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Description  |
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BACKGROUND OF INVENTION
1. Field of the Invention
This invention relates to electrical pickups adapted for use with
multistringed musical instruments having strings formed of ferromagnetic
material to produce an output signal, the amplitude of frequency of which
is representative of the vibrations of a ferromagnetic string. In the
preferred embodiment, an electromagnetic pickup is adapted for use with a
guitar or electric bass guitar.
2. Description of Prior Art
The use of electrical pickups for stringed musical instruments having
ferromagnetic strings is well known in the art. The modern commerical
trends seem to point to the hum cancelling type pickups that in the most
common instances are in the single coil stacked position or the double
coil side by side arrangement. U.S. Pat. No. 4,524,667 describes an
example of the former, and U.S. Pat. No. 4,501,185 describes an example of
the latter.
Most of modern commercial pickups have an oblong shaped coil form usually
molded in plastic having hollow cavities through the said coil form
wherein a magnetic iron cylinder, cylindrical magnet or threaded iron core
with screw adjustment being fitted into each above said cavity.
U.S. Pat. Nos. 4,442,749, 4,026,178 and 4,133,243 feature one of the above
core embodiments. Unfortunately sound vibrations in the air may be
transmitted to the pickup and may set one or more internal parts of the
pickup into resonant vibration to produce accompanying flux changes in
output signals at the resonant frequency which, through positive feedback,
sustain the resonant vibration and produce microphonic or squealing sounds
from the speaker or speakers. The high material density of the
conventional iron cores that fill the coil form cavities, relative high
density of plastic coil forms in combination with the coils and the very
close positions of said components to one another offer a disadvantage
relating to suppressing microphonics. A feature in U.S. Pat. No. 3,962,946
deals with the above problem by separating each magnet from the major
portion of its opening wall by a vibration dampening layer of silicon
rubber or other resilient material. Resilient pads are also placed between
the pickup housing and pickup parts enclosed thereby for the same purpose.
U.S. Pat. No. 3,962,946 discloses a pickup with a cup-shaped housing member
having two side walls and a top wall made of brass and electrically
connected to a base plate, forming an electric shield. U.S. Pat. No.
4,364,295 discloses a pickup shielding means by electro-depositing
conducting metal onto a plastic form. The difficulty here is that dies or
molds are very costly in regards to metal stamping and mold injection
forms. This cost may not be a hardship to a large manufacturer, but maybe
cost impractical to a small manufacturing entity.
Sound pickups of the humbucking type require very accurate positioning of
the components, assembly and set up being tedious and costly, having
delicate coil assemblies and sometime brittle magnets and are often
subjected to rough handling.
SUMMARY OF THE PRESENT INVENTION
The invention relates to a new, novel and unique electrical pickup for a
stringed musical instrument having ferromagnetic strings. In the first
embodiment, the electrical pickup includes a pair of axially spaced coils,
each of said coils mounted within a bushing, said bushing made of flexible
rubber-like plastic. The above said magnetic bushings having a hollow
cylindrical shape with thin walls are pressed and fixed into a hollow
cavity in the pickup body, said block-like body made of non-magnetic
material preferably wood. The coil is axially wound around a round
bobbin-like form preferably made of wood or relative low density materials
like wax impregnated paper or cardboard, although plastic will work as a
latter preferred embodiment. The winding axis of coils and coil forms are
perpendicular to the plane of strings on the musical instrument. The
pickup housing is in the shape of a rectangular solid having two large
surfaces, said surfaces having a top surface facing said strings and
having a bottom surface positioned away from said strings. Electrical
shielding means are fixed to the surface and within pickup body cavities,
said means being a non magnetic electrical conducting sleeve or electrical
conducting paint; having a non-magnetic electrical conducting plate
attached to the top of the pickup body, a non- magnetic electrical
conducting plate attached to the bottom of pickup, the said former and
latter plates electrically connected to the shield within the pickup body
cavity walls. Sound producing means being a pair of electrically insulated
conducting coils electrically connected in series in an out of phase
relationship. The magnetic polarities of the inner surfaces of said
magnets are reversed to one another. Each coil assembly may work with a
plurality of strings and arranged as to increase the effectiveness of the
pickup. All inside adjoining surfaces of said pickup are tight fitting and
fixed with a super glue type of penetrating adhesive that upon complete
assembly results in a near solid block-like mass.
In the second embodiment of the pickup of the present invention the above
pair of hollow magnetic cylinders are replaced by one flexible rubber-like
plastic magnet, formed by looping a straight magnetic strip into a figure
eight configuration; each cavity within the hollow loop of the figure
eight configuration shape magnet accepts a coil assembly. The entire
surface face of the inside of the first magnetic loop having a polarity
opposite to the entire inside surface of the second loop.
In the third embodiment of the present invention a stacked co-axial
arrangement may be employed having one pair of conducting coils, said
coils wound axially in opposite directions, a winding axis perpendicular
to the plane of the strings, said coils wound on an oblong shaped coil
form, first coil winding electrically insulated from second coil winding
by a thin paper-like spacer, said coils electrically connected in a series
out of phase relationship. Magnetic means being a permanent flexible
magnet formed in the shape of a hollow oblong bushing, the inside face of
the said hollow magnet having a N polarity at the top and S polarity at
the bottom, the outside face of said magnet having a N polarity at the top
and a S polarity at the bottom.
It is a primary objective of the present invention to provide a new and
improved sound pickup for a stringed musical instrument having low
material cost, fast and easier assembling, all components lending
themselves to be formed and fabricated utilizing a basic inexpensive
production and tooling setup.
Yet another object of the present invention is to provide a new and
improved sound pickup which can withstand rough handling and take physical
abuse.
Yet another object of the present invention is to provide a new and
improved sound pickup that produces a high quality tone of an improved and
novel nature.
Yet another object of the present invention is to provide a new and
improved sound pickup having an improved shielding means.
Yet another objective of the present invention is to provide a new and
improved pickup having a low magnetic draw on the strings and improve
string sustain.
Yet other advantages of the present invention are that the simple
geometrical configurations of the pickup components lend themselves well
to simplifying the alignment of machine tool operations assembly and jig
set-ups.
Yet another advantage of the present invention is that sound producing
means is accomplished very economically and simply by sandwiching the
pickup body between two flat non magnetic electrical conducting plates,
brushing the inside surface of the pickup body cavity or cavities with
electrical conducting paint and electrically connecting them; thus
eliminating the need for a dish shaped stamped metal or electroformed
shielding cover; the initial expense of making dies for such cover being
very costly and cost inefficient for a small production run.
Another advantage of the present invention is that the magnet, coil and
bobbin assemblies are positioned in a tight fitting relationship in
regards to their locations and are pressed into the pickup body, glued
with a penetrating type of super glue, sandwiched between a flat metal
cover plate on top and a flat metal base plate on the bottom of said
pickup body; said cover and base plates fixed to pickup body with
non-ferrous screws.
Yet another advantage of the present invention is that the permanent magnet
or magnets can be made of a rubber-like plastic flexible material which
has a low cost.
Yet another advantage of the present invention is that a rubber-like
plastic magnet can easily be shaped into a bushing or looped into a figure
eight configuration having two hollow cavities;the rubber-like walls of
the above mentioned magnets suppressing microphonics by internally
dampening the coil windings and coil forms from vibrations travelling
through the air and through the pickup body.
Another advantage of the present invention is that there is no need for an
iron or a magnetic core member to be positioned or fitted through and
along the central axis of the coil form being an improvement in regards to
suppressing microphonic squeal in the central axis section of the coil
windings.
Yet another advantage of the present invention is that because a hollow
opening to fit a core assembly is not needed in the axis position in the
coil forms, the improvement being more space available on a coil form to
accept more turns of coil winding wire or accommodate heavier gauge coil
wire if so desired.
Yet another advantage of the present invention is the improvement regarding
directing a strong fixed field of magnetic flux through the coil means in
combination with a weak path of magnetic flux in the string area thereby
producing an improved tone of novel quality; magnetic flux passes almost
directly into coil means through a very small distance between the inner
surface of a hollow magnet and the outside surface of the coil which
results in a very dense magnetic field passing through the coil assemblies
and a weaker flux field passing through the strings thereon lessening the
magnetic pull on the strings which will improve sustain. High ratio of
coil surface and magnet surface contact increase signal gain to help
compromise for the weaker flux path above the pickup in the string region.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a top plan view with upper shield cover removed representing one
embodiment of the electromagnetic pickup of the present invention:
FIG. 2 is a sectional view of the embodiment of FIG. 1:
FIG. 3 is a top plan view with shielding cover removed of another
embodiment of the electromagnetic pickup of the present invention:
FIG. 4 is a view of the magnet assembly of the embodiment of FIG. 3:
FIG. 5 is yet another top plan view with shielding cover removed of the
electromagnetic pickup of the present invention:
FIG. 6 is a sectional view of the embodiment of FIG. 5:
FIG. 7 and 8 each present a crossectional view showing lines of magnetic
force being directed from a permanent magnet means into one of the strings
of the musical instrument and relates to various embodiments of the
invention.
FIG. 9 is a wiring diagram of a pair of coils relating to various
embodiments of the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring now to FIGS. 1, 2, is a version of the magnetic pickup 10 as
referred to in the first embodiment in the SUMMARY OF THE PRESENT
INVENTION. The transducer 10 includes a base plate 12 of brass or similar
rigid, non-magnetic material, suitable for mounting purposes. The base
plate 12 includes a mounting foot plate 12a at each of its two ends, used
to mount the pickup onto a stringed musical instrument (not shown) such as
a guitar, mandolin, or bass guitar. The strings of said guitar instrument
are shown schematically in FIG. 1 by the dashed lines designated 14. A
pickup body 18, made of non-metallic material preferably wood or plastic
is positioned longitudinally below strings 14. The pickup body 18 has two
hollow cavities 18a and 18b; non-metallic electrical conducting paint 20
is fixed to the inside surface of the cavity walls 18a and 18b. A pair of
hollow cylindrical permanent magnets 2 and 3 made of flexible rubber-like
plastic material are shaped into a hollow bushing. The entire inside
surface 2a of magnet 2 is polarized having a N polarity and the entire
outside surface 2b of magnet 2 is polarized having a S polarity. The
entire inside surface 3a of magnet 3 is polarized having a S polarity and
the entire outside surface 3b of said magnet is polarized having a N
polarity. Magnet 2 is fitted within cavity 18a, magnet 3 is fitted within
cavity 18b, magnet 2 and 3 having their inside axis perpendicular to the
surface of strings 14. The top surface of magnets 2 and 3 fitting flush
with top of pickup body 18, and the lower surface of magnets 2 and 3
disposed a bit shallow within cavities 18a and 18b. FIG. 2 shows a pair of
identical shaped coil forms 6, 7 wherein the top surface 6b of coil form 6
being circular, and the base 6a of coil form 6 radially extending outward
forming a flange 6a, the top surface 7b of coil form 7 being circular, and
the base 7a of coil form 7 radially extending outward forming a flange 7a.
The top 6b, 7b of coil forms 6, 7, may be removed (not shown) after
insertion within magnet means 2, 3; wax poured filling space previously
occupied by tops of coil forms 6b and 7b. The preferred material of coil
form 6, 7 being wood although plastic may be used. A coil means 4 is
positioned on the inside of magnet means 2, a coil means 5 is positioned
on the inside of magnet means 3; coil means 4 is axially wound on coil
form 6, coil means 5 axially wound on coil form 7. The winding direction
of coil means 4 being in opposite direction to coil means 5, winding axis
of said coils 4, 5, being perpendicular to surface of strings 14. Coil
means 4, 5, (FIG. 9) being electrically connected in series out of phase
relationship. Completed coil form assembly 4, 6 being disposed into cavity
18a, completed coil form assembly 5, 7 being disposed into cavity 18b,
coil form flange bases 6a, 7a resting flush with the bottom of pickup body
18. Magnetic means 2, 3 (FIG. 7), forms a very dense path of flux 42 (FIG.
7), through the coil assemblies 4, 5. The flux lines 42 pass from the
inside surfaces 2a, 3a of magnetic means 2, 3 through coil means 4, 5
through an air gap 40 (FIG. 7) (not shown) into strings 14. The flux lines
42 flow around and along the string 14 in a radial path back through a
second air gap (not shown) towards the outer edge surfaces 2b, 3b of
magnets 2, 3 forming a magnetic circuit that sweeps each string at
different angles and at varying mode positions resulting in an improvement
in overcoming flat harmonic response in the generated tone when playing
two or more strings. Magnetic means 2, 3 being of soft rubber-like
plastic, effectively dampens physical vibrations traveling through the air
and through the pickup body 18, the improvement here suppressing
microphonics. The pickup body 18, magnetic means 2, 3, coil means 4, 5,
and coil forms 6, 7, are dimensionally formed to a tolerance wherein they
can be made to fit snugly and hold their proper position without shifting
before final gluing within the pickup body 18; wherein the assembly
comprising 2, 3, 4, 5, 6, 7, 18 is dipped in a solution of a thin
penetrating type of super-glue adhesive to permanently fix all parts. A
cover plate 13 made of brass or similar rigid non-magnetic material being
fixed to the top of pickup body 18. Cover plate 13 and base plate 12 are
electrically connected (not shown) to the surface of electrical conducting
paint 20, forming shielding means. Base plate 12 is fixed to the bottom of
pickup body 18, fixing means for base plate 12 and cover 13 being brass
screws. The resulting pickup assembly 10 resembles a near solid
rectangular block-like mass that can withstand physical abuse and is
durable; the simple geometric shape of components offer an improvement in
regards to manufacturing, and simplifying tooling set-up and assembly.
FIG. 3, 4 refers to a second embodiment of the pickup as mentioned above in
the SUMMARY OF THE PRESENT INVENTION. A permanent magnet 15 made of
rubber-like flexible plastic is looped into a figure eight forming two
closed circular cavities 15a and 15b. Magnet 15 is formed from one
straight piece of flexible magnetic strip (not shown); first large surface
of said magnetic strip (not shown) having a first polarity and second
surface of said magnetic strip having a second polarity. The polarity of
entire surface 15a inside the first loop of magnet 15 being N and the
polarity on entire outside surface of said loop 15c being S, the polarity
of entire surface 15b inside the second loop of magnet 15 being S and the
polarity of entire surface 15d outside second loop being N. Pickup body 19
formed with two hollow cavities 24, 25 and a hollow slot 26; magnet 15 is
fitted flush within cavities 24, 25, 26. Coil 4 (FIG. 2), coil form 6
(FIG. 2), are disposed within magnet hollow 15a; coil 5 FIG. 2), coil form
7 (FIG. 2) are disposed within magnet hollow 15b. Electrical conducting
paint 20 being fixed to pickup cavity walls 24, 25, 26 and electrically
connected to base plate 12 (FIG. 2) and cover plate 13 (FIG. 2). Assembly
and fixing details similar to that of the pickup of the first embodiment
mentioned above. The advantages of this embodiment being that one magnet
in a humbucking circuit provides magnetic means, improves method for
suppressing microphonics, and provides mounting means for a pair of coil
and bobbin assemblies.
FIG. 5, 6 refers the third embodiment of the pickup as was disclosed in the
SUMMARY OF THE PRESENT INVENTION. The transducer 10 has one oblong shaped
coil form 34; coil form 34 having a radially extended flange 34a at its
base, the winding axis of coil form 34 being perpendicular to strings 14.
An electrical non-conducting spacer 35 is placed at the center of the coil
form 34 dividing the inside area of coil form 34 into an upper cavity
containing conducting coil 36 and a lower cavity containing conducting
coil 37. Coils 36, 37 are axially wound being perpendicular to the surface
of strings 14. The direction of the winding in coil 36 is opposite to that
in coil 37; coils 36, 37 being electrically connected in series out of
phase relationship. An oblong shaped permanent flexible rubber-like
plastic magnet 38 closely surrounds coil assembly 36, 37. Magnet 38 has a
N polarization on both surfaces of its upper half and a S polarization on
both surfaces of its lower half. Magnet 38 is attached within a hollow
cavity 39a of pickup body 39. A layer of non-magnetic electrical
conducting paint 20 being fixed to the inside of an oblong shaped cavity
39a. Pickup body 39 being preferably made of wood but plastic may be used.
Top surface 34b of coil form 34 and top surface of oblong shaped magnet 38
fit flush with top surface of pickup body 39. Top surface 34b of coil form
34 may be removed after insertion into magnet means 38, wax poured into
space previously occupied by upper coil flange 34b. Lower edge of magnet
38 extends down along pickup cavity wall 39a until it stops a small
distance short of the lower side of pickup body 39. Flanged base 34a of
coil form 34 seats into space left short by the lower end of magnet 38.
Bottom surface of flanged base 34a being flush with the bottom of pickup
body 39. A base plate 12 of brass or similar rigid, non-magnetic material,
suitable for mounting purposes includes a mounting foot plate 12a at each
of its two ends used to attach said pickup onto the stringed instrument
(not shown), a cover plate 13 made of brass or similar rigid, non-magnetic
material are electrically connected to the electrical conducting paint 20
inside pickup body cavity wall 39a forming shielding means. Base plate 12
and cover plate 13 fixed to pickup body 39 with non-ferrous screws. A
dense flux path 42 (FIG. 8) passes from the inside surface 38a of magnet
38 through coils 36, 37 continuing through the air 40 (FIG. 8) above
pickup body 39 sweeping strings 14 in a radial path returning through the
air space 40 below strings 14 to outside surface 38b of magnet 38
completing the magnetic circuit. Assembly and fixing details similar to
method disclosed above relating to the electromagnetic pickup of the first
embodiment.
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