All About Electric Guitar Pickups

May 1, 2009

 

 
WHEN WE’RE TALKING ABOUT ELECTRIC GUITAR tone, pickups are where it all starts. Certainly wood, strings, hardware, and fingers all interact to produce the note, but the pickup translates it into the signal that makes it electric. The beating of that alnico butterfly’s wings triggers the sonic motion that peaks as a hurricane of tone at the cone of a speaker several yards of wire away. The complexity of that interaction between magnet, coil, and metal dictates that any little change in the design or construction of a pickup will alter the sound it produces.

A pickup does the reverse of many electromagnetic devices that we might be more familiar with in everyday life, such as speakers and small electrical motors. Instead of receiving an electrical signal and translating it into motion by manipulating magnetic forces, a pickup senses motion (string vibration), and, through this motion’s disruption of its magnetic field, translates that motion into an electrical signal.

A guitar pickup consists of two main “active ingredients” alongside a collection of inactive ingredients. The actives are the magnet( s) and the wire coil. The inactive ingredients are the coil former (or “bobbin”), and a number of other parts that are used in some designs, but not in others, including a base plate, a cover, pole-adjustment screws, wooden (or other) spacers used to keep certain parts from contacting each other, and wax or paraffin used to seal the coil to keep out moisture and dampen vibrations. As you can imagine, a whole heck of a lot depends on the way in which that magnetic field is disrupted, and this accounts for a big portion of the variables in the entire equation of the guitar pickup. In addition, much also depends on every factor of the pickup’s manufacture. Let’s look at the major variables in play:

• Different magnet structures (or magnet-and-pole piece structures in many designs) will respond differently, because they are creating different types and shapes of magnetic fields.

• Different-sized or differently structured pickups will present different magnetic fields, and will therefore present different readings of the strings’ vibrations to the coil.

• Different types of coils will translate the disrupted magnetic field differently, and therefore send a differently shaped signal down the wire to the amp. And, of course, differing numbers of turns of wire in an otherwise similar coil will also lead two pickups nominally of the same “type” to produce slightly different signals.

• Different string types will affect the magnetic field differently, according to the type of steel they are made from, their condition, their gauge, and other factors. Although these conditions are not part of the pickup itself, it’s worth remembering that their interaction with the magnetic field is where it all begins.

THE MAGNET

Different types of magnets are reputed to have their own sounds—although the influence of the magnet on the pickup’s signature tone goes way beyond the type of magnetic material used to construct it. The two most common magnets, alnico and ceramic, are commonly characterized as being, respectively, sweet and dynamic, and hard and powerful, but those descriptions are shortsighted. Skilled pickup manufacturers know that a lot depends on how you use the magnet. Some early ceramic-magnet pickups were indeed thick, dull, and muddy sounding, but many makers have learned to adapt their designs to this more powerful magnetic material, and, as a result, have produced nuanced, musical pickups.

Alnico, on the other hand, benefits from its legacy as the “vintage magnet”—the material that all great pickups of the ’50s and ’60s were made from—but it can still sound very different, depending both on how it is used, and which variation of it is used. Alnico— made up of aluminum (around ten percent), nickel (around 18 percent), and cobalt (around 12 percent) in an alloy that also contains copper (around 6 percent) and iron (54 percent)—comes in different grades according to its magnetic strength. Most common in pickup manufacturing is alnico V, also the strongest of the popular grades, which exhibits a bold, clear response. But makers wanting a softer, rounder response will often employ alnico II, and III and IV will occasionally be used to fine tune pickup response somewhere in between. Some makers have also started to use other types of “rare earth” magnets such as neodymium and samarium cobalt in their designs.

Just as significant as the magnetic material itself is the way it is used. Different sizes of magnets will obviously exhibit different strengths, but where the magnet is placed in the pickup has an enormous effect on the unit’s overall sound. Pickups manufactured with pole pieces that are made from actual magnets sound different from pickups made with magnets mounted below them, transferring their magnetism to steel pole pieces placed within the coil. Using pole pieces made from actual magnets—and placing these within the coil—tends to add to the clarity, definition, and overall brightness of the pickup. This rule applies whether you are using six (or 12) individual alnico or ceramic magnet pole pieces, or a single bar magnet as a blade-style pole piece (or a pair of them, as in the case of a humbucker). On the other hand, using steel pole pieces connected to a magnet mounted beneath the coil makes for a fatter, grittier, and somewhat more raw tonality.

It’s also worth noting that metal base plates on humbuckers, P-90-style pickups, and Telecaster bridge pickups interact with the pole pieces, and, therefore, the magnetic fields of those pickups. The Tele pickup, in particular, demonstrates how everything in the vicinity of a pickup can interact with its performance. The base plate raises the pickup’s inductance—and fattens up its tone a little—and the resonant, semi-floating steel bridge plate that the whole contraption is mounted in also contributes to the unique tone of this pickup.

SIZE & STRUCTURE

Many players consider pickup size and structure merely in terms of single-coil or humbucker. But we can learn a lot about variations in pickup design and tone by zooming in the microscope on an even tighter focus. Even when we examine two singlecoil pickups with the same six individual alnico V rod pole pieces, the differences in the shapes of the coils that are wrapped around these poles will still make a significant difference in the sounds of the pickups. For this comparison, let’s imagine a wide, flat Fender Jazzmaster pickup, and a tall, narrow Fender Stratocaster pickup. Even loaded with the exact same pole pieces and wound with the same number of turns of the same wire, the Strat pickup will sound brighter and more tightly focused, while the Jazzmaster pickup will sound a little warmer and rounder. This is because the wider pickup shape contributes to a wider aperture—or “magnetic window”—that samples vibrations from a wider region along the length of the strings. A longer sample of the vibrating strings introduces more competing frequencies that, when blended, lead to a little phase cancellation, and a slightly warmer, less defined, and less brightly focused sound. The narrower pickup samples a narrower section of vibrating strings, and therefore exhibits more chime and harmonic sparkle.

The same phenomenon contributes to the differences in tone between humbuckers and single-coils. The two side-by-side coils in a traditional, full-sized humbucker present a far wider magnetic aperture than that of even a wide-bodied single-coil pickup, and therefore a thicker, warmer tone (in addition to any hum-rejection considerations in these designs). This is why many players who seek bright, twangy, sparkling sounds opt for single-coil pickups—even if it means they have to put up with the extra noise— while those seeking smoothness, creaminess, and warmth go for humbuckers.

THE COIL

Most guitarists are at least a little aware of the variables of wire gauge, and number of turns of wire—both of which make a major contribution to a pickup’s sound. Many also know that increasing the turns of wire means a higher DC resistance reading. Not only will more or fewer turns of wire increase or decrease the perceived “power” of any pickup, such changes will also alter its sound. Take three Strat-style pickups, all wound with the same wire. The average or standard wind would read about 6k ohms DC. A pickup wound to 8k would not only sound louder, but it would also have more midrange content and less high end. Another pickup wound to 4.8k would be both brighter and thinner than the norm. This is not to imply that more winds is better—plenty of players have discovered the tonal virtue of less-powerful pickups, which can have better clarity and dynamics than super-hot pickups.

While 42 AWG (American Wire Gauge) is the most common thickness, many manufacturers use thinner wire when they need to stack more turns onto a bobbin to create high-output pickups, or to achieve adequate specs when space is tight. Most classic Fender and Gibson pickups use 42-gauge wire, although Fender’s smaller Telecaster neck pickup traditionally uses 43-gauge, and Gretsch’s unusual DynaSonic pickup (originally manufactured by Rowe/DeArmond) uses 44-gauge wire. Changing wire gauge changes your pickup’s tone, too, and while using a thinner wire might let you really pack the coil, it will also result in a pickup that sounds different from one with the same DC readings, but wound with thicker wire.

Yet another variable is found in the precision with which a coil is wound. Some fans of vintage Fender pickups, for example, cite winding techniques that involved handguiding the wire onto the rotating coil that induce a certain irregularity into the layering process—what is often referred to as “scatter winding”—and they credit this with some of the magic in these pickups. Wind a coil too loosely, and it will be microphonic (as the wire resonates with sound waves, it can induce unwanted feedback howl into the signal). The right amount of looseness and microphonic tendencies, on the other hand, can lead to a liveliness that might add another dimension to a pickup’s sound. Manufacturers also “pot” pickups in a bath of hot wax or paraffin to seal out air and moisture—as well as to dampen unwanted vibration within the coil—but some makers will tell you that over-potting will reduce a pickup’s liveliness.

As you can see, many variables abound in this world, and you need to play as many pickups as you can get your hands on in order to better understand the tonal palettes they present. But when you know a little bit about the interaction of different magnet types, pickup shapes, and coil specs, you’re already a long way down the road to understanding how a replacement pickup might work in your guitar.

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