Creating music is a perfect hobby for anyone into hacking, and the amount of musical hacks and self-made instruments we come across here makes that supremely evident. It’s just a great match: you can either go full-on into engineering mode as music is in the end “just” applied physics, or simply ignore all of the theory and take an artistic approach by simply doing whatever feels right. The sweet spot is of course somewhere in between — a solid grasp of some music theory fundamentals won’t hurt, but too much overthinking eventually will.
The obvious choice to combine a favorite pastime like electronics or programming with creating music would be in the realm of electronic music, and as compelling as building synthesizers sounds, I’ll be going for the next best thing instead: the electric guitar. Despite its general popularity, the enormous potential that lies within the electric guitar is rarely fully utilized. Everyone seems to just focus on amp settings and effect pedals when looking for that special or unique sound, while the guitar itself is seen as this immutable object bestowed on us by the universe with all its predestined, magical characteristics. Toggle a pickup switch, and if we’re feeling extra perky, give that tone pot a little spin, that’s all there is to it.
The thing is, the guitar’s electrical setup — or wiring — in its stock form simply is as boring and generic as it can get. Sure, it’s a safe choice that does the job well enough, but there’s this entirely different world of tonal variety and individual controllability locked inside of it, and all it really takes is a screwdriver and soldering iron to release it. Plus, this might serve as an interesting application area to dive into simple analog electronics, so even if guitars aren’t your thing yet, maybe this will tickle your creativity bone. And if bass is more your thing, well, let me be ignorant and declare that a bass is just a longer guitar with thicker, lower-tuned strings, meaning everything that follows pretty much applies to bass as well, even if I talk about guitars.
However, in order to modify something, it helps to understand how it functions. So today, we’ll only focus on the basics of an electric guitar, i.e. what’s inside them and what defines and affects their tone. But don’t worry, once we have the fundamentals covered, we’ll be all settled to get to the juicy bits next time.
The Electric Guitar: Pickups and Potentiometers
Presumably everyone has seen an electric guitar and knows what they look like, but not everyone has necessarily played one or concerned themselves with how they actually work. To keep the physics simple, an electric guitar works by moving a ferromagnetic object — the strings — through a fixed magnetic field — the pickup — which generates an electrical signal from the strings’ vibrations — the actual sound — that is then routed through the volume and tone control to the guitar’s output plug. From here, the signal can then be amplified and modified into any shape and form imaginable, which is where the amp settings and effect pedals take over then.
The ferromagnetic part is crucial here, so in order to make this work, you’ll need steel strings, which is why you won’t find nylon strings on an electric guitar. Well, at least rarely, though there are other types of pickups than the magnetic pickup described here that aren’t relying on magnetic flux: optical pickups that use the same concept but pick up the string vibration as it moves through light, and piezo pickups that pick up the vibrations from the body the strings are attached to. The latter ones are usually found in bowed string instruments and acoustic guitars, but you can also get magnetic pickups specifically for a steel-string acoustic if need be.
So what’s a magnetic pickup then? Essentially, it’s a just a big inductor, typically in the mid to high single-digit Henries area, constructed from thousands of copper wire windings around a magnetic core. To add more focus to each string, round pole pieces are added that give them their typical look. Pole pieces are either made out of steel and are attached to a bar magnet on the bottom, or are rod magnets and the sole magnetic component. Sometimes they’re made as screws to adjust the height to each string individually, in other cases they’re of fixed same length (flat pole) or fixed variable length (staggered pole). Then there are also rail pickups that use a single metal blade instead of individual poles. If neither of that is visible, they’re simply covered.
The amount of copper wire windings, the wire’s gauge, and the magnetic material (usually ceramic or an Alnico alloy) and amount thereof all play with and against each other to define its output signal strength and frequency response — and with that, the sound it produces. The winding pattern itself will also have some impact, but since most pickups are machine made nowadays, it’s not as big of a variable as it used to be in the earlier days of hand-wound pickups, where imperfections gave each pickup its very own, unique character (and why there’s such a magical myth surrounding them).
As for the volume and tone control, the volume control is usually just a potentiometer with the pickup signal on one terminal, ground on the other, and the output signal on the wiper. Turn it to 10, and the wiper has the least resistance getting the full volume, turn it to 0, and the signal is discarded. The tone control on the other hand is another potentiometer that forms along with a capacitor (and of course the pickup itself) a variable low-pass filter, allowing us to cut off the higher frequencies and darken the sound on its way to the output jack.
That’s basically the gist of an electric guitar, but there’s obviously a bit more to in practice. After all, there’s thousands and thousands of different guitars out there, and that can’t be without a reason. But which one to choose?
A Guitar’s Character
Well, possibly the biggest factor in choosing a guitar is simply its looks. When I was 11 years old, I saw a Gibson SG in a paper catalogue my cousin had lying around, and it was love at first sight. In fact, the sole reason I started playing guitar was that specific guitar.
After playing acoustic for a few years and saving up enough to get an electric, the local store didn’t have any in my price range. I went for a second-hand Hohner ST Lynx Superstrat instead. A few years later I tried again, this time I got lucky and finally became the proud owner of the cheapest Epiphone copy there was, the G-310. Did it sound great? Eh, I’d say the Superstrat was definitely superior. But did it matter? Absolutely not! To me, it was the best guitar ever.
So albeit anecdotal, there’s little doubt that looks affect how you feel about a guitar, and tone may be secondary. Also, certain guitars are associated with certain genres, and the psychological impact of that can’t be neglected either. In the end, it’s all a matter of personal taste anyway, and all the theory about a guitar won’t be relevant if you simply don’t like it. It’s like fancy expensive wine, just because it’s good on paper doesn’t mean you’ll actually enjoy drinking it.
Sadly people tend way too often to mistake personal taste for a matter of right vs wrong, resulting in unreasonably passionate and fruitless arguments — but who am I to tell you this? We’ve all had our share of arguing about spaces versus tabs, vi versus emacs, or pineapple on pizza.
My point here is that music is highly subjective, and everyone will have to define for themselves what’s right or wrong, what sounds good and what doesn’t. That being said, this is still about modifying a guitar’s tone, so let’s take a look at the factors that will define the tone that we are going to alter later on.
On The Origin Of Tone
Let’s say we pluck the open A string on a regularly tuned guitar, which is an A2 with a fundamental frequency of 110 Hz. What happens is that the string vibrates with that fundamental frequency, along with numerous additional, overlapping multiples of it — so in this case 220 Hz, 330 Hz etc. — of varying amplitudes, known as harmonics or overtones.
Their exact mix and actual amplitudes will vary depending on the string tension and where you actually play, i.e. the location of your fingers or pick, and with what force.
The string tension relates to the string gauge as well as the guitar’s scale length, i.e. the length of the strings between the nut and bridge (or rather double the length from the nut to the 12th fret to account for slight variations in the length for intonation reasons). A longer scale length requires more tension to reach the same pitch compared to a shorter scale length, as do thicker strings compared to a thinner gauge, also affecting how high or low you can tune the guitar. Too little tension and the strings just end up wobbling without producing any useful tone, too much tension and something’s gonna snap — if you’re lucky it’ll only be the string and not the neck of the guitar.
How that wild mixture of harmonics is going to end up as our actual signal, and therefore tone, depends of course on our pickup’s properties that determine its frequency response.
A Closer Look At Pickups
As I said earlier, the combination of winding count, wire gauge, and magnetic material define the pickup’s frequency response and output signal strength. For example, a higher winding count tends to suppress the higher frequencies, resulting in a darker, “warmer” tone. This could be countered with a magnetic core material of higher flux density (Alnico II vs Alnico V or ceramic) to get a signal with the same voltage levels but less windings, which leads to the general idea that Alnico II pickups have a warmer tone compared to Alnico V.
Lowering the wire gauge (44 AWG vs 42 AWG for example) on the other hand will fit more windings into the same physical space, which also changes the total wire length, which changes both the signal strength and frequency response. So it really all interacts with each other, and the frequency response is rarely linear anyway. To no surprise, there’s an enormous selection of pickups out there as a result.
To keep the selection a bit less overwhelming, we can split them up a bit. The high-level category to distinguish them is whether they’re active or passive. It mainly defines if they require an external power supply to function, in which case active circuitry is added to filter and pre-amplify the signal. I’ll mostly ignore active pickups here, as adding active electronics feels a bit like cheating and we might as well just add entire effects straight to the guitar — not that there’s anything wrong with that, it’d actually be a great subject on its own.
Active or passive, either way, pickups come in two main varieties: single coil and humbucker pickups. Single coils are pretty much what the name suggests: a single coil of copper windings around the magnet. Humbuckers on the other hand are constructed from two coils connected in series. Why that name? Because they buck the hum a single coil may pick up from interfering AC power supplies. To achieve that, the coils are wound in opposite directions and are facing opposite polarity of the magnet. That way, external interference is phase cancelled while the actual signal is added up — essentially like differential signaling.
But pickup properties are only one part of the equation.
Location, Location, Location
With the harmonics’ nodes and antinodes distributed along the string, each harmonic’s amplitude differs in every location, so the tone we actually end up with also depends where exactly the pickup is placed along the body. The most common locations are close to the bridge, close to the neck, and somewhere in the middle if there’s a third one — hence they’re named bridge, neck, and middle pickup respectively.
As the graphic above shows, we’ll get the widest and simultaneously most consistent variety with a moderate fundamental frequency amplitude on the bridge pickup, making them generally sound brighter and sharper. The neck pickup on the other hand is a bit more complex with more emphasis on the fundamental frequency, resulting in an overall fuller, darker tone, with the occasional risk of turning it to mud.
The variation is visible in the (unscientifically gathered) spectrum graphs, with some more variation in the neck pickup. The fourth harmonic is especially striking as the neck pickup is usually located right around the fourth harmonic’s node. Manufacturers usually account for these differences with dedicated pickups for each position, and mixing them up may yield interesting results.
A noteworthy special case are slanted pickups like the bridge pickup on a Stratocaster or Telecaster (as seen above), where the higher strings are picked up closer to the bridge, and the lower strings slightly further away, giving some brighter, clearer highs and deeper, alluring lows. That is unless you’re playing left-handed on a right-handed guitar, in which case you will have the exact opposite, and one reason why Jimi Hendrix had such a unique sound.
So the pickups and their locations have pretty much the biggest impact on a guitar’s sound, and there’s still plenty of details about them that I’ve left out so far. Don’t worry, we’ll get to them eventually, but for today, we’ll focus on the remaining major influence on the sound: the volume and tone controls.
But, But, What About…
If you followed any discussion on guitars, you’re probably wondering when I’ll talk about tonewood, i.e. how mahogany from southern Honduras planted during a new moon creates an entirely different tone in an electric guitar than mahogany from western El Salvador harvested on a Wednesday, along with everything else in that category: how different types of glues, finishes, and color pigments affect tone, how that classic paper-in-oil capacitor sound is superior to modern polyester, left vs right leg for bone nuts, and how twisting a piece of Billy Gibbons’ beard between the 4087th and 6142nd coil winding gives you that warm vintage tone™ (Poe’s Law may apply).
Myriads of forum discussions, blog posts, and videos arguing whether and how any of that affects the tone or not are in existence, and years later we’re still none the wiser. So let’s be real, if something requires that much attention, intensive experimentation, and countless blind testing and comparisons in order to prove or disprove if something has any impact in the first place, and the main outcome of all that effort is just more people trying to confirm or disprove the results, there’s only one logical conclusion for the overall picture of it: it simply doesn’t matter.
“The guitarist should have gone with a maple body” said no one ever during a gig or while listening to an actual song. If you believe some specific wood, finish, or capacitor is superior to another, great, and if you don’t, also great. Whatever makes you happy is probably the right choice then. For all I know, hearing a difference or lack thereof might as well be genetic like soapy cilantro or funky asparagus — the discussions certainly are equally pleasant.
So let’s stick with the more relevant and interesting parts. Plus, it’s all passive component tolerances anyway.
As mentioned, the volume control is a potentiometer, and the tone control is a low-pass filter made from a potentiometer with a capacitor. The exact configuration depends on the guitar, though a single main volume and main tone control is probably the most common one. However, many Gibsons for example have a dedicated tone and volume control per pickup, while a Stratocaster has a main volume and a separate tone control for the neck and middle pickup with a shared capacitor. Others might ditch the tone knob altogether, and a bass oftentimes replaces a pickup switch in favor of dedicated volume controls for each pickup.
Whichever way they’re configured, the components’ values (for passive pickups) range typically between 250 kOhm and 1 MOhm for the potentiometers, and between 10 nF and 100 nF for the capacitors. Rule of thumb combinations for single coil pickups are 250 kOhm potentiometers and 47 nF capacitors, and 500 kOhm and 22 nF for humbuckers respectively.
Why that variation? Looking back at the pickup properties, more coil windings suppresses the higher frequencies, and since humbuckers consist of two coils in series, they naturally have a higher total winding count. As a result, single coils usually produce a brighter, snappier sound compared to humbuckers, which some might prefer and is the reason they exist despite their humming shortcomings. So the idea of different value combinations is to compensate for that: avoiding that a single coil becomes too shrill by cutting off the highs more drastically, while keeping the humbucker sound from becoming too muddy by cutting them off more gradually.
Of course, in reality, things are a little bit more complex. But the thing is, numbers won’t get you far here anyway, as pickup manufacturers aren’t too transparent about the details. They may state the DC resistance and what magnets are used, but that’s where it most of the time ends. You might get some rough treble, mids, and bass chart along with a relative output signal strength to compare between their pickup range, but nothing you could fill in any math formulas. Not that there would be much sense in that either though. For one, there’s plenty of other variables at play in wiring as a whole, and more importantly, numbers will hardly tell you what sounds good to you.
Once again, it all boils down to personal taste, and trial-and-error experiments are the way to find out for sure. The good thing about it is that of all the components involved in shaping the tone of a guitar, the volume and tone controls are the easiest we can modify with a noticeable impact — and chances are we have everything we need for that lying around anyway. I mean, sure, you can open up the pickup and wind it up again differently to change the tone (and if that’s really your thing, you should probably let us know) or simply buy a new one. But sometimes, changing a capacitor or adding a resistor in the right place might be all it takes to sweeten up the tone to your liking.
Now that we’ve covered the grounds for electric guitars and their tone, we’re all set to get started with some real-world tone modifications next time. We’ll look more into some ways to change the volume and tone control behavior, some alternative options for their use altogether, and how to get completely kinky with the pickup wiring.
In that sense, stay tuned — but not necessarily in EADGBE.