There is no shortage of reasonably built,
attractively finished import basses on the market these days, and
for as little as $180, you can buy something you might actually
enjoy playing. While these predominantly Asian imports can
serve as a great starter bass (or even a “hazardous duty” axe for
a pro), for some it is impossible to resist the pull of Turd Polishing
Syndrome. “Oh man, this bass would be so much cooler
with Nordstrand Pickups and a Mike Pope preamp!” they think.
“And then I’ll get a Babicz bridge, Gotoh tuners, and refinish
it in seafoam green.”
|Pot Mechanics: Moving the wiper farther from the “hot” side of the circuit increases the resisitance between lugs 1 and 2 and lowers the resisitance between lugs 2 and 3. The additional resistance between lugs 1 and 2 lowers the output.
The primary indicator of T.P.S. is the subject’s belief that
modifying a $180 bass with $820 worth of parts will somehow
create a $1,000 instrument. Many folks happily play their creations
for years; in fact, the number of online mega-threads
dedicated to the humble Chinese “SX” (Essex) brand staggers
the mind. But for some, this process leads to the inevitable
“walk of shame” terminating in the for sale section, where
the gritty reality of T.P.S. is learned: There is no recouping. Of
course, for the modder-in-training, import basses are a great
platform for experimentation, and in many cases simple, inexpensive
mods can produce big improvements in overall performance.
Before you drop $400 on new pickups, one of the least
expensive ways to improve the sound of a cheapo is to upgrade
the potentiometers, otherwise known as “pots.”
A standard passive bass routes the signal from the pickup(s) to
the volume pot, to the tone pot, and then to the output jack.
What is found under the hood of a stock P-Bass looks so simple,
it inspires even electronically challenged folks like myself to
give it the old DIY try. While not hard to wire up correctly,
there are some factors that could make swapping your pots a
pot-ential nightmare. For starters, there are two types of pot
commonly employed: linear taper and audio taper (sometimes
called a logarithmic, or “log” pot). For general purposes, you’ll
want audio taper, as it produces a smoother and more musical
sweep from “0 to 10.” A linear pot will reach what sounds like
full value abruptly—from “0 to 3,” for example, and you’ll hear
little change for the rest of the sweep. However, this characteristic
can be useful in other circumstances (below).
Pots come in different values, usually expressed in kilohms (kΩ,
sometimes just read as “K”), a measure of resistance. A pot’s
resistance affects the total load of the circuit in your
bass, influencing the tone in somewhat predictable
ways. As you increase the resistance of the pot (and
so, the entire circuit), the bandwidth increases as
well, accentuating high frequencies. For example, a
standard setup on a J-Bass with single-coils employs
250kΩ pots for volume, volume, and tone. The
darker effect of a 250K pot is meant to balance the
inherent brightness of most single-coil pickups. With
humbuckers, 500K pots are recommended, as their
brighter response counterbalances the decrease in
high frequency typical of heavily wound dual-coil
pickups. Although hum-canceling, a split-coil P-Bass
pickup has only one coil under each string, making
250K pots the stock choice. If you want to upgrade
your instrument while preserving the basic character,
use better-quality pots of the original value—
when you ditch the schwag and upgrade to primo
like Alpha, Bourn, or the ubiquitous CTS pots, there
will be a distinct improvement in clarity, and a more
“solid” feel to the rotation.
Cooking With Pots
Pots of specific values can be seen as part of a tone
recipe. Putting a 500kΩ pot into a P-Bass can have
several results. As a volume pot, 500K will effectively
brighten the tone and provide a bit more output.
However, it can also cause an impractical drop in
volume from “10 to 8”—a problem that can be mitigated
by the use of a linear pot. A 500kΩ tone pot
will extend the high-frequency output as well, but
rolling back on the control will still produce the
response of a 250K pot. The pickup has a profound
influence in the total circuit—something to consider
when thinking about pot values. For example, many
people use 500K for one or both pots with “hot”
P-style pickups like the Seymour Duncan Quarter
Pounder or DiMarzio DP146. The inherently stronger
midrange of these pickups can benefit from the
increased highs a 500K pot can induce, making it
a common mod for players using heavy effects and
overdrive. Using a 1MΩ (megohm) pot can get
extremely bright, and in the volume position, may
be too much for anything but a super dark pickup.
But many pickups can benefit from the extended
high end of a 1MΩ tone pot, while retaining the
ability to roll it off.
What Size Pot?
On a more mundane level, there are some measurements
you’ll want to be aware of. First, there are regular
pots, and mini pots; figure out which you’ll need.
A measurement worth checking is the mounting hole
size: ⅜" is standard, but not always with imports. Whether you’re buying new
knobs, or reusing the old ones, you’ll want to note whether they require split-shaft
pots with a 6mm shaft diameter, or solid shaft—typically ¼" diameter.
The height of the shaft is also worth noting; most pots have a ⅜" shaft, but the
threading area beneath it can be ⅜" or ¾" in the case of a long-shaft model. If
you buy the wrong height, you may have trouble installing the pots correctly.
Bust A Cap
You may have noticed a small capacitor wired between the hot terminal and the
casing of the tone pot (ground). The capacitor is what turns the pot into a tone
control, by “bleeding” the highs to ground, creating a variable lowpass filter.
Even though the signal at the cap doesn’t make its way to your output jack,
its presence in the circuit makes it a part of the tone recipe. Typically in a passive
bass, you’ll see a cap with a value of .047μF (microfarads). While different-brand
caps of the same value have distinct characteristics, their actual values
can vary ±20% or more, making it tough to pick a predictable winner—but a
popular choice is the Sprague “Orange Drop” capacitor, found for many years
in Fender and Gibson instruments. The real fun begins when trying caps with
different values: Lowering the value sets a higher corner frequency (where the
high rolloff begins), removing less of the highs as you rotate to “0.” But another
effect is the shift in the resonant peak frequency; higher-value caps lower the
resonant peak, which is most noticeable with the tone control completely off.
If you’re looking for dark, punchy tone, a .047μF cap rolled back will put you
in the ballpark. If you want to preserve more mids
and highs as you roll back the tone, look into lower-value
As you can see, even the seemingly simple task of
swapping pots can be fertile ground for geekery of
immense proportions … and it gets way deeper. But
with this general information, you can begin to form
your own ideas about tone recipe, and at very least,
not buy the wrong part! When swapping out the
guts of your axe, remember that no single element is
the magic bullet; you are dealing with an integrated
system where all parts contribute to the result. A
wide tone palette is possible, even with simple passive
electronics—but if you’re cooking up your own
recipe, don’t forget the pot!