Electronics And Guitars: Pickups

Electronic theory for guitars/pickups/amps/effects, part 1: pickups.

Electronics And Guitars: Pickups
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Intro And Disclaimer:

This article/any following articles are intended as guides, for people looking to learn more about effects/amplifiers/signal analysis with reference mostly to guitars. It is by no means intended as a complete guide to everything, but more of a starting point to initiate discussion/ get people going in designing their own guitar gadgets, most likely pedals/pickups/amplifiers. I will try not to drown you in equations and if I'm going too slow/too fast then let me know.

The Author:

Given that in this field a certain amount of trust is required, my name is Andrew I'm in my mid 20's and I have a Masters degree in Electronics from Sheffield University. My main hobby is guitar but, alas, in reality I'm not particularly amazing at it. Until recently I never really combined my hobby with my livelihood but I figure it'd be an adventure to find out about it. Where to start? Well, lets start on the guitar, if this one goes down well or at least is not laughed at, I'll move onto overdrive/distortion pedals, the good old true bypass, echo's, wah's and amplifiers, and for the real crazies out there we can always handle some DSP (digital signal processing).

The Guitar Signal:

So, where to begin in this adventure; well let's start with an overview. Just about all guitarists know that when you pluck a note/strum a chord, that you are essentially vibrating a bunch of metal wires. These wires are placed close to your pick-ups (magnets wrapped in coils of wire) where an electrical current is induced in the coils because of the disruption caused in the flux around the magnet, this current being induced is the reason we don't need batteries on most guitars. (No this is NOT a source of free energy those that have thought about it, your arm is expending much more effort moving those strings then any energy that comes out of them).

Now For Some Electronics:

So I'm not going to bore you with why moving metal objects in a magnetic field induce current - that's just a description of the laws of physics, what I will bore you with is why Pickups all sound different; Everything in electronics comes down to V=IR (voltage is current x resistance). That equation gets me out of just about every single hole/problem I've ever been involved in (although shouting it at a gig when you're string breaks mid- solo is by no means an advisable course of action... though if you try it let me know). A good and somewhat useless way of visualizing this equation is a motorway. If you look at V as the average Speed of traffic, I as the amount of cars getting through, and R as the amount of lanes you've got to play with you can get a vague impression of how Electrical current works So right now you're asking yourselves how coils of wire around a magnet can sound different from each other when the equation is so simple? That or you're questioning whether this is one article too many and it's probably time to close you're browser and to return to the real world. Well, actually R from our equation up above is a funny character, especially when dealing with coils of wire (this is where our motorway image completely falls apart), see if you have very small gaps in wire, or, if you coil wire up tightly it starts to exhibit capacitance and inductance respectively (I can deal with these more extensively at some point in the future). The thing with capacitors and inductors is that their resistance changes with frequency (impedance) so we end up with; V = I * (R + (1/(2*pi*frequency*Capacitance)) + (2*pi*frequency*inductance)) The interesting thing we end up with here is that we have a non-linear relationship, so depending on how many coils each pickup has/ how they are spaced you have very specific tonal characteristics for every pickup just depending on how it's wired (regardless of the quality of magnet used).

Why Can't I Get A Humbucker Sounding Like A Single-Coil?:

Single-coil pick-ups act, annoyingly, as antenna's (antenna's are any long piece of non-shielded wire/metal), the humming you can hear most of the time in the background is probably the mains (50/60Hz). For reference the low E on your guitar is probably 82.4Hz. Humbuckers are clever because as you can visually see it's for the most part 2 single-coils hacked together, HOWEVER, the second single coil has its windings reversed and its magnets are out of phase with each other which effects to make the random noise in each single-coil cancel it each other out but double the guitar signal (WOAH! Clever stuff), however having two wires coiled next to each other creates a lot more inductance, lowering the resonant frequency (the frequency at which you get the best response, ala V=IR... Above). This is why humbuckers have much less of a sharp attack then a single-coil, because it can't react as-well to sharp sounds (higher frequencies)

The Signal We End Up With:

Well take a look at you jack cable, What you have is a signal and a ground (the middle is the signal), the induced current (after going through your volume/tone resistors) looks like a sine-wave on the signal connector when looked at respective to ground (without a ground the signal is meaningless). Why does it look like a sine-wave? Well you're string is vibrating up AND down - opposite directions within the magnetic field.

Further Questions?

So now for some discussion, a lot of people talk about sustain generated by the wood of their guitar, any ideas how this actually (if it ever?) makes it into an electronic signal? Answers below.

21 comments sorted by best / new / date

comments policy
    james_size
    it would be interesting to go on to how different pickups give different results in that equation in a qualitative sense e.g. what is the effect on perceived sound with tighter windings, different spacing etc
    rubbishskater
    If I can get hold of a few cheap pickups to pull apart/ play with I'll have a go at it, without some kind of audio reference I think it might end up reading like a slightly more complicated version of this
    JimDawson
    lol, love how you HAD to put a comment about free energy in there! I've seen a lot of crap about this when I was simply trying to find actual information on solar panels, windmills and magnetic generators on Youtube. As for your question, I am no expert but wouldn't the wood of the guitar have at least some effect on how your strings vibrated? You can feel an electric guitar vibrate a bit as the strings go. If the wood the strings are attached to is vibrating, I think it makes sense to think that it would have at least some positive effect on the sustain; (EDIT: Or not. Forget this paragraph, I don't know what I am talking about lol.) that vibration should move the strings a bit. I really can't see it making too much of a difference with an electric guitar though. Pretty legit guide!
    britlohse
    The type of wood and its shape determine what frequencies will resonate more and although this is not nearly as apparent as in instruments such as violins and cellos, it does have an effect. So it's not really that The wood has an effect on how the strings vibrate, the vibration of the strings interacting with the wood has an effect on the overall sound being produced.
    BradIon1995
    It does make a difference, but it's more about the wood, hardware and electronics combination. All three of these things are fairly insignificant on their own, so you can have a guitar with crappy wood and good electronics and hardware and it'll sound almost as good as a guitar with good wood. Electronics play more of a significant part in tone than anything else I believe.
    jinsu2301
    I'm not an expert but I would say that the sustain depends on how well the wood/hardware parts resonate with the strings. if you have wood that needs a lot of energy to start resonating, it's gonna "suck the tone out of your strings" and that results in low sustain. if the body resonates well with the strings, they will swing longer, wood and strings are "supporting each other".
    rubbishskater
    Interesting, I hadn't really considered it before but does that mean that, at certain frequencies ( the resonant of the overall guitar and the individual resonances of the wood/hardware) a lot of sustain is generated whereas less so at other points, do guitars have sustain hot-spots as it were?
    Zigioman
    Rubbishskater, here is an cool example of effect. At about 110 they do a comparison between a Gibson Standard Les Paul, a Studio LP, and an Epiphone LP
    ruletheneck
    Not sure about you guys, but I know for a fact that some notes on my guitar don't sustain as long as others a semitone away (cold-spots, if you will). More noticeable in the upper register - I'm guessing this is because the frequency difference between the pitch of the string and resonant frequencies of the instrument?
    masonr08
    I'm not very good with electronics, but this is what I got out of it: Single-coil~~great for lead Humbuckers~~Ok for lead but better for rhythm Am I right or am I off by a long shot?
    rubbishskater
    I don't think you can quite distinguish like that, people's prefer different tones for different jobs, as the article suggests, single coils have a sharper attack ( higher frequencies have a better response) then humbuckers but funk guitarists for instance may want that for their rhythm playing. As always with tone, it's very subjective.
    vrodjen
    Thanks for trying to dumb it down for us. I enjoyed reading your article.
    base851
    Someone correct me if I'm wrong, but my understanding is that tone woods, being more resonant, act to sustain the string's vibration rather than absorb it.
    ruletheneck
    heyyyy just started electricity topic in phys (am in high school) and beginning to understand this! good vibes! so yeah, nice article - hoping there will be another installment?
    rubbishskater
    There's a bypass one awaiting review, trying to plan a more detailed pickup one but it's not there yet
    Battery Chicken
    You lost me at "V = I * (R + (1/(2*pi*frequency*Capacitance)) + (2*pi*frequency*inductance))"
    rubbishskater
    Sorry, it's difficult to explain equations properly in the article format, essentially it just means that the original V=IR is not the complete picture. Because R when dealing with an alternate current/ guitar signal is actually frequency dependant based on the capacitance and inductance. It just shows how the coils of wire (inductance)/ gaps(capacitance) in wire have an effect on what frequencies you get the best response