Electromagnetic pickup for stringed instruments

An electromagnetic pickup for electric guitars has one or two dual-coil assemblies wherein an inner coil is wound around a bobbin and then an outer coil around the inner coil. In the dual-coil assembly the inner coil replaces the entire or part of wall space of pole piece holes in a plastic molded bobbin. The outer and inner coils in the dual-coil assembly are electrically connected in-phase to produce single coil pickup sound. The outer coil or the serially connected inner and outer coils are connected to a coil in the other pole piece/bobbin/coil assembly out-of-phase to generate humbucking pickup sound.

This application is a continuation-in-part of application no. 2012/0118129, filed on Nov. 16, 2010, now abandoned.

BACKGROUND OF THE INVENTION

An electromagnetic pickup (pickup, hereinafter) converts the vibrations of plucked strings of an electric guitar, which are located on top of the pickup where electromagnetic fields are formed, into an electrical signal. In general a single coil pickup (SC pickup, hereinafter) comprises of a set of pole pieces made of magnetic or ferromagnetic materials, magnetic wire coil, bobbin plates, and lead wires. The SC pickup is sensitive to external magnetic fields created by speakers, power transducers, fluorescent light sources and so on, resulting in undesired humming noise.

Such humming noise can be reduced or eliminated by combining two magnetic sensing coils electrically out-of-phase so that two signals generated by the external sources can be cancelled each other. The electromagnetic signal from guitar strings can be preserved either by setting the two coils magnetically out-of-phase or by isolating one of the two coils magnetically from the strings.

The most popular hum-cancelling pickup with the side-by-side configuration was introduced by Lover (U.S. Pat. No. 2,896,491). The pickups built according to this invention have been called PAF (Patent Applied For), which was printed on the bottom plate of those pickups in the early days. In this document the hum-cancelling pickup with the side-by-side configuration is referred to simply as the HB (Hum-Bucking) pickup, hereinafter. It is to be noted that the hum-cancelling pickup with the stacked configuration will be referred to as the stacked hum-cancelling pickup.

A pickup has a unique response characteristic to string vibrations resulting in a unique tone color. Pickup tone is dependent on many parameters, which include magnet materials, pole pieces, bobbin materials and structures, magnet wire gage, magnet wire coating materials, the number of wire turns and so on. Although external factors such as guitar builds, effects pedals and amplifiers can color the tone characters to some extent, they cannot completely override the original tone of the pickup. That is why old classical pickups including the said PAF are still popular, and also, a number of different pickup products are available in the music industry.

Two most distinctive tone colors are generated from aforementioned SC and HB pickups. The SC pickup usually produces a clear and bright sound with a focus on the treble to mid-range domain, whereas the HB pickup produces a warm and thick sound with a focus on the mid-range domain. The majority of electric guitar players use both types of pickups depending on the needs. Because it is inconvenient and impractical to change guitars for different pickup sounds in the middle of performance, many guitar builders and pickup makers offer the option of “coil-splitting”, by which a guitar player can use only one of the two coils in the HB pickup, or more rarely “combining”, in which two individual SC pickups are electrically connected like one HB pickup. However, both methods do not deliver a purposed SC or HB sound very well. A coil-split pickup sound is typically thinner and less lively than a genuine SC pickup sound. On the other hand, a combination of two genuine SC pickups does not usually produce a good HB pickup sound defined by warmth and fullness. As a result, pickups that can produce both HB and SC sounds are hardly found.

From a set of experiments it was found that one of the most critical factors, which make the difference in sound characteristics between a genuine SC pickup and a coil-split HB pickup, was the space between the coil and the pole pieces and that such space in the HB pickup can be made closer to that of the SC pickup without damaging or changing the sound characteristics and form factor of the HB pickup. The details of this invention and embodiments are described in the next sections.

SUMMARY OF THE INVENTION

This invention is about a method to wind the HB pickup to obtain a clear and bright SC-like pickup sound from one of its pole piece/bobbin/coil assemblies. At least one of the two pickup bobbins is made such that the surface of pole pieces is in contact with the innermost wires of a coil, or the distance between the two is closer than that of the traditional HB pickup. This can be made possible by eliminating or thinning the wall of pole piece holes in a molded plastic bobbin. An inner coil is wound around a bobbin such that the space occupied by the pole piece hole wall is now filled with the inner coil. An outer coil is then wound on top of the inner coil according to a designated HB winding specification. The outer coil or the serially connected inner and outer coils are electrically connected to a coil wound around the other bobbin to obtain a HB pickup sound, whereas the inner and outer coils wound around the same bobbin are electrically connected in-phase to produce a SC pickup sound. In effect this invention makes the HB pickup and the electric guitar employing one or plural of them versatile in terms of tonal variations.

DETAILED DESCRIPTION

FIG. 1shows a top view of a SC pickup placed underneath strings10. The corresponding side views and partial cross-sectional diagrams are illustrated inFIG. 2. The pickup shown in the figures comprises of top bobbin plate11a, bottom bobbin plate11b, permanent magnet pole pieces12or ferromagnetic pole pieces13, a magnet bar14, and magnetic wire coil21. Two bobbin plates,11aand11b, hold straight a set of pole pieces,12or13, and the coil21is wound around the pole pieces12or13. A magnetic field is generated by permanent magnet pole pieces12so that the vibration of the strings10is converted to electrical signal through the coil wire21. When ferromagnetic pole pieces13are used, a magnetic bar14is situated under the assembly of pole pieces13and bottom bobbin plate11bto generate a similar magnetic field.

FIG. 3shows a top view of a HB pickup placed underneath strings10. The corresponding side view and partial cross-sectional diagram are illustrated inFIG. 4. Ferromagnetic pole pieces13are put inside and run through two bobbins,11and11′, made of molded plastic. A magnet bar14is situated on the bottom side of the bobbins11and11′. In the original PAF structure, one of the two bobbins,11or11′, holds screw-type pole pieces. In this document all pole pieces13are described as straight cylinders for convenience sake in illustration of the present invention. The magnetic bar14is sandwiched by two rows of extended ferromagnetic pole pieces13such that two pole piece sets13of two bobbins,11and11′, are induced with opposite magnetic polarities generating a closed circuit of magnetic field. The base plate15is placed under the magnet14and pole pieces13to hold them in place. Two magnetic wire coils,21and21′, whose specifications can be identical or different, are wound around two bobbins,11and11′, respectively. The magnetic wire used in both SC and HB pickups is generally a copper or silver wire coated with thin polymeric insulation. Hereinafter, the magnetic wire coil will be referred to as simply “coil”.

In order to illustrate the embodiment of the present invention more effectively a simplified diagram is used for coils.FIG. 5shows a cross-sectional view across BB′ inFIG. 4and includes a bobbin11, a pole piece13and a coil21. On the right-hand side the coil21is simplified as a box with two crossing lines. The following figures will use this simplified convention.

FIG. 6illustrates the basic idea of this invention. The bobbin11for the HB pickup is generally made of molded plastic. It has holes for pole pieces13and those holes have a wall11cwith a certain thickness. The traditional SC pickup does not have such a wall11caround pole pieces12or13because top and bottom plates,11aand11b, are separate parts and make up a bobbin shape by holding pole pieces12or13straight them. In this invention the wall space of pole piece holes11cis replaced with an inner coil wire21b. Then an outer coil21ais wound on top of the inner coil21b. The outer coil21aand the inner coil21bare electrically connected in-phase to produce a SC pickup sound that is fuller than a sound from a typical coil-split HB pickup. The pole piece/bobbin/coil arrangements with one coil and dual coils (inner and outer coils) are referred to as one-coil assembly and dual-coil assembly, respectively, hereinafter.

One way to eliminate the wall space11cis to use separate top and bottom bobbin plates,11aand11b, combined with ferromagnetic pole pieces13. It can be also realized with the molded plastic bobbin by eliminating the outward part of the pole piece hole wall11c.FIG. 7(a)illustrates a cross-sectional view of an example of pole piece hole wall structure11cin a traditional molded plastic bobbin11andFIG. 7(b)shows an example of the same after removing the outward wall of pole piece holes for embodiment of this invention. The bobbin shown inFIG. 7(b)can still be molded as one piece because the remaining wall structure can connect and support top and bottom plates,11aand11b.

It is important to note that this invention is applicable to any HB pickups wherein two pole piece/bobbin/coil assemblies are situated side by side. For example, this invention can be embodied into the “blade” pickup invented by Stich (U.S. Pat. No. 4,364,295 granted in 1982). In case of the blade pickup, the pole piece13illustrated inFIG. 6represents a cross-section of a ferromagnetic blade pole piece.

In other embodiments, the wall thickness may be reduced instead of being completely removed to obtain a specific type of SC pickup tone while maintaining the specification of the outer coil21a. In traditional HB pickups, the pole piece hole wall thickness for cylinder-type pole pieces13is about 0.8 mm. Therefore, the pole piece hole wall thickness, or in more general term, the minimum distance between the outer surface of pole pieces13and the innermost wires of the inner coil21bmust be smaller than 0.8 mm.

As illustrated inFIG. 8, one bobbin11a/11bor both of bobbins,11a/11band11a′/11b′, can be wound with dual coils in a HB pickup. Note that two bobbin plates11a/11bor11a′/11b′ can be separate top and bottom plates or a part of the single molded plastic piece as mentioned earlier. In case of the single dual-coil arrangement, the HB pickup sound is made by electrically connecting the outer coil21ato the coil21′ in the other bobbin11′ out-of-phase. In case of the double dual-coil arrangement, a HB pickup sound is made by electrically connecting the outer coil21aof one bobbin11a/11bto the outer coil21a′ of the other bobbin11a′/11b′ out-of-phase. Practically, any coil (for example, outer coil21b, inner coil21a, or serially-connected inner and outer coils,21band21a) wound around one bobbin11a/11bcan be combined with any coil of the other bobbin11a′/11b′. Each pair of dual coils,21a/21bor21a′/12b′, can be wound with its own specifications so that it should generate a unique SC pickup sound.

FIG. 9shows a HB pickup structure employing one dual-coil assembly on the left side. This HB pickup has six outgoing wire tips due to the added inner coil21b, whereas the traditional HB pickup has four outgoing lead wires.FIG. 10illustrates an example of the coil wire tips,21a-1,21a-2,21b-1,21b-2,21′-1and21′-2, connected to a shielded 4-conductor lead wire31. The shielded 4-conductor lead wire31consists of ground31aand four conductor wires,31b,31c,31dand31e. With the traditional HB pickup, four coil wire tips are soldered to those four conductor wires of the shielded lead wire31. In the example illustrated inFIG. 10, two coil wires,21aand21′, used for a HB pickup sound are connected to the lead wire31the same way, in which four coil wire tips,21a-1,21a-2,21′-1and21′-2, are soldered to four conductor wires,31b,31c,31dand31e, of the lead wire31, respectively. The one tip of the inner coil21b-1is soldered to the ground wire31aand the other tip21b-2to one tip of the outer coil21a-1electrically in-phase. The lead wire31is soldered onto a DPDT (Dual-Pole, Dual-Throw) toggle switch32, such that the outer coil21aof the dual-coil bobbin11a/11band the coil21′ of the other bobbin11′ are connected to an output circuit33at one side of the toggle switch32(upper toggle inFIG. 10) and the dual coils21a/21bin series are connected to the same output circuit33at the other side of the toggle switch32(lower toggle inFIG. 10). More switches can be used to select tones from a HB pickup with double dual-coil assemblies or a combination of multiple HB pickups with dual-coil assemblies.