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BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a humbucking pick-up assembly for stringed
musical instruments and, more particularly, to a pick-up assembly for
stringed musical instruments including a magnetized, signal coil and an
unmagnetized, disassociated, humbucking coil.
2. Description of the Prior Art
The present invention relates broadly to electrical musical instruments of
the stringed type. It is particularly applicable to an electrical guitar
or similar musical instrument having a plurality of stretched strings
extending across a body and a neck, between the head of the instrument and
a bridge assembly connected to the body, in which the strings are caused
to vibrate by plucking or picking same.
In order to derive an output from such an electrical guitar or other
similar electrical musical instrument, the instrument is conventionally
provided with an electromagnetic pick-up comprising a number of magnetic
elements (pole pieces) having wound therearound a conductive coil.
Typically, one such magnetic element is disposed directly beneath each
string of the instrument. The strings are constructed of a magnetizable
substance, such as steel, and, therefore, become part of the conductive
path for the magnetic lines of flux of the pole pieces. Accordingly, when
any of the strings are caused to vibrate, this causes a disturbance in the
magnetic field of the associated pole piece. This has the effect of
generating a voltage in the conductive coil, which voltage may be suitably
amplified and transmitted to a loudspeaker system.
With such an electromagnetic pick-up construction, a number of problems
exist. Electric guitars and other similar electrical musical instruments
are used in areas having strong magnetic fields from lighting fixtures,
motors, transformers, and the like, and these magnetic fields are sensed
by the pick-up as an extraneous noise source. In the United States, such
source typically has a frequency of 60 Hz, the usual power line frequency.
These magnetic fields induce voltages in the coil which are also amplified
and transmitted to the loudspeaker system, manifesting themselves in an
objectionable hum.
In order to overcome this problem, it is known to provide a pick-up for an
electrical musical instrument including a pair of identical pick-up
assemblies, each having a plurality of magnetic pole pieces and a coil,
the pick-up assemblies being positionable in parallel, spaced, closely
adjacent relationship. All of the pole pieces of one of the pick-up
assemblies have their north poles adjacent to the strings and their south
poles relatively remote from the strings whereas all of the pole pieces of
the other pick-up assembly have their south poles adjacent to the strings
and their north poles relatively remote from the strings. The coils of the
two pick-up assemblies are wound in opposite directions and the two coils
are connected either in series or in parallel. Because the direction of
current flow in each coil is governed by the magnetic polarity, the
direction of current flow in one coil is opposite to that of the other
coil for each string. However, since the directions of the windings of the
two coils are opposite, the signal induced in each coil as a result of
string vibrations is additive and the output signal is the sum of the
signals induced in each coil.
On the other hand, signals picked up by the coils from power line sources
produce currents in the coils which are independent of the magnetic
polarity and, accordingly, such power line sources produce voltages that
are in phase. However, since the coils are wound in opposite directions,
these in phase signals cancel and the output signal is the difference
between the power line signals induced in each coil. This means that any
noise from power line sources, which is otherwise manifested as an
objectionable hum, is effectively reduced or cancelled. It is for this
reason that such an arrangement is typically characterized as a humbucking
arrangement.
While the use of pairs of pick-up assemblies in a humbucking arrangement is
effective in eliminating extraneous noise, a new problem is created, that
being that the sound produced by a humbucking pick-up assembly is not as
sharp and as clear as that obtainable from a single pick-up assembly. The
reason for this is felt to be that each pick-up assembly of the humbucking
pair interferes with the operation of the other pickp-up assembly of the
pair. This is because the coil of each pick-up assembly acts as a load for
the coil of the other pick-up assembly and the magnetic field of one
pick-up assembly interferes with the magnetic field of the other. Thus, it
would be desirable to provide a humbucking pick-up assembly having the
tone producing qualities of a single coil but this has been unobtainable
heretofore.
SUMMARY OF THE INVENTION
According to the present invention, this problem is solved by providing an
electrical musical instrument of the stringed type with a humbucking
pick-up having the tonal qualities of a single coil pick-up. This is
achieved by the combination of a number of effects. First of all, the
present pick-up includes a pair of pick-up assemblies, only one of which
is magnetized. The first and second pick-up assemblies are physically
disassociated so that the reactance of the unmagnetized pick-up assembly
does not interfere with the magnetized pick-up assembly. The unmagnetized
pick-up assembly is also lowered further into the body of the instrument
than the magnetized pick-up assembly to further disassociate the two
pick-up assemblies. Finally, rather than simply being connected in series
or in parallel, the outputs of the two pick-up assemblies are summed at
the negative input of an operational amplifier, which negative input is a
virtual ground, so that neither coil acts as a load for the other coil.
Briefly, in a pick-up for an electrical musical instrument of the type
including a body, a neck having a head, a bridge assembly connected to the
body and a plurality of strings positioned between the head and the bridge
assembly, the present invention comprises a first pick-up assembly
positioned between the neck and the bridge assembly, the first pick-up
assembly including at least one magnetized pole piece and a coil wound
therearound, a second pick-up assembly positioned in spaced relationship
to the first pick-up assembly, between the neck and the bridge assembly,
the second pick-up assembly including at least one unmagnetized pole piece
and a coil wound therearound, the pole piece of the second pick-up
assembly being spaced from the strings by an amount greater than the
spacing between the pole piece of the first pick-up assembly and the
strings, and first and second resistors for connecting the coils of the
first and second pick-up assemblies, respectively, to the negative input
of an operational amplifier.
OBJECTS, FEATURES AND ADVANTAGES
It is therefore the object of the present invention to solve the problems
encountered heretofore in providing a humbucking pick-up for an electrical
musical instrument of the stringed type. It is a feature of the present
invention to solve these problems by providing a humbucking pick-up for an
electrical musical instrument of the stringed type having a sound which is
characteristic of the sound from a single coil pick-up. An advantage to be
derived is a humbucking pick-up having a far more desirable sound. A
further advantage is a humbucking pick-up including a pair of pick-up
assemblies wherein the interference of one pick-up assembly to the other
is minimal.
Still other objects, features, and attendant advantages of the present
invention will become apparent to those skilled in the art from a reading
of the following detailed description of the preferred embodiment
constructed in accordance therewith, taken in conjunction with the
accompanying drawings wherein like numerals designate like or
corresponding parts in the several figures and wherein:
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a top plan view of an electrical musical instrument of the
stringed type incorporating a pick-up constructed in accordance with the
teachings of the present invention;
FIG. 2 is an enlarged sectional view taken along the cross section of the
pickup in FIG. 1; and
FIG. 3 is an electrical diagram of the pick-up of the instrument of FIG. 1.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now to the drawings and, more particularly, to FIG. 1 thereof,
the present invention is illustrated as being incorporated in an
electrical guitar, generally designated 10, including a body 11, a fretted
neck 12, and a head 13 connected to one end of neck 12, the other end of
neck 12 being connected to body 11. Tensioned between head 13 of guitar 10
and a body-connected bridge assembly 14 are a plurality of strings 15
which generally lie in a single plane parallel to the face of body 11.
Strings 15 are constructed of a magnetizable substance, such as steel, and
are graduated in diameter in a conventional manner.
Positioned on the face of body 11 is a pick guard 16 which is typically
made from plastic or other scratch resistant material. Also mounted on the
face of body 11 is a volume control 17, a tone control 18, and a
two-position switch 19.
In order to derive an output from guitar 10, it is provided with an
electromagnetic pick-up, generally designated 20, which forms the subject
matter of the present invention. Vibrations of strings 15, as a result of
plucking or picking the same, produce an electrical signal in pick-up 20,
which signal may be suitably amplified and transmitted to a loudspeaker
system.
Referring now to FIGS. 1-3, pick-up 20 includes first and second pick-up
assemblies 30 and 40 which are positioned in spaced relationship between
neck 12 and bridge assembly 14. It is unimportant as to whether pick-up
assembly 30 or pick-up assembly 40 is positioned closer to bridge assembly
14. Pick-up assemblies 30 and 40 have some features in common, but are
generally quite different. Each includes a plurality of identical
metallic, unmagnetized elements (pole pieces) 31 and 41, respectively. The
number of pole pieces in each pick-up assembly is preferably identical and
preferably the same as the number of strings 15. However, such is not
required and each pick-up assembly 30 and 40 can have any number of pole
pieces from one or more.
Pick-up assemblies 30 and 40 are generally constructed and mounted in body
11 in a conventional manner. That is, pick-up assemblies 30 and 40 include
upper and lower support plates 33 and 34 and 43 and 44, respectively,
through which pole pieces 31 and 41, respectively, extend and bottom
support plates 35 and 45, respectively, which extend below lower support
plates 34 and 44, respectively. Coils 32 and 42, formed from a large
number of turns of fine conductive wire, are wound around pole pieces 31
and 41, respectively. The wire in coils 32 and 42 is insulated, such as
with varnish or lacquer, and the entire assemblies comprising the pole
pieces, the supporting plates and the coils are preferably dipped in a
suitable varnish or lacquer. Coil 32 extends between support plates 33 and
34 and coil 42 extends between support plates 43 and 44.
As stated previously, the individual pole pieces 31 and 41 are not
magnetized, but are made from a magnetizable substance. Only pick-up
assembly 30 is magnetized and the magnetic field is preferably produced by
positioning a bar magnet 36 in contact with the bases of pole pieces 31.
Preferably, a magnetic keeper 37 also extends along the bottom surface of
magnet 36. It should be particularly noted that pick-up assembly 40 has
neither a bar magnet nor a keeper.
Pick-up assemblies 30 and 40 are positioned within channels 21 and 22,
respectively, in body 11. A spring 38 extends between keeper 37 and the
bottom of channel 21 to urge pick-up assembly 30 upwardly. A cap 39
surrounds and contains the structure of pick-up assembly 30. A plurality
of screws 23 extend through cap 39 and hold pick-up assembly 30 within
channel 21 and body 11. Cap 39 extends through pick guard 16. Accordingly,
the manipulation of screws 23 permits the height of pick-up assembly 30 to
be adjusted. Pick-up 40, on the other hand, does not extend through pick
guard 16 and is captured within channel 22 in body 11 by pick guard 16.
As known in the art, movement of strings 15, as in the strumming or playing
of guitar 10, results in a voltage being induced in coil 32. As will be
described more fully in connection with FIG. 3, this voltage is
transferred to the input circuit of an operational amplifier 50 before
being conducted to a suitable loudspeaker system. On the other hand, since
pole piece 41 is not magnetized, movement of strings 15 does not induce a
voltage therein.
On the other hand, signals picked up by coils 32 and 42 from power line
sources are totally independent of magnetic fields so that both coils 32
and 42 produce currents which are proportional to received noise. Coils 32
and 42 may be wound in opposite directions or otherwise connected in an
out of phase relationship so that these signals cancel. Thus, in a
conventional manner, noise from power line sources, which is otherwise
manifested as an objectionable hum, may be effectively reduced or
cancelled.
Turning now to FIG. 3, first ends of coils 32 and 42 are connected to
circuit ground. The opposite ends of coils 32 and 42 are connected via
resistors 51 and 52, respectively, which are parts of a summing circuit
53, to the negative input of operational amplifier 50, the output of which
is connected to a first terminal 54 of switch 19, switch 19 having another
terminal 55 which is connected directly to coil 32. Switch 19 has an arm
56 which is connectable either to terminal 54 or 55.
Operational amplifier 50 is a conventional circuit well known to those
skilled in the art. It is significant to note that summing network 53
applies the signals from coils 32 and 42 to the negative input terminal of
operational amplifier 50, which is a virtual ground. By making the
junction between resistors 51 and 52 a virtual ground, neither coil 32 nor
coil 42 has any significant loading effect on the other. Additional
circuitry (not shown) will be associated with operational amplifer 50,
such circuitry being well known to those skilled in the art and not
relevant to an understanding of the present invention.
Coils 32 and 42 are each provided with separate tone control circuits 60
and 70, respectively. While such tone control circuits might not be so
simple, for explanation purposes, tone control circuit 60 is shown as
including a variable resistor 61 and a capacitor 62 connected in series
between coil 32 and circuit ground and tone control circuit 70 is shown as
including a variable resistor 71 and a capacitor 72 connected in series
between coil 42 and circuit ground. According to the preferred embodiment
of the invention, variable resistors 61 and 71 are mechanically
interconnected and become the tone control circuit 18 of instrument 10 so
that the magnetized coil 32 and the unmagnetized coil 42 may be balanced
simultaneously.
Coils 32 and 42 are either wound in opposite directions or, if the coils
are wound in the same direction, the opposite ends of the coils are
connected to summing circuit 53. Because coil 42 is unmagnetized, it is
not responsive to string vibrations. On the other hand, coil 42 does pick
up noise signals because such signals are not dependent on a magnetic
polarity. Because of the manner of connecting coils 32 and 42 to summing
circuit 53, as just described, coil 42 is capable of operating in a
humbucking arrangement with coil 32.
In operation, it is seen that by unmagetizing pick-up 40, laterally
displacing and physically lowering pick-up 40 relative to pick-up 30, and
by summing coils 32 and 42 at the negative input of operational amplifier
50, the effect of pick-up 40 on pick-up 30 is minimized and the sound
produced by pick-up 20 is essentially that which would be achieved by coil
32 alone. The physical disassociation of pick-up assemblies 30 and 40
insures that pick-up assembly 40 does not interfere with the magnetic
reactance of pick-up 30. The electrical connection of coils 32 and 42 also
minimizes any loading effect of coil 42 on coil 32.
It is highly desirable that pick-up 20 function if the preamplifier circuit
including operational amplifier 50 becomes inoperative, either because of
problems associated therewith or because the batteries that run same in
guitar 10 go dead. Accordingly, the output of operational amplifier 50 is
connected to terminal 54 of switch 19 and coil 32 is connected to terminal
55 of switch 19. When connected to terminal 54, operation is as previously
described. When connected to terminal 55, the signal from coil 32 is
conducted directly to the amplification system, thereby bypassing summing
resistor 51 and maximizing the signal strength conducted to the amplifier.
It is obvious that in this latter case, there will be no humbucking.
While the invention has been described with respect to the preferrd
physical embodiment constructed in accordance therewith, it will be
apparent to those skilled in the art that various modifications and
improvements may be made without departing from the scope and spirit of
the invention. Accordingly, it is to be understood that the invention is
not to be limited by the specific illustrative embodiment, but only by the
scope of the appended claims.
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