Add-on modification device for string instrument pickup

I claim:

1. An add-on signal modification device for modifying at least one of the amplitude, frequency, and reverberation characteristics of the output signal of an electromagnetic pickup for a musical instrument having a plurality of magnetic strings, the pickup including a magnetic structure for generating a magnetic field, the magnetic structure including at least one permanent magnet, at least one pole piece, and an electrical pickup coil disposed in encompassing relation to the pole piece, all mounted in a housing adapted for mounting on a musical instrument with the top of the pickup facing the magnetic strings and the magnetic field of the pickup intersecting a predetermined portion of the strings so that vibration of each string generates an electrical output signal in the coil, the pickup having a top of predetermined size and configuration, the add-on signal modification device comprising:

a thin, flat paramagnetic permanent magnet member, magnetized transversely to its thin dimension;

and mounting means for mounting the permanent magnet member of the signal modification device on top of a pickup, between the pickup and the strings, so that the magnetic field of the permanent magnet member modifies the magnetic field of the pickup and thereby modifies the output signal of the pickup.

2. A signal modification device for an electromagnetic pickup for a musical instrument having a plurality of magnetic strings, according to claim 1, in which the permanent magnet member of the signal modification device is a thin, flat, paramagnetic sheet of resin impregnated with particulate permanent magnet material.

3. A signal modification device for an electromagnetic pickup for a musical instrument having a plurality of magnetic strings, according to claim 2, in which the permanent magnet sheet is uniformly magnetized so that the entire surface of the sheet facing the pickup is of one polarity and the entire surface of the sheet facing the strings is of the opposite polarity.

4. A signal modification device for an electromagnetic pickup for a musical instrument having a plurality of magnetic strings, according to claim 2, in which the permanent magnet sheet is magnetized transversely to its thin dimension in a pattern such that parts of the surface area of that permanent magnet sheet facing the pickup have one polarity and other parts of the surface area of that permanent magnet sheet facing the pickup have the opposite polarity.

5. A signal modification device for an electromagnetic pickup for a musical instrument having a plurality of magnetic strings, according to claim 4, in which a central longitudinal part of the permanent magnet sheet is magnetized in one direction and at least one edge longitudinal part of the permanent magnet sheet is magnetized in the opposite direction.

6. A signal modification device for an electromagnetic pickup for a musical instrument having a plurality of magnetic strings, according to claim 5, in which both longitudinal edges of the permanent magnet sheet are magnetized in the opposite direction from the central longitudinal part of the permanent magnet.

7. A signal modification device for an electromagnetic pickup for a musical instrument having a plurality of magnetic strings, according to claim 4, in which at least a portion of the permanent magnet sheet is unmagnetized so that parts of the surface area of that permanent magnet sheet facing the pickup have n polarization.

8. A signal modification device for an electromagnetic pickup for a musical instrument having a plurality of magnetic strings, according to claim 4, in which laterally transverse parts of the permanent magnet sheet are magnetized in one direction and are interspersed with laterally transverse parts of the permanent magnet sheet magnetized in the opposite direction, so that the permanent magnet sheet presents alternating transverse stripes of opposite polarity to the pickup and to the strings.

9. A signal modification device for an electromagnetic pickup for a musical instrument having a plurality of magnetic strings, according to claim 2, in which the mounting means comprises at least one rim element, affixed to an edge of the permanent magnet sheet, for mounting on the pickup.

10. A signal modification device for an electromagnetic pickup for a musical instrument having a plurality of magnetic strings, according to claim 9, in which the rim element engages the side of the pickup device housing.

11. A signal modification device for an electromagnetic pickup for a musical instrument having a plurality of magnetic strings, according to claim 10, in which the rim element is of elongated configuration and engages a major portion of one side of the pickup housing.

12. A signal modification device for an electromagnetic pickup for a musical instrument having a plurality of magnetic strings, according to claim 10, in which there are at least two rim elements engaging opposite sides of the pickup housing.

13. A signal modification device for an electromagnetic pickup for a musical instrument having a plurality of magnetic strings, according to claim 2, in which the device further comprises a thin, flat sheet of ferromagnetic material, other than a permanent magnet material, affixed to and extending across a substantial part of one surface area of the permanent magnet sheet.

14. A signal modification device for an electromagnetic pickup for a musical instrument having a plurality of magnetic strings, according to claim 13 in which the further ferromagnetic sheet comprises two ferromagnetic sheet members aligned with each other and spaced from each other by a short air gap extending transversely to the strings.

15. A signal modification device for an electromagnetic pickup for a musical instrument having a plurality of magnetic strings, according to claim 14, for use with a pickup having a plurality of magnetic poles, one for each string, in which each further ferromagnetic sheet member includes a plurality of apertures, each aperture aligned with one pickup pole.

16. A signal modification device for an electromagnetic pickup for a musical instrument having a plurality of magnetic strings, according to claim 14, for use with a musical instrument having n strings and a pickup having n poles, in which each ferromagnetic sheet member includes n/2 apertures aligned with alternate pickup poles, the apertures in one ferromagnetic sheet member being aligned with different poles than the apertures in the other ferromagnetic sheet member.

17. A signal modification device for an electromagnetic pickup for a musical instrument having a plurality of magnetic strings, according to claim 16, in which each ferromagnetic sheet member also includes n/2 projections aligned with and extending into the apertures in the other ferromagnetic sheet member.

18. A signal modification device for an electromagnetic pickup for a musical instrument having a plurality of magnetic strings, according to claim 17 in which each of the two ferromagnetic sheet members is smaller than the permanent magnet sheet and includes a multiplicity of peripheral projections extending from the ferromagnetic sheet member toward one side edge of the permanent magnet sheet.

19. A signal modification device for an electromagnetic pickup for a musical instrument having a plurality of magnetic strings, according to claim 13, in which the further sheet of ferromagnetic material includes a multiplicity of apertures, plural apertures for each string.

20. A signal modification device for an electromagnetic pickup for a musical instrument having a plurality of magnetic strings, according to claim 19, in which the further ferromagnetic sheet comprises two ferromagnetic sheet members aligned with each other and spaced from each other by a short air gap extending transversely to all of the strings.

21. A signal modification device for an electromagnetic pickup for a musical instrument having a plurality of magnetic strings, according to claim 2, in which the device further comprises two thin, flat sheets of ferromagnetic material, other than permanent magnet material, affixed to and extending along opposite sides of the permanent magnet sheet, one ferromagnetic sheet engaging the top surface of the pickup and the other facing the strings, each ferromagnetic sheet covering a substantial portion of a surface of the permanent magnet sheet.

22. A signal modification device for an electromagnetic pickup for a musical instrument having a plurality of magnetic strings, according to claim 21, in which each further ferromagnetic sheet comprises two ferromagnetic sheet members aligned with each other and spaced from each other by a short air gap extending transversely to the strings.

23. A signal modification device for an electromagnetic pickup for a musical instrument having a plurality of magnetic strings, according to claim 22, for use with a pickup having a plurality of magnetic poles, one for each string, in which each further ferromagnetic sheet member includes a plurality of apertures, each aperture aligned with one pickup pole.

24. A signal modification device for an electromagnetic pickup for a musical instrument having a plurality of magnetic strings, according to claim 23, for use with a musical instrument having n strings and a pickup having n poles, in which each ferromagnetic sheet member includes n/2 apertures aligned with alternate pickup poles, the apertures in one ferromagnetic sheet member being aligned with different poles than the apertures in the other ferromagnetic sheet member.

25. A signal modification device for an electromagnetic pickup for a musical instrument having a plurality of magnetic strings, according to claim 24 in which each ferromagnetic sheet member also includes n/2 projections aligned with and extending into the apertures in the other ferromagnetic sheet member.

26. A signal modification device for an electromagnetic pickup for a musical instrument having a plurality of magnetic string, according to claim 25, in which each of the ferromagnetic sheet members is appreciably smaller than the permanent magnet sheet and includes a multiplicity of peripheral projections extending from the ferromagnetic sheet member toward one side edge of the permanent magnet sheet.

27. A signal modification device for an electromagnetic pickup for a musical instrument having a plurality of magnetic strings, according to claim 21, in which each sheet of ferromagnetic material includes a multiplicity of apertures, plural apertures for each string.

28. A signal modification device for an electromagnetic pickup for a musical instrument having a plurality of magnetic strings, according to claim 2, for use with a pickup having at least one magnetic pickup pole projecting a given height above the pickup housing, in which the mounting means includes a support member having a thickness approximately equal to that given height, through which the pickup pole projects, for supporting the permanent magnet above the top of the pickup pole.

29. A signal modification device for an electromagnetic pickup for a musical instrument having a plurality of magnetic strings, according to claim 28, for use with a pickup having plural magnetic pickup poles, one for each string, in which the support member has plural apertures, one for each pickup pole.

30. A signal modificaiton device for an electromagnetic pickup for a musical instrument having a plurality of magnetic strings, according to claim 2, in which the signal modification device further comprises at least one thin, non-magnetic film covering one side of the permanent magnet member and bonded to the permanent magnet member to protect the signal modification device.

31. An add-on signal modification device for modifying at least one of the amplitude, frequency, and reverberation characteristics of the output signal of an electromagnetic pickup for a musical instrument having a plurality of magnetic strings, the pickup including a magnetic structure for generating a magnetic field, the magnetic structure including at least one permanent magnet, at least one pole piece, and an electrical pickup coil disposed in encompassing relation to the pole piece, all mounted in a housing adapted for mounting on a musical instrument with the to surface of the pickup facing the magnetic strings and the magnetic field of the pickup intersecting a predetermined portion of the strings so that vibration of each string generates an electrical output signal in the coil, the pickup having a top of predetermined size and configuration, the signal modification device comprising:

a thin, flat base member having a configuration and size corresponding generally to that of the pickup top;

and at least one thin, flat, paramagnetic principal permanent magnet member, magnetized transversely to its thin dimension, mounted on the base member in alignment with at least one of the strings,

the modification device being adapted for mounting of the base member on the top of the pickup between the pickup and the strings so that the magnetic field of the permanent magnet member of the modification device modifies the magnetic field of the pickup and thereby modifies the output signal of the pickup.

32. A signal modification device for a electromagnetic pickup for a musical instrument having a plurality of magnetic strings, according to claim 31, in which the base member is formed of a non-magnetic material.

33. A signal modification device for an electromagnetic pickup for a musical instrument having a plurality of magnetic strings, according to claim 32, in which the non-magnetic material of the base member is a resin.

34. A signal modification device for an electromagnetic pickup for a musical instrument having a plurality of magnetic strings, according to claim 33, in which the signal modification device further comprises at least one thin, non-magnetic film covering one side of the base member and bonded to the base member to protect the signal modification device.

35. A signal modification device for an electromagnetic pickup for a musical instrument having a plurality of magnetic strings, according to claim 31, in which the signal modification, device comprises a plurality of thin, flat, paramagnetic high energy principal permanent magnet members each mounted on the base member with at least one principal permanent magnet member aligned with each string.

36. A signal modification device for an electromagnetic pickup for a musical instrument having a plurality of magnetic strings, according to claim 35, in which the base member is formed of a non-magnetic material.

37. A signal modification device for an electromagnetic pickup for a musical instrument having a plurality of magnetic strings, according to claim 36, in which the non-magnetic material of the base member is a resin.

38. A signal modification device for an electromagnetic pickup for a musical instrument having a plurality of magnetic strings, according to claim 37, in which the signal modification device further comprises at least one thin, non-magnetic film covering one side of the base member and bonded to the base member to protect the signal modification device.

39. A signal modification device for an electromagnetic pickup for a musical instrument having a plurality of magnetic strings, according to claim 35, in which the base member is a sheet of resin impregnated with particulate permanent magnet material that affords a paramagnetic permanent magnet of much lower energy than the principal permanent magnets and in which at least a portion of the base member is magnetized in a direction transverse to its thin dimension.

40. A signal modification device for an electromagnetic pickup for a musical instrument having a plurality of magnetic strings, according to claim 39, for use with a musical instrument having n strings, the signal modification device having at least n principal permanent magnet members, and further having n portions of the base member, each aligned with one string, magnetized in a direction transverse to the thin dimension of the base member.

41. A signal modification device for an electromagnetic pickup for a musical instrument having a plurality of magnetic strings, according to claim 40, in which the signal modification device further comprises a least one thin, non-magnetic film covering one side of the base member and bonded to the base member to protect the signal modification device

42. A signal modification device for an electromagnetic pickup for a musical instrument having a plurality of magnetic strings, according to claim 35, in which the surface area of principal permanent magnet members for some of the strings is different than for other strings.

43. A signal modification device for an electromagnetic pickup for a musical instrument having a plurality of magnetic strings, according to claim 31, in which the device further comprises mounting means, affixed to the base member, for mounting the base member on the top of the pickup.

44. A signal modification device for an electromagnetic pickup for a musical instrument having a plurality of magnetic strings, according to claim 43, in which the mounting means includes at least one rim element on the base member that engages the side of the pickup device housing.

45. A signal modification device for an electromagnetic pickup for a musical instrument having a plurality of magnetic strings, according to claim 44, in which the rim element is of elongated configuration and engages a major portion of one side of the pickup housing.

46. A signal modification device for an electromagnetic pickup for a musical instrument having a plurality of magnetic strings, according to claim 44, in which there are at least two rim elements engaging opposite sides of the pickup housing.

47. A signal modification device for an electromagnetic pickup for a musical instrument having a plurality of magnetic strings, according to claim 31, in which the signal modification device further comprises at least one thin, non-magnetic film covering one side of the base member and bonded to the base member to protect the signal modification device.

Description Submit all comments and votes

BACKGROUND OF THE INVENTION

For many years, electromagnetic pickups have been utilized on musical instruments having steel strings. Such pickups have been employed with guitars, bass guitars, banjos, mandolins, and a variety of other instruments. An electromagnetic pickup for a musical instrument incorporates a magnetic structure for generating a magnetic field that intersects a portion of the instrument strings; the magnetic structure of the pickup includes at least one permanent magnet and frequently has a separate high-permeability pole piece for each string. On the other hand, some electromagnetic pickups have a single pole that spans a number of strings. The pickup has an electrical coil or coils to generate a signal which is subsequently amplified and reproduced by a speaker or other transducer as the audio output of the musical instrument. The coils are customarily disposed in encompassing relation to the magnetic core or cores. This relatively simple electromagnetic structure is fitted into a housing that may or may not be part of the magnetic structure. Whether or not a part of the magnetic structure, a principal purpose of the housing is to protect the pickup from dirt and other contaminants.

A wide variety of individual constructions have been used for electromagnetic pickups employed with musical instruments such as guitars. Frequently, the efforts of the pickup designer have been directed toward achieving an output signal from the electrical coil that is as close as possible to a faithful reproduction of the sound that would be developed by the instrument functioning as an acoustical device. This is not always the case, however; some electromagnetic pickups have been designed to give a particular distortion deemed desirable by the designer or by a musician.

For electromagnetic pickups in general, as applied to musical instruments having steel or other ferromagnetic strings, there may be a problem in obtaining an output signal of sufficient amplitude. This may be a minor problem, with modern electronic technology, because a very weak signal can often be adequately amplified. On the other hand, a reasonable output amplitude is desirable because it reduces the necessity for subsequent amplification, and thus reduces the likelihood of inadequately controlled distortion. An output signal of appreciable amplitude also aids in achieving an acceptable signal-to-noise ratio

A more pronounced problem, in most electromagnetic pickups for musical instruments has to do with the frequency response. The overall "sound" derived from the output signal is usually critical to the requirements of the musician. Some musicians want to have the output signal as close as possible to the acoustic output of the instrument, at least in theory. Others, however, want to have a distortion that is acceptable to them, one that represents their own concept or technique for interpretation of music. The frequency response characteristics of the pickup are critical in this regard. A similar situation is presented by the sound characteristic known to musicians as "sustain"; sometimes accented "sustain" is desirable in the view of the musician using the pickup and sometimes it is not.

SUMMARY OF THE INVENTION

It is a primary object of the invention, therefore, to provide a new and improved add-on device for modifying at least one of the amplitude, frequency, and "sustain" characteristics of the output signal of an electromagnetic pickup for a musical instrument having a plurality of magnetic strings, an add-on device which can be employed with a variety of different pickup constructions.

Another object of the invention is to provide a new and improved add-on modification device for an electromagnetic pickup for a plural magnetic string musical instrument that appreciably increases the amplitude of the output signal, regardless of substantial variations in the construction and operation of the pickup itself.

Another object of the invention is to provide a new and improved add-on signal modification device for an electromagnetic pickup for a musical instrument having plural electromagnetic strings that produces different frequency emphasis effects in the output signal from the electromagnetic pickup.

A specific object of the invention is to provide a new and improved add-on modification device for an electromagnetic pickup for a plural magnetic string instrument, particularly a guitar, that is simple and inexpensive in construction, that can be readily mounted upon a pickup, and that has indefinite life, producing the effects noted above without requiring any change in the pickup itself.

Accordingly, the invention relates to an add-on signal modification device for modifying at least one of the amplitude, frequency, and "sustain" characteristics of the output signal of an electromagnetic pickup for a musical instrument having a plurality of magnetic strings. The pickup includes a magnetic structure for generating a magnetic field, the magnetic structure including at least one permanent magnet, at least one pole piece (the magnet may be the pole piece), and an electrical pickup coil disposed in encompassing relation to the pole piece, all mounted in a housing adapted for mounting on a musical instrument with the top of the pickup facing the magnetic strings and the magnetic field of the pickup intersecting a predetermined portion of the strings so that vibration of each string generates an electrical output signal in the coil. The pickup has a top of predetermined size and configuration. The add-on signal modification device comprises a thin, flat, permanent magnet member, magnetized transversely to its thin dimension. Mounting means are provided for mounting the permanent magnet member of the signal modification device on top of the pickup, between the pickup and the strings, so that the magnetic field of the permanent magnet member modifies the magnetic field of the pickup and thereby modifies the output signal of the pickup.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of an electromagnetic pickup for a guitar, equipped with an add-on signal modification device constructed in accordance with one embodiment of the present invention;

FIG. 2 is a side elevation view of the pickup and the add-on signal modification device of FIG. 1;

FIG. 3 is a detail view taken approximately as indicated by line 3--3 in FIG. 2;

FIG. 4 is a plan view of an add-on signal modification device, for an electromagnetic pickup, constructed in accordance with another embodiment of the invention;

FIG. 5 is an end view of the device of FIG. 4;

FIG. 6 is a plan view of a different embodiment of the invention;

FIG. 7 is a sectional view taken approximately as indicated by line 7--7 in FIG. 6;

FIG. 8 is a plan view of yet another embodiment of the invention;

FIG. 9 is a bottom view of a component that may be employed in the device of FIG. 8;

FIG. 10 is a sectional view taken approximately as indicated by line 10--10 in FIG. 8;

FIG. 11 is a sectional view illustrating a further embodiment of the invention;

FIGS. 12-15 illustrate other modifications of the magnetization patterns that can be used in the invention, particularly the add-on signal modification devices of FIGS. 1-5;

FIG. 16 is a perspective view of an add-on signal modification device according to another embodiment of the invention;

FIGS. 17-19 illustrate modifications of the device of FIG. 16; and

FIG. 20 is a sectional view of another modification of the device of FIG. 16.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1-3 illustrate a signal modification device 20 constructed in accordance with a first embodiment of the present invention, mounted as an add-on device upon an electromagnetic pickup 21 for a musical instrument (e.g., a guitar). Pickup 21 has a base plate 22 that is affixed to the top 23 of a musical instrument having a plurality of magnetic strings 24. Thus, strings 24 may be the strings of a guitar, the strings extending above and in spaced relation to the top surface 23 of the guitar neck or body, depending upon where the pickup is mounted. Appropriate mounting devices 25 secure pickup 21 on the guitar body 23.

As previously noted, a wide variety of different magnetic constructions have been utilized for the electromagnetic pickup 21. Consequently, no specific magnetic structure has been shown for the pickup in FIGS. 1-3. However, any electromagnetic pickup 21 on which the signal modification device 20 may be employed should include a magnetic structure for generating a magnetic field, that magnetic structure including at least one permanent magnet and at least one pole piece; the magnet may be the pole piece. For the construction shown in FIG. 1, it is assumed that there are six pole pieces 26, one for each string 24 (see FIG. 1). On the other hand, as previously discussed, a single pole piece may serve all of the strings 24.

Pickup 21 includes an electrical pickup coil, not shown, that is disposed in encompassing relation to the pole pieces 26. In some constructions there may be six separate coils, all connected together. All operating elements of pickup 21, including the pole pieces, the permanent magnet (or magnets), and the electrical pickup coil (or coils), are disposed in a single pickup housing 27 that includes base 22. Fasteners 25 thus mount housing 27 on the surface 23 of the guitar s that the top surface 28 of the pickup housing faces strings 24 and the magnetic field or fields generated by pickup 21 intersect strings 24. Consequently, vibrations of strings 24 generate electrical output signals in the coil of pickup 21, in the usual manner.

The add-on modification device 20, one embodiment of the present invention, is quite simple in construction. It comprises a thin, flat permanent magnet sheet 31. Usually, sheet 31 is formed of a resin material, preferably relatively flexible and slightly elastomeric, that has been heavily impregnated with particulate permanent magnet material. Such permanent magnet resin sheets are readily available commercially. One acceptable permanent magnet resin material is made and sold by 3M Company under the trademark PLASTIFORM; another permanent magnet resin material that may be utilized in device 20 for the permanent magnet 31 is made and sold by B.F. Goodrich Company under the trademark KOROSEAL. A permanent magnet resin material of this kind typically has a maximum energy product (BH) of 1.6 or less; the material is paramagnetic and has a permeability only slightly above unity. A permeability of 1.07 is typical.

As indicated in FIGS. 2 and 3, the permanent magnet strip or sheet 31 is magnetized transversely to its thin dimension; thus, sheet 31 is magnetized vertically as shown in these two figures. The permanent magnet strip has a configuration corresponding approximately to that of the top surface 28 of pickup housing 27; some variation is acceptable. Thus the permanent magnet sheet 31 covers most of the top surface 28 of pickup 21 and preferably covers all of that part of the pickup housing surface 28 that is located below strings 24. In the add-on modification device 20 of FIGS. 1-3, the permanent magnet 31 is shown as being slightly narrower and somewhat shorter than pickup housing surface 28; it should be nearly as wide as the housing and, indeed, may exceed both the housing width and housing length slightly.

The modification device 20, being designed for addition to an existing pickup, preferably includes mounting means, affixed to the permanent magnet sheet 31, for mounting that sheet on the top surface 28 of a pickup housing, such as the housing 27 of pickup 21. In the construction shown in FIGS. 1-3, the mounting means comprises an edge portion or rim 33 that is affixed to three sides of the permanent magnet sheet 31. This edge portion 33 of device 20 may be formed of molded or extruded resin and can be joined to the edges of permanent magnet sheet 31 by adhesive bonding, ultrasonic welding, or any other desired bonding technique The edge portion 33 of device 20 extends down along the side walls of housing 27 for pickup 21 and serves as an aid to anchoring permanent magnet sheet 31 of device 20 on the top 28 of pickup 21. The magnetic field of permanent magnet 21 also plays a major part in maintaining the permanent magnet sheet 31 on the top of housing 27, due to magnetic attraction between pickup poles 26 and the add-on magnet 31. For this purpose it may be necessary to magnetize sheet 31 in the opposite direction to that illustrated in FIGS. 2 and 3, depending upon the orientation of the permanent magnet fields in poles 26 of pickup 21.

The operational effect of the add-on signal modification device 20 on pickup 21 depends in part on the normal construction and operational of the pickup. For virtually any pickup construction, device 20 materially increases the amplitude of the output signal. In addition, the add-on modification device 20 usually affects the frequency response of pickup 21 so that its output signal places greater emphasis upon either high or low frequency components, depending upon the specific construction employed in the pickup. Some experimentation may be necessary in this regard. In addition to altering the frequency response, in most instances, device 20 modifies the "sustain" characteristics for the output signal from electromagnetic pickup 21.

FIGS. 4 and 5 illustrate another add-on signal modification device 40 constructed in accordance with the invention. Device 40 can be substituted directly for device 20 in FIGS. 1-3. The overall effect on the output from electromagnetic pickup 21 may be appreciably different, however, when device 40 is used, from that afforded by the previously described modification device 20.

Device 40 comprises a thin, flat permanent magnet sheet 41. Again, sheet 41 may be formed of a flexible resin impregnated with particulate permanent magnet material. That is, sheet 41 may be formed of the same kinds of permanent magnet materials as the sheet 31 of device 20. Moreover, the permanent magnet sheet 41 of modification device 40 is again magnetized in a direction transverse to its thin dimension. However, the magnetization of the permanent magnet 41 is not uniform throughout its surface. Thus, the central portion 44 of the permanent magnet strip or sheet 41 is magnetized so that its upper, outer surface constitutes a north pole and its inner, lower surface, facing a pickup, is a south pole. On each side of sheet 41, however, there is a narrow strip 45 that is magnetized in the opposite direction. Thus, each side strip 45 of sheet 41 is magnetized so that its upper, outer surface is a south pole and its lower, inner surface is a north pole. As before, the permanent magnet sheet 41 may be provided with a rim 43 to aid in mounting the sheet on an electromagnetic musical instrument pickup (e.g., pickup 21, FIGS. 1-3).

The add-on signal modification device 40 of FIGS. 4 and 5, like device 20 of FIGS. 1-3, usually increases the amplitude of the output signal from an electromagnetic musical instrument pickup with which it is associated, such as pickup 21 of FIGS. 1-3. It also modifies the frequency and "sustain" response characteristics of the pickup. As before, the overall effect on these response characteristics of the pickup depend in substantial part upon the construction employed in the pickup itself, as well as the construction of the modification device 40.

FIGS. 6 and 7 illustrate another signal modification device 50, used as an add-on device for modifying operating characteristics of the output signal from an electromagnetic pickup 51 for a stringed musical instrument. In FIGS. 6 and 7 the add-on device 50 is shown mounted on top of the housing 57 of the electromagnetic pickup 51, the pickup being secured to the surface of a guitar, banjo, or other like musical instrument by appropriate fasteners 55 that extend through a base plate 52 for the pickup (FIG. 6) The strings 54 of the instrument, which of course must also be of steel or other magnetically permeable material, extend across but are spaced from the top 53 of the pickup housing 57; see FIG. 7.

The add-on signal modification device 50 includes a thin, flat, permanent magnet sheet 61 of the same type as used in previously described embodiments. Permanent magnet 61 is magnetized transversely to its thin dimension and has a configuration approximately corresponding to that of the top surface 53 of pickup 51. Like permanent magnet 31 of the embodiment of FIGS. 1-3, permanent magnet 61 may be uniformly magnetized throughout its area.

Pickup device 50, however, includes four steel strips 62, 63, 64 and 65. Each of these steel strips 62-65 should be formed from ferromagnetic stock. Each includes a multiplicity of external projections 66 along the edge of the strip. Each of the steel strips 62-65 also includes a plurality of central projections 67 that are received in indentations 68 in the mating steel strip. Thus, as shown in FIG. 6, the ferromagnetic strip 62 has a plurality of projections 67 that fit into indentations 68 in the strip 63 that is aligned with strip 62 on top of permanent magnet 61. Similarly, strip 63 has a plurality of projections 67 that fit into indentations 68 in strip 62. Each projection 67 is aligned with one of the strings 54 of the musical instrument o which pickup 51 is mounted. The overall result is a space 69, shown exaggerated in FIG. 7, between the two steel strips 62 and 63; space 69 extends for the full length of the signal modification device 50, with one of the projections 67 under each string 54 (FIG. 6). The strips 64 and 65 on the opposite side of permanent magnet 61 (FIG. 7) have the same configuration as the upper, outer strips 62 and 63 and are preferably aligned with the upper, outer strips. Thus, device 50 can be mounted on housing 53 with strips 62 add 63 facing strings 54, as shown, or may be mounted with strips 64 and 65 facing the strings if the polarity of the pickup poles 56 requires reversal of magnet 61.

The add-on signal modification device 50, FIGS. 6 and 7, has the effect of increasing the amplitude of the pickup output signal; in that respect, it is similar to the modification devices of previous figures. For a pickup with individual magnet poles for the individual instrument strings 54, such as poles 56 (FIG. 6), steel plates 62-65 modify overall operation so that the output signal from pickup 51 exhibits characteristics more closely simulating those of a single-core electromagnetic pickup as in U.S. Pat. No. 4,809,578, even though the pickup itself may be a multi-pole device like that shown in U.S. Pat. No. 3,236,930. Stated differently, the ferromagnetic plates 62-65 function as a mounting means to aid in affixing permanent magnet 61 to pickup 51 and also have a substantial effect on the frequency and "sustain" response characteristics of the output signal from pickup 51.

FIGS. 8-10 illustrate another add-on signal modification device 70 for modifying the operational characteristics of the output signal of an electromagnetic pickup 71. It may be assumed that pickup 71 employs an internal construction of the kind described in U.S. Pat. No. 4,809,578, which has a single elongated central core or pole piece that spans all of the strings 74 of a guitar or other musical instrument on which pickup 71 is mounted. Pickup 71 has a base 72 (FIG. 8) with fasteners 75 used to mount the base on the surface of a guitar or like instrument (not shown). Modification device 70 is mounted on the top of pickup 71; see FIG. 10.

Device 70 includes a thin, flat permanent magnet 81 (FIG. 10). This permanent magnet is preferably formed from a sheet of elastomeric resin impregnated with particulate permanent magnet material, such as the aforementioned PLASTIFORM and KOROSEAL materials. As in the previously described embodiments, the permanent magnet sheet 81 is magnetized in a direction transverse to its thinnest dimension; see FIG. 10. Furthermore, as is apparent from FIGS. 8 and 10, the permanent magnet sheet 81 has a configuration corresponding generally to that of the upper surface 73 of the housing of pickup device 71.

The add-on signal modification device 70 of FIGS. 8-10, being designed for use on an existing pickup 71, includes mounting means for mounting the device on the pickup; in this instance the mounting means comprises four steel sheets or strips 82-85, all affixed to the permanent magnet sheet 81. Sheets 82 and 83 are on the top surface of permanent magnet 81; each is provided with a pattern of apertures 86 corresponding to a multiplicity of projections or teeth on the central core of pickup 71 as described in the aforementioned U.S. Pat. No. 4,809,578. The steel plates or sheets 82 and 83 do not contact each other; instead, there is an elongated gap 88 between the two steel sheets. Steel sheets 84 and 85, on the other hand, are mounted on the bottom surface of permanent magnet 81. Each is provided with a plurality of indentations or slots 87 that are aligned with the apertures 86 in the two top steel strips 82 and 83. Again, the steel strips 84 and 85 do not engage each other; they are separated by a longitudinal gap 89. Modification device 70 may also include a plurality of tabs 90 affixed to the permanent magnet 81 or to the upper steel strips 82 and 83. Tabs 90 project downwardly, engaging the sides of the housing for pickup 71 to help maintain device 70 in place on the top surface 73 of the pickup.

The add-on signal modification device 70, like previously described embodiments, enhances the amplitude of the output signal from the pickup 71 with which it is used. Furthermore, device 70 modifies the frequency and "sustain" characteristics of that output signal so that the overall audio output produced by a transducer such as a loudspeaker, employing the pickup signal following amplification, has a different timbre and overall "sound" than would otherwise be obtained by pickup 71.

FIG. 11 illustrates yet another embodiment of the present invention in the form of an add-on signal modification device 100 mounted upon and utilized to modify the output of a pickup generally indicated at 91. Pickup 91 is of the type, such as the pickup shown in U.S. Pat. No. 3,236,930, that has an individual permanent magnet or permanent magnet pole for each string 94 of the musical instrument. In FIG. 11 only one of these poles or magnets 96 is shown. In this pickup construction, however, each pole 96 projects above the top wall 93 of pickup 91. As a consequence, if the signal modification device 100 were mounted only on the tops of poles 96, it would be quite unstable.

In device 100 this situation is obviated by a support member 106, preferably formed of molded resin material, that fits onto the top 93 of pickup 91. Support 106 may have rim elements 107 that engage the side walls of the housing of pickup 91 to further stabilize the mounting of device 100 on