How to build a Common Emitter Amplifier

[@connorshaw216]

I wanted to thank you for putting all this content out. I'm a 3rd year apprentice electrician who likes to play with electronics in my free time. I've tried being self taught but didnt know where to start as far as what's possible. But watching your, "circuits you should know" videos gave me a wonderful sense of direction. Thanks for the work man!

[@kelvingreen3736]

Managed to build this. My first bread board circuit. Will be building more from your videos. Thanks for the clear explanations it makes it easier to learn about this fun subject. Hope you keep going forever with these.

[@Blackmage50]

Great stuff! I'm studying amplifiers to build a 12vdc controller. I need to run it with a pwm signal. This should get me movie in the right direction.

[@davidcourtney1398]

Can you show it being used? That would help provide a more concrete understanding of what purpose it serves. Thanks.

[@batticha462]

In this case the human ear is better than the oscilloscope !

[@pgmik-e2v]

Massive thanks for the video. Im working on those for my project and your explanation have been easily the best one i have found anywhere.

[@learnelectronics]

Glad to help

[@HenryYong]

In your next video, can you show us how you calculated the values for the resistors? Thanks

[@jackotoole2265]

Thanks for your video. Quick question, in the video you call the emitter resistor 220 ohms but write 200k on the schematic. Which should it be?

[@davidprice2861]

Good demo, showed simple linear amp very well. Thanks.

[@energyforever720]

thanks for uploading. question for anyone who knows the answer: is there a way to adjust how much it amplifies or are these transistors made with a fixed non variable amplification amount, like a resistor is made to have a fixed resistance?

[@learnelectronics]

Change feedback resistor to a potentiometer and Violà you can adjust gain. It ain't pretty but it will work.

[@stefanb.933]

for the frequency of 8 hz, what value should the capacitors have?

[@isoguy.]

Just awsome, thank you for sharing this project with us. I dont know how you do it but when you explain things all the mystery and fog seem to clear making difficult topics (for us newbies) understandable. I have the breadboard on my bench at this very moment an am now rooting for components.

[@MichaelWillems]

Wait, what? The bypass capacitor between emitter and grounds is there to effectively short AC, so we get higher amplification of the AC input signal - right?

[@torjusaanderaa3749]

You are a really good educator! Thanks for this videoes, they are very helpfull even tho it's a lot to grasp. On thing i still don't understand tho. You are using only one npn transistor, yes ? But you get aplification on both the + and the minus side of the ac signal ? I thought you needed coupled transistors for this, one npn and one pnp, and divide the signal?

[@Broken_Yugo]

As I understand it with a class A amplifier you bias the base pin high enough that the negative swing of the input signal doesn't pull the base low enough to turn the transistor off completely, and ideally keep the transistor in a linear operation region. This is why class A is inefficient, it idles with the active device part way on and dissipating power.

[@georgechambers3197]

Nice display job on the new scope. Is any heat generated in the 2N2222? Thanks, Paul another good explanation, and video!

[@bblod4896]

Noticed some noise on your sine wave. Are you using the Pevono PS305H to power the circuit? I've noticed that mine introduces a little bit of noise in the signal. so I built a low-power linear power supply that's much cleaner then the switching power supply.

[@learnelectronics]

No I blew up the penovo.

[@bblod4896]

@@learnelectronics What! LOL...It has self destruct failsafe systems. How is this possible?

[@Plasma.Prince]

So you fed a 1v DC signal into the input, and got 7.2v at the output. A few questions: What was the amount of amperage going into the circuit and being outputted by the circuit? Was the amperage amplified too? And can this circuit amplify steady DC currents instead of an AC signal? Thanks, hope you see this soon.

[@sattarsharif2428]

is it OK that you had both grounds connected of the scope?

[@mikeoliver3254]

Fun little amp to play with. Nice explanation Paul. These amps scale up really nicely to. Can you set one up with an op amp so we can see the differences in the set up?

[@learnelectronics]

Look at my opamp playlist.

[@twobob]

Would have been cool to see the bandwidth of this :) Thanks very much

[@MalagasOnFire]

Busted!!! Connected the power red probe first :P It happends... It works. Thats it

[@gappuma7883]

What do you mean?

[@MalagasOnFire]

@@gappuma7883 at 6:44 the red probe (positive) was connected before the back probe ( negative) and Paul usually connects black ( negative) first to be referenced.

[@gappuma7883]

Yes but isn’t that when there is power connected already? So that the two don’t affect eachother with their different potentials?

[@s.sradon9782]

how does the capacitor type affect the circuit?

[@Alina-er9vv]

Can you vary the frequency for a bit, for us to have an idea about the frequency response.

[@steve-si3oz]

Great explanation!!

[@ricka1939]

Paul, thanks for this video! I have a basic question. Why is the output pulled off of the collector instead of the emitter? I see everyone does it this way, but I thought that the collector is just the raw power input that feeds the amplification selected by the value of the base, with the output going to the emitter. Where did I go wrong?

[@learnelectronics]

High-side/low-side. Check out this link: electronics.stackexchange.com/questions/188072/difference-between-high-and-low-side-switching-of-power

[@richardattenborough5360]

Thanks!

[@MsFireboy2]

Paul question Have you come across any Motorola 2N3904 NPN transistors? Second I built a Colpitts oscillator circuit. Used the 2N3904 great clean output signal. Then I substituted a 2N2222 distortion at lower half of the wave. Then finally a 2N4401 distortion both up and down. Thoughts on this?

[@garvasrani8410]

Can someone tell me how to choose the values of the capacitors?

[@saladinelbahy1620]

Can I use 2N3409 transistor?

[@aviandragon1390]

Yes, for this demonstration it will work perfectly. Just be aware that the 3904 has a maximum collector current of 200mA rather than the 800mA capability of the 2222 (depends on manufacturer). This is only relevant if you intend to drive a load (i.e. speaker) with your circuit. An oscilloscope is designed not to load the circuit.

[@robertcalkjr.8325]

Thanks Paul.

[@learnelectronics]

Welcome my friend

[@abinmahfodh]

Would it work if my input signal is PWM?

[@Laediin]

Excellent video. I do have a question though. You setup your voltage divider to provide approximately 1.8V to the base. It seems like that value is intentional, is it to get the transistor into a state where pretty much any amount of signal will cause it to turn on and amplify?

[@learnelectronics]

Take a look at the 2n2222 data. I chose that value to be in the middle of the linear region of operation. Tjat way we have plenty of swing both ways.

[@alcoyot]

What I don’t understand is how the signal gets to the output.

[@Alex-rv8gw]

next time must show the input and output wave in the scope at the same time

[@michaelcostello6991]

This video did not explain how to select resistors. Very general information.

[@pokemonXD1]

For the voltage divider to the left, I think that depends on the transistor you use. In another video of his about the same thing he said that you would have to check your transistor's datasheet for the resistor values.

[@michaelcostello6991]

I am now reading. "Art of Electronics" to catch up on theory as youtube videos really dont go into enough detail. It can be downloaded on internet and is widely recommended.

[@tohtorizorro]

Second video on the subject and yet you didn't really explain how any of the resistor (or capacitor) values are chosen.

[@industrialdonut7681]

randomly xD

[@michaelpadovani9566]

I have all these components so i may give this a shot. Q-is there a freq when a class A breaks down? Hi or lo?

[@learnelectronics]

Its more the transistor cant handle the frequencies. The amplifier will work at any freq, but if you get up in the MHz range you are going to want RF rated components.

[@michaelpadovani9566]

I thought it was transistor dependent, thanks for confirming!

[@jclowersitc4866]

Very cool...it’s on my list.

[@davidflying15]

Thanks for all your very well explained projects 👍, could I ask, you used the cap to block DC in the base, then you set up a DC voltage divider, transistor side of the cap? I'm confused.

[@mohammadsufyan5902]

ty

[@muhammadtalha3596]

WILL YOU PLEASE ALL THE USED IN THIS PROJECT AND PROVIDE THEIR LINK SO I CAN PURCHASE THEM EASILY AS SOON AS POSSIBLE

[@s.sradon9782]

what's with the amplification classes?

[@larryshaver3568]

what value should the emitter capacitor be, you didn't say

[@learnelectronics]

it really doesnt matter as its just blocking dc but used .01uF for all

[@flgrt122]

The emitter resistor provides negativ feedback, when the collector current increases so does the voltage drop across the emitter resistor. This reduces the base emittor voltage and thus the collector current. The gain without the emitter cap is roughly Rc/Re. With the emitter cap the emitter resistor is bypassed for AC, and the gain is much higher. The size of Ce impacts the response at low frequencies, so normally the is a electrolytic with a few uF to go to 20 Hz or below.

[@larryshaver3568]

@@learnelectronics great is a 50v capacitor big enough?

[@larryshaver3568]

@@learnelectronics i see, i think i'll build a couple of these

[@alicekichlu215]

WHY DID YOU NOT USE ELECTROLYTIC CAPACITORS AND, WHAT TYPE ARE THESE?

[@learnelectronics]

electroliytics are polarized. i use multi-layer ceramic

[@menzimdunge5995]

What I don’t understand is how the signal gets to the output.

[@cubixmem]

The AC signal is suppose to ride with the DC signal

[@aviandragon1390]

If you think strictly in terms of conventional current (positive to negative), you *could* say that "technically" the signal doesn't ever get to the output. It essentially varies the resistance of the transistor, which drops more or less of the input voltage across it, in order to mimic the input signal on the output line. Hopefully this act of mental gymnastics is helpful for you.