Biasing an Audio Transistor

Biasing an Audio Transistor

[@davejaguar6532]

Thank you. That's the clearest explanation and demonstration of this concept that I've yet seen.

[@AllAmericanFiveRadio]

Thank you, and your welcome.

[@marklowe7431]

Electronics is one skill teaching is another, you do both very well. Excellent video, thank you

[@reginaldmcnab3265]

I agree!

[@joernone]

Rick, Probably the greatest benefit of your vids is that they'll digitally remain here for a very long time to come, long after we current viewers are gone. I'd say you're generating a pretty solid and worthwhile legacy. As usual, great job, my friend. Regards, John

[@IzziedeD]

and provide value to people over a decade later

[@clueless_andy]

damn...

[@bypass666666]

This was extremely informative and more easy to understand than many other videos on the same subject I have seen. Many thanks for sharing.

[@AllAmericanFiveRadio]

Thanks donotfret, I used a sine wave generator for this demo. The same generator can produce square wave also. Most KZbinrs are interested in audio equipment so that's why the sine wave. The transistor is making the sine wave at the output. At the output the transistor varies it's resistance which causes the DC to vary. I used a sine wave at the input so it varies the DC as a sine wave at the output.

[@AllAmericanFiveRadio]

Everything in the circuit influences the amplification potential of the circuit. R4 is the load of the circuit, R1,2,3 are the biasing resistors, they set the voltage at the base that allows the transistor to work properly. If R4 was changed to 8 ohms, R1,2,3 would need to be changed to set the base so that the transistor will work properly for an 8 ohm load. The amplification of the transistor is the beta of the transistor.

[@Mosfet510]

Great video, it was nice to see one that wasn't rushed! You have probably made a lot of people comfortable enough to try experimenting by showing what to avoid and what makes the transistor happy.

[@dave251430]

Awesome video, You're one of the few people on KZbin that actually educate.... keep up the great work and very much appreciate your videos. Take Care, Dave

[@ashrocks8443]

From what I given to understand, the capacitor at the emitter, allows for the signal to be conducted whereas the resistor at the emitter acts as a voltage source courtesy of the current flowing from the collector. Thank you for the clear explanation :)

[@AllAmericanFiveRadio]

Thank you, and your welcome.

[@joestone5040]

Thanks for this video! Seeing how the changes in R3 and R2 affect the signal was really helpful.

[@jimadams2473]

Very nice explanation of how transistors work. Very clear description of the bias voltages. Thanks!!!

[@demios99]

I have no real knowledge of electronics (actually, I'm yet to become a beginner :)), but despite that, all the concepts you're describing here appear so simple and easy to understand. As joernone said, a real legacy! Thank you very much for the education you provide.

[@AllAmericanFiveRadio]

R4 is the load, R1 is the emitter resistor which helps set the bias point or working point at the base. R2 and R3 are chosen to also set the bias/working point, there resistance are high enough not to short out the incoming signal. Resistors are generally the cheapest way to bias the transistor.

[@abeleballestri612]

Excellent explanation how a bias is made for an NPN transistor.thanks very much

[@AllAmericanFiveRadio]

Thanks

[@James1toknow]

Covered this in my last semester. You described biasing very good. You covered saturation but not cut off.. over all still fantastic.

[@AllAmericanFiveRadio]

That because if your building and audio amplifier your not wanting to bias to cutoff or saturation, but I have other videos that do get into saturation and cutoff

[@James1toknow]

Right, I was just saying.

[@AllAmericanFiveRadio]

I know, I tried to stick to a single subject and make the video short as possible. I must say between Google+ and KZbin, it is beginning to be a real challenge finding comments and responding to them. I sure hope things settle down soon. I may have even block someone without knowing it. Not a complaint, just an observation.

[@James1toknow]

true

[@socencounter]

A not-so-easy concept explained in a simple way! Thank you!!!

[@AllAmericanFiveRadio]

The linearity usually determines how fast the volume/signal increases and decreases. If there is distortion and it is not due to the input sign being distorted it can only be clipping at the top or bottom or both. Thanks.

[@abeleballestri612]

Ca very simple and nice explanation of how a bias in a transistor ,in this case a NPN , works and how the voltage and currents reacts according to their bias..!i have learnt a lot from this simple lesson. Thanks very much indeed , I enjoyed it. Abele. Suisse

[@AllAmericanFiveRadio]

Thanks

[@cedrickdelacruz8228]

This vid deserves a like, keep it up mate! I hope i will learn more of your videos. Cheers!

[@AllAmericanFiveRadio]

Thanks

[@moonaroma1]

Super Awesome video. Its really easy to understand. Extremely thank you to the video creator/owner :)

[@bodx7812]

very useful in designing low ang high level amplifiers...this is the part of where you can achieve good output response if it gets exact and proper biasing.....

[@AllAmericanFiveRadio]

I have worked in many electronic labs each costing millions of dollars. Companies would not spend this money if experimentation and testing was not absolutely necessary. THANKS!

[@AllAmericanFiveRadio]

When you want to build a transistor circuit the first thing to do is to decide what it is you are going to drive with the transistor, my circuit was R4. If I wanted to have R4 at the collector on or off, all I need do is change R2, lower it's resistance enough so it turns off the transistor which will make the collector maximum positive. Then remove R2, and R3 should Drive the transistor into saturation, making the collector voltage very low.

[@AllAmericanFiveRadio]

@marsenification Well, you could use just the common ground and the Plus 9 VDC or just the common ground and the Negative 9 VDC. If you want to make a power output audio amp you could use it as 18VDC and just forget about the common ground from the power supply. If you want positive 18VDC use the negative 9VDC as ground in the circuit. If you want negative 18VDC use the positive 9VDC as ground in the circuit.

[@gecogexx]

This is explained very well, thank you. these are awesome lab examples for beginners.

[@smiley235]

Great video. And as someone mentioned earlier, very pleasant to listen to and easy to follow, thumbs up from me

[@AllAmericanFiveRadio]

@miyukiTS C2 blocks the DC from the circuit in front this one or from a signal source, and only lets the AC signal through to the base to be amplified. If a DC signal was allowed through, it would mess-up the basing of the base of this transistor.

[@AllAmericanFiveRadio]

Don’t remember the voltage of the input signal, it saw small, less than a volt. For class A you bias the tube/transistor so that the input signal can swing the output equally between the top and the bottom of the power source for the output.

[@AllAmericanFiveRadio]

If you know the resistance of the load, the current required to operate the load, and the voltage of the power supply, then you go to the specification sheet supplied by the manufacturer for the transistor you're using. Here you will find the bias voltage needed for your current situation. Then you have to decide on the resistors to supply the bias voltage, that's ohms law.

[@angellizarraga4170]

If you keep doing this, you will teachers desappear...thks a lot for your time and knwowlegde and pacent, and... the list go on...

[@AllAmericanFiveRadio]

Thanks

[@AllAmericanFiveRadio]

The easiest way is to look at other circuits. The trend for biasing is higher resistance in the front end and lesser resistance toward/at the speaker, in audio amplifiers. This setup did have a good range of resistances for R2 and R3, that would still produce a good output, did not get to show because of time. Tubes usually dont have R3 resistors in the circuits because the internal elements of the tubes supplies it.

[@GrantsPassTVRepair]

Well done. Your video is easy to follow.

[@AllAmericanFiveRadio]

This is done most often in switching circuits. The major current flow in this circuit is through E to C. When the base becomes positive enough the transistor goes into saturation which is the highest current flow possible for this circuit. The current flow through the base is still small. Go down to Radio Shack and buy some 10 cent transistors and experiment. That is how you really learn.

[@terencewright2223]

Very good , an excellent video to watch. Thank you.

[@AllAmericanFiveRadio]

Thanks and your welcome.

[@freewayross4736]

Yo i found this gem in 2023 thank you sir

[@AllAmericanFiveRadio]

Thank you and your welcome.

[@terminate5888]

I experienced the same problem when I was designing my CE amplifier. I choose the values of r1 and r2 so that the base-emitter voltage of the transistor was at 0.7V by setting the base to 1.6V, which is the voltage drop across r2. But when I put it all together on the breadboard the circuit didn't work, and the base voltage was 0.58V and the base-emitter voltage was only 0.57V. I realized that I couldn't have any old combination of R1 and R2 to give the correct biasing of 1.6V at the base. As R2 was too high, so even though the base voltage was calculated to be 1.6v, it was much lower as most of the current was flowing through r1 and the base-emitter junction of the transistor. So when biasing the transistor the value of R2 needs to be lower than the base-emitter resistance and so R1 needs to be higher to control the biasing current and the base voltage.

[@AllAmericanFiveRadio]

That's why there are electronic labs. I have worked in many electronic labs that coast many million of dollars to build and maintain. These companies would not spend that money if it was not absolutely necessary.

[@AllAmericanFiveRadio]

@flurng R1 produces a voltage drop for the emitter which produces a bias voltage for the base. C1 stabilizes this voltage. Without C1 the bias voltage will change more when current flows through E and C of the transistor. The more the bias voltage changes, the more the the current flow is influenced by the current through the transistor changing the characteristics of the amplifier.

[@GroverCricketDaisy]

Thanks great video with a well structured explanation I learn't a lot

[@AllAmericanFiveRadio]

Thank you, and your welcome.

[@AllAmericanFiveRadio]

Thanks rschandran Yes the beta does matter. The higher the beta, the higher the gain of the transistor. So a high beta transistor can be easier to over drive by the input signal. Everything is important in the circuit. I think the best/fastest way to learn is to study existing circuits of the type you want to build. A lot of time and experimenting has gone into a successfully executed circuit.

[@1959Berre]

Very fine explanation, I like your style, nice and easy. Thank you.

[@AllAmericanFiveRadio]

+1959Berre Thanks

[@orgami100]

+AllAmericanFiveRadio ... If only my electric class teacher would've explained it like that ( CK722 ) it would've been really helpful...

[@wetering]

Thank you for this extremely informative video!

[@AllAmericanFiveRadio]

Thanks and your welcome.

[@AllAmericanFiveRadio]

Thanks DaxtonProducer I'm glad the video helped.

[@salmanmazhar9044]

After this short lecture my concept about biasing of transistor is build. Thanks

[@AllAmericanFiveRadio]

Thank you, and your welcome.

[@gvrp2008]

Thank you for a lucid presentation

[@gseries2567]

thank you from Greece :)

[@AllAmericanFiveRadio]

Your welcome and thanks.

[@philipsilvester]

thanks for sharing, i know finally understand...THANK YOU

[@AllAmericanFiveRadio]

R4 is the load/current limiting resistor. Without it the transistor would burn out. If you build this circuit you will get the same results, I used no magic. C2 blocks DC but lets the AC signal through. R1 & C1 are for biasing, together they act like a battery.

[@dhawalsinghkushawaha8827]

thank you so much, I was searching for this only.

[@AllAmericanFiveRadio]

Thanks and your wellcome.

[@raguaviva]

Awesome job!! Thanks for sharing, it helped me a lot!!!

[@mitchmarks500]

Great video, better than some college professors.

[@AllAmericanFiveRadio]

Mitch Marks Thanks

[@aljosagajst8725]

alot better than my professor

[@AllAmericanFiveRadio]

The emitter resistor creates a voltage drop which raises the bias on the base by the same amount. With the capacitor crossed it, it does act like a battery. The resistor and capacitor last much longer than a battery.

[@stanvincent7106]

the maths is simple voltage divider vbase=vbattery*r2/(r2+r3) the vbase must equal approx veb which in silicon transistors is about 0.7volt (actually 0.6-0.7V depending on current) plus the voltage drop across r1 which is emitter current times r1 .but for max signal output and less distortion vcollector to emitter should be (supply voltage /2). that means rest of volts are across r4 as r4 here is much bigger than r1. lets say vsuppply is 18v .then v/2=9volts that means icollector (almost same as iemitter) is 9/33k=0.27ma volts across r1 is 150*.27/1000=0.04 volts i.e virtually zero. so vbase=0.7+0.04=0.74v or so this requires 18*r2/(r2+r3)=0.74v choose r2+r2 big enough not to load down the signal source say 500k r2+r3=500k so 18*r2/500k=0.74 so r2=20k so r3=500k-20k=480k nearest r2=two 10k resistors in series and r3=470k exact result vb=18*20/490=0.734 close enough in practice make r1 bigger so vb+vacross r1 is less sensitive to individual transistor characteristic and also enabling r2 to be a bit bigger not to load the source. (note there is a limit to how big r2+r3 is as the noise generated from the resistors themselves can start to affect the noise output of the circuit. the lower r2+r3 the lower that noise but the more load is placed on the input.Ideally the a/c input resistance should equal or bigger than a/c source output resistance.The input resistance is r2 in parallel with r3 i.e. r2 as r3 much bigger ( and also in parallel with transistor input resistance- in this case beta times re where re=30/(iemitter in ma) in this case re=30/0.27=111 ohms. if the capacitor where removed the input resistance due to the transistor would be beta times r1 a much bigger number than r2 usually. e.g. beta=400 input res=r2 para r3 para 400*(150+111) (=104k)=16.2k the gain of the circuit is virtually r4/re=33000/111=297 if the capacitor is removed the gain is r4/(re+r1)=33000/(111+150)=126 assuming the input resistance to the circuit has not greatly reduced the input signal voltage. .

[@AllAmericanFiveRadio]

And then you build it in a lab for testing and adjustment.

[@AllAmericanFiveRadio]

Thanks very much Dave.

[@mixolydian2010]

Nice, thank you very much for the explanation and graphics work, helped a lot.

[@AllAmericanFiveRadio]

I Googled “two transistor amplifier circuit” and of course there are lots and lots of circuits to look through.

[@AllAmericanFiveRadio]

@marsenification I'm not sure how you wanted to use your dual supply. I would need to know what are the voltages of the power supply. If you can get from 6 to 9 VDC out of it, that is all you need for most transistor circuits.

[@thejavaman53]

This was a very detailed explanation.

[@AllAmericanFiveRadio]

Thanks

[@Techno888]

Very well explained thank you great job! This will help me develop more amp projects.

[@AllAmericanFiveRadio]

Two equal resistor would split the voltage in half. That bias voltage maybe to high, but the bias voltage is also dependent on the load you are driving and also how you want to drive it. Class A will have a different bias voltage than an On-Off function.

[@aljosagajst8725]

Nice explanation, thanks. Why is the optimal bias at 6v? What is wrong with setting it at little below clipping, around 9,50v in that case? This would give alot more output power, thats the reason I`m wondering why not set it that high.

[@AllAmericanFiveRadio]

It's 6VDC because I'm using a 12VDC power supply. If and amplifier clips it produces distortion.

[@JJ-kf2uk]

@@AllAmericanFiveRadio Ummm you're using 18V for the supply. Please explain how you arrived at the initial R1, R4 and C1, C2 values. In other words the math behind setting gain, limiting current and determining frequency response.

[@Dad-ij2qy]

Good explanation. Good test setup. Thank you for sharing.

[@AllAmericanFiveRadio]

Thank you, and your welcome.

[@MicroscopicAllan]

Really like you videos. Thank you very much for the nice explanation on transistors.

[@QAhkam]

Very nice demonstration, Thanks for sharing.

[@GerardoZuniga]

great ! better explain than my teacher!

[@AllAmericanFiveRadio]

Thanks gecogexx I have a few videos for beginners. If you have any ideas let me know.

[@planker]

Good presentation. I haven't been using the Oscope enough, its time to give it a few choirs.

[@AllAmericanFiveRadio]

You can learn a lot about circuits, using an Oscilloscope. Thank you.

[@AllAmericanFiveRadio]

Everything is obvious after you know the answer. You just keep on learning and more things begin to make sense.

[@alexandercyborg5308]

Old video but great explained bias process..

[@AllAmericanFiveRadio]

It was true then, and it is true today.

[@rafaellarios3707]

That looks like a LEADER LBO520A oscilloscope, doesn't it? I used to have one 30 years ago. You just made me remember when I had to design an audio amplifier when I was a student. The only thing I don't remember is how to select the emitter capacitor. As that was my first course of electronics, the professor just gave us an empirical rule where its reactance had to be who knows how many times the emitter resistor's value. Can you please say how you select it? Thanks sir ! Good video!

[@zbyszekskibinski]

Excellent show, thank you. As far as I noticed on the oscilloscope as you decreased the resistance of R3, before the transistor got into complete saturation and signal disappeared there was some clipping in its amplitude. Does it sound as nonlinear/unlinear distortion? That explains what happens with the signal when resistors drift off their values. I would really appreciate if you uploaded some videos with IC amplifiers as well. Thanks a million.

[@AllAmericanFiveRadio]

The fastest way to lean circuits is to find some that you are interested in and build them, get them working, then modify the circuit to see what happens.

[@donotfret]

Great vid, what would I do if I wanted a pulse dc instead of a signwave? Whats making the signwave anyway when a dc is connected? I'm guessing the r1 c1 tank is inducing a signwave?

[@AllAmericanFiveRadio]

@wow1022 Flea markets and Ham Fests are a good place to look for a used one. Good Luck!

[@abelincolnparth]

This helps, but could you tell us the exact type of transistor you used and also the signal that was being amplified?

[@AllAmericanFiveRadio]

General purpose transistor 2N2222. Signal was small 1/8 VAC or less.

[@ravneetpalsingh]

Amazing video sir. If you can show the working of R1 and C1 in another vid, it would be great.

[@AllAmericanFiveRadio]

Thanks submission123456 It can be! It depends on your purpose for the circuit. Here are the three popular configurations. Common collector (this video), common emitter, and common base amplifiers. Just Google them and you will get lots of information. Also look for my video on Navy Electronic training. The link to the downloads is in the description of the video. 24 volumes, PDF files.

[@AllAmericanFiveRadio]

THANKS!

[@AllAmericanFiveRadio]

@marsenification Yes but usually a common ground is needed between power supplies.

[@RadioDude1969]

Ok, I think I get the point; what really matters, is the current flow - not the voltage alone. If the current flow is limited to safe level, virtually any voltage can be applied at the base. On the other hand, I guess that even a low voltage, say 1 V, could destroy the transistor without any current flow limiting at all. Thanks...

[@miyukiTS]

I am new to electronics and my question is why you have a capacitor C2 on the base lane?

[@AllAmericanFiveRadio]

@ravneetpalsingh It is a 2n2222 from Radio Shack.

[@K5DVT]

Why is a capacitor and resistor(instead of a battery) needed on the emitter of the transistor use?The tube circuits had a smaller battery on the grid.Does this act the same?

[@AllAmericanFiveRadio]

Thanks! Glad it helped.

[@AllAmericanFiveRadio]

Thanks John.

[@AllAmericanFiveRadio]

I was using the Leader Audio Generator 27. It was set on high and about mid output. Still not a very strong signal. About 1.8-2.7VAC

[@donotfret]

@AllAmericanFiveRadio great, I'll check out the class a oscillators. TY

[@AllAmericanFiveRadio]

I have read a number of books and if you could understand them, you did not really need to read them, so Im not sure what the point was. I like getting to the point. Most everything in electronics developed from experimentation first, then came the measuring and then the math. Math help to predict result and is an important starting point.

[@AllAmericanFiveRadio]

They are very interesting. I uploaded the Navy Electronic Courses to my server. There are 24 PDF volumes and they are excellent. I did a video on the Navy Courses and the link to the download URL is in the 'more info' of the video. I think you would like it. It is great information.

[@ro4pvb1c]

Liked and subscribed. Can you explain a vacuum tube amp and maybe show the diagram. I'm looking forward to such video. There are tons of them out there but it seems no one can explain the way you do. You make it seem soo easy. Please show how to build a simple vacuum tube amp !

[@AllAmericanFiveRadio]

Lafayette Guitar Amplifier Signal Flow kzbin.info/www/bejne/qp6vfnyaiduchck Audio Coupling Capacitor, how it Functions in a Circuit kzbin.info/www/bejne/hnKzn6qOa76cf68 AA5 Radio Signal Flow kzbin.info/www/bejne/sJzRoWN8hNCDjrc Control Grid, Triode Tube kzbin.info/www/bejne/gZCke4V_qLOfiJI Searching My AllAmericanFiveRadio Channel kzbin.info/www/bejne/apyac6x-ps1rgNU The Vacuum Tube Shortwave Radio password 'allamericanfiveradio' www.richardmcwhorter.com/vacuumtuberadio/

[@satyabanukil779]

why forward bias and reverse bias is required with illustration should be helpful for me to get a practical idea on the subject. Thanks

[@ramynovaes9739]

i'm brazilian, and not speach english very well...but you teach so well that even me can understand.( sorry, my english is to bad kkkk)

[@AllAmericanFiveRadio]

Thanks and your welcome. I hope my videos help.

[@AllAmericanFiveRadio]

That's great! And thanks.

[@AllAmericanFiveRadio]

Thanks Simon Spiers

[@cbherlen]

I didnt get it fully, but thank you very much.

[@insylem]

Question: At 2:30, you mention that the capicator is 0.02uF (Micro farad) However, the diagram shows 0.02MDF. Wouldn't a capitol M stand for Mega like 10M ohm is 10 Mega Ohms? Also, why say 0.02 micro, instead of 20 nano?

[@AllAmericanFiveRadio]

I had been working on some early radios 1920-1940's. Back then MDF=uF.

[@RadioDude1969]

I really enjoy your videos - this one is noe exception! Howerver, here's a few things I am wondering about: 1) How come you can apply almost 12 V on the base without destroying the transistor. I thought even 1 V would be too much? 2) What is the purpose of the input capacitor C2? 3) What is the purpose of R1 in parallel with C1? Thanks!

[@imho2278]

I wondered how the transistor survived too!

[@AllAmericanFiveRadio]

Clipping occurs here because the circuit tries to put out more, Neg or Pos or Both, than the power supply can deliver.

[@flyingfrancisco]

HI Rick In this video what was the input signal of the base of the transistor thru the capacitor. thx

[@belabertalan]

Great video! Which engineering books do you recommend?

[@AllAmericanFiveRadio]

Thank you. This is a GREAT study. Navy Training Course NEETS www.compatt.com/Tutorials/NEETS/NEETS.html

[@belabertalan]

@@AllAmericanFiveRadio Thank you

[@AllAmericanFiveRadio]

The NPN transistor is from a Radio Shack Pack of general purpose transistors.