In the second of a four-part series for Mojotone’s tech-savvy readers, we explore the many variables in the design, materials, and construction of a pickup’s coil that can lead to differences in response and sound. Part one, last month, offered a basic introduction to pickup essentials, and further parts we’ll look at other components and construction techniques in greater detail.
Length of Wire
One of the biggest determining factors in any pickup coil’s performance is found in the amount of wire wound onto the coil; that is, the overall length of the wire used, and the amount of wraps around the bobbin or coil former that it takes to complete the coil. Considering pickups that are otherwise similar in all other ways, the more wire you have in any given coil, the stronger the signal it will produce when you pick a note, and the more powerful it will sound. More wire doesn’t just mean a more powerful pickup to drive the amp harder, though, it also brings a change to the pickup’s frequency spectrum, and players who feel they want a “hotter” pickup might not also want tonal changes that come hand in hand with it.
Increasing the amount of wire wrapped around a coil increases midrange response but attenuates treble and bass along with it; the reverse applies for removing turns of wire from a “standard” number of turns in any given design, in relative turns (and keep in mind, this stuff is all relative!). Up to a point, increasing a pickup’s midrange emphasis by adding more wire can work to the advantage of a weak pickup with a harsh, brittle treble response, as the high strings will sound smoother and fuller with an increase in output coupled to a decrease in pure highs. Coupled to this, however, the wound strings—which perhaps sounded just right as they were—will round out too, possibly becoming muddy or flabby or indistinct sounding if the increase in winds is taken to extremes.
One of the main considerations in all of this is that you usually can’t have it both ways: if you love the sound of a vintage-style, lower-wind pickup but also want a hot pickup to drive your amp harder, chances are you’ll have to compromise a little somewhere… or just step on an overdrive pedal. These are all relative and “just for example,” but you get the idea: any change in spec will often alter different performance factors. The amount of wire is far from the only factor to consider here. The type of wire and the way it is wound into a coil are also of huge significance.
Wire Gauge
Manufacturers in the earlier decades used different gauges of wire to achieve different ends: thinner wire to squeeze more onto a thin or compact bobbin, for example, or thicker where room allowed. These days, makers will tend to use the wire that most closely matches the type of pickup they intend to emulate—or in an entirely original design, the wire best suited to their purpose—although 42-gauge (also called 42 AWG for “American wire gauge”) is the most common.
A typical vintage-spec Stratocaster pickup coil wound with wire until it’s full might accommodate, for example, get to 8,000 turns of 42-gauge wire before you run out of room. If you want even more than that for a “hotter” pickup you might be able to squeeze a little more on there, or you need to use thinner 43-gauge wire instead, which lets you increase the length of wire and to wind it on more tightly too. Alternatively, if you’re designing a pickup from the ground up and space is too tight to allow enough 42-gauge wire for an acceptable output, you might use 43- or 44-gauge instead, just to get enough signal out of it without necessarily trying to make it “hotter”. Higher gauges were used in many old DeArmond pickups for just this reason, while several high-output pickups also use it to achieve their desired ends, and Fender’s petite Telecaster neck pickup has traditionally used 43-gauge wire to get enough output from the design, which is notably smaller than a Telecaster bridge pickup or a Strat pickup.
Worth noting here is the fact that a change in wire gauge doesn’t just allow you to pack on more wire; it introduces a change in sound, too. This change is likely to affect the balance of highs, mids and lows, the pickup’s relative clarity or snarl, and other factors. Exactly how it affects these depends on other aspects of the design and how the coil is constructed, but be aware it will make a difference. For one example, Fender’s very early 1950 Broadcaster bridge pickup used 43-gauge wire and had a bright, fat, somewhat gnarly-edged bite to it, whereas standard Telecaster bridge pickups that followed were otherwise largely similar in construction but used 42-gauge wire, and their flavor of twang was somewhat clearer and tighter as a result, yet still meaty and bold.
Insulation Formulation
What happens when you wind several thousand revolutions of uninsulated wire around something? It becomes one big electric contact, and unending short. For this reason, all pickup coil wire is insulated to keep the entire length isolated from its neighboring wraps as it coils round the bobbin.
Why should the type of insulation matter? It’s just the stuff that coats the wire, and the wire’s what generates the signal, right? True, but every minute variable in the way a pickup is made can have an (often surprising) effect on how it creates a signal, so it’s conceivable that different insulation materials might introduce different characteristics to the coil.
The most commonly used insulating coatings are Formvar, plain enamel, and polyurethane, and each results in a slightly different thickness of insulation, and different degrees of relative stiffness or flexibility in the wire, too. Formvar-coated wire was used in Fender Stratocaster pickups until about 1964, when the company changed to plain enamel, and this slightly thicker, heavier Formvar therefore is the coating material you will hear bragged about most in the literature of contemporary winders keen to point out how rigidly they adhere to vintage Fender Strat specs. That being said, plenty of players have discovered the sonic charms of Fender’s so-called “gray bottom” pickups (named for their gray fiber bottom plates) that came into use around 1964 and into the ’70s, so often it’s not a matter of better or worse, but of “different."
On the other hand, Gibson used plain enamel-coated wire for both its P-90 single coils and PAF humbucking pickups, while Fender was always using plain enamel for its Telecaster pickups, so this type of wire has come to be an essential ingredient of any repro PAF or vintage-style Tele pickup. On one hand, many great pickup makers will tell you “wire is wire.” On the other, many will also expound at length on the fact that insulation will both vary in thickness according to the material it is made from and will affect the inductance and capacitance of the coil according to that thickness.
Arguably, the insulating material also affects mechanical vibration, and therefore resonance within the pickup, according to how hard/brittle or absorbent it is. In these ways a change of insulation coating material can indeed change the sound of the pickup in a very real way. As for what is better or worse, that will depend on the overall design of the pickup, and the tone you seek to achieve, so it’s best to read makers’ specs and descriptions regarding their individual designs, and to trust the best pickup winders to use materials that they feel are right for the job.
Coil Winding Technique
Even when the same coil wire and components are used to make otherwise similar pickups, the way in which the coils in those pickups are wound will have an effect on their final sound. Which is to say, the even- or unevenness, tightness or looseness, regularity or irregularity with which the wire is wound onto a pickup’s bobbin or coil former will impact the results in different ways.
All of these factors are introduced into the pickup’s construction by the winding technique, which is often influenced by whether the coil is wound on an automated machine (and what type of machine), on a machine with the wire hand-guided onto the coil as it builds up, or with even more hand work (few pickups are truly “hand wound,” however, which is no surprise when you consider how much time it would take to turn a coil by hand 8,000 to 10,000 times to get all the wire on there! Instead, the hand element usually involves how the wire is fed or guided onto the coil as it spins on some motorized device).
Today, many pickups are wound in a specific attempt to replicate the “happy accidents” found in the randomness or irregularity of the best sounding vintage pickups. Aficionados often attribute some of the magic of good vintage-style reproduction pickups to a degree of looseness in the wind, which translates to a slightly microphonic pickup. By “looseness” we’re not talking about wire that’s flopping around to the extent that the coil is changing shape, or producing excessive feedback howl even at moderate volumes. But a touch of microphony can contribute to a lively sounding pickup, and when a coil is acting both as a microphone that pickups up direct guitar-body resonance in addition to its electromagnetic sensing of string vibration, it’s conceivable that it is producing a richer, more complex signal.Alongside this, the neatness and consistency with which the turns of wire are laid into the coil, or layered, is also responsible for certain sonic properties. The term “scatter wound” describes a coil that has been wound with a degree of calculated randomness, if you will. Manufacturers that employ this technique site the arguably sloppy winding of some vintage pickups, where wire was not layered up wrap upon wrap, precisely, as it formed around the bobbin, but occasionally made skips and jumps up and down the coil’s vertical plane. Coils might also be built up unevenly, with the wire stacked more widely or heavily toward the bottom or the center. Sloppy or not, scatter winding is also accredited with a liveliness of tone, and many modern manufacturers seek to reproduce it.
Counter to this, other makers will promote the precision and regularity of their turns, and credit this with superior sounding pickups. A more tightly, evenly wound pickup is often considered smoother and clearer sounding, less prone to feedback, and might genuinely be the preferred choice for players seeking singing contemporary high-gain lead tones, for example.
And all of this goes double for humbuckers, where the effects of coil winding are compounded because two coils will interact to produce a signal. In recent years, for example, many makers have discovered that one of the keys to creating an accurate-sounding reproduction of the hallowed Gibson PAF is to combine coils with different numbers of winds—one with 3,800 turns of wire, for example, with another of 4,300 turns. Since these mismatched coils result in slightly less phase cancelation when their signals are combined, they are attributed with enhancing the bite, edge, and high-end complexity of the pickup, and lending a certain single-coil-like depth to the midrange and a clarity to the lows. Less phase cancellation also means a little less hum cancellation, however, so evenly matched coils excel in noise rejection, while also being more smooth and even sounding, where that might be desirable.
Wax Potting
Too much microphony can lead to squealing feedback, especially from guitars played via high-gain amps or pedals. To quell this, many pickups are “potted” (dipped in melted wax or paraffin) to provide an overall dampening insulation within the coil windings to subdue unwanted vibration at high volumes. Akin to what is discussed above, an un-potted pickup’s microphony can be another vintage-associated characteristic, enhancing bite, edge, complexity and harmonic content. For smoother overdrive and less squeal at high volumes, though, potting is usually desirable. While potting is essential for some pickups intended for certain playing styles, others will benefit from being left unpotted.
Coil Shape
Given the “everything makes a difference” premise that we’ve worked on thus far, it won’t surprise you to hear that the basic physical shape of the coil will also influence how it sounds. Whether the same type and amount of coil wire is stacked up in a tall, narrow, vertical oval like a Stratocaster pickup (which tends to sound brighter and more focused) or a wider, fatter, more horizontally inclined oval like a P-90 (which tends to sound thicker and warmer), this shape can make a big difference in the final tone.
As we know from Part I of this series, however, Strat pickups and P-90s have differences other than mere coil shape, so let’s compare two designs that are closer to being alike in all other ways. Consider Fender’s Jazzmaster and Stratocaster pickups: both have six alnico rod-magnet pole pieces and are held together by fiber top and bottom plates. Now, wind the same amount of wire around both configurations and you will get pickups with similar output levels, but significantly different sonic signatures: the narrow, tall Strat pickup will be tighter and brighter; the wide, thin Jazzmaster pickup warmer and thicker (though, of course, still pretty bright too).
Much of this goes back to the basics of the electromagnetic device: building this structure around a different framework, and thereby rendering the ultimate shape of the device differently, also changes the structure of the magnetic field and results in pickups that read string vibration slightly differently. And that is compounded by the fact that differently shaped coils also simply behave differently, even when loaded with the same type and amount of wire, because the wire is spread along a different geometrical pattern.
The wider pickup shape contributes to a wider magnetic window, which samples vibrations from a wider region along the length of the strings. A longer sample of the vibrating strings means more competing frequencies which, when blended, lead to a little phase cancellation and, therefore, a slightly warmer, less defined, less brightly focused sound. I’m talking extremes here, but you get the picture—and anyone who’s played a Jazzmaster and a Stratocaster side by side has heard the sonic differences that result from very similar ingredients.