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.