Introduction to Amplifiers: Class A

[@OrangeDragon04]

This guy can explain amplifiers better than my actual electrics teacher, who has a: "What I say and what's on the test are two different things" approach.

[@khanra17]

He just says a resistor here, a capacitor there and never explained why. And you are calling it a good explanation?

[@OrangeDragon04]

​@@khanra17 This video serves as marely an introduction. And he actually explains the functions, pros and cons pretty well. 3:00. Of course, it took a bit more searching for answers in different videos and on the internet in general and the test was pretty easy.

[@georgechambers3197]

Now that's a class-eh amplifier. Simple and inefficient just like me. Another good one Paul, thanks!

[@learnelectronics]

+George Chambers lol thanks

[@boogiewoogie2010]

Your efficiency in sense of humour is 100% !! 😜

[@khanra17]

He just says a resistor here, a capacitor there and never explained why. And you are calling it a good explanation?

[@vincentrobinette1507]

If you put a standard silicon diode in series with the resistor between the base and ground, it would compensate for the base-emitter junction voltage. That would make it, so the output maintains a perfect 1/2 supply voltage, regardless of supply voltage. It would also offer temperature compensation, especially, if the diodes can be physically close to the transistor, so they can be the same temperature. On the second schematic, using the Darlington, (two transistors) use TWO diodes. 1N4148 work very well in small signal amplifier stages like this.

[@jasoneyes01]

Amplifiers and Oscilloscopes, soo much rewarding fun. Thanks for this series!

[@productionspf]

Great video, he's the Bob Ross of electronic ;-)

[@michaelpadovani9566]

Good idea for a series. I knew Darlington pair before you mentioned it thanks to your previous video! Always learning.

[@m.iodinehanifanfirdaus673]

how the calculation of res and cap on that circuit ?

[@WistrelChianti]

Is there a good way of moving from understanding transistors as switches where there's a load above or below, and capacitors from +v to gnd, to this sort of thing where there are resistors above and below the transistor and capacitors in series on the input?

[@shyammohabir8283]

good explination .. the output will be 180 deg out of phase from the input signal.

[@paulmacgiollacaoine8619]

Can you explain what is meant by “biasing the transistor” and why it’s done?

[@learnelectronics]

Biasing is setting the current at which the transistor will run. It's done so that you can get the transistor kinda "in the middle" of the active region where it's most effective.

[@MrChamesy]

This is AWESOME thank you thank you thank you! Really wanting to get into Audio amplifier projects and really like the old vintage style amps so much, would love to see more of this kind of stuff!

[@kapoon]

You know, I'm russian from Kazakhstan, graduated from university two years ago. And I can say that our learning is crap, that's why I'm here. Because It's really hard to find something that explained good on russian, and I understand more from you even while I don't understand third of what you say. Somebody take me from here XD

[@nicolasnicolas3889]

That train sounded cool as!!! Woo woo! Choo choo!

[@learnelectronics]

I used to live about 100feet from the tracks. I don't anymore

[@nicolasnicolas3889]

@@learnelectronics I grew up living 100ft from the local main line in the Staffordshire UK. There were 3 tracks and a set of lights really close, big hole in the fence where we used to rescue our footballs! ;D

[@natetete1379]

This video is great for people who are enrolled in electrical engineering. Everything you said makes sense but nothing you said meant anything to me. Could you explain more in depth. Like could you explain what is happening to the electrical signal at each point. Electricity goes in other electricity is summed in the capacitor or something

[@qw-hq5xr]

If you want to be able to understand how this stuff really works you should check out a udemy course called crash course electronics and pcb design - videos like this kind of assume you already have a basic understanding

[@arash4232]

Hi. Does the amplifiet filter the signal? Which kind of filter does it apply; low pass, high pass or band pass, please?

[@Andyzzzz501]

What is the 2nd capacitor doing, you just said for a “little bypassing”, why what does that mean ? On the input the first capacitor is there to stop DC from being passed through, so at least you explained very well what it does, but why is it so import to prevent DC from being allowed to pass ? Finally you explained the bias resisters briefly and luckily for me, I already know why they are needed, but I’m sure many people seeing this would not, and might have appreciated an explanation for why you need to displace the input sine wave vertically. Finally, the function of the last two resistors aren’t explained very well neither… Perhaps a follow up video explaining these, i.e. going a little deeper would be nice!

[@ravichandel8690]

sir can you recommend any books to make basic audio amplifier and to make professionla audio amplifier

[@FREEAIR_1973]

One question, you said capacitor before the base to make sure no dc current is going to the transistor, ok, but is it not suposed the transistors to work in dc and it must be filtered after the transistor or i am confussed?

[@cuppajoe101]

Hey, great video! I'm trying to learn how to read circuit diagrams and watching you draw it in order and explain each step really helped. I especially liked when you said the names of each special mini-circuit.

[@learnelectronics]

Thanks. I have almost 400 videos on this channel. Hope some of them help you.

[@dedogs]

Why do you need resisters?

[@flamescales7422]

Why resostor us connect from collector to base

[@jeanious2009]

Shouldn’t the output be at the emitter?

[@Coneman3]

Naive question perhaps but which type of amp is best for sound quality? Are top end exotic ones all one type?

[@learnelectronics]

Im not an audio expert, they each have their uses.

[@YouAllKnowBob]

Only 25 more to go! I can't wait until we get to the class Z amp! 😉

[@learnelectronics]

+Robert Gibbons Uh, I think we'll stop at D.

[@YouAllKnowBob]

Yeah, you're probably right. Class E and up would get way too complicated! 🤓

[@victoriagondwe1251]

@@learnelectronics i can't find the continuation of the series:(

[@gartmorn]

The train I was on yesterday went through Darlington! Just a wee aside!

[@learnelectronics]

+gartmorn ahh Darlington

[@kenlanier2131]

Hey Paul , You helping me out once more, part of my ELN131 class we have to give a group presentation on "Class A" amplifier :) Big Gain, Bad Efficiency Thanks! -Ken

[@Asdayasman]

I enjoyed that you were literally unable to call it an "amplifier" first time every time, instead calling it a "transistor".

[@fieldtrailer]

Question: Why do we put the loads on top or more specifically, use the transistors to sink current (NPN)? It seems it would be more standard and easier to troubleshoot if the load was sourced from the transistor. Take a light bulb controlled by a light switch. If the switch is on the neutral side of the bulb, you can't tell if the source voltage is present or not when you measure across the light. If the switch is on the line side of the light bulb, you can tell more accurately if the switch is open (no voltage) or if the bulb is burned out. Same with this ckt. You can't tell by measuring across the load if the voltage is the issue or if the transistor is the issue. If the load was being sourced, you could measure across it and tell if the transistor is open or shorted. So in this example, you PNP transistors instead of NPN. I'm no expert, just asking.

[@talideon]

This is one of those circumstances where electron flow makes more sense than conventional flow.

[@Enigma758]

Because due to the diode drop, the base of an NPN transistor must be .7v greater than the emitter in order to turn the transistor on. If your power supply is 5v and your load requires 5v, you would not be able to turn it on because that would require at least 5.7v at the base. If you want your switch to be "high side" as you suggest, then use a PNP transistor, not an NPN. In my example, the base must be 4.3v (one diode drop) or less to turn the transistor on.

[@Enigma758]

@@talideon I don't see how that makes one bit of difference.

[@sandrapetani9629]

Thank you . I've understood them better

[@tipko1863]

Could you maybe explain what does biasing mean?

[@learnelectronics]

Transistor Biasing is the process of setting atransistors DC operating voltage or current conditions to the correct level so that any AC input signal can be amplified correctly by thetransistor.

[@20thcenturyboy85]

@@learnelectronics Thanks for this explanation about Biasing!

[@davidnguyen5028]

Hi, I’m a subscriber. My class A amp, (adcom gfa5802) just recently developed a slight buzzing hum on the left channel. Do you think the filter capacitors for the left channel are bad? I checked the DC voltage at the speaker terminals and they’re at 0.025V, so I think the coupling capacitors are fine. Or do you think it’s something else? Thanks in advance.

[@learnelectronics]

A buzz is usually related to a grounding problem.

[@Uraim]

i got 23.245% Efficiency (the amp not done yet, i need a put a 2R resistor as Re and i dont have R2 resistor yet placed. also the capacitor not placed parallel to Re)

[@j.clowers7223]

Very useful....now onto the infrasound generator!

[@learnelectronics]

+J. Clowers shhh

[@masoudiranpour6417]

we know everything about this simple and base of Amp when used of little transformers in driver and out put stages ...for example in old single wave small radio..please speak about modern ..and new design professional Amps how transistors must couple together ? when we use all wave .not half wave !!! ..for double current _ v 0 .+v . thanks ..was perfect !!!

[@drabara]

Are you using a gate on your audio recording ?

[@learnelectronics]

Yes

[@elikemahiaku9181]

Fantastic and simple video thanks.....

[@w8lvradio]

Why is there a capacitor coming from the emitter?

[@thespectre2012]

To bypass AC current

[@matthewkleinmann]

This is a common thing with audio amps. It allows you have a different operating point for AC (audio) frequencies than for DC. In this case think of the cap across the emitter resistor as a resistor who;s value changes with frequency. At very high frequencies, the cap will have a value much smaller than the emitter resistor, while at very low frequencies, the cap will have a value much higher than the emitter. At DC, the cap looks like an open circuit,not even there at all. So if the amp is just sitting there with no audio input, the limiting factor keeping the emitter from ground is the emitter resistor. If you apply audio, as the audio frequency incenses, the cap comes into play, and becomes more dominant as the frequency goes up. If you look at the frequency response plot of an amp of that ilk, you will notice that the low frequency has a roll off. That is from the combination of that cap, and the input cap (usually to a much smaller extent), , and the not shone in this example, but necessary, output coupling cap.

[@spacecraftbuildingservices]

great and informative as ever

[@luckmoremwakudza6049]

Thank you sir. Well explained. Have subscribed to your channel

[@boybravo689]

Thumbs up done sir

[@fransmurati2370]

"Class A" what does "class" represent, how many classes is there, what is the difference between classes and how and when are they used.

[@learnelectronics]

I have an amplifier playlist that will answer your question.

[@mardav1545]

Does this work for square waves as well as sinewaves?

[@learnelectronics]

yes

[@skyz3ra]

Rly enjoyed this

[@Ramy_Ramz]

Thank you

[@EddieandSophieViney]

“Nice wishes” to you sir

[@ralphyrocket5770]

Bad Ass Sir!!! clear and to the point!!!

[@dhighness4854]

Thanks allot man!

[@salamkhorga4884]

Great thanks dear

[@emadabuhagag222]

THANK YOU

[@urstrulyhemanthsai]

👍👍👍👍👍

[@oguzcan815]

support

[@vishalshinde5252]

cutting the 2 half cycles does not just give you a circle

[@gentleumunnah9330]

Great work sir.please I wish to have your e-mail so that I can send you an email about important details.Thanks 👏👍

[@siavoshkasravi398]

I think you should have put degree sign after 30 not percent.

[@bobhiggins8746]

Draw it bigger. Useless

[@learnelectronics]

Get better eyes. Rude.