TSP #23 - Tutorial on the Design and Characterization of Class-B and AB Amplifiers

In this episode Shahriar continues his investigation of discrete Bipolar amplifier design. The advantages and disadvantages of Class-A amplifiers are explained. The conceptual schematic of a Class-B amplifier is presented which leads to the introduction of Class-AB amplifier circuit to overcome the 'dead-zone' impairment of a push-pull Class-B design. To further improve the Class-AB amplifier and lower its input impedance, a final Class-A followed by Class-AB amplifier is presented The component parameters are calculated and the schematics is explained in detail. All circuits are then implemented on a breadboard and tested both in the time domain and frequency domain. All schematics can be downloaded from The Signal Path website.
Please note that in the schematic diagram the diode D1 is backwards! In the measured circuit the diode is placed correctly which is why the measurement results are correct.
The Signal Path Blog
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[@Thesignalpath]

*Please note that in the schematic diagram the diode D1 is backwards! In the measured circuit the diode is placed correctly which is why the measurement results are correct.*

[@ve2zzz]

Also, in the X-Y scope, Y is input and X, output.

[@7137271]

I thought that looked funny, and kept trying to figure out how that was going to work.

[@andr27]

Video posted 8y ago and only 10 months ago errata? :)

[@SJayanth]

The reason for no output at 5v p-p input I think is because the current through the first stage of transistors went too high and the gate voltages for the next stage of transistors fell below 0.6, thus, there was no output. Anyway, we started to build amplifiers right? but, neither of the 2 designs could output a voltage higher than the input, then, how can we call these as amplifiers? Please, reply quickly. And thanks for the video.

[@torkalovolodymyr5097]

@@SJayanth It amplifies current. Before it you need add stages which amplify voltage - in common emitter configuration.

[@Hexor1211]

This video and TSP #15 are the best intro into audio amplifier design I've seen. Many college electronics Subjects fail to explain it so simple.

[@WhiskeyRichard.]

You have no idea how long I've been looking for some kind of tutorial on amplifiers that doesn't just mathematically develop the small signal model. Thank you kindly, and to boot, it's super straightforward and clearly explained.

[@WhiskeyRichard.]

Why doesn't this guy prof Oh wait stupid question

[@jonothankaplan]

@@WhiskeyRichard. hi

[@BobSolimeno]

WOW! What a great tutorial - very clearly explained, spot-on comparisons of the different amplifier designs, and beautiful hands-on lab experiments to demonstrate relative performance. And what a neat and organized lab you have!! Thank you so much!! Can't wait to dive in the the many, many other videos you have published.

[@Thesignalpath]

This is a conceptual schematic diagram. Both diodes D1 and D2 require a bias current to maintain their junction voltage. But, perhaps more importantly for you to consider, my channel has received about 1300 comments so far. You are the first to use obscene language. My channel is a place to exchange information politely and I would like to keep it that way.

[@AltayBrusan]

Thanks for your sharing. I am really disappointed with those that do not consider the value of these videos for the others. thanks and please don't loss your motivation. Your channel is valuable.

[@VLWhite88]

The answer of the puzzle: You have clipping, your input signal exceeds the supply voltage

[@andymouse]

Correct ! no prize now though Lol ! 10 years later !

[@serviceshoptoday]

I see some very good comments below. Early in the video the dead spot is caused voltage consumption called (Diode Drop). For the "Question" I agree with the comments bellow. Supply voltage, headroom, saturation, and gain. Very good information. Very well made and thought out. Feel like part of the class. Thank you!

[@vispi1944]

Thank for the excellent video presentation. First explaining the theory of various classes of amplifiers and demonstrating their workings on the oscilloscope gave a very good idea of their positive and negative characteristics. Please make a video on how to design a working amplifier, explaining how to calculate and choose parameters of various components. With such knowledge, as yours, you can write books for hobbyists and professionals. We need more videos like this.

[@bloguetronica]

How come have I never seen this! This is a great "must watch" video and, despite its age, should be recommended by KZbin.

[@jonramsey6348]

Yea totally..... finding this video on KZbin is like finding a diamond in a pile of shattered glass

[@neeleshkumar8406]

Same here ,

[@johnadams9041]

Thank you man for the video! This is the best explanation what I ever see. I am not professional and I sow so many videos trying to understand the bias and the class of amplifiers.. Thanks to you know finally understand a lot!. Thank you ! You just have big talent to be a good teacher! God bless you !

[@Thesignalpath]

Class-D is a good option. I may do a tutorial on that later.

[@MrAtomicLlama]

I can't commend you enough for putting these videos together. They're tremendously helpful for somebody like myself - trained as a scientist many years ago - rediscovering the joys of electronics. Thanks, and best wishes!

[@bassk94]

just learned more in 39 minute video then in 16 weeks of advanced electronics taught by some old fart with no clue Awesome video Thank you

[@graemelaubach3106]

You are a better teacher than all of my profs combined, you make concepts so easy to understand and more importantly you make it fun because you're just an awesome dude. I wish you the best in these trying times.

[@Thesignalpath]

Thank you!

[@omniyambot9876]

wholesome comment lol agree 0:09

[@einball]

He talks about turning off the bias voltage when the input equals zero. -- Great video! I really liked it! Made me happy about the next few months of studying :)

[@n1gdawg]

I really wanted to hear some audio through each! Great video as always.

[@thebrakshow7415]

Great tutorial! your D1 is oriented incorrectly and signal needs to be applied to each base of the transistors and not to the middle of the diode network. Adding some input caps to kill any dc is a good practice. Also, consider using a Vbe multiplier for the a-ab amplifier. It saves you a transistor plus you can use a potentiometer to dial in the biasing current.

I just wanted to write this as well. In Class AB amplifier diode orientation is wrong.

[@simoncheung2427]

i can’t believe after i watch a whole video and looks everything make sense

[@m1geo]

Just came to write this! 😂

[@Thesignalpath]

I appreciate your enthusiasm. I am trying to cover a wide audience. Don't worry, there are tutorials on DSB and SSB mixers and complex constellations for wireless transmission which will target a more advanced audience.

[@chupascz]

You are awesome teacher! Thousand times better than all my high school el. teachers. Not to mention I have to translate from english. Your 'lucky bamboo' is larger than the last video.

[@jimm2099]

Shahriar, Very good videos, I wish I had instruction like this in high school "Electronics I" instead of electron hole theory in the early 80's. Not many high schoolers back then were designing semiconductors. I like you very practical theory and demonstration techniques in all your videos, especially the analog circuits Thanks very much!!!

[@todkapuz]

I remember this from when I took my amateur radio tests.... 15-20 years ago.... but never have actually seen it real-life. Very cool.

[@SaadouneZinji]

Your class AB circuit makes no sense. Since Vin is connected to the anode of the top diode, and when it is at 0 volts, the cathode of the top diode should be -0.6V when that diode is conducting. So the voltage there should be - 0.6V and not +0.6V. Thus your top transistor is turned off until Vin reaches 1.2 V. This makes your circuit worse than a class B amplifier. Your crossover distortion has double in size and importance. The top diode should be pointing down rather than pointing up. There should also be a biasing circuit that will ensure that both diodes are forward biased and that they conduct at all times. This is why this class of amplifiers has an efficiency of about 50%. The biasing resistors for both diodes should be high enough so that a small current is pulled from the power supply at all times.

[@Thesignalpath]

+said jellouli The diode in the schematic shown in the video is backward. It has been corrected on the schematic that is posted on my website. The actual circuit being measured is correct which is why it works.

[@mrmoon7484]

you have no idea about "Shahriar". He is world class Electronics engineer. Much more knowledgeable than you

[@alicekichlu215]

I DISAGREE!

[@micglobal]

@The Signal Path, I love your channel, but you should consider re-shooting this video with the corrected schematic shown because of such a glaring error that's inconsistent with your explanation.

[@neilgroves3592]

The error is already explained....no need to reshoot.

[@Buddargh]

D1 in your class AB example is not correct.

[@weststarr2046]

Another awesome shot my friend, specially when it comes to measuring. Good stuff around there... THANKS a lot for sharing your knowledge and the way you explain it. BLESS 🎩🙏🏾...!!!

[@lonewanderer01]

So is it that you've reached saturation in the transistor?

[@ve2zzz]

Saturatio will be reached if the input signal (peak) reaches the NPN' collector's voltage + 0.6 volt (an PNP collector -Vcc + -0.6V). In the deadzone, both transistors are in cutoff region.

[@SJayanth]

The reason for no output at 5v p-p input I think is because the current through the first stage of transistors went too high and the gate voltages for the next stage of transistors fell below 0.6, thus, there was no output. Anyway, we started to build amplifiers right? but, neither of the 2 designs could output a voltage higher than the input, then, how can we call these as amplifiers? Please, reply quickly. And thanks for the video.

[@akkudakkupl]

Clipping! What do I win? :D

[@davidcottrell1308]

Very thorough and to the point...thanks!

[@Performa01]

Very true. On top of this, without bias current for the diodes and output transistors this simplified schematics won't work anyway.

[@MellexLabs]

The effect of the xy plot is due to over saturation in the final stage where the output transistors reach VDD and cannot switch any longer. However of you analyze the saturated output on the analyzer you will see the harmonic tones will still be amplified producing a horrible sound. The way to control this is to limit the gain of the overall amp by providing a negative feedback loop to the input stage, a differential input stage of matched transistors works well to assist in the loop control. However I am not sure if the total bandwidth of amp is still preserved with negative feedback...

[@cityzen8539]

whoa..im amazed with all those gears you have there

[@VikasGupta-ex3sb]

Hello. this video is very much helpful in practically understanding the crossover distortion in class b amplifier. I request you to please provide the actual circuit diagram with the specific component values, which you have implemented on the breadboard. I want to implement this circuit on breadboard and study it individually.

[@CoolDudeClem]

Good video and well explained. My guess for the part near the end of the video is the input signal becoming to strong driving the transistors into saturation, but I could be wrong. Right now I'm actually listening to this through a valve amplifier I made!

[@roylumsden1017]

excellent usage of electronic language, clearly understood.

[@thecrikster]

The answer to the question is that the input signal is hitting the +/- power rails of the amplifier circuit. Either you would need to keep the input signal within that limit or increase the power supply voltage. Ultimately, you might have to redesign the circuit to work with the required higher power supply voltage.

[@AureliusR]

Okay, at about 12 minutes I was so, so confused. I created the schematic in Qucs and what I thought was the case turned out to be true -- adding those diodes means you now need to get to 1.2V in order to turn the transistors on -- it makes the problem *worse*. I did figure out that one of the diodes was backwards. Then I saw a commenter say that the signal needs to applied to the bases of the transistors still, which makes a bit more sense, but I don't understand how the diodes could be doing anything at all in that scenario. EDIT: I just simulated that, and all I have is the class B output... I saw your comment also saying the diodes need a bias current to have their forward junction voltage appear at the base of the transistor. This is starting to make a bit more sense now, as I couldn't for the life of me understand where that 0.6V was coming from. EDIT 2: Okay, so I finally got the simulated circuit working as intended (I believe) but... I don't have any gain! I actually have a bit of loss. The input is 1Vpp, I have Vcc and Vee as +/-5V, the diodes have about 2.5mA bias current, and the output does look very clean indeed. But it's only about 900mVpp... where is my gain?

[@Thesignalpath]

Glad you got it working. Note that this circuit has power gain, but no voltage gain.

[@123cyr]

Yes, also biasing resistors between the transistor bases and supply I think?

[@andymouse]

This is pure gold...cheers.

[@michaelpukmel9175]

Thank you very much for the video. Your lecture is very clear and well done!

[@ourplesoop]

Really informative video. I would have liked to see the THD quantified but otherwise I was happy with the detail.

[@UpcycleElectronics]

Wow, you answered so many questions I had about the interaction of input impedance, the buffer, and preamplifier stage of an amplifier design. Thank you. (liked/subscribed) -Jake

[@Desmaad]

The non-lnear bits you see when you REALLY crank up the input to the A+AB amplifier is clipping, I believe; the amplifier has reached the limit of input voltage it can take, so voltage no longer increases over time.

[@ernestb.2377]

Very nice short tutorial. 👍 I also see that here, 11 years ago, you have significantly less equipment compared to now 😁 Keep up the good work!

[@seanz1983]

Thanks again Shahriar, your tutorials are always entertaining as well as educational, especially the magnetic levitation experiment. Just finished building mine. One question, where did you find those bench stands for your equipments?

This was a great video! Are you planning on making videos about other amplifier types as well? That would be great!

[@x86cowboy]

Input swing of 5Vpp, +2.5V and -2.5V power rails. I think that means the output is being clipped; which is where the X-Y distortion is coming from.

[@Hanz_theengine]

Brilliant, absolutely loved it! Much better than my teacher...

[@ivanv754]

The effect happens when the output saturates!

[@shamalperera4875]

Verylike .......what is sir "dc control "power amplifier ??

[@sivalley]

Answer: Input signal level approaches 1st stage supply voltage forcing 1st stage to saturate since there is no longer a voltage difference across BE junction, second stage responds by not turning off and holding output at rail voltage. Commonly referred to as output clipping and very damaging to resistive loads that cannot dissipate a DC bias current that appears across it.

[@arunkumarpalanisamy9509]

answer to your question: the power transistor can can voltage swing only between +2.5v and -2.5v i.e, 5v(pp). when input is more than that power cannot be provided by the power amplifier!

[@MBAgeeJr68]

Thank you for this clear tutorial and refresher for me. I am jealous of your collection of test equipment!

[@martinda7446]

Just a minor point, the distortion is called 'crossover distortion' and the history of manufacturers to overcome this and other areas of harmonic distortion is fascinating with the THD wars and giving us 0.0001% thd and below. 0.1% is considered ideal and was given us first by H J leak in his ''point one'' amp series in around 1948 (from memory)

[@TheLawnWanderer]

+mart fart push-pull ultra linear valve amplifiers are no joke. The circuit family is called Williamson amplifiers.

[@martinda7446]

TheLawnWanderer Leak predated the Williamson and I dont beleive it was ultra linear design I think williamson used ''overall'' negative feedback as a first and envisaged a triode output not pentode/tetrode. Blumlein invented ultralinear in the 30s along with many other great discoveries.

[@TheLawnWanderer]

mart fart point one wasn't UL, but triode connected instead. The later ones were UL though, really no point to not use UL. Pretty much all modern amplifiers in that style are UL with the option to switch to triode with a simple switch.

[@Hexor1211]

Puzzle for the Day (36:30) - We are looking at amplifier going to saturation (clipping). Input signal is to large and output transistors are in saturation region (collector current changes little or none versus base current). We can see that one transistor (negative swing) goes into saturation before the other transistor.

[@jimshaw4424]

I really loved this tutorial. You have a great way of explaining electronic circuits. Keep up the good work.

[@burakg7246]

Hello, Mr. Path. Many thx for all the valuable content you provide! I've got a question: All the push-pull examples you show, are designed with a rail-to-rail power supply. How would a design look when a single supply line is used? Would it still have a symmetrical design regarding the npn-pnp sections? And which point would be the source signal fed? Again at a symmetry-point?

[@Thesignalpath]

In one of my earlier videos (spark generator), I show how you can create a mid-rail voltage for a single supply operation of opamps.

[@burakg7246]

@@Thesignalpath Thanks for the response, I'll check it out.

[@jamesmasonic]

why didnt you show the biasing part in the first amplifier on the left? you are telling the dc bias is causing an unnecessary power dissipation even if there is no input signal right? but your drawings has no bias? this is a bit confusing..

[@orti1283]

You don't need further biasing when using a bipolar source for a class A amplifier, as the negative source at the emmiter keeps base-emmiter voltage above 0.6V even when input voltage is 0. Oops! Just realized this is a 2 year old comment hahah

[@parkerd2154]

@@orti1283 Are you sure about that? Do you have a reference? I was assuming it was a small signal phenomenon like the OP suggested.

[@orti1283]

@@parkerd2154 I'm 100% sure, you can check Microelectronic Circuits and Devices by Mark Horenstein :)

[@zohirbailiche7322]

Dude.... The diode you were pointing at at 11:17 is in wrong direction... Doen't it?🤔

[@realchristopher4334]

This is a very old video! But a very good old one! Thank to God of Science that my 'luck' is good! This is the best ever 'tutorial' on amplifiers! Shahriar's A + AB design actually works and works frighteningly well! I mean, I simulate it. I have nearly zero hope that simulators (I use Multisim) are accurate, let alone precise, but when I match those measured and simulated numbers they are frighteningly similar! I say this because (simulated) component data are far from realistic. I do not mean the intricacies such as temperature, vibration, and so forth. I actually mean basic characteristics such as saturation, breakdown, and so on. Most op-amp, for instance, have zero limitation, you can feed them kilo volts input and kilovolts of power supply and the the output signal still looks normal! Same goes for diodes. I now wonder how to actually make it an amplifier, which component to change. The circuit is not exactly an amplifier but a current/voltage follower. There is no amplification.

[@s.r.m.m8789]

چون تقویت کننده شما در اون ناحیه به اشباع میرفت.تشکر بابت مطالب اموزندتون

[@mbabaeevideos]

Thanks Shahriar. But you've placed the top diode D1 in the first AB amplifier schematics in revere polarity.

[@davefourtracksmusic7685]

ok good lecture what about class D amplifier is class D good for a DJ power amp ?

[@hlove]

at 28:17, you say the input is on the horizontal (x) axis, and the output is on the vertical (y) axis. Shouldn't it be the other way around (input on vertical and output on horizontal)? Because for inputs between -0.6V and +0.6V, output = 0V.

[@Thesignalpath]

The spectrum analyzer is AC coupled at its input. Furthermore, the output load of the amplifier is 10Ohms. Therefore, adding another 50Ohm in parallel has minimal impact.

[@AMahmoudAAal]

the output voltage can't exceed the Vcc

[@gyrgrls]

It can with an inductive collectorr load!

[@generatorlabs]

Very good video. The tutorial was not overwhelming. A perfect mix of theory and practical hands on visual elements to glue it all together. Thanks for your work.

[@Thesignalpath]

The spectrum analyzer can have up to 30VDC at its input without damage. That is because it is AC coupled. Furthermore, it can see up to 30dBm of input power which I could not generate.

[@permitivitym4318]

holy cow with all those equipment's. you have more stuff than what I have in my bench at work

[@permitivitym4318]

that's a $10,000 scope

[@LolanBadeauxMakes]

yes he has an awesome bench setup. i so jelly =)

[@alicekichlu215]

I AGREE!

[@eduardorubin7661]

You just saved my thesis. Thank you!!

[@deanedgx]

would the Class A+Class AB configuration be what Quad calls a 'current dumping' amplifier?

[@relaxationTherapy001]

awesome video, shahriar...keep up the good work.. answer to the quiz is "with increasing input voltage u r saturating the transistors gradually that's y output is getting clipped off. after all you'll never get output higher than the driving supply voltage.."

[@Thesignalpath]

Even though your statement is true, that is not the source of the problem! Something else happens before that.

[@yxk081]

CHEERS MATE GREAT ONE. Significantly helpful. If you could have some thing similar on class D, would be great.

[@zaroaster8348]

I have recently discovered your tutorial in the internet they are all very informative thank you for taking time to explain complex electronic concept all so very nicely I am very thankful. My answer to your quiz question at the end of the video about the non-linearity region of the signal is; I think the bandwidth limitation of the transistors in the circuit.

[@Thesignalpath]

Class A, B, and AB amplifiers are fundamental building blocks. They hardly 'a waste of time'.

[@ninguno1756]

HI thank you for the video. Very clear. Next time can you make a video continue the same thing and explain open loop an close loop. And de feedback thing and oscillations an phase. Regards

[@antoniocastrocarballal4051]

Many thanks for the explanation, Shahriar, absolutely clarifying!!!

[@Lowracerman]

Very educational. college was fun. I could have learned more if we had enough equipment for everyone in the class to experiment with.

[@Thesignalpath]

You need a small current flow through D1 and D2. and one of the diodes is backward. I have added a note to the video.

[@MarysKiril]

About that puzzle... it seems that the higher the input level, the closer the emitter potential of Q1 gets to V+, so less current is available to go into the base of Q3 and so the output levels off, falling behind the rise in input potential. Love your videos by the way, the topics, the format, the explanations, everything. Thanks a lot for making them.

[@andymouse]

And 10 years later...The signal is clipping and your correct ! unfortunately you have no prize !

[@AltayBrusan]

Two questions: 1- How is it possible to have 0.6V (or -0.6V) on the other side of the diode when there is no input? 2-Why spectrum analyzer shows the power in negative? (Is it reflected power ?) Thanks for who help me with these questions :)

[@LeelooMinai]

Great tutorial. I noticed probe tip attachments in the video that seem convenient for probing a breadboard. Any idea where those can be bought?

[@drstrangelove09]

What is the model number of that Haako soldering iron? Kinda looks like a FM204-CP.

[@SIedgeHammer83]

Clipping, Amp cannot provide enough power that causes the the wave to cut off at the peak. How to solve this issue? Get a stronger a Amplifiers, or don't drive it too hard.

[@taz0k2]

+SIedgeHammer83 or perhaps it is a problem with the "rails". If you have +2.5V and -2.5V then sooner or later you would need more. Or expressed in another way: eventually the +-2.5V would not be able to supply enough the amps going through the 10 ohm load which would not be able to get high enough voltage over it.

[@hailstress]

+taz0k2 It has always been better to explain it that way, when you come to think of an amplifier generally. You fetch voltage from the power source that corresponds the value of Gain times the Input. So if I have an input signal of 1 volt and a gain of 10, I should be getting a 10 volt in a perfect world. But the device should have a power source that enables it to fetch that voltage. I hope I helped make it clearer. That was a great video by the way, I have stomped on and it looked interesting, never boring. :) Great work. Keep it up.

[@hailstress]

+taz0k2 You could follow up this video, with a frequency response analysis. Discuss the parasitic capacitance, design for linear response over a bandwidth. Discuss the phase shift, and delay. It will be very helpful, much more interesting as well.

[@MellexLabs]

you solve it with negative feedback to the input stage... this will limit the gain of the overall amp...

[@mohamedmamdouh3748]

In class AB when the input 0 v it is not necessary the voltage after diode to be 0.6 v if u enter 0v dc on diode and measure voltage after it , the voltage still equals zero

[@hemantpant3114]

diode D1 in class AB is opposite nyways very good explanation Thanks

[@myvaz4kaimp227]

Nice message !

[@robdb787]

Agree with hemant, diode D1 is wrong way around. Otherwise perfect lecture.

[@Thesignalpath]

You are right. This is a simplified diagram. I have added a note the video to clarify that.

[@Thesignalpath]

Sorry, I did not have enough time.

[@gregzinhao]

The spectrum analyzer haven't a 50ohm input impedance? How you put it direct on the circuit?

[@ovi_4]

You talking about applications in the region of 30-40GHz (oh my gosh,,,) I wonder what kind of applications would they be. I thought that for anything above 10-11 GHz it them becomes a military matter Only they have the budget and the means to be able to play with such ultra crazy high frequencies.

[@schwinn434]

I'm lost about the diodes added to this circuit; I've tried modeling this right circuit with the diodes added in LTspice, and I get an answer of 44.99uV and 44.99uV at the base of Q1 and Q2, respectively, using the .op command in LTspice. There is something I'm just basically missing (after all these years) when trying to understand the biasing of transistors. I still wouldn't even know how to write the mesh, and nodal equations to determine the voltages at the bases of Q1 and Q2 - since, the voltage into the base is an AC signal, and not a DC signal to establish DC biases on the bases of Q1 & Q2. (That is, I might have understood this circuit if it had a DC source biasing the diodes on, at the bases of Q1 & Q2, but not simply an AC input source.) I understand that the diodes where added in order to eliminate the cross over distortions; yet, I just don't understand how these diodes actually do this - that is, I couldn't show any type of equations which would arrive at 0.6VDC and -0.6VDC at the bases of Q1 & Q2, respectively. I've even went back a watched a few mesh and nodal analysis examples on KZbin for transistor circuits but all the examples of mess and nodal analysis I've found are circuits with DC biasing sources, and no AC source analysis. "Any" help on understanding this would be greatly appreciated!

[@lukesnake123]

this video is absolutely fantastic. brilliant, really.

[@EJP286CRSKW]

Good video but it exhibits a very common confusion, Your Class A amplifier is single-ended Class A. There is also push-pull Class A which you don't address. Your class B amplifier is really class C as the conduction angle is

[@JLSoftware]

In the Class A, how can current be flowing if there is "no signal?" With no signal, wouldn't the transistor be off, and thus no current flowing????

[@motormadness9975]

class A is biased in dc operation, he is referring to zero ac voltage

[@musicmakelightning]

I'm guessing you were a great TA as a PhD candidate...wish you were around when I was an undergrad (though, you probably weren't yet born) ;). You teach with great clarity and enthusiasm and remind me why I was so excited to become an EE...which is really uplifting in my, ahem, older years.

[@johnadams9041]

Hi sir ! I have a simple question about the hFE of the final transistors of an NSA amplifier operating in the parallel SEPP circuit . Particulary I am talking about Pioneer A9 ,which is working in parallel SEPP with a high frequency DC servo bias. So the question is should the end power transistor have the same hFE? Likes the the class letter and likes a digit number to prevent the distortion?

[@Crytek1337]

Im using 2SC3858 npn transistor and 2SA1494 pnp transistors. I used the same values but a bigger power supply. Im going to make a audio amplifier but it didnt work :(! Can you pleeeeeeeeease help me??

[@shaberahamza5729]

shouldn't the diodes be backwards for AB type?

[@marionetadelplaneta]

+Shabera Hamza yes

[@_majortom_]

yes

[@arts9591]

The signal question could be because there is an (a)(b) BETA manufacturing product capacity limitation Saturation and Breakdown Regions

[@camelazo]

Hello community i have a silly question , why in the amplifier A+AB the amplified signal ( in blue) is less Vpp than the input source? (yellow one), Regards. 35:16