In the first of a four-part series for Mojotone’s tech-savvy readers, we take a deep dive into the basics of how guitar pickups work, and what helps them do their thing. In following parts we’ll look at the individual components and construction techniques in greater detail.
Guitarists today know more about pickups than ever before, yet there are still so many variables in the world of these passive electronic devices that the details can sometimes make your head spin. Pickups are broadly akin to other electromagnetic devices employed in music electronics, and are really among the simpler of such things. Like a dynamic microphone, they translate sound waves (in this case, in the form of a vibrating steel string) into an electronic signal, but while even the simplest mic—think Shure SM58—has a moving diaphragm, they use no moving parts to do so.
As simple as they may be, however, any handful of pickups you test will sound anywhere from subtly to dramatically different, and that’s all down to the materials they’re made from, and the way those are put together. This issue we’ll look at some of the basics that influence these alterations in tone and response, then move on to a deeper dive into individual specifications in further installments.
How They Work...
Let’s kick it off with a quick look at how these things work in the first place. Most musicians understand that a speaker produces sound when the electrical signal hits an electromagnetic coil that’s attached to a flexible paper cone and suspended in proximity to a fixed magnet, causing the coil to move and the cone to vibrate along with it. Pickups work somewhat in the reverse, but without the moving-part element of the equation.
A pickup is an electromagnetic device that produces a magnetic field above the position where it’s mounted. And we all know, of course, that our guitar strings pass through this field. When you pick a string, its disruption of this magnetic field translates that motion into an electrical signal in a coil of thin wire wound within the pickup, which then travels down further lengths of wire to your amplifier. In short, electromagnets can translate an electrical signal into motion by exerting magnetic force, or do the reverse and translate motion into an electrical signal; pickups do the latter.
A Pickup’s Major Components...
There are two primary parts required to make any traditional electromagnetic pickup function: a source of magnetism, and a coil of wire. Some are as simple as a coil wrapped around a magnet, usually with some inert fiber or plastic base or bobbin to hold everything in place. Fender Stratocaster and Telecaster pickups, for example, use six individual magnets—one for each string—with a coil wound around them. Gibson’s Firebird Mini-Humbuckers or original Melody Maker single-coil pickups similarly have a bar magnet within a coil (or two, in the humbucker’s case).
The other and more common Gibson types, though, the P-90 and the full-sized PAF-style humbucker, have steel pole pieces within the coils themselves rather than magnets. These screw-like poles are threaded through the bobbin around which the coil of wire is wound, and into a base structure that puts them in contact with magnet(s) mounted below the coil.
Almost all pickup designs merge these components in ways similar to these. Which is to say, the topologies outlined in the above paragraph—pickups made with magnets within the coils vs. those made with steel pole pieces within the coils in contact with magnets mounted below—describe virtually every type of pickup made for electric guitar, while also defining two of the most significant variables in pickup making, whether you’re talking humbuckers or single-coils. Gretch Filter’Trons or Charlie Christians? Magets below, with steel poles or blades threaded through the coils. Gretsch Dynasonics (aka DeArmond Model 200) or the popular DeArmond “S-cover” gold foils? Magnets within the coils.
Furthermore, each of these two basic topologies has what we might call a “core sound,” and these simple differences in construction help to define how they sound different as a result. Obviously, there will be enormous differences between pickups depending on a wide range of other factors—more of which below—but here are the broad characteristics identifiable in these two main approaches to pickup making:
Magnet within coil: Articulate, bright, clear, with enhanced treble. With individual magnet pole pieces single-string definition is improved further; with bar magnets it’s often slightly “blurrier”.
Steel within coil, magnet below: Round, thick, a touch gritty at times, a little snarlier and gnarlier, and often with more aggressive midrange.
Note that these aren’t absolutes, but they are pretty consistent starting points for defining the core sound of differently constructed pickups. Consider types of pickups that you might already hear in your “mind’s ear,” and you’re likely to see how they follow suit. Also consider, for example, that when Gibson wanted more clarity out of the gnarly, thick, slightly gritty sounding P-90 in 1954 engineers Seth Lover and Walter Fuller simply replaced the threaded steel screws with individual bar-magnet sections within the coil of what was otherwise essentially a P-90 to create the Alnico (aka “staple top”) pickup. Voila! Improved clarity and enhanced treble content—exactly what Gibson president Ted McCarty was asking for. Naturally, humbucking and single-coil pickups of each kind sound a little different, but they still share these basic characteristics.
Once you understand these basic templates, it’s important to be aware that there are many variables at play which can make even pickups that are seemingly of the same type sound quite different. Examine the number of different mix-and-match combinations of all of the following, for starters, and you begin to see how many nuanced alternatives there are in the world of pickup making.
Different types of magnet structures (or magnet-and-pole piece structures in many designs, as above) will respond differently, because they are creating different types and shapes of magnetic fields.
Differently sized or differently structured pickups will create different magnetic fields and will “read” string vibration differently, which leads to different translations of the strings’ vibrations within the coil.
Different coil designs—pickup wound in different shapes, in different patterns, with different gauges of wire, or with more or less wire—will translate the disrupted magnetic field differently, and therefore differently shape the signal sent to the amp.
Different formulations of steel components such as pole pieces, slugs, or base plates will contribute to subtle differences in different pickups’ sound and performance.
And lest we forget… different string types will affect the magnetic field differently, according to the type of steel they are made from, any coating or plating on the wound strings, their condition, their gauge, and other factors, resulting in a different performance from any given pickup.
Considering all the potential variables, it’s easy to see why makers’ efforts to chase the “Hole Grail” of various vintage pickups has proved a major endeavor even for the most skilled practitioners. Alter one variable, and another begins to behave differently. Tweak that one, and still further variables alter their impact upon the design.
I’ll go deeper into related categories in future installments, hoping to build a reference base that helps you determine in advance what types and variations of pickup might be best suited to any sound you seek. In the meantime, be aware that these variables exist, and that the slightest little tweak in the outwardly simple recipe of any given electromagnetic pickup might leave you wailing the blues rather than twanging out honky-tonk.