 . In such embodiment whichever B 1 , B 2  battery has the higher voltage will power circuitry  90 , with diodes D 1 , D 2  preventing the higher voltage battery from trying to charge the remaining battery, and guarding circuitry  90  against reverse polarity should B 1  be inserted backwards in housing  130 . A protective fuse F 1 , perhaps two amps or so, protects both batteries and circuitry  90  from damage in case of an electrical short. In practice a single 18650 3.7 V battery B 1  can comfortably provide several amps A of current i(t) to maintain temperature of mouthpiece  20  between about 80° F. and about 90° F., as set by the musician, perhaps about 5 W to 10 W of heat. Switch SW 1  enables the musician to turn system  10  ON or OFF and preferably is mounted within cylindrical housing  70 , with a protruding lever. When SW 1  is in the ON position, current flows through optional green LED 1  to confirm visually to the musician that power is indeed on. Optional red LED 2  confirms visually to the musician that circuitry  90  is working and that heat is being generated. In typical use, the green LED 1  remains on, and red LED 2  will come on and off as the electronic circuitry causes more or less (e.g., no) current i(t) to flow through element R. Resistors shown in series with LED 1 , LED 2  provide a protective current limiting function 
     As soon as SW is ON, current will flow through LED 1 , and the green LED turns on, to confirm power is applied to the circuitry. U 1  is a generic operational amplifier that is operated in closed-loop fashion to compare two input DC voltages, Vref and Vt. Resistor R 5  provides positive feedback to help ensure that the output of U 1  is either fully high or fully low, rather than at some intermediate indeterminate level. This in turn will cause MOSFET Q 1  to be fully on, in which case i(t) is maximum, or fully off, in which case i(t) is zero. 
     The non-inverting input (+) of U 1  sees a fixed or first reference voltage Vref that is a fraction of power supply voltage VCC, the fraction determined by a first resistor divider comprising resister R 2  in series with resistor R 3 . R 3  preferably is bypassed with a capacitor to help stabilize U 1  by bypassing transients. The inverting (−) input of U 1  sees a second voltage Vt that is a fraction of VCC determined by a second resistor divider comprising thermistor Rt and, collectively, potentiometer R 1  in series with scaling resistor R 1 ′. Collectively R 1 +R 1 ′ are bypassed with a capacitor to enhance stability of U 1 . 
     Thermistor Rt, preferably is in close thermal proximity to R, and potentiometer R 1  is in series with scaling resistor R 1 ′. In a preferred embodiment, as thermistor Rt heats up due to its thermal proximity to R, its internal resistance decreases. Note that at increasing temperatures, as magnitude of thermistor Rt decreases, magnitude of voltage Vt increases. 
     If mouthpiece  20  is too cold for the musician, then Vref&gt;Vt, and if the mouthpiece temperature is too high, the Vref&lt;Vt. When Vref&gt;Vt, the output of U 1  will be high, which will turn-on FET Q 1 , which will cause LED 2  to turn on, which red glow visually assures the musician that heat is being generated. When Q 1  is turned on, it conducts an increased magnitude time-varying current i(t), which also flows through heating element R (or  80 ). R will then radiate heat proportional to i(t) 2 ·R. Since R is in thermal proximity to mouthpiece  20 , especially when thermally conductive silicon elastomer  100  is employed, the heat it radiates will increase temperature of the mouthpiece. If however Vref&lt;Vt, the output of U 1  will be low, which will turn off FET Q 1 , reducing magnitude of current i(t) to essentially zero. R will now radiate less heat, e.g., it does not cool down instantaneously, and the temperature of mouthpiece  20  will decrease. It is seen that Q 1  operates digitally in a full-on or full-off mode, and that i(t) may be described as pulse-width modulated. When Q 1  it turned fully-on, although i(t) is maximum, voltage across Q 1  is nil, and heat dissipation in Q 1  is nil. In addition, when Q 1  is turned fully off, voltage across Q 1  is VCC but i(t) is zero, and again heat dissipation in Q 1  is nil. In this mode of operation, Q 1  dissipates little power, and a lower power device may be used for Q 1  than would otherwise be the case. Further, a preferred closed-loop mode of operation prolongs battery life, as effective duty cycle of operation is substantially less than 100%. 
     Of course one could operate embodiments of the present invention without closed-loop feedback, although such embodiments would require the musician to frequently readjust the level of heat desired, as ambient temperature changed, and as battery condition depleted. In addition, closed-loop operation can lengthen the operating time for battery B 1  before recharging or battery substitution is required. In general the advantages of closed-loop operation substantially outweigh the slight additional cost of more electronic components. 
     In a preferred embodiment, potentiometer R 1  is mounted within cylindrical housing  90  with its shaft protruding through the housing wall, and with a knob (AJD) affixed to the shaft end, as shown in  FIG. 2 . Thus at any time the musician may adjust the knob (ADJ) on potentiometer R 1  to dynamically increase or decrease the temperature off the mouthpiece as desired. The musician can leave the ADJ knob alone as ambient temperature changes, because the closed-loop operation of circuitry  90  will automatically correct i(t) as required. If desired, ON/OFF switch SW 1  could use the same shaft as potentiometer R 1 , such that at full counterclockwise, SW 1  is OFF, and turning the shaft clockwise turns SW 1  ON and varies magnitude of R 1 . For use in cold weather, the musician will typically turn SW 1  ON perhaps fifteen minutes before the musical instrument will be played, to allow mouthpiece  20  to be heated up to a desired temperature by system  10  before use. 
     As described, embodiments of the present invention provide a retrofitable heater system that may be affixed to the mouthpiece of a brass musical instrument without modification of the instrument. Preferred embodiments include electronic circuitry that enables the musician playing the instrument to dynamically control mouthpiece temperature at any time, even while playing the instrument. A closed-loop feedback aspect of the invention enables the heater system to maintain a desired temperature, even if ambient temperatures changes while the instrument is being used, or even if battery B 1  voltage begins to drop. Optional LEDs provide confirmation to the musician that the heater system has been turned on, and is indeed generating heat. When play for many hours in very cold weather is anticipated, the musician may carry one or more pre-charged extra batteries B 1 . At a lull in the music play, battery compartment access door  130 - 2  may be quickly opened, and a fresh battery substituted for the depleted battery. Alternatively, power supply housing  130  may house more than one battery, with batteries used in parallel to extend battery operating time. 
     Modifications and variations may be made to the disclosed embodiments without departing from the subject and spirit of the invention as defined by the following claims.