CHEAP AND EASY BASS MODS BY HEIKO HOEPFINGER
In my debut column, we looked at why you might consider modding your bass and
how to determine whether or not it’s even a
good idea [“Bass Mods: When, Where, and
Why?,” April 2012]. Having weighed those
considerations, let’s now look at two cheap
and non-destructive mods that add functionality and tonal variety to your instrument.
We’ll begin our modding adventure
by working with passive electronics. The
advantage is that passive wiring is pretty
easy to follow and we only have to deal
with a few parts—pickups and volume or
tone pots. If you decide later that digging
into the more complex world of pickup
construction and design is the way you
want to experience tonal nirvana, these
mods will still remain useful.
For starters, we’ll focus on the ever-popular Fender Precision and Jazz basses.
Remember that even spin-offs made by
other companies often mimic the original P
and J bass pickup and wiring schemes.
Pickup;wiring;basics. Typically, pickup
coils are wired either individually (a single-coil pickup) or together. When you add
another coil to a single-coil pickup, the second coil is wired either in series or parallel
to the first, and can also be configured in or
out of phase with it.
Parallel mode is the standard configuration, whether you use a 3-way pickup selector switch or two volume controls, as on a
J-style bass. Switching these coils to series
mode results in a more powerful low end and
more lower-mids, while losing some higher
frequencies. Both series and parallel wiring
require either two pickups or one humbucker
with 4-conductor wiring that provides access
to both the beginning and end of each coil.
Many P-style pickup replacements offer
4-conductor wiring, so you can explore series
mode on these instruments too.
Out-of-phase wiring is not a very useful
option for bass, as it cancels out your low
end and thus rarely makes musical sense.
(Hey, give it a try if you’re a closet soloist
with no bandmates to upset.)
Series/parallel switching. The most
popular mod for the J-style bass is to add
series/parallel switching to the two single-coil pickups. This expands the instrument’s
sonic spectrum with an almost P-like hum-bucking sound and has no real downside.
Usually the J-style bass comes with two
parallel volumes and a treble blend. Simply
Fig. 1. (Left) Series/parallel wiring for a J-style bass. Fig. 2. (Right) Blend-pot wiring for a J-style
bass. Wiring diagrams courtesy of Seymour Duncan.
adding a 2-way DPDT (
double-pole/dou-ble-throw) switch does the whole job. So
exactly what are we going to do? Glad you
asked! See Fig.;1.
Instead of using a separate DPDT
switch, I’d recommend replacing the neck
pickup volume pot with a combined
potentiometer and push/pull or push/push
switch. Doing this eliminates the need to
drill any holes, so returning your bass to its
original state is a no-brainer.
With this wiring scheme, once you
switch into serial mode, the neck volume
acts as a master volume—totally bypassing the bridge volume. (Some other series/
parallel wirings keep the bridge volume pot
in the circuit, which requires you to have
the pot fully on to get in serial mode. Not
The balance pot mod. Sometimes you
want your instrument to simply be quiet.
In that instance, the two volume-pot design
requires more effort—you have to roll both
knobs off—and this is especially true when
you have a particular pickup mix that you
want to recall. One way to avoid this is to
wire up a volume-plus-balance-pot configuration (Fig.;2). A balance (or blend) pot
retains your pickup mix while giving you
one master volume to dial in.
A balance pot consists of two logarithmic
volume pots that work in reverse to each
other. With the logarithmic scale in mind,
its easy to see that these pots are normally
not at 0 Ω when both are in their mid position, where you’d expect and want to have
both pickups at full volume. So, depending
on balance pot manufacturer and build tolerances, the overall volume can be a bit less
for larger views of these diagrams
than 100 percent. (If you find it’s a lot less,
you’ve probably wired the scale upside down
and everything needs to be swapped.)
Adding a kill switch. Another way to
avoid having to turn down two volume
knobs to achieve silence is to wire up a
mute (aka “kill”) switch. A kill switch can
be very handy, especially onstage. If you’ve
already managed to install a DPDT switch
for the series mode, you can use a second
one for a full mute. Cut the hot wire on its
way to the output jack and solder both ends
to one of the middle pins. Then bridge each
of the two outer pins and attach a separate
ground to one of the bridges. Now one
position will bridge both “hot” ones, while
the other one connects both to ground. If
you’re using a push/pull DPDT, it’s a good
idea to wire the “kill” in the up position.
In our wiring diagrams, white is hot
and black is ground. Color codes from
other pickup manufacturers will differ, but
if you visit their websites, you should be
able to determine what colors they use for
hot and ground. Thanks for reading and
stay tuned for more cheap and easy mods
in upcoming issues.
HEIKO HOEPFINGER is a German
physicist and long-time bassist, classical
guitarist, and motorcycle enthusiast. His
work on fuel cells for the European orbital
glider Hermes got him deeply into modern
materials and physical acoustics, and
led him to form BassLab ( basslab.de)—a
manufacturer of monocoque guitars and basses. You can
reach him at email@example.com.