Cheap and Easy Bass Mods
April 6, 2012
$0$0 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.$0 $0In 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.$0 $0We’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.$0 $0For starters, we’ll focus on the everpopular 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.$0 $0Pickup wiring basics. Typically, pickup coils are wired either individually (a singlecoil 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.$0 $0Parallel 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.$0 $0Out-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.)$0 $0Series/parallel switching. The most popular mod for the J-style bass is to add series/parallel switching to the two singlecoil pickups. This expands the instrument’s sonic spectrum with an almost P-like humbucking sound and has no real downside.$0 $0Usually the J-style bass comes with two parallel volumes and a treble blend. Simply adding a 2-way DPDT (double-pole/double- throw) switch does the whole job. So exactly what are we going to do? Glad you asked! See Fig. 1.$0 $0Instead 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.$0 $0With 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 very useful.)$0 $0The 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.$0 $0A 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 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.)$0 $0Adding 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.$0 $0In 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.$0 $0 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 firstname.lastname@example.org..