What is the difference between a J pickup and a P pickup?
There are actually three major varieties of pickups for electric
bass. The P, or Precision Bass, pickup is made of two distinct
parts. The two parts are mounted in an offset manner so that
each one picks up the vibrations of two strings. The signal is
combined before being sent to the volume/tone circuit. These two
distinct halves of the pickup are each a single coil and are wired
in opposite directions to reduce hum. P basses usually have one
pickup.
The J, or Jazz Bass, pickup is made in one piece and is slightly
narrower than the P style and is long enough to pick up signal from
all of the strings. The J style pickup is a single coil. J basses
usually have two pickups, one nearer the neck, and one nearer the
bridge. The bridge pickup tends to produce a thinner tone than either
the other J pickup near the neck, or the Precision style pickup.
The third type of pickup is called a "soapbar" due to its shape.
It is also a one piece pickup, like the J style, but is usually
about twice as wide as the J style. The soapbar can be wired in
several configurations, including single coil and humbucking.