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Understanding Guitar Wiring
How a magnetic pickup works
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Updated 10/03
Through the process of inductance, an electrical current
is generated (see generator) in a coil of insulated
wire, which is then sent to the amplifier. If you have
a coil of insulated wire wrapped around a magnet you
create a simple generator. If the magnetic field of
the generator is held in proximity to an oscillating
(vibrating) ferrous material, then an alternating (or
AC) electrical current will be generated. Conversely,
if you wrap a coil of wire around a ferrous material,
a nail, for example and apply an electrical charge to
that coil, the ferrous rod (the nail) will turn into
an electromagnet.
One misconception that a lot of people have is that
the guitar amplifier is sending a current to the guitar—this
is not true. A cable plugged into a guitar amp will
not shock you—unless there is a severe grounding
problem with the amp! The pickup generates an AC signal
and sends it to the amplifier, via the various pots
and switches. The amplifier then takes this weak signal
(measured in millivolts and typically never exceeding
2 volts) and through a series of gain stages, boosts
the signal to a voltage and amperage that can drive
the speakers.
The specific parts and their purpose
The Bobbin and Frame
Different types of pickups have different bobbin and/or
frame construction. Traditional or vintage-style Fender
single-coils have the simplest construction with polepieces
pressed directly into the flatwork. Humbuckers and other
single-coil pickups have a molded plastic bobbin to
accept ferrous slugs, adjustable polepieces or screws,
or permanent-magnet polepieces, depending upon the design
of the pickup. Humbuckers also utilize a metal frame
(usually brass so that it doesn't affect the magnetic
field), to which the various components attach.
The Coil of Copper Wire
The pickup coil-wire or magnet-wire is wrapped around
the bobbin assembly. The fine wire is either machine-wound
or hand-wound depending upon manufacturer specs or the
desired tone. The 42 or 43-gauge wire must be handled
very carefully, as it's very thin and fragile. Different
pickups utilize more or less turns of copper wire. This
is one way that manufacturers can change the output
and tonality of a pickup design. Coils generally have
anywhere from 6,000 to 8,500 turns of wire.
The Magnets
Depending upon the design of the pickup, magnets come
in a wide variety of shapes and sizes. Magnets can also
be made from various permanent-magnet materials, such
as AlNiCo and ceramic.
The differences between single-coils and humbuckers
There are many differences between single-coil and
humbucking (hum-canceling) pickup designs—everything
from inherent tonal qualities to their size and shape.
A humbucker must have two coils that are wired to that
they effectively cancel 60-cycle hum. To achieve this
cancellation in the traditional sense, the coils must
have opposite magnetic polarity and are wired electrically
out-of-phase.
A pickup is simply an antenna. A single-coil pickup
is nothing but a big antenna for hum and RF interference.
When two coils of the proper magnetic polarity and electrical
phase are combined, they will effectively filter out
RF interference without canceling the output or sound
of the pickup. This is a humbucker!
Understanding 4-conductor pickups
To understand a 4-conductor pickup, we must first
study a single-coil pickup since a humbucker is simply
two single-coils combined as one pickup. A single-coil
is comprised of three primary components: magnet(s),
the coil that has a “start” and a “finish”
and the bobbin. Think of a single-coil as a 2-conductor
pickup—the start and the finish. When a single-coil
is wired, typically the start is connected to ground,
and the finish is hot.
Since a humbucker is two coils each with their own start
and finish, we now have four conductors. The four conductors
can be wired in a variety of ways. First, the coils
can be wired in series or parallel, the coils can be
in-phase or out-of-phase with each other. The traditional
humbucker is wired in series, out-of-phase (see diagram
#1). The series link gives a boost to the output
(parallel reduces output and gives a more nasal tone),
and the out-of-phase correlation acts to cancel the
hum.
Coil polarity and phase relationships
Determining a coil's magnetic polarity is very important for achieving hum-canceling combinations of coils from two different pickups. Many humbucking pickups by various manufacturers have the same type of polepieces for both coils. In other instances, you can use a known pickup's coil(s), to see if it repels or attracts the other pickup. Remember, similar magnetic polarities repel each other, while opposite poles attract.
Use the chart below to help determine what the phase relationship will be between two coils. This chart assumes the typical parallel connection—the connection you get with a selector switch.
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