Fig. 1 Comparing passive highfrequency
roll-off (indicated by
the colored resonance peaks)
with the cut-and-boost fl exibility
of an active 4-band EQ (black)Last month, we learned how passive
tone controls offer limited possibilities
for altering a bass guitar’s sound [“PassiveTone Controls,” June 2012]. This raises a
question: To gain more control over our
sound, should we turn to onboard active
electronics or simply rely on our amps to
do the job instead?
In the ’80s, active tone controls became
widely popular among bass players—particularly
those who came up in the ’70s,
when the bass began to take a more prominent
role in popular music. (Interestingly,
guitarists didn’t embrace active electronics
with as much enthusiasm during this
time.) As with all fashions, the trend to “go
active” later went back to passive, and now
bass design swings back and forth between
these two camps.
Forums are filled with flame wars
between proponents of each approach.
Some in the pro-active camp paint the
passive bassist as a nature boy gripping an
oiled-finished, natural-wood bass. Not to be
outdone, many pro-passive players characterize
active bassists as nerdy knob-addicts
whose technical interests keep them from
practicing. Let’s see if we can cut through
some of the noise and look at the facts.
Fundamentally, a passive system is one
that doesn’t require any additional electric
power. The components are passive parts
like resistors and capacitors. By contrast,
active components are transistors, op
amps, or other integrated circuitry—all
of which require external power to operate.
While passive tone controls can only
cut a specific frequency (and this is typically
limited to high-frequency roll-off ),
an active tone control can cut and boost
several frequencies at a time. This is determined
by the number of frequency bands
in a given system. The most common are
2- or 3-band systems with controls for
bass, treble, and usually mids.
More elaborate active systems offer
low- and high-mid controls or even parametric
EQ, where you can sweep through
a wider frequency range. Fig. 1 shows a
frequency chart with a 4-band active EQ
superimposed on the passive curves we
looked at last month. Admittedly, this is
just a rough overlay and the comparison
is a bit unfair, but hopefully, you get the
idea of the extended possibilities provided
by an active EQ system.
The main argument for having an active
system is tonal flexibility, but there’s another
benefit: Passive circuits possess a high
impedance, which basically means that any
load (like a cable) you put after them alters
the tone. This weakens the signal and sucks
up the treble and even some midrange.
Also, plugging a high-impedance device
into an amp’s mismatched input just makes
your bass sound bad.
Active circuits have a buffer that lowers
the output impedance and essentially isolates
the system from such loading effects.
In practice, this means that you can use
long cables or pass your signal through
several pedals without losing much of the
original signal. And plugging an active circuit
into a mismatched amp input doesn’t
have much influence on the signal. With an
active circuit, the signal usually sounds and
feels stronger, cleaner, and more detailed.
Given these properties, shouldn’t everybody
have active EQ in their instruments?
Yes, because buffering and tonal flexibility
can be a huge advantage. Imagine
being able to play in different venues
through different amps, yet your familiar
tone is always right at your fingertips—and
there’s no extra luggage to carry around. It’s
pure comfort. And when you need to cut
through the band or mix, you always have
the ability to boost the midrange just a bit.
No, because you love your sweet, passive
tone and nothing is missing. You hate
to deal with batteries. You always use the
same amp or outboard preamp and your
rig offers plenty of EQ and tone-sculpting
options. You like to keep all the electronics
outside your instrument because that makes
it easy to experiment with your sound and
make changes in your signal path.
Once again, we realize the ultimate
answer doesn’t exist! I see active preamps
as an affordable luxury. First of all, don’t
even think about putting an active circuit
into a bad-sounding passive bass. Active
electronics are designed for flexibility, not
sound repair. If your bass is sounding too
thin or weak, take a closer look at your amp
and instrument. Active circuits are often
called preamps, but real amplification is not
their job. As with everything in your signal
chain, the weakest part ruins it all. The
advertising always claims product X is the
most dynamic, flexible, power-saving, and
quiet unit available. Learn to interpret the
numbers and stay skeptical.
Because active circuits use batteries,
make replacing them easier by having a
quick-swap housing that requires no extra
tools. Also, shop for circuits that indicate a
low-battery condition hours before the cell
actually dies. And remember, a true-bypass
switch that lets you go passive is a musthave.
If your favorite circuit doesn’t come
with this, any simple 2-way (DTDP) switch
does the job.
Ultimately, the passive-versus-active
discussion comes down to this: You
must start with a good passive tone.
Depending on your needs, you either
end there or go beyond by enhancing the
passive tone with an active circuit. But
remember, you don’t need active pickups
in an active tone system. Active pickups
have an internal buffer or preamp, and
this gives them a low-impedance output
—which may be just what you want. But
you can combine any active and passive
pickup or circuit, and we’ll explore this
when we focus on pickups.
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
chefchen@basslab.de..