Geek Speak: All About Pickups - BassPlayer.com

Geek Speak: All About Pickups

We all think basses are cool for many reasons: the deeply satisfying feeling of a good groove; the instrument’s genre-hopping flexibility; the gorgeous design and materials of a particularly beautiful specimen.
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WE ALL THINK BASSES ARE COOL FOR MANY reasons: the deeply satisfying feeling of a good groove; the instrument’s genre-hopping flexibility; the gorgeous design and materials of a particularly beautiful specimen. All true, but I’d like to draw your attention to a slightly more obscure source of bass coolness: pickups. Of the many technological miracles that must perfectly coalesce to turn a clacky, barely audible unplugged instrument into a thundering emissary of Odin’s fury, pickups might be the most fascinating.

EMG PJX Set Active Ceramic PJ Bass If you have no idea how pickups work, their ability to transform vibrating strings into an electrical signal that perfectly captures the pitch, timbre, and amplitude of your playing probably seems like major voodoo. What’s so nerdalicious, though, is that even when you do know how they work, it’s still mind-blowing. I could extoll the practical virtues of pickup awareness—you’ll be a savvier consumer, with a deeper awareness of how to get certain tones, blah blah—but that’s not really the point. The point is that pickups are the closest thing in the bass world to magic, ranking only behind people-sometimes-pay-us-to-play on the list of minor bass miracles.

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STUFF YOU LEARNED IN SCHOOL & PROBABLY FORGOT

For the long-since-graduated, remember in school when you were knee deep in Beowulf or calculus or 11th-century English history and you thought, How could this possibly matter at all when I grow up? And now that you’re a grown-up, you realize that you were pretty much right? Well, to understand how pickups work, it helps to revisit one of those long-forgotten classes: physics.

Aguilar AG 5M Music Man Pickup Bass pickups rely on forces described in the principles of electromagnetism to operate. The most relevant mathematical description of the principle is known as Faraday’s law. Here’s the basic idea for our purposes: When a coil of wire is used to focus and concentrate a magnetic field, and that magnetic field is disturbed by a ferrous material (meaning it contains some iron and thus responds to magnetism), a voltage is induced in the coil of wire. In the case of bass pickups, copper wire is turned many thousands of time around magnetic “polepieces.” The polepieces are either made from magnetic material or are rods or bars of steel that physically touch a magnet that runs the width of the pickup. Either way, when a coil of wire is looped around a magnet, it produces a well-controlled magnetic field inside the loop that rapidly decreases in strength with distance from the loop. In a bass pickup, plucking the ferrous string causes a disruption in this magnetic field, inducing an alternating current in the copper wire that happens to be an excellent analog of the waveform and amplitude of the plucked string. This electrical signal then exits the output of the bass, gets recorded, and enters the ears and hearts of millions. See, physics is cool, especially when you don’t have to worry about grades!

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DiMarzio Split P Bass Pickup HUM BE GONE

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Now that the science-y bit is behind us, let’s dive in to the differences among pickups. As you probably know, pickups can be divided into two broad groups: single-coils and humbuckers. Each has a distinctive tone, but they differ most importantly in their resistance to electromagnetic interference or “hum.” Single-coil pickups (like those in a J-Bass, for example) function as a kind of antenna. In the U.S., the “mains” electricity—the electricity coming out of the wall—is a current that alternates at 60Hz. In the modern electrified world, the electromagnetic interference from the mains is omnipresent. This interference induces a voltage in a single-coil pickup at 60Hz, which is audible as hum. Shielding a bass’s control cavity can help reduce the hum, but it’s still virtually impossible to eliminate in a true single-coil pickup. The ingenious remedy for this is the humbucker, which Gibson first popularized for guitar in 1955.

Nordstrand Big Single Pickup The humbucker operates on this basic principle: An instrument’s signal is generated by a pickup’s magnet in conjunction with the wire coil, but electromagnetic interference is influenced only by the wire coil. Combining two single-coil pickups and aligning the magnets for opposite polarity, and wiring the coils in opposite directions, achieves a hum-cancelling or “humbucking” effect. The opposition in polarity and winding direction does not influence the strings’ signal, but the hum is sensitive to the direction of the winding. Since the two pickups are wired out of phase with each other, and then electrically connected, the hum induced in the wire coil is eliminated due to phase cancellation. The actual signal travels through unimpeded. Typically humbuckers are wired in series, meaning the end of one of the wire wraps is connected to the beginning of the other. The result is a stronger, higher-output tone. Humbuckers can also be wired in parallel, resulting generally in a lower-output sound. Some basses with humbuckers also incorporate a “coil-tap” switch, allowing the player to change a pickup’s operation from humbucking to single-coil.

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PICK UP A PICKUP

One of the coolest developments of the past several years in bass has been an explosion in aftermarket pickup manufacturers. Newer entrants like Nordstrand and Aguilar have joined a market long dominated by Bartolini, EMG, Seymour Duncan, and DiMarzio. Competition breeds innovation, and the current slate of pickups on offer represent many clever approaches to the age-old task of electrifying a vibrating string. While not cheap, a pickup upgrade is still one of the most effective ways to breathe new life into an instrument. It’s especially effective at un-cheapifying the sound of a cheap bass.

Next time we’ll take a closer look at all the stuff in the control cavity that’s wired to the pickups. But for now, take a moment to reflect on the sheer brilliance of the engineers behind the bass pickup. Not to bum you out, but I bet they paid attention in physics class.

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