FILM PIEZOELECTRIC PICKUPS FOR STRINGED MUSICAL INSTRUMENTS

Abstract: A pickup for a stringed musical instrument according to the first aspect of the invention has a core, a piezoelectric transducer element, a contact strip, and an output lead. The core is elongated and multi-faced, and has an electrically conducting face. The piezoelectric transducer element includes a piezoelectric film that has a first surface, and a second surface opposite the first surface. A first electrode covers at least part of the first surface, and a second electrode covers at least part of the second surface. The piezoelectric transducer element covers substantially all of the electrically conducting face of the core, and is attached to the core with its first electrode in contact with the electrically conducting face of the core. The contact strip contacts at least part of the second electrode of the piezoelectric transducer element. The output lead has a first conductor connected to the electrically conducting face of the core, and a second conductor connected to the contact strip. In a first variation, the piezoelectric transducer element is enlarged and serves not only as a piezoelectric transducer element, but also provides an electrical shield and insulator for the pickup. In a second variation, two thicker piezoelectric transducer elements are stacked on the core to increase the electrical output of the pickup without a reduction in capacity.

Description: Film Piezoelectric Pickups for Stringed Musical Instruments Field of the Invention The invention concerns electrical pickups for acoustic guitars, and, in particular, piezoelectric pickups using a piezoelectric film as the transducer element. Background of the Invention Acoustic guitars, which are the traditional form of guitar, produce a significant output of direct sound energy, largely due to the ability of the body of the guitar to pick up and amplify the vibrations of the strings. As a result of this mechanism, the body contributes considerably to the tonal quality of the sound produced by the guitar. Acoustic guitars produce sufficient direct sound output for them to be usable without amplification when played in small rooms in front of small audiences. To be heard in larger auditoriums, amplification is necessary. For amplification to be used, some means for picking up the sound output of the guitar must also be used. Electrical pickups for acoustic guitars must be distinguished from electrical pickups for electric guitars because the primary mechanism by which each kind of guitar produces sound is quite different. Electric guitars produce sound by using one or more electric coils to pick up the vibration of the strings (which must be of a magnetic material, normally steel) in a magnetic field. The electrical output of the coils is then amplified and the amplified signal is then reproduced by means of a loudspeaker. Electric guitars produce relatively little direct sound energy themselves, and are heavily reliant on amplification if they are to be heard by more than only the player. Unlike the body of an acoustic guitar, the body of an electric guitar contributes relatively little to the direct sound energy output and to the tonal quality of the sound produced by the loudspeaker. The conventional approach to picking up the sound on an acoustic guitar is to use a microphone mounted on a stand and directed towards the top of the guitar. A microphone works quite well for solo or small ensemble performances of classical music, but presents at least four problems in performances of more popular music: (1) it restricts the player's ability to move around during the performance; (2) it may pick up too much noise from the action of the player ' s fingers and hands on the strings and top of the guitar (such noise is called "top noise"); (3) it may pick up its own amplified output, leading to acoustic feedback problems; and (4), when the player shares the stage with loud instruments such as drums, keyboards, and electric guitars and basses, it makes achieving the desired sound balance difficult because it picks up sounds from these other sources in addition to sounds from the acoustic guitar. As a result of these problems, there has for a number of years been a tendency towards using self-contained acoustic guitar pickups which allow the acoustic guitar itself to produce an electrical output signal that is fed by a long cable, or a radio-frequency or infra-red transmitter/receiver arrangement to suitable amplification and loudspeaker equipment. Such a self-contained pickup arrangement can solve the problems discussed above. Because it is desirable not to use steel strings on acoustic guitars, and acoustic guitars therefore lack the fundamental mechanical-to-electrical transducer mechanism of the electric guitar, the considerable amount of art relating to electric guitar pickups is not applicable to acoustic guitar pickups. Basic requirements for a self-contained acoustic guitar pickup can be stated as follows: (1) the pickup must convert the mechanical vibrations of the guitar strings and body into an electrical signal; (2) the pickup must pick up some top noise, but top noise pick up should not be excessive; (3) the pickup should pick up the sound of the guitar without adding colorations of its own; (4) the pickup (together with any amplification required) should have a high electrical signal-to-noise ratio; (5) the pickup should not pick up hum, buzz and other externally induced noise; (6) the pickup should pick up the output of each string more-or-less equally; (7) it should be easy to install the pickup in the guitar, and should require a minimum of modifications to be made to the guitar itself; and (8) it should be easy to remove the pickup and restore the guitar to pickup-less operation. A number of acoustic guitar pickups are already commercially available. The FRAP pickup, described in US-PS 3,624,264 uses three ceramic or crystalline piezoelectric transducers orthogonally mounted on three of the walls of a small box-shaped enclosure filled with silicone rubber. The pickup is attached to the body of the guitar by means of a wax or other suitable adhesive. The transducers are arranged so that one transducer detects motion along the*-ax * s, another detects motion along the -axis, and the third detects motion along the z-axis. The outputs of the transducers are fed in parallel into a buffer amplifier. This pickup has a low electrical output, so it suffers from signal-to-noise ratio problems. Another approach is the combination piezoelectric transducer and saddle ofΦaggs, described in US-PS 4,314,495. The saddle is the part of the bridge of an acoustic guitar on which the strings rest. Practical embodiments of the Baggs pickup use six series-connected ceramic or crystalline piezoelectric transducers, one for each string, encapsulated in epoxy resin in a U-shaped brass channel transducer housing. The transducer housing is an integral part of a saddle formed using a fibre resin material such as that sold under the trademark Micarta. The channel construction of the transducer housing together with the suspension of the piezoelectric transducers in epoxy resin, is thought to reduce top noise. Installing a Baggs pickup in a guitar requires that the normal saddle-slot in the bridge be machined to increase its width to 1/8" (3.2 mm) and its length to 2.875" (73 mm). The changes to the saddle slot mean that if the pickup is removed, it must be replaced by a non-standard saddle. Moreover, since the pickup includes a completely new saddle, the guitar must be re-intonated when the pickup is installed. Finally, the brass insert in the Baggs pickup makes it more rigid than a normal saddle, which changes the playing action of the guitar. Adjustments to the shape of the saddle are required to restore the action to normal. The Baggs pickup reduces top noise by connecting the transducers under the A and D strings out of phase with the transducers under the other four strings. This arrangement causes phasing problems when the electrical output of the guitar is mixed with any signal that includes a component representing the acoustic output of the guitar. The Fishman pickup is described in US-PS 4,727,634, US-PS 4,774,867, US-PS 4,944,634, and US-PS 5,029,375. This pickup uses six small (1/16" dia. x 0.02," 1.6 mm dia. x 0.5 mm) cylindrical ceramic piezoelectric transducers, one for each string. The pickup fits in the bottom of a standard 3/32" (2.4 mm) wide saddle slot, and can be used with the existing saddle if about 1/16" (1.6 mm) is removed from the bottom of the existing saddle. This pickup is easy to install, and does not require that the guitar be re- intonated, but it suffers from the general defects of pickups based on ceramic or crystalline piezoelectric transducers discussed below. Moreover, the pickup is complex, since it requires separate components to mount the individual transducers resiliently, to interconnect them, and to screen them , from outside interference. All acoustic guitar pickups based on ceramic or crystalline piezoelectric transducers suffer from a number of common problems: (1) such transducers have mechanical resonances in the audio frequency range that colour the sound of the guitar; (2) the mechanical mountings of such transducers have their own mechanical resonances in the audio frequency range that further colour the sound of the guitar; and (3) such transducers are small and are thus awkward to handle in such assembly operations as attaching wires to them, etc. A new form of piezoelectric material, a polarized homopolymer of vinylidene fluoride (PVDF), has recently become available. This material is sold under the trademark "KYNAR." Full information about this material can be found in the KYNAR Piezo Film Technical Manual (Pennwalt Corporation, 1987). PVDF film has a number of properties that make it advantageous for use in acoustic guitar pickups: it has a high output voltage for a given mechanical stress; it has a low mass and a low Q, which means that it responds instantly to a mechanical input, and introduces little coloration of the sound. Electrical contacts can be made to the surface of the film itself by painting electrodes on the surface of the film with conductive paint, or, preferably for mass-production, silkscreening electrodes on the surface of the film with conductive ink, or vacuum depositing metal electrodes on the surface of the film. Attaching leads to the electrodes presents problems, however, because of the material's low softening point and low resistance to tearing. The manufacturer suggests that a low-temperature solder can be used. This enables a reliable electrical contact to be made, but does not result in a mechanically strong attachment between the electrodes and the output lead. The use of PVDF film as an acoustic guitar pickup is described at page 43 of the KYNAR Technical Manual. A piece of 28 micron thick film, about 3" by 1" has electrodes on both sides. It is electrically shielded on both sides by means of a metallic foil and mechanically protected by a layer of a flexible plastic laminate. Electrical contacts are made (the manual does not say how) between the electrodes on the film and an output lead. The complete transducer is attached to the top of the guitar using double- sided tape. A practical embodiment of this pickup uses sprung mechanical contacts to connect the electrical output of the transducer to the output lead. This results in a bulky arrangement, compared with the rest of the pickup, the contact device being a flat rectangular box about 1.2 x 1.2 x 0.2 inches (30 x 30 x 5 mm). An alternative form of acoustic guitar pickup using PVDF film is described in Kynar Piezo Film News, No. 1 (Pennwalt Corp., 1987) at page 4. A piece of PVDF transducer film about 2.8 x 0.7 inches (71 x 18 mm) is glued to the sides and bottom of standard-sized saddle. The film is metallized completely on the outside and metallized in six segments, one for each string, on the inside (i.e., the side closer to the saddle). There is no mechanical protection or electrical shielding; the player ' s hand can induce an objectional buzz into the output of the pickup if it gets too close to the pickup. This pickup is also relatively short lived: the saddle material is not as durable as bone, the material normally used for making saddles, and the whole pickup must be replaced and the guitar re-intonated, if the saddle wears out. The pickup has a large plastic connector assembly on one end which requires that the width of the saddle slot in the bridge must be increased to about 0.22" (5.6 mm) for a length of about 0.3" (7.6 mm) and the length of the saddle slot must be increased by about 0.07" (1.8 mm). This pickup is therefore inconvenient to install, and difficult to replace if no longer desired. Practical embodiments of this pickup are sold as part of the Gibson™ Symbiotic Oriented Receptor System (S.O.R.S.). Summary of the Invention The invention relates to improved pickups for stringed musical instruments, principally guitars, using PVDF or a similar piezoelectric plastic film transducer element. Pickups according to the invention can be installed in an acoustic guitar without the need to modify the standard saddle slot, and have the advantages of simplicity, compactness, and high signal-to-noise ratio. A Type I pickup for a stringed musical instrument according to the first aspect of the invention has a core, a piezoelectric transducer element, a contact strip, and an output lead. The core is elongated and multi-faced, and has an electrically conducting face. The piezoelectric transducer element includes a piezoelectric film that has a first surface, and a second surface opposite the first surface. A first electrode covers at least part of the first surface, and a second electrode covers at least part of the second surface. The piezoelectric transducer element covers substantially all of the electrically conducting face of the core, and is attached to the core with its first electrode in contact with the electrically conducting face of the core. The contact strip contacts at least part of the second electrode of the piezoelectric transducer element. The output lead has a first conductor connected to the electrically conducting face of the core, and a second conductor connected to the contact strip. Preferably, the strength of the attachment between the output lead and the core is increased by attaching, in addition, the outer conductor of the output lead to a part of the core that is electrically isolated from the part of the core to which the inner conductor is attached. A Type II pickup for a stringed musical instrument according to the second aspect of the invention has a larger piezoelectric transducer element. The enlarged piezoelectric transducer element serves not only as a piezoelectric transducer element, but also an electrical shield and insulator for the pickup. The pickup according to the second aspect of the invention has a core, a piezoelectric transducer element, a contact strip, and an output lead. The core is elongated and multi-faced, and has an electrically conducting face. The piezoelectric transducer element includes a piezoelectric film that has a first surface, and a second surface opposite the first surface. A first electrode covers at least part of the first surface, and a second electrode covers substantially all of the second surface. The piezoelectric transducer element covers substantially all of the electrically conducting face of the core. The piezoelectric transducer element is wrapped around the core, and adapts itself generally to the shape of the core. The - first electrode of the piezoelectric transducer element contacts the electrically conducting face of the core, and the second electrode provides an electrical shield around the core, the piezoelectric film, and the first electrode. The contact strip contacts at least part of the second electrode of the piezoelectric transducer element. The output lead has a first conductor connected to the electrically conducting face of the core, and a second conductor connected to the contact strip. A Type III pickup for a stringed musical instrument according to the third aspect of the invention provides a greater electrical output than the pickups according to the first and second aspects of the invention. A pickup according to the third aspect of the invention has a core, a first piezoelectric transducer element, a second piezoelectric transducer element, and an output lead. The core is elongated and multi-faced, with a first face opposite a second face. The first piezoelectric transducer element is connected in parallel with the second piezoelectric transducer element. Each piezoelectric transducer element comprises a piezoelectric film that has a first surface and a second surface, a first electrode on the first surface, and a second electrode on the second surface. The piezoelectric transducer elements are responsive to more than one string. The first piezoelectric transducer element is stacked on the core with its second electrode in contact with the first face of the core. The second piezoelectric transducer element is stacked on the first piezoelectric transducer element with its first electrode in contact with the first elec- trode of the first piezoelectric transducer element. The output lead is attached to the core and has a first conductor and a second conductor. The first conductor electrically contacts the first electrode of the first piezoelectric transducer element and the first electrode of the second piezoelectric transducer element. The second conductor electrically contacts the second electrode of the first piezoelectric transducer element and the second electrode of the second piezoelectric transducer element. All three types of pickup described can also be adapted for use in other types of stringed instruments which translate the vibrations of the strings into variations of pressure. Further details of the pickup are given in the drawings and the detailed description of the invention which follow. Description of the Drawings Figure 1 is a perspective view showing the main parts of a typical acoustic guitar. Figure 2 is a perspective view showing a pickup according to the invention. Figure 3(a) is a cross-sectional view of the bridge of a typical acoustic guitar taken along the line X-K in figure 1, showing a pickup according to the invention installed under the saddle in the saddle slot. Figure 3(b) is a cross-sectional view of the bridge of a typical acoustic guitar taken along line A- A' in figure 3(a), showing a pickup according to the invention installed under the saddle in the saddle slot. Figure 3(c) is a cross-sectional view of the bridge of a typical acoustic guitar taken along line B-B' in figure 3(a), showing a Type I pickup according to the first aspect of the invention installed under the saddle in the saddle slot, and showing a cross-sectional view of the pickup itself. Figure 4(a) is a perspective view showing mainly the upper face of the core of a Type II pickup according to the second aspect of the invention. Figure 4(b) is a plan view of the part of the lower face of the core of a Type II pickup according to the invention, to which the output lead is attached, showing the plated-through hole and the lead anchor pad. Figure 5(a) is a perspective view showing the lower face of the core of a Type II pickup according to the invention, and how the inner conductor of the output lead is inserted into the plated-through hole in the core. Figure 5(b) is a cross-sectional view taken along line C-C of figure 5(a), showing how the inner conductor of the output lead is attached to the plated-through hole and the braid of the output lead is attached to the lead anchor pad. Figures 6(a) through 6(f) are perspective views showing the output lead and the lower face of the contact strip and six different arrangements for attaching the contact strip to the braid of the output lead of a Type II pickup according to the invention. Figure 7(a) shows a plan view of the piezoelectric transducer element, and the dimensional relationship between the piezoelectric transducer element and the core of a Type II pickup according to the invention, which is shown in perspective view in figure 7(b). Figure 7(c) is a cross-sectional view of the piezoelectric transducer element of a Type II pickup according to the invention, taken along the line D-D' in figure 7(a). The figure also shows how adhesive is applied to the face of the piezoelectric transducer element. Figure 8(a) is a cross-sectional view of a Type II pickup according to the invention, showing the initial assembly of the piezoelectric transducer element and the core, in which the piezoelectric transducer element is wrapped around the core in two wrapping operations. Figure 8(b) is a cross-sectional view showing the initial assembly of the piezoelectric transducer element and the core, in which the piezoelectric transducer element is wrapped around the core in a single wrapping operation. Figure 8(c) is a cross sectional view of the core and piezoelectric transducer element assembly after the piezoelectric transducer element has been wrapped around the core before the contact strip is attached. Figure 8(d) is a cross-sectional of the core and piezoelectric transducer element assembly after the piezoelectric transducer element has been wrapped around the core and the contact strip has been attached. Figures 9(a) through 9(f) show schematic cross-sectional views of a number of variations on the basic piezoelectric transducer element, core and contact strip assembly of a Type II pickup according to the invention. Figure 10(a) is a longitudinal cross section of a Type III pickup according to the third aspect of the invention. Figure 10(b) is an exploded view of the transducer part of a Type III pickup according to the invention. Figure 11 is a transverse cross sectional view of the transducer part of a Type III pickup according to the invention. Figure 12(a) is a perspective view of the first face of the core of the preferred embodiment of a Type III pickup according to the invention. Figure 12(b) is a plan view of the second face of the core of the preferred embodiment of a Ttype III pickup according to the invention, showing details of the anchor pad and the plated-through hole into which the first conductor of the output lead is inserted. Figure 13 is a longitudinal cross sectional view of a Type III pickup according to the invention, showing how the output lead is attached to the core. Figure 14 shows plan views of the piezoelectric transducer elements of a Type III pickup according to the invention: Figure 14(a) is a plan view of the lower piezoelectric transducer element showing how the periphery of the first electrode is inset from the periphery of the piezoelectric film. Figure 14(b) is a cross sectional view of the lower piezoelectric transducer element taken along line A-B in figure 14(a). Figure 14(c) is a plan view of the upper piezoelectric transducer element showing how the periphery of the first electrode is inset from the periphery of the piezoelectric film. Figure 14(d) is a cross sectional view of the upper piezoelectric transducer element taken along line A-B in figure 14(c). Figure 15(a) shows a plan view of the contact strip of a Type III pickup according to the invention before the contact strip extension is bent through 90 degrees. Figure 15(b) shows the preferred way of attaching the contact strip to the outer conductor of the output lead in a Type III pickup according to the invention. Figure 16 shows a plan view of the insulating layer of a Type III pickup according to the invention. Detailed Description of the Invention The structure of a normal acoustic guitar is shown in figure 1. Neck 1 is attached to body 5. Strings 72 are attached to body 5 by means of anchor points 3 at one end and at the other end by tuning mechanism 12. The strings rest on saddle 63, which is mounted in saddle slot 68 in bridge 70. The mechanical vibrations of strings 72 are transmitted by saddle 63 to bridge 70 and hence to body 5, and cause body 5 to vibrate. Vibrating guitar body 5 effectively couples the vibrations of strings 72 to the surrounding air. Saddle 63, together with nut 61, also defines the vibrational length of each string. By adjusting the precise point on the saddle at which each string makes contact with the saddle, the guitar is intonated, so that when each string is stopped at its octave fret, the note produced is at the same pitch as the second harmonic of the open string. Figure 2 shows a pickup 60 according to the invention. The pickup comprises transducer 50 and coaxial output lead 200. Because the length of the pickup is over forty times its width, figure 2 and most of the other drawings showing the pickup and its components show the pickup and its components in broken form, so that details of the width and thickness of the pickup can be depicted. Figures 3(a) and 3(b) show cross-sectional views of a pickup according to the invention installed in saddle-slot 68 of the bridge 70 of a guitar, the top of which is shown as 75. The pickup is installed in a guitar by de-tensioning strings 72, and removing saddle 63. Hole 65, about the same diameter as the width of saddle slot 68 (3/32" or approximately 2.4 mm), is drilled through bridge 70 and the top 75 of the guitar at one end of saddle slot 68. About 1/16" (1.6 mm) of material is removed from the bottom of saddle 63, to reduce the height of saddle 63 by the thickness of the transducer part 50 of the pickup. Output lead 200 is threaded through hole 65, and transducer 50 is installed at the bottom of saddle slot 68. Saddle 63 is then re-inserted in saddle slot 68, strings 72 are re-tensioned and the guitar re-tuned. Transducer part 50 of the pickup sits at the bottom of saddle slot 68 in bridge 70 and is sandwiched between the bottom of saddle 63 and the bottom of saddle slot 68. Because the height of saddle 63 is reduced to compensate for the thickness of transducer 50 in the bottom of saddle slot 68, the distance from the top 75 of the guitar to the top of saddle 63 (and hence the height of strings 72 above top 75) is the same as it was before pickup 60 was installed. No re-intonation of the guitar is therefore necessary. Figure 3(c) shows a cross-sectional view of a Type I pickup according to the first aspect of the invention installed in the saddle slot of a guitar. Transducer 50 sits at the bottom of saddle slot 68 in bridge 70 and is sandwiched between the bottom of saddle 63 and the bottom of saddle slot 68. The tension of the strings 72 exerts a force on saddle 63 in the vertical direction depicted in figure 3(c). Saddle 63 is free to move in the vertical direction, and thus exerts a static compressive load on the upper face of transducer 50. The lower face of transducer 50 in turn transmits the compressive load to bridge 70 and hence to the rest of the guitar. Figure 3(c) shows the core 100 in contact with the bottom of saddle slot 68. The core has a conductive face 130. The piezoelectric transducer element comprises piezoelectric film 401 with electrodes 405 and 410 on opposite faces of the film. The electrode 405 is attached to the conducting face 130 of the core. The contact strip 300 is attached to the second electrode 410. The bottom of the saddle 63 rests on the contact strip 300. The output lead 200 (figure 3(b)) has two conductors. One, preferably the inner conductor, is connected to the conductive face 130 of the core; the other, preferably the braid, is connected to the contact strip 300. The basic transducing element of transducer 50 comprises first electrode 405, the part of second electrode 410 adjacent first electrode 405, and the part of piezoelectric film 401 between first electrode 405 and second electrode 410. When the strings are tensioned, the static load on transducer 50 compresses film 401 and causes a D.C. voltage difference between electrodes 405 and 410. However, since the transducer is essentially capacitive, this D.C. voltage gradually decays to zero. If string 72 is struck, the tension in the string varies, which varies the vertical component of the force applied to saddle 63. This causes the load applied to transducer 50 to vary. Transducer 50 transmits the varying force to bridge 70 and hence to the body of the guitar, which causes the body of the guitar to vibrate as the body of an acoustic guitar is designed to do. The vertical component of the movement of the top of the guitar applies a force to the lower face of transducer 50 via bridge 70. Transducer 50 is therefore subject to a dynamically varying compressive force, which produces an a.c. voltage difference between electrodes 405 and 410. The a.c. voltage difference between electrodes 405 and 410 represents the varying compressive force on transducer 50 due to the vibrations of the strings and the body of the guitar. This voltage thus includes components representing the vibration of the strings and the vibration of body of the guitar resulting from the vibration of the strings. The a.c. voltage difference between the electrodes produces a corresponding a.c. voltage difference between core 100 (in contact with electrode 405) and contact strip 300 (in contact with electrode 410), and hence between the conductors of output lead 200. Output lead 200 feeds the a.c. voltage difference to a suitable amplifier and loudspeaker (not shown) for reproduction. The conversion mechanism of the active part of the Type II and Type III pickups to be described below is essentially the same as that for the Type I pickup just described. The structure of a Type II pickup according to the second aspect of the invention will now be de¬ scribed. The pickup comprises four basic components which will be described in turn: core 100, output lead 200, contact strip 300 and piezoelectric transducer element 400. Figure 4 shows core 100. Core 100 is an essentially rectangular piece of 1/32" (0.8 mm) thick material, about 2.75" (70 mm) long by 1/16" (1.6 mm) wide. At least one end of core 100 is preferably rounded, as shown in figure 4; alternatively, one or both ends can be straight-cut. A variety of materials can be used for core 100, the main purpose of which is to support piezoelectric transducer element 400, and to anchor output lead 200. An all-metal core will serve these purposes, but, because all of its surface is conducting, it tends to pick up more unwanted interference than an insulating core with one or more conductive surfaces. This means that an all-metal core requires more screening than an insulating core with one or more conductive surfaces. Finally, an all-metal core colours the sound more than a plastic core: for most purposes the more neutral sound of a plastic core is desirable. Preferably, plastic cores with one or more conductive surfaces are cut from a sheet of fibre-glass printed circuit board 105, clad on each side with 1 ounce per square foot (0.3 kg per square meter) of copper, the overall thickness of the board being 1/32" (0.8 mm) . Before the sheet of printed circuit board is cut into individual cores, the sheet is drilled with at least one 0.030" (0.75 mm) diameter hole 120 per core. Also before the sheet of printed circuit board is cut into individual cores, copper is selectively removed from both sides of the boards to form the metallization patterns required for each core. Copper removal is preferably done by a mask and etch process well known in the art. Copper may be left on all of the conductive face 130 of each core, but it is preferred that copper be removed from a narrow strip 134 around the periphery of each core, and, in addition, that copper be removed to form a short, narrow track 132 connecting hole 120 with the rest of the conductive face 130 of the core, as shown in figure 4(a). The narrow track 123 in the vicinity of hole 120 facilitates soldering output lead 200 in hole 120. Copper may be removed from substantially all of the other side of the printed-circuit board, to form the second face 135 of each core. A small annulus 162 of copper around each hole 120 is left on each core to facilitate plating through the hole. Removing copper from face 135 of each core electrically isolates the part of transducer element 400 in contact with face 135. This reduces top noise because face 135 is closer to the top of the guitar than to the strings when the pickup is installed in the guitar. Preferably, an additional copper annulus, surrounding copper annulus 162 surrounding plated-through hole 120 but insulated from it, is left on each core to serve as the lead anchor pad 138 for the second conductor (normally braid 205) of output lead 200, as shown in detail in figure 4(b). The inner diameter of lead anchor pad 138 is preferably the same as the outer diameter of inner insulator 210 of output lead 200. The outer diameter of lead anchor pad 138 is preferably the same as the width of core 100, i.e., about 1/16" (1.6 mm). Copper may be left on the other side of the board if it is desired to have some pick up from the part of transducer element 400 in contact with face 135 of the core. If copper is left on face 135 of the core, each core should also have a second plated-through hole 125 at the other end of the core from hole 120 to interconnect the two faces. Lead anchor pad 138 must be isolated from face 135 by a suitable removal of copper. Hole 120, and, optionally hole 125, are then plated through using techniques that are well known in the printed circuit board-manufacturing art. It is also preferable that both sides of the sheet be plated with 20 μ" (0.5 μm) of gold to prevent tarnishing and the formation of a rectifying contact between conductive surface 130 of core 100 and electrode 405 of piezoelectric transducer element 400, and to facilitate soldering the braid of output lead 200 to lead anchor pad 138. Additionally, lead anchor pad 138 is tinned. The sheet of printed circuit board then cut into individual cores with the above-stated dimensions. Alternatively, the sheet of printed circuit board can be cut up into individual cores before the gold plating, hole-drilling, copper removal, plating-through, and lead anchor pad tinning operations. Single-sided printed circuit board without plated-through holes can be used for core 100, but such an arrangement is less strong, and hence is likely to be less reliable, than an arrangement with plated- through holes. The assembly of output lead 200 and core 100 is shown in figure 5. Output lead 200 is a suitable length (usually about 15" (0.4 m)) of sub-miniature co-axial cable about 1/16" (1.6 mm) in diameter. Coaxial cable is required to prevent output lead 200 from picking up hum and other unwanted noise. Braid 205 and insulator 210 of output lead 200 are stripped back using known techniques to expose about 1/16" (1.6 mm) of inner conductor 215. Inner conductor 215, and, if it is to be soldered, braid 205, are prepared for soldering using well-known techniques. If output lead 200 is to be soldered to core 100 using normal temperature solder, as is preferred, this must be done before piezoelectric transducer element 400 (figure 7) is attached to core 100, otherwise the temperatures required to melt normal temperature solder will melt piezoelectric film 401. Alternatively, output lead 200 can be soldered to core 100 using a low-temperature (< 90 β C) indium-tin solder. Inner conductor 215 is pushed through hole 120 and soldered using well-known techniques. Soldering may be carried out by hand after the printed circuit board has been cut into individual pieces, before core 100 is wrapped with piezoelectric transducer element 400, or, using low-temperature solder, after wrap¬ ping. Alternatively, output lead 200 may be soldered to core 100 by flow-soldering before the sheet of printed circuit board is cut into individual cores. Inner conductor 215 may also be attached to core 100 by electric welding. In the preferred method of attaching output lead 200 to core 100, core 100 has the preferred lead anchor pad 138, and output lead 200 is stripped through its braid 205 and inner insulator 210 to expose about 1/32" (0.8 mm) of inner conductor 215. When the lead has been stripped, no inner insulator 210 should be visible. Care must be taken to ensure that braid 205 is cut cleanly so that uncut strands of braid 205 do not come into contact with inner conductor 215. Exposed inner conductor 215 and braid 205 in the vicinity of exposed inner conductor 215 are then tinned. Inner conductor 215 is then inserted into plated-through hole 120 such that the tinned end of braid 205 comes into contact with lead anchor pad 138. Heat and solder are then applied to solder inner conductor 215 to hole 120 and heat is applied to sweat solder tinned braid 205 to tinned lead anchor pad 138. A cross section of the resulting assembly is shown in figure 5(b). Irrespective of the method used to attach output lead 200 to core 100, inner conductor 215 and/or, for example, solder, should not protrude from the top of plated-through hole 120. This ensures that the bottom of saddle 63 contacts the top face of the pickup evenly along the whole of its length. The relative arrangement of core 100 and output lead 200 shown in figure 5(a) defines the upper and lower faces 130 and 135, respectively, of core 100. Output lead 200 extends from lower face 135. Several alternative configurations of contact strip 300 are shown in figure 6. In some variations on the basic pickup design, including the preferred embodiment, contact strip 300 is mounted on the bottom (bridge side) of transducer 50; in other variations, contact strip 300 is mounted on the top (saddle side) of transducer 50. Contact strip 300 can be as simple as a rectangular piece of 0.002" (0.05 mm) thick foil 305 cut to the same width as the largest face 130 or 135 of core 100, i.e., about 1/16" (1.6 mm). Foil 305 is about the same length as core 100 if it is top mounted (figure 6(f)), and about 0.1" (2.5 mm) shorter than core 100, i.e., 2.4" (60 mm) if it is bottom mounted (Figure 6(a)). When it is bottom- mounted, foil 305 must be shorter than core 100 so that it does not obstruct the access of output lead 200 to its connection point to core 100 at hole 120. Copper, brass, or some other suitable conductive material may be used for foil 305. Output lead 200 can be attached to a bottom-mounted contact strip 300 in a number of different ways, some of which are shown in figures 6(a) through 6(e). In the simplest configuration shown in figure 6(a), a hole is made in braid 205 of output lead 200 about 1/4" (6 mm) from the end, and inner conduc¬ tor 215 and insulator 210 are pulled through the hole. The resulting empty length of braid is twisted together, bent at right angles to the long axis of output lead 200, and soldered to the back of foil 305 by solder 310. If normal-temperature solder is to be used, this must be done before contact strip 300 is attached to piezoelectric film element 400, otherwise the soldering process can melt piezoelectric film element 400. Before they are soldered, foil 305 and output lead 200 are preferably correctly positioned relative to one-another by means of a. suitable jig (not shown). Alternatively, braid 205 can be soldered to the back of foil 305 after contact strip 300 has been attached to piezoelectric film element 400 if low- temperature (< 90 °C) indium-tin solder is used. This method of attaching braid 205 of output lead 200 to contact strip 300, although simple, is not favoured because it makes the bottom of the pickup uneven, which prevents the pickup from seating in the saddle-slot uniformly across its width. Contact strip 300 can be extended over the full 2.5" length of the core by making a small hole 325 in foil 305, as shown in figure 6(b). Hole 325 needs only to be large enough to provide clearance for insulator 210 of output lead 200 to pass through it. The gap between contact strip 300 and braid 205 is then filled with solder. An alternative way of attaching braid 205 of output lead 200 to contact strip 300 that is stronger than a simple soldered butt-joint is to extend the length of copper foil 305, as shown in figure 6(c). The end of contact strip extension 313 is formed to provide braid receptacle 315. Contact strip extension 313 is bent through 90° relative to foil 305, so that the long axis of receptacle 315 is at right-angles to the long axis of foil 305. Output lead 200 passes through receptacle 315, and braid 205 is soldered to receptacle 315 with normal or low-temperature solder 310, as discussed above. The diameter of the completed assembly is still small enough to pass through the hole made in the bottom of the saddle slot to accom¬ modate the output lead. A further way of attaching output lead 200 to contact strip 300, and of providing a reliable electrical and mechanical connection is shown in figure 6(d). Crimp receptacle 320 is attached to foil 305 by soldering, welding or some other way, and output lead 200 is crimped in crimp receptacle 320 using a suitable crimping tool. Crimp receptacle 320 can be made from beryllium copper but other materials well known in the art with suitable electrical and mechanical properties can be used. Alternatively, and preferred, since it gives the pickup a flat bottom to facilitate uniform seating in the saddle slot, as shown in figure 6(e), foil 305 and crimp receptacle 320 can be fabricated from a single piece of beryllium copper foil or other suitable material. Further advantages of crimping are that it (1) can be done as one of the last operations of the assembly process, which means that parts do not have to be pre-aligned, and (2) does not involve heating, which could melt piezoelectric transducer element 400 or otherwise distort the pickup. Preferably, a variation on the configuration shown in figure 6(c), in which receptacle 315 omitted, is used. Contact strip extension 313 is about 1/4" (6.25 mm) long and 1/32" (0.8 mm) wide, and is bent through 90° relative to foil 305. Braid 205 of output lead 200 and contact strip extension 313 are tinned using techniques well known in the art, after which the two components are brought into contact and heat is applied to sweat solder them together. The arrangements shown in figures 6(c) through 6(e) can be adapted to provide soldered or crimped connections to output lead 200 from a top-mounted contact strip 300. For instance, a modification of the arrangement of figure 6(c) is shown in figure 6(f). Foil 305 is extended longitudinally to form contact strip extension 313. Contact strip extension 313 is bent through 90° so that it is at right angles to the main part of foil 305. The end of contact strip extension 313 is formed to provide receptacle 315 which conforms to the outer surface of output lead 200. Output lead 200 is inserted into receptacle 315 from the bottom as shown and is soldered in place with solder 310. Alternatively, receptacle 315 may be omitted and the plain end of contact strip extension 313 may be sweat soldered to braid 205 as previously described. Figure 7(a) shows piezoelectric transducer element 400, which is formed by depositing first and second metallized electrodes, 405 and 410 respectively, on an essentially rectangular piece of piezoelectric film 401. For this application, a PVDF film such as that sold under the trademark "KYNAR" by Atochem Sensors, Inc. is the preferred material for the piezoelectric film. A film thickness of 52 μm (about 0.002") gives the best compromise between output voltage and mechanical flexibility, and is thus preferred. First electrode 405 is formed by partially covering the front side 403 of film 401 with a metallized layer, applied by painting with conductive paint, silk-screening with conductive ink, or vacuum depositing a metallic film. First electrode 405 is in the form of a strip, with its long axis parallel to the long axis of film 401. If the width of core 100 (figure 7(b)) is W and the thickness of core 100 is t, in the preferred embodiment, the width of electrode 405 is about W and electrode 405 is located about W + t from one edge 440 of film 401, as shown in figure 7(a). In an alternative configuration of first electrode 405, the capacitance of the pickup is increased by increasing the width of electrode 405 to W + 2t, the electrode being located about W from one edge 440 of film 401. Second electrode 410 is formed by covering all of the back side 408 of film 401 with a metallized layer, applied by any of the methods men¬ tioned above. A web of film is cut into individual films 401 by means of a knife, or, preferably, the web is die cut. The length of film 401 is the same as the length of core 100, but two approximately 0.1" x (W + (2.5 mm x (W 4- /)) rebates 422 and 424 symmetrically disposed about electrode 405 are cut out from one end of film 401, as shown in figure 7(a). Rebates 422 and 424 enable piezoelectric transducer element 400, when it is wrapped around core 100, to cover all of core 100 except the small area in the vicinity of hole 120 at one end of lower face 135 of core 100 where the connection between core 100 and output lead 200 is made. This enables electrode 410 to provide as much electrical shielding of the connection between core 100 and output lead 200 as possible without obstructing the access of output lead 200 to core 100. The sides and end of core 100 are exposed in the region where output lead 200 connects to core 100. Theoretically, electrode 410 could provide shielding to the sides and end of the core by extending electrode 410 and film 401 to cover such areas, but it is difficult to attach such extended parts of film 401 to the sides and end of the core reliably. Instead, the sides and end of the core are screened by applying a conductive paint to the exposed surfaces of the core. The paint should also partially overlap electrode 410 to provide an electrical contact between the painted area and electrode 410. The width of film 401 is sufficient to wrap around core 100 once with a complete overlap on longest face 130 or 135, i.e., approximately (3W + 2i). If some wastage of film material can be afforded, the width of film 401 may be made greater than 3W + 2/) to facilitate handling. Excess film material can be trimmed off towards the end of the assembly operation. If one or both ends of core 100 are rounded, piezoelectric transducer element 400 should have a matching rounded profile as shown in figure 7(a). If electrodes 405 and 410 are applied by painting, the web of piezoelectric film must be cut into individual films 401 before the electrodes are applied. If the electrodes are applied by silk-screening or vacuum deposition, they can be applied before the web is cut into individual films 401. Cutting after silk¬ screening or vacuum deposition is possible because silk-screened or vacuum-deposited electrodes can be applied with sufficient precision to leave an un-metallized guard band in the region where the web is to be cut, which avoids the possibility of an electrical short between the electrodes at the cut edge. If significant pick up from the back of the pickup is desired, a further first electrode (not shown) must be deposited on the same side of film 401 as electrode 405, and positioned so that it makes contact with face 135 (which must be conductive if pick up from the back is desired) of core 100. Simply gluing the film to a conductive face of core 100 with conductive glue does not produce a significant electrical output: the film must be metallized as described above. Piezoelectric transducer element 400 is attached to core 100 by means of a conductive adhesive. Various kinds of adhesives based on acrylic, silicone, or urethane polymers can be used: in the preferred embodiment, a layer 415, about 0.001" to 0.002" (25 μ to 50 μm) thick, of type 9703 conductive adhe- sive, manufactured by 3M Corporation, is applied over all of the front side 403 of piezoelectric transducer element 400. Preferably, core 100 is laid on adhesive layer 415 of piezoelectric transducer element 400 so that upper face 130 of core 100 is aligned with first electrode 405, as shown in figure 8(a). Piezoelectric transducer element 400 is laterally located on core 100 such that its edges are approximately flush with the ends of core 100. The two protruding pieces 417 and 419 of piezoelectric transducer element 400 are then wrapped around core 100 in two consecutive wrapping operations, ending up with two layers of film covering lower face 135. Alternatively, piezoelectric transducer element 400 can be laid on core 100 as shown in figure 8(b), so that adhesive layer 415 is juxtaposed with lower face 135 of core 100, and edge 440 of piezoelectric transducer element 400 touches edge 140 of core 100. Piezoelectric transducer element 400 is laterally located on core 100 such that its edges are approximately flush with the ends of core 100. Piezoelectric transducer element 400 is then wrapped in a single wrapping operation all the way around core 100 such that it finally overlaps lower face 135 of core 100 again, i.e., lower face 135 is covered by two layers of film 401. Figure 8(c) shows a cross section of transducer 500 after piezoelectric transducer element 400 has been completely wrapped around core 100 by either method. The preferred wrapping method is also preferred if single-sided printed circuit board is used for core 100. Alternatively, if a single-step wrapping operation is required, piezoelectric transducer element 400 can be wrapped starting on the non-copper side of the board, so that first electrode 405 contacts the copper side of core 100, or wrapping can start on the copper side of core 100 if first electrode 405 is relocated so that its outer edge is flush with edge 440 of piezoelectric transducer element 400. All that now remains is to establish electrical contact between the second conductor (normally braid 205) of output lead 200 and second electrode 410 by attaching contact strip 300 to bottom 505 of core and piezoelectric transducer element assembly 500, i.e., to the face of assembly 500 from which output lead 200 emerges (or will emerge). Contact strip 300, which may or may not at this point of the assembly process already be attached output lead 200, is coated on the inner face of foil 305 with a layer 510 of conductive adhesive, such as type 9703 made by 3M Company, and placed in contact with bottom 505 of core and piezoelectric transducer element assembly 500. Figure 8(d) shows a cross-sectional view of the completed transducer 50 with contact strip 300 glued in place. If output lead 200 is not already connected to core 100 and/or contact strip 300, this can now be done to complete assembly of the pickup. Only attachment methods that do not run the risk of melting film 401 can be used if lead attachment is carried out at this stage of the assembly process, i.e., after transducer 50 is fully assembled. Piezoelectric transducer element 400 is wrapped around core 100 such that first electrode 405 is in electrical contact with a conductive part of core 100, for example upper face 130. Since one conductor of output lead 200 is in electrical contact with a conductive part of core 100 (or will be in contact if output lead 200 is connected to core 100 after piezoelectric transducer element 400 is wrapped around core 100), this one conductor is in electrical contact with first electrode 405. Contact strip 300 is electrical contact with second electrode 410 of piezoelectric transducer element 400. Contact strip 300 is also in electrical contact with the other conductor of output lead 200. Thus, each conductor of output lead 200 makes electrical contact with one of the electrodes 405, 410 of piezoelectric transducer element 400, the contacts being made without exceeding the physical dimensions of transducer 50 (comprising the core, piezoelectric transducer element, and contact strip assembly) and output lead 200. Figure 9 shows partially exploded cross sectional views of a number of possible variations on the locations of electrode 405 and contact strip 300 of transducer 50. In all of the variations, electrode 410 covers all the back side of film 401, and core 100 is oriented so that conductive face 130 is in contact with first electrode 405, so, for simplicity, these features are not shown in the drawings. Also, to simplify the drawings, film 401 is depicted as a single line, without thickness. Each variation produces a different "sound," so different applications and artistic preferences may favour one configuration over the others. Figure 9(a) shows the arrangement described above, which, to the inventor, is the preferred embodiment of transducer 50. In variations (a), (d), and (f), electrode 405, and hence the transducing element, is closest to the strings, which reduces the amount of top noise produced by these variations. In variations (b), (c), and (e), electrode 405 is closest to the top of the guitar for those that prefer more top noise. In variations (a) through (d), contact strip is bottom mounted, which usually increases the coupling be¬ tween the saddle and the transducer, and hence the efficiency of the pickup. However, because contact strip 300 is relatively soft, top mounting it, as in variations (e) and (f), can improve efficiency and string- to-string uniformity if, for example, the bottom of the saddle is uneven. In variations (b) and (d), electrode 405 is located beneath a double thickness of film 401. Fabricating the variations is simply a matter of doing one or more of the following, and so will not be described in detail: (1) changing the location of electrode 405 on film 401, (2) placing electrode 405 in contact with top face 130 or bottom face 135 of core 100, and (3) top mounting or bottom mounting contact strip 300. The structure of a Ty e III pickup according to the third aspect of the invention will now be described with reference to figure 10. The electrical output of the Type III pickup is greater than that of Type I and Type II pickups. This is achieved by using a piezoelectric film that is considerably thicker than that used in the Type I and Type II pickups. The thicker film generates a greater electrical output voltage for a given mechanical stress, but has a lower capacitance. Lower capacitance is disadvantageous because, for a given preamplifier input impedance, it reduces the low-frequency output of the pickup. To overcome this disadvantage, two piezoelectric transducer elements are stacked on top of one another with their first electrodes in contact and their second electrodes interconnected. This arrangement connects the two transducer elements in parallel and recovers most of the capacitance lost as a result of using the thicker film. A further increase in electrical output is achieved by substantially eliminating adhesives from the construction of the pickup. Figure 10(a) is a longitudinal cross section of a Type III pickup, showing the basic arrangement of core 100, output lead 200, contact strip 300, lower piezoelectric transducer element 400, and upper piezoelectric transducer element 450. Core 100 has a first face that is divided into two conducting areas, contact area 110 and output lead connecting area 120, that are isolated from one another by an insulating area. Second face 130 is electrically conducting over most of its area and is connected to contact area 110 by means of at least one plated-through hole 140. A further plated-through hole 150 electrically interconnects output lead connecting area 120 with conducting annulus 160. Conducting annulus 160 is electrically isolated from second face 130. More details of core 100 are given below in connection with the description of figure 12. Inner conductor 215 of output lead 200 is inserted into plated-though hole 150, and is mechanically attached and electrically connected to plated-through hole 150, preferably by soldering. Inner conductor 215 is thus electrically connected to output lead contact area 120. Outer conductor 205 of output lead 200 is mechanically attached and electrically connected to anchor pad 194, again preferably by soldering. Anchor pad 194 is part of second face 130, thus, outer conductor 205 is in electrical contact with second face 130, and, via plated-through hole 140, to contact area 110 on the first face of core 100. Thus, both conductors of output lead 200 are mechanically attached to core 100, and make electrical contact with different conductive areas of core 100. Figure 10(b) is an exploded view showing core 100, lower and upper piezoelectric transducer elements 400 and 450 respectively, and contact strip 300. Piezoelectric transducer elements 400 and 450 have substantially the same width as the first face of core 100. The length of lower piezoelectric transducer element 400 is substantially equal to the length of contact area 110 of the first face of core 100; the length of upper piezoelectric transducer element 450 is substantially equal to the length of core 100. Lower piezoelectric transducer element 400 comprises a strip of piezoelectric film 430 with first electrode 410 deposited on one side and second electrode 420 (not shown) deposited on and substantially completely covering the other side. Upper piezoelectric transducer element 450 comprises a strip of piezoelectric film 480 with first electrode 460 (not shown, but the periphery of first electrode 460 is shown by dotted line 462) deposited on one side and second electrode 470 deposited on and substantially completely covering the other side. The periphery of the first electrode (410 or 460) of each piezoelectric transducer element is inset from periphery of the film (430 or 480, respectively) on which it is deposited so that when the piezoelectric transducer elements are stacked with their first electrodes in contact, second electrodes 420 and 470 (which do extend to the periphery of the film) shield first electrodes 410 and 460 more effectively. ^ Lower piezoelectric transducer element 400 is placed on the first face of core 100 so that second electrode 420 (not shown) covers contact area 110. Upper piezoelectric transducer element 450 is placed on top of lower piezoelectric transducer element 400 so that it completely covers core 100 and first electrode 460 (not shown) of upper piezoelectric transducer element 450 contacts first electrode 410 of lower piezoelectric transducer element 400. The part 490 of first electrode 460 that is not covered by first electrode 410 overlaps output lead connecting area 120. Contacting means 165 ensures a reliable electrical contact between the exposed part 490 of first electrode 460 and output lead connecting area 120. Preferably, a piece of self-adhesive copper tape folded in half is used for contacting means 165. Contacting means 165 connects first electrodes 410 and 460 (not shown) of piezoelectric transducer elements 400 and 450 respectively to output lead connecting area 120 and hence to inner conductor 215 of output lead 200 (figure 10(a)). More details of piezoelec¬ tric transducer elements 400 and 450 are given below in connection with the description of figure 14. Contact strip 300 has substantially the same width as core 100, but is somewhat longer. Extension 310 of contact strip 300, which is preferably somewhat narrower than contact strip 300, is secured to the outer conductor of output lead 200. Contact strip extension 310 covers the exposed end of core 100, and contact strip 300 is bent relative to contact strip extension such that it substantially covers second elec¬ trode 470 of second piezoelectric transducer element 450, as shown in figure 10(a). Thus, contact strip 300 electrically connects second electrode 470 of upper piezoelectric transducer element 450 to outer conductor 205 of output lead 200, and hence to second electrode 420 of lower piezoelectric transducer element 400. The two piezoelectric transducer elements are thus connected in parallel. More details of contact strip 300 are given below in connection with the description of figure 15. The components of the transducer part 50 of the pickup (figure 2), i.e., core 100, piezoelectric transducer elements 400 and 450, and contact strip 300 (figure 10(a)), are assembled essentially without adhesives to prevent the cushioning effect of several layers of adhesive from reducing the electrical output of the pickup. Transducer part 50 of the pickup is wrapped in an insulating layer to hold its components together. The insulating layer also physically protects and electrically insulates the transducer part 50 of the pickup. Figure 11 shows a transverse cross section of the transducer part 50 of the pickup showing insulating layer 600 wrapped around it. To hold insulating layer 600 tightly wrapped around transducer 50, insulating layer 600 is wrapped 1 and 1/4 times around transducer 50, such that there is an overlap of insulating layer 600 on the bottom of transducer 50. More details of insulating layer 600 are given below in connection with the description of Figure 16. The six basic components of the pickup will now be described in turn: core 100, output lead 200, contact strip 300, piezoelectric transducer elements 400 and 450 and insulating layer 600. Figure 12(a) shows core 100. Core 100 is an essentially rectangular piece of 1/32" (0.8 mm) thick material. The length of the core is substantially equal to the length of the saddle slot; in the preferred embodiment, which is suitable for most acoustic guitars, the length of the core is about 2,73" (69.3 mm). The preferred width of the core of a pickup for use in a standard 3/32" (2.4 mm) wide saddle slot is 0.075" (1.9 mm); the preferred width of the core of a pickup for a wider-than-standard 1/8" (3.2 mm) wide saddle slot is 0.110" (2.8 mm). Preferably, at least the end of core 100 to which output lead 200 will be attached is rounded, as shown in figure 12(a); alternatively, one or both ends can be straight-cut. A variety of materials can be used for core 100, the main purposes of which are to support the other components of the pickup, to provide the pickup with physical strength, to interconnect the electrodes of piezoelectric transducer elements 400 and 450 and the conductors 205 and 215 of output lead 200, and to anchor output lead 200. The core 100 is preferably made from double-sided fiberglass printed circuit board 1/32" (0.8 mm) thick. One of the various methods for making the core from a sheet of printed circuit board described above in connection with the Type II pickup can be used for the Type III pickup. The core 100 has at least two 0.030" (0.75 mm) diameter holes. Hole 150 is located in the part of core 100 that will become output lead connecting area 120, and hole 140 is located in the part of core 100 that will become contact area 110. Preferably, an additional hole 170 is located in the part of core 100 that will become contact area 110. All holes are plated-through as described above. Copper is removed from a narrow strip 180 of the first face of the core 100 to divide the first face into contact area 110 and output lead connecting area 120. Preferably, copper is also removed from the periphery of output lead connecting area 120 to provide the shape shown in figure 12(a). Although copper may be almost entirely removed from the second face 130 of core 100, leaving only annulus 160, anchor pad 194 and a track interconnecting anchor pad 194 and plated-through hole 140, it is preferred to leave second face 130 almost completely covered with copper. Leaving second face 130 substantially completely covered with copper enables second face 130 to provide some electrical shielding, and gives the pickup a flat bottom surface, which helps the pickup seat snugly in the bottom of saddle slot 68 (figure 3(b)). Thus, it is preferred that copper be removed from second face 130 only as shown in figure 12(b). Copper is removed from annular area 190 surrounding annulus 160 and plated-through hole 150 to isolate annulus 160, hole 150, and output lead connecting area 120 (figure 10(a)) from second face 130. It is also preferred to remove copper from second face 130 to form anchor pad 194 sur¬ rounding annular area 190. Anchor pad 194 facilitates soldering outer conductor 205 of output lead 200 to second face 130. The inner diameter of lead anchor pad 194 is preferably substantially the same as the outer diameter of inner insulator 210 of output lead 200 (figure 10(a)). The outer diameter of anchor pad 194 is preferably substantially the same as the width of core 100. Anchor pad 194 is connected to the rest of second face 130 by track 196. Preferably, both sides of the core 100 are plated with 20 μ" (0.5 μm) of gold to prevent tarnishing and the formation of a rectifying contact between contact area 110 and second electrode 420 of lower piezoelectric transducer element 400. Anchor pad 194 is also tinned to facilitate soldering the outer conductor 205 of output lead 200 to it. As in the Type I and Type II pickups, the output lead 200 of the type III pickup is a suitable length (usually about 15" (0.4 m)) of sub-miniature co-axial cable about 1/16" (1.6 mm) in diameter. Coaxial cable is required to prevent output lead 200 from picking up hum and other unwanted noise. The options for attaching the output lead 200 to the core 100 described above in connection with the Type II pickup also apply to the Type III pickup. The preferred method, described above, of attaching output lead 200 to core 100 in the Type II pickup is also the preferred method of attaching output lead 200 to core 100 of the Type III pickup. The completed assembly is shown in figure 13. Irrespective of the method used to attach output lead 200 to core 100, nothing (e.g., inner conductor 215 and/or, solder) should protrude from the top of plated-through hole 150. This is to ensure that the bottom of saddle 63 (figure 3(a)) contacts the top face of the pickup evenly along the whole of its length. A plan view of contact strip 300 is shown in figure 15(a). Contact strip 300 includes a rectangular piece of approximately 0.002" (0.05 mm) thick foil 305 cut to substantially the same width as the first face of the core and about 1/4" (6.25 mm) longer. Copper, brass, metallized plastic, or some other suitable conductive material may be used for foil 305. The width of foil 305 is reduced to about 1/32" (0.8 mm) over the last 1/4" (6.25 mm) of its length to form extension 310. Extension 310 is bent through 90 degrees relative to foil 305 as shown in figure 9(b), and, if necessary, is bent inwards slightly so that it comes into contact with outer conductor 205 of output lead 200. The various options for contact strip 300, and for attaching contact strip 300 to output lead 200, described above in connection with the Type II pickup can be adapted for use in the Type III pickup. In the preferred method, contact strip 300 is attached to output lead 200 by soldering, as shown in figure 15(b). Outer conductor 205 of output lead 200 and extension 310 are tinned prior to assembly using known techniques, after which the two components are brought into contact and heat is applied to sweat solder them together. This is done before contact strip 300 is bent through 90 degrees and placed on upper piezoelectric transducer element 450 to avoid melting or otherwise distorting one or both piezoelectric transducer elements. Figure 14(a) shows a plan of lower piezoelectric transducer element 400 and figure 14(b) shows a cross section along line A'B'. Lower piezoelectric transducer element 400 is formed by depositing first and second metal electrodes, 410 and 420 respectively, on an essentially rectangular piece of piezoelectric film 430. Figure 14(c) shows upper piezoelectric transducer element 450 and figure 14(d) shows a cross section along line AB. Upper piezoelectric transducer element is formed by depositing first and second metal electrodes, 460 and 470 respectively, on an essentially rectangular piece of piezoelectric film 480. The same methods for depositing electrodes discussed in connection with the Type II pickup can be used to deposit the electrodes of the Type III pickup. The Type III pickup uses the same PVDF film as used in the T pe I and Type II pickups, except that the preferred film thickness is 110 μm (about 0.004"), which gives the best compromise between output voltage and capacitance. A web of piezoelectric film is cut into individual films 430 and 480 by means of a knife, or, preferably, the web is die cut. The width of piezoelectric films 430 and 480 is substantially equal to the width of core 100 (figure 10). The length of piezoelectric film 430 in lower piezoelectric transducer element 400 is substantially equal to the length of contact area 110 of the first face of core 100, i.e., about 2.53" (64.3 mm) in the preferred embodiment. The length of piezoelectric film 480 in upper piezoelectric transducer element 450 is substantially equal to the length of core 100, i.e., about 2.70" (68.6 mm) in the preferred embodiment. The ends of piezoelectric film 480 are preferably cut to match the shape of core 100 as shown. In lower piezoelectric transducer element 400, first electrode 410 partially covers one side of film 430. First electrode 405 is rectangular in shape and its edges are inset from the longer edges of film 430 by approximately 0.01" (0.25 mm), and from the shorter edges by approximately 0.03" (0.75 mm). Second electrode 420 fully covers the other side of film 430. In upper piezoelectric transducer element 450, first electrode 460 partially covers one side of film 480. First electrode 460 is rectangular in shape and its edges are inset from the longer edges of film 430 by approximately 0.01" (0.25 mm), and from one of the shorter edges by approximately 0.032" (0.81 mm), and from the other of the shorter edges by about 0.065" (1.65 mm). Second electrode 470 fully covers the other side of film 480. Referring to figures 10(a) and 10(b), the pickup is assembled by stacking piezoelectric transducer elements 400 and 450 on core 100, which preferably has been pre-assembled with output lead 200 and contact strip 300. Lower piezoelectric transducer element 400 is first placed an core 100 such that its long edges are flush with the long edges of core 100, one of its ends is flush with the end of core 100 remote from output lead contacting area 120, and second electrode 420 contacts contact area 110. Contacting means 165 is next applied to output lead connecting area 120. A email drop of conductive silicone can be applied to output lead connecting area to provide contacting means 165; alternatively, a small piece of 0.002" (50 μm) thick metal (such as brass) or conductive plastic foil is attached to output lead connecting area 120 by means of a thin layer of conductive adhesive, such as type 9703 made by 3M Company. A second thin layer of conductive adhesive is applied to the exposed surface of the foil after the foil has been attached to output lead connecting area 120. Preferably, contacting means 165 is a rectangular piece about 0.125" by 0.04" (3.2 mm by 1 mm) of about 0.003" (75 μm) thick self- adhesive copper tape, folded in half along its short axis with its adhesive side on the outside. The preferred copper tape is 3M Company type 1181, the adhesive layer of which is conducting. Contacting means 165 is placed on output lead connecting area 120 with its long axis aligned with the long axis of output lead connecting area 120. Finally, upper piezoelectric transducer element 450 is placed on top of lower piezoelectric transducer element 400 and core 100 such that it is flush with core 100 on all sides. This aligns first electrode 460 of upper piezoelectric transducer element 450 with first electrode 410 of lower piezoelectric transducer element 400. The part 490 of first electrode 460 that is not in contact with first electrode 410 makes contact with contact means 165, and hence with output lead connecting area 120 and inner conductor 215 of output lead 200 (figure 10(a)). Electrical contact between second electrode 420 of lower piezoelectric transducer element 400 and second electrode 470 of upper piezoelectric transducer element 450 is established by bending contact strip 300 (already attached to output lead 200) through 90 degrees so that contact strip 300 contacts second electrode 470 of upper piezoelectric transducer element 450. The piezoelectric transducer elements 400 and 450 and contact strip 300 are held in place on core 100 prior to wrapping the pickup with insulating layer 600 by placing a small drop of cyanoaαylate adhesive on the exposed ends of piezoelectric transducer elements 400 and 450, contact strip 300 and core 100 remote from output lead 200. Excess adhesive is immediately removed by blotting with a piece of absorbent paper. This ensures that the adhesive is applied only to the very ends of the components and does not interfere with the electrical contact between the components. The pickup is completed by adding insulating layer 600. Insulating layer 600 provides electrical insulation and mechanical protection, and holds together the components of the transducer part 50 of the pickup (figure 2) (i.e., the core, piezoelectric transducer elements and contact strip). Insulating layer 600 comprises a piece of paper, plastic or other insulating material die cut to the shape shown in figure 16. The length of insulating layer 600 is substantially equal to that of core 100, i.e., 2.7" (68.6 mm) in the preferred embodiment. Its length is reduced by about 0.1" (2.5 mm) in cut-out areas 610 and 620 to provide an aperture for output lead 200 when the insulating layer is wrapped around transducer 50. The width of insulating layer 600 is equal to three times the width plus twice the thickness of transducer 50, i.e., about 0.435" (11 mm) for the normal 3/32" (2.4 mm) wide version. Insulating layer 600 may be scored at the points at which it coincides with the corners of transducer 50 to make it easier to wrap. A non-adhesive plastic film or paper can be used for insulating layer 600, the layer being secured with a thin film of a suitable adhesive applied at least in the area covering the bottom of the pickup where there is a double thickness of insulating layer. A self-adhesive film of plastic or paper, such as 3M Company Magic™ adhesive tape, can also be used for insulating layer 600. In the preferred embodiment, 0.002" (50 μm) thick self-adhesive label paper, 3M Company type 7109, is used. A suitably shaped piece of label paper is cut and placed symmetrically on top of the assembled pickup. One of the protruding sides of the tape is wrapped down the side and across the bottom of transducer 50, then the other protruding side of the tape is wrapped down the other side and across the bottom of transducer 50. This envelops transducer 50 and provides two layers of tape on the bottom of transducer 50. Insulating layer 600 leaves unprotected the sides and end of the pickup in the vicinity of output lead 200. This part of the pickup is protected by painting it with a layer of opaquing fluid for copies. A water-based opaquing fluid, such as Liquid Paper® Just for Copies® opaquing fluid is preferred. After the opaquing fluid has dried, a layer of cyanoaαylate adhesive is applied to its surface. This considerably increases the hardness and durability of the dried opaquing fluid. Finally, the transducer part of the pickup is painted with a conductive paint. The conductive paint provides further electrical shielding for the pickup, although, for most applications, this extra shielding is unnecessary since the core, the contact strip, and the second electrodes of the piezoelectric transducer elements provide sufficient electrical shielding. The painted area extends over the outer conductor of the output lead in the vicinity of the transducer part of the pickup to provide an electrical connection between the conductive paint layer and the outer conductor of the output lead. Further variations on the pickups described herein can be applied to any stringed instrument, such as a violin, in which a string passes over a bridge (or a saddle forming part of a bridge), and which allows a suitably-shaped pickup to be inserted between the saddle and the bridge or between the bridge and the top of the instrument.

Claims: Claims I claim: 1. An electro-mechanical pickup for a musical instrument, comprising: an elongated multi-faced core having an electrically conducting face; a piezoelectric transducer element, comprising: a piezoelectric film including a first surface and a second surface opposite the first surface, a first electrode covering at least part of the first surface, and a second electrode covering at least part of the second surface, the piezoelectric transducer element covering substantially all of the electrically conducting face of the core, and being attached to the core with the first electrode in contact with the electrically conducting face of the core; a contact strip in contact with at least part of the second electrode; and an output lead, having a first conductor and a second conductor, the first conductor being connected to the electrically conducting face of the core, and the second conductor being connected to the contact strip. 2. The pickup of claim 1, wherein the core comprises: an elongated insulating layer disposed between a first conducting layer and a second conducting layer, the first conducting layer and the second conducting layer each at least partially covering the insulating layer, the first conducting layer providing the electrically conducting face of the core; and a plated-through hole connecting the first conducting layer to at least part of the second conducting layer, and the plated-through hole connects the first conductor of the output lead to the first conducting layer. 3. The pickup of claim 2, wherein the second conducting layer includes an electrically-isolated lead anchor pad substantially surrounding the plated-through hole, and the second conductor of the output lead is additionally attached to the lead anchor pad. 4. The pickup of claims 1, 2, or 3, wherein the first electrode is attached to the electrically conducting face of the core by means of a conductive adhesive, and the contact strip is attached to the second electrode by means of a conductive adhesive. 5. An electro-mechanical pickup for a musical instrument, comprising: an elongated multi-faced core having an electrically conducting face; a piezoelectric transducer element, comprising: a piezoelectric film including a first and a second surface opposite the first surface; a first electrode covering at least part of the first surface; and a second electrode covering substantially all of the second surface, the piezoelectric transducer element covering substantially all the electrically conducting face of the core, and being wrapped around the core and adapting itself generally to the shape of the core with the first electrode in contact with the electrically conducting face of the core and the second electrode providing an electrical shield around the core, the piezoelectric film and the first electrode; a contact strip in contact with at least part of the second electrode; and an output lead, having a first conductor and a second conductor, the first conductor being connected to the electrically conducting face of the core, and the second conductor being connected to the contact strip. 6. The pickup of claim 5, wherein the core comprises: an elongated insulating layer disposed between a first conducting layer and a second conducting layer, the first conducting layer providing the electrically conducting face of the core; and a plated-through hole connecting the first conducting layer to at least part of the second conducting layer, and the plated-through hole connects the first conductor of the output lead to first conducting layer. 7. The pickup of claims 5 or 6, wherein the piezoelectric transducer element is rebated, the rebated areas providing access to the core when the piezoelectric transducer element is wrapped around the core. 8. The pickup of claim 6, wherein the first conducting layer covers substantially all the insulating layer, and the second conducting layer covers substantially all the insulating layer. 9. The pickup of claims 6, 8, or 9, wherein the second conducting layer includes an electrically-isolated lead anchor pad substantially surrounding the plated-through hole, and the second conductor of the output lead is additionally attached to the lead anchor pad. 10. The pickup of any of claims 5, 6, 7, 8, or 9, wherein the contact strip comprises a conductive foil, the length of foil being slightly shorter than the length of the core, and the width of foil being substantially similar to the width of the core. 11. The pickup of any of claims 5, 6, 7, 8, or 9, wherein the first electrode is attached to the electrically conducting face of the core by means of a conductive adhesive, the piezoelectric transducer element is secured in its wrapped state by means of an adhesive, and the contact strip is attached to the second electrode by means of a conductive adhesive. 12. The pickup of any of claims 5 through 11, wherein the length and width of the first electrode of the piezoelectric transducer element are substantially similar to the length and width of the electrically conducting face of the core. 13. The pickup of any of claims 5 through 11, wherein the length of the first electrode of the piezoelectric transducer element is substantially similar to the length of the electrically conducting face of the core, and the width of the first electrode of the piezoelectric transducer element is substantially equal to the sum of the width and twice the thickness of the core. 14. The pickup of any of claims 5 through 13, wherein the second electrode of the piezoelectric transducer element provides an electrical shield for the ends of the core. 15. A stringed musical instrument, comprising: a bridge having a saddle slot, a saddle in the saddle slot, a plurality of strings, each string contacting the top of the saddle, an electro-mechanical pickup in the saddle slot, the electro-mechanical pickup having substantially the same width and length as the width and length of the saddle slot, and having at least two surfaces, one surface being in contact with the bottom of the saddle, the other surface being in contact with the bottom of the saddle slot, the electro-mechanical pickup comprising: an elongated multi-faced core having an electrically conducting face; a piezoelectric transducer element, comprising: a piezoelectric film including a first surface and a second surface opposite the first surface; a first electrode covering at least part of the first surface; a second electrode covering at least part of the second surface, the piezoelectric transducer element covering substantially all of the electrically conducting face of the core, and being attached to the core such that the first electrode is in contact with the electrically conducting face of the core; a contact strip in contact with at least part of the second electrode; and an output lead having a first conductor and a second conductor, the first conductor being connected to the electrically conducting face of the core, and the second conductor being connected to the contact strip; and a hole in the bottom of the saddle slot for receiving the output lead, the diameter of the hole being no greater than the width of the saddle-slot. 16. The stringed musical instrument of claim 15, wherein the second electrode covers substantially all of the second surface of the piezoelectric film, and the piezoelectric transducer element is wrapped around the core and adapts itself generally to the shape of the core, the second electrode providing an electrical shield around the core; the piezoelectric film and the first electrode. 17. An electro-mechanical pickup for a musical instrument having a plurality of strings, comprising: an elongated multi-faced core having a first face opposite a second face; a first piezoelectric transducer element connected in parallel with a second piezoelectric transducer element, the first piezoelectric transducer element comprising: a first piezoelectric film having a first surface and a second surface; a first electrode on the first surface; and a second electrode on the second surface, the second piezoelectric transducer element comprising: a second piezoelectric film having a first surface and a second surface; a third electrode on the first surface; and a fourth electrode on the second surface, each piezoelectric transducer element being responsive to more than one string, the first piezoelectric transducer element being stacked on the core with the second electrode in contact with the first face, and the second piezoelectric transducer element being stacked on the first piezoelectric transducer element with the third electrode in contact with the first electrode; and an output lead attached to the core, the output lead having a first conductor and a second conduc¬ tor, the first conductor electrically contacting the first electrode and the third electrode, and the second conductor electrically contacting the second electrode and the fourth electrode. 18. The pickup of claim 17, wherein the first face of the core is conducting and comprises a contact area and an output lead connecting area, the first electrode is in electrical contact with the output lead connecting area, the second electrode is in electrical contact with the contact area, and the first conductor of the output lead is attached to and is in electrical contact with the output lead connecting area. 19. The pickup of claim 18, wherein the second face of the core is conducting and includes an anchor pad, the second conductor of the output lead is attached to and is in electrical contact with the anchor pad, and the second face of the core is electrically connected to the contact area. 20. The pickup of claims 17, 18, or 19, wherein the core, first piezoelectric transducer element, and second piezoelectric transducer element are covered with an insulating layer. 21. The pickup of claim 20, wherein the insulating layer comprises a substantially rectangular piece of paper wrapped one and one-quarter times around the core, first piezoelectric transducer element, and second piezoelectric transducer element, and secured by a thin layer of adhesive applied in the area where the insulating layer overlaps itself. 22. The pickup of claim 20, wherein the insulating layer comprises a substantially rectangular piece of self-adhesive film wrapped one and one-quarter times around the core, first piezoelectric transducer element, and second piezoelectric transducer element. 23. The pickup of any of claims 17, 18, or 19, further comprising a contact strip stacked on the second piezoelectric transducer element, the contact strip electrically connecting the fourth electrode to the second conductor of the output lead. 24. The pickup of claim 23, wherein the core, first piezoelectric transducer element, second piezoelectric transducer element and contact strip are covered with an insulating layer. 25. The pickup of claim 24, wherein the insulating layer comprises a substantially rectangular piece of paper wrapped one and one-quarter times around the core, first piezoelectric transducer element, second piezoelectric transducer element, and contact strip and secured by a thin layer of adhesive applied in the area where the insulating layer overlaps itself. 26. The pickup of claim 24, wherein the insulating layer comprises a substantially rectangular piece of self-adhesive film wrapped one and one-quarter times around the core, first piezoelectric transducer element, second piezoelectric transducer element, and contact strip. 27. The pickup of any of claims 17 through 26, wherein the length and width of the first piezoelectric transducer element are substantially equal to the length and width of the contact area, and the length and width of the second piezoelectric transducer element are substantially equal to the length and width of the core. 28. The pickup of any of claims 17 through 26, wherein the periphery of the first electrode is inset from the periphery of the first piezoelectric film, the second electrode covers substantially all of the second surface of the first piezoelectric film, the periphery of the third electrode is inset from the periphery of the second piezoelectric film, and the fourth electrode covers substantially all of the second surface of the second piezoelectric film. 29. An electro-mechanical pickup for a musical instrument having a plurality of strings, comprising: an elongated multi-faced core having a first face opposite a second face, the faces being conducting over a substantial portion of their area, the first face comprising a contact area and an output lead connecting area separated " by an insulating area, the second face comprising an anchor pad, the second face being electrically connected to the contact area; a first piezoelectric transducer element connected in parallel with a second piezoelectric transducer element, the first piezoelectric transducer element comprising: a piezoelectric film having a first surface and a second surface; a first electrode on the first surface, the periphery of the first electrode being inset from the periphery of the film; and a second electrode substantially covering the second surface, the second piezoelectric transducer element comprising: a piezoelectric film having a first surface and a second surface; a third electrode on the first surface, the periphery of the first electrode being inset from the periphery of the film; and a fourth electrode substantially covering the second surface, each piezoelectric transducer element being responsive to more than one string, the length and width of the first piezoelectric transducer element being substantially equal to the length and width of the contact area, the first piezoelectric transducer element being stacked on the core with the second electrode substantially covering and in electrical contact with the contact area, the length and width of the second piezoelectric transducer element being substantially equal to the length and width of the core, and the second piezoelectric transducer element being stacked on the first piezoelectric transducer element with the third electrode, substantially covering and in electrical contact with the first electrode, and substantially covering and in electrical contact with the output lead connecting area; an output lead having a first conductor and a second conductor, the first conductor being attached to and in electrical contact with the output lead connecting area, and the second conductor being attached to and in electrical contact with the anchor pad; and a contact strip stacked on the second piezoelectric transducer element, the contact strip electrically connecting the fourth electrode to the second conductor of the output lead.

Inventors: TURNER ROBERT ALAN, TURNER, ROBERT, ALAN
Applicants: TURNER ROBERT ALAN, TURNER, ROBERT, ALAN
Application year: 1992
Main classification: G10H3
IPC codes: G10H3