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.
Practical Considerations in Constructing the Amplifier
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Do curso por University of Rochester
Princípios da Engenharia de Som e Produção Musical: Parte 1 - Som Musical e Eletrônico
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University of Rochester
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Week 6 - Guitar Pickup and Effects Analysis MB & Design and Construction of a Guitar Amplifier MB
Building the guitar amplifier, how to solder, getting the amp to work - systematic testing and troubleshooting. Visualizing sound waves, frequency content and tone, signal modification in electro-acoustic systems, tube amplifiers and distortion, wah pedal, talk box.
Conheça os instrutores
Robert ClarkProvost and Senior Vice President for Research and Professor
Mechanical Engineering
Mark BockoDistinguished Professor and Chair
Electrical and Computer Engineering
Well, now that you have some idea how the basic amplifier circuit works, we want to
go to the lab now. And show you how to build it and how to
test it, and what it should sound like when it's working correctly.
So, to do that, I want to introduce a PhD candidate here at the University of
Rochester, Dave Anderson. Dave designed the amplifier it's gone
through a few iterations, and so if I'm sure with a large number of people out
there, building this, and trying it out. Some of you may have improvements that
you might want to add and we encourage you to discuss those on the forums.
But we have a fairly robust design now that you can go ahead and order the kit
from online, as we told you about earlier, or
you can just get the components. We're giving you all of the schematics
and designs that you need. If you have other ways of procur,
procuring the components. you're certainly welcome to build this
any way you want but we wanted to make it easy for you by providing a kit.
So anyway, I wanted to introduce Dave and then he's going to take you through some
of the details about how the thing should look and sound.
If it's working correctly and talk a little bit about some of the detailed
nitty gritty information you need on how to make good solder joints and important
things like that. So Dave, welcome.
>> Well, thank you very much. So yes as Doctor Baco said my name is
Dave Anderson, I'm a PhD candidate here. I have designed this amplifier kit
specifically for this course. Now this kit is designed to teach about
tone, distortion, and how we actually implement those in physical circuits.
So now I'd like to demonstrate for you how the amplifier sounds in several
different configurations. There are three knobs on this amplifier.
First of all, there's just a main volume knob, [MUSIC], there's a tone knob, which
controls the amount of high frequencies present.
And then there's also a gain knob, which controls the amount of distortion.
First of all, I'll play the guitar with the tone knob turned all the way down and
the distortion turned all the way down. [MUSIC].
Now let's turn the tone knob up just a little bit.
[MUSIC].
Now let's turn it all the way to full. [MUSIC].
Now, let's turn the tone knob, back to bottom and turn the gain slightly up.
[MUSIC]. Now, let's turn the gain all the way up,
with tone still turned all the way off. [MUSIC].
Now let's leave the gain all the way up and turn the tone to half way.
[MUSIC]. And now I'll show tone turned all the way
up and gain turned all the way up. [MUSIC].
Let's take a look now at how changing the gain of this circuit influences the
appearance of the output wave form. This circuit is designed to have a soft
clipping effect which uses diodes. Now, there are two types of distortion
that you'll find in guitar amps. There's a soft clipping effect and hard
clipping effects. Distortion is created when an output wave
form is chopped off at the top and does not appear smooth any more, that is,
rather straight along the top. Now a soft clipping effect rounds off
those edges, and a hard clipping effect keeps very sharp edges where the top is
chopped off. So first of all, I'm going to demonstrate
how the guitar amp sounds with the gain turned all the way down, and you can see.
[MUSIC]. Now you can see that there's very little
clipping happening. Now when I turn the gain all the way up,
[MUSIC] the distortion effect is much more pronounced.
And you can see that there's quite a bit more clipping happening at the top of the
wave form. Let's talk about the case of the guitar
amplifier. Now we're not actually supplying a case
with the kit, and there are a few different ways you can make one.
Here I have constructed a case in about 20 minutes and for less than $5 out of
foam board and some thick card stock. And it works very well, its able to hold
up the speaker, and it sounds really nice.
It's heavy enough, it was very cheap to make, very quick to make.
You can hold it together with duct tape, works very well.
If you want to get a little more fancy, you can assemble a box for the amplifier
out of wood. It'll give you a slightly different
sound. takes quite a bit longer, and will be a
little bit more expensive. Now if you want to use this as a base
amplifier you can also add a back to the amp, that'll give you quite a bit more
base response. For this one I've left the back open so
it's, it's up to you how to build the case for the amplifier.
Let's get into some of the details of now of how the amplifier's constructed and
what components you're going to be finding in the kit.
So the Amplifier Topology is as such here.
First of all, you have a Tone Stage, this amplifies the voltage and also controls
the amount of high frequencies that pass on to the next stage.
The Gain Stage provides the distortion. The power stage provides the current
which drives the low impedance speaker. This is the circuit board.
Mine is sort of a yellowish brown color because it's just a prototype.
Yours is going to be more of a green color such as this one.
The green color comes from a layer called the solder mask, [SOUND].
This is the AC/DC converter and this is the jack for that converter.
It plugs in like this, pretty simple. This jack fits into these three holes and
will be soldered in place. [SOUND].
Now let's, take a look at the Integrated Circuits that are included with the kit.
You have this chip here which actually provides two Op Amps.
Now this chip is directional, I have a blown up version here that has a notch
and a dot that are both at the front of the circuit next to pin one.
So you need to make sure to find the notch and the dot on your actual physical
device and place that where the dot is indicated on the circuit board.
This is the power Op Amp, now it's constructed differently and a bit bigger,
because it gets much hotter, and a heat sink will be attached to it.
These components are all diodes. These black ones are called signal
diodes, and this is a light emitting diode, an LED.
These are also directional components, on the LED, the positive terminal is the
longer of the two. On the signal diodes, the positive
terminal, is, the end of the black body that does not have the gray stripe.
So the gray stripe indicates the negative terminal.
The dirctionality of this is also indicated on the circuit board.
Now let's take a look at several different types of capacitors.
Electrolytic capacitors have large values and are generally polar.
This means that if they are inserted incorrectly into the circuit board, they
could fail or even explode. You need to be very careful not to insert
these in the wrong polarity. The polarity of the actual can is
indicated in two ways. First of all, the two leads are a
different length, just like the LED, where the longer lead symbolizes the
positive end. On the side of the can there's also a
stripe pointing to the negative lead. You can see that here on this large
device and on the smaller device can be seen here.
Other types of capacitors are film and disc.
This is a disc capacitor. And here is a film capacitor.
These have codes on them to represent the value of the capacitance.
There will be three numbers. The first digit is actually just the
first digit, the second digit is again the second digit, and then the third is a
multiplier. So for instance, if the capacitor said
104, that would be 10 times 10 to the th picofarads.
Pico is 10 to the minus 12, so that comes out to be 100 nanofarads, or sometimes
written as 0.1 microfarads. Now if you had 221, that would be 22
times 10 to the 1st, is 220 picofarads. Now let's look at the resistors that
you'll find. We're going to be using all through hole
resistors that look like this. And also have a color code that
symbolizes the value of the resistance. So a gold stripe stands for negative 1,
black is 0, brown is 1, red is 2, orange 3, yellow 4, green 5, blue 6, violet 7,
gray 8, and white is 9. So if you were looking at the, the
resistor in this fashion, the first stripe is just like in the capacitor, the
first digit. The second stripe is the second digit,
and then you have a multiplier again. One of the most common resistors that
you'll see is brown, black, red. Brown is 1, black is 0, and red is 2.
So that's ten times ten to the 2nd is 1,000 ohms or one kiloohm.
A different kind of resistor is a potentiometer or sometimes called a pot
as seen here. This is a variable resistor.
The two outside terminals have a constant resistance across them, and the inner
terminal has a variable resistance that changes as you turn the knob.
This is what we will be using for the volume, gain, and tone controls.
Let's now discuss good soldering practice.
You will need, or hopefully already have a good soldering station and some solder.
Soldering is not easy, but with practice and caution, you can achieve some very
good results. Now, a soldering iron has a sweet spot
that is not actually on the tip, but just off to the side.
This is where the soldering iron gets hottest, and where you should heat up the
solder and the components. So, to solder a component onto the
circuit board, you place the lead through the top, and then bend the lead to keep
it in place. You touch the soldering iron to the lead
to heat it up on the sweet spot, touch it with some solder.
Remove the solder first and then the soldering iron.
Let it cool, and you have a good solder joint there.
Now some things to avoid are what we would call a cold solder, which can be
seen over here. I've done this on purpose, to
demonstrate. This is a big glob of solder, over here,
that is very dull in appearance. And, has, has not made a good electrical
connection between the component and the circuit board.
You also want to be very conservative with how much solder you use.
Over here, on the IC socket I have, used way too much solder.
So much so that, one pin, is actually connected to the next pin over, because,
all of the solder is spilling over. If you've made a mistake, there are two
good ways to fix it. You can use solder wick, which is a braid
of copper wire designed to soak up excess solder.
You can place that onto a big glob here with the soldering iron and it will soak
up all of the excess. My favorite way it to use a desoldering
pump. Where you melt the solder and then suck
all the excess off. This type of integrated circuit is not
designed to dissipate a lot of heat. So when you actually solder it to to the
circuit board you could damage it. For this reason we solder a socket onto
the circuit board. Which has no electronics in it so it can
take the heat from soldering. And then we plug the integrated circuit
into the socket.
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