Let's start with F2. We want an

NPN transistor.

Let's zoom out a little bit.

Right click. You actually want to pick a realistic transistor not just an

ideal model.

Pick new transistor. These are very common transistors. 2N2222...

I've got a couple of those in my parts box so that sounds great.

Okay we'll

add a resistor on the collector.

A resistor on the emitter.

A couple of resistors to form the DC voltage bias.

Let's add a capacitor so that we are only

amplifying AC. Let's

add another capacitor so that there's an AC path to ground.

And let's add a resistor there so we can have some control over the gain.

Start drawing some wires now...

Ok almost done... and never ever forget ground.

Now we're going to want two separate voltage sources here.

F2... go to voltage source...

Let's put a voltage source here. It should be referenced to ground.

Do that with the source here and

at the top of our voltage divider.

Now this is where DC voltage sources come into play.

Let's give it a dc voltage of 9V. We're going to power our amplifier

with that. And like I said we need a second voltage source.

We need an input signal that we're going to amplify. Voltage source here...

Escape... Reference it to ground...

F3 to draw wires... excellent.

Okay let's add some component values. I have built

so many of these things that I know by heart that this little trick will work.

Make all the resistors 10k except for this one.

Let's make the one that controls the gain a very little value...

1 ohm. We want a lot of gain. And we make the capacitor values

pretty high, 1uF so that we let as much AC through as possible so

we get a large

AC gain. And don't worry if you don't know values from memory like I do

this is just to show you how to construct the circuit in the simulator

and simulate it then tweak it and just see what happens.

Now this time we don't want to do an AC analysis sweep of many frequencies

we just want to see how this amplifier performs at one specific frequency. Let's say

400Hz because that's roughly a male voice.

Right click, Advanced.

We're not going to put in the small-signal value over here.

We are going to use the Function. Sine... DC offset is

0 volts. Amplitude is

very small let's make it 20 millivolts. Frequency is

400 Hz... and we can just leave the rest blank.

Okay time to set up the simulation.

Edit simulation command. We're not doing AC analysis anymore.

Now we want to do a transient analysis.

Now what the transient analysis does is it starts up the circuit at certain

default values.

For example nine volts over here and

0 volts for the initial sine wave over here. And then

it calculates every single voltage in the entire circuit, every voltage and

every current at every node at a fraction of a second later.

And then it'll do it again a fraction of a second later. It'll just keep doing that

over and over and over again

until you get graphs of voltage and current versus time

for every single voltage in the circuit. And the only value we really need to

change here is the stop time.

This determines how long we're going to run the simulation for.

So let's run it for 100 milliseconds which is actually quite a

long time.

Okay... put the box wherever I want.

Now Simulate, Run...

And this is the output of our amplifier let's see what happens.

So check it out. On the output

we have a voltage swing of about

1 volt peak to peak. On the input we have

that tiny little 20 millivolt input signal.

So the amplifier is working great. We have a DC offset... I mean we can easily remove

that with a capacitor over here...

but the amplifier is working exactly as expected. Now let's have some fun

tweaking the circuit.

Let's say I don't want 1 volt peak to peak let's say I think that's just

too much and

I only want to have 0.5V peak to peak.

Let's reduce the gain of this amplifier.

So I go over here, changing this resistor value will do that.

Let's change that to 100 ohms.

Okay simulate again.

Output... well it looks like we've got 5.6V minus 4.6V so

we still have 1V peak to peak so that didn't reduce

the gain of the amplifier like I wanted. So we're going to have to go over here

again

and tweak the value. Change it to

1 kilohm.

Simulate again and see what happens.

And now we're much closer. We've got about 5V to 5.35V.

It looks like we've overshot our target by a little bit so

let's change it to 800 ohms.

Run the simulation again... and sometimes you just have to do this in engineering.

Just keep doing things over and over again until you get the result that you

want.

Okay looks like we've got about 0.45 volts on the amplifier

now

and that's roughly where I want it to be so let's let's just leave it at that.

And if you're curious let's poke around at some of the other voltages

in the circuit. Over here we would expect this to be a flat line

nine volts and yes it is.

In the middle of our voltage divider... 10k here 10k there...

were dividing evenly by two

so this should be 4.5 volts.

Yes it is! 4.5 volts and we've got our little 20 millivolt

AC swing laid on top of it. And we can just keep looking at all kinds of

currents and voltages in the circuit to

see whatever we want to see and analyze whatever we want to analyze

and make adjustments accordingly.

Okay that covers the basics of circuit simulation so give it a try!