In this course students learn the basic concepts of acoustics and electronics and how they can applied to understand musical sound and make music with electronic instruments. Topics include: sound waves, musical sound, basic electronics, and applications of these basic principles in amplifiers and speaker design.
Construction of a Guitar Pickup
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來自 University of Rochester 的課程
音频和音乐工程基础：第 1 部分，音乐声电子
284 個評分
從本節課中
Week 4 - AC Signals & Loudspeakers and Radiation RC
Electric guitar electronics, pickup design, pickup placement and tone, volume control circuits, tone control circuits. Overview of a simple guitar amplifier, power supply, volume control, preamp, tone control, power amp section.
與講師見面
Robert ClarkProvost and Senior Vice President for Research and Professor
Mechanical Engineering
Mark BockoDistinguished Professor and Chair
Electrical and Computer Engineering
Okay. Now that we've been beating on you with
all of this discussion of AC circuit analysis, and then signal analysis, and
Fourier transforms, and all that kind of stuff.
We're finally in a position where we can talk about something that probably was
the reason you signed up for the course in the first place.
And that is the topic of guitar pickups. Now, we're going to talk a little bit
about how they work, and they're a great example of the kind of electromagnetic
transducer that Rob was talking about in, in his lectures on loudspeaker design.
And the other thing now is that with the AC circuit analysis techniques that we
have, we can start to understand something about the frequency response of
different pickup designs. And why different designs sound
differently, why do they sound the way they do.
So, before we get into the analysis of guitar pickups, let's just talk a little
bit about what they look like. Well, guitar pick ups are typically, this
is kind of a kind of a starting structure for a, like a fender guitar amplifier
pickup, a fairly common design. So, it's a series of magnets with the
north and south poles, and there's one per string.
And those magnets are, these are maybe three quarters of an inch long, one and a
half centimeters or so. And they they're held together by a
couple of hard, cardboard forms that the the magnets poke through.
And, after that structure is put together, then you wrap many many turns
of very fine wire. So, it could be anywhere from 5,000 to
6,000, or even more turns of wire. And it's extremely fine to be able to
cram that much wire into that small of an area.
typically 44 gauge wire, which is about two times the diameter of a human hair.
So, if you try to wrap pickups, you have to be very careful and to not break the
wire. And we have a huge box full of wire that
was from guitar pickup wrapping trials, where it, the wire broke in about the
4800th turn out of 5000 turns. And so, you have to start all over again,
unless you're adept at splicing wire together that's about the size of a human
hair. Now, once you've built this pick up
structure, typically you don't see all of this, it's just under a plastic cover.
But if you take your guitar apart and look inside, you'll probably see this or
there's often tape wrapped around the turns of the wire.
So, if you have an old guitar pickup from a non functional guitar and you don't
care about it then it's, it's, it'd be a great experience to take it apart.
So, the let's talk a little bit about exactly how they work.
Now, they work by using Faraday's Law, which is the basic governing equation for
inductors. So, Faraday's law says that the voltage
that is induced on the terminals of that inductor is related to the time rate of
change of the magnetic flux linking that coil.
And of course it, it depends upon the number of turns, and this minus sign is
here because Lenz's law that we discussed earlier.
So, here's a drawing of a typical guitar pickup, dih, ih, at least one pole piece
or one one magnet. So, the magnet has a south pole and a
north pole, and the wire's coiled around it.
Now, in, in a real guitar pickup, the wire is coiled around all the magnets
together. But it essentially works the same as, as
this. So, if you wanted to make individually
wrapped guitar pickups, one for each string, then it would look like this.
Now, the other thing that is essential is that the string has to be magnetic.
It has to be a steel string to work with a, with a, guitar pickup.
If you try to put bronze strings, like from your acoustic guitar on your
electric guitar, it's just not going to work because the material is not
magnetic. So, what happens is this permanent magnet
in the pickup induces magnetic dipole in the string.
So, it's just like you know, if you have a a magnet in your, that you're playing
with. And let's say you touch the magnet to a
screwdriver which perhaps is not magnetized initially.
Then, what'll happen is you will magnetize the screwdriver tip just by
having it in the proximity of the other magnet.
So, what's happening down in a microscopic level is the little from
magnetic domains in the magnetic material composing the string are aligned by the
applied magnetic field of the permanent magnet here.
So, what you've done now is you've made this string into a small permanent magnet
itself. And so, a little, the piece of the string
above the pole piece is now magnetized, and there's a magnetic field circulating
around just like the magnetic field from this permanent magnet.
Leaving the North Pole and coming into the South Pole.
Now, when the string moves, what happens is this magnet becomes closer to the
coils of wire and farther away. And so, the magnetic field from the
magnetism of the string itself changes the amount of flux, link magnetic flux,
linking the turns of the pickup. So, it's important to, to note that the
pickup coil and the permanent magnet in the pickup, there's no relative motion of
the two of those. They, so, the signal being generated in
the pickup is not from this permanent magnet.
But the permanent magnet just plays the role of magnetizing the string, and then
the vibrating string as it moves up and down is going to vary the amount of
magnetic flux through the turns of the pickup.
Now, there's a great website with a animation.
This is from the the National Magnet Lab at Flordia State University.
And they have a very nice Java animation that shows the function of, of a electric
guitar pickup, and we'll take a look at that in a minute
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