Nicely done. I feel like I just went through a EE lesson on class AB amp circuits! :) Will there be a part 3 to this series?

Great to hear from you! And yes those pens are awesome.

I'm looking forward for part 3!!! :-D

Yes you are correct I didn't check the quiescent current in the SPICE simulation which will definitely introduce mismatch with the calculated power dissipation. If you have time, please find the SPICE quiescent current and re-run the computation in Maxima and let me know by replying to this comment. Yes part-3 will be coming on how to perform typical thermal calculations and heat sink design to keep operating junction temperature of output transistors within thermal limits. Cheers!

@@SmithKerona Did you ever make Part 3?

Electrical capacitive effects are negligible on loudspeakers because we are dealing with low frequencies in the audio spectrum. But certain loudspeaker mechanical effects are modeled in the electrical domain by capacitance with appropriate values and circuit configuration. Like I said in the video, the model included is a first order approximation which neglects some electrical and mechanical effects.

If you have LTspice download the following simulation and run it. It shows you how to implement a step down XFMR in a real world circuit such as power supply. docs.google.com/document/d/1FsQSZnfkQHuAiSy9G3K7h1u3uwhVJwqDRgmRC1JbG74/edit?usp=sharing You should copy the text in this file and save it with file extension .asc and open it with LTspice. FYI I am using a current source to excite the primary winding.

The advantage of comman emitter amplifiers is that you have nearly rail-to-rail output voltage swing. So the power dissipation at peek power is considerably lower than in the case of emitter follower amplifiers. Some people don't like common emitter amplifiers because they are suspected to have higher THD, especially odd harmonics, compared to emitter follower amplifiers. But this is the question what you want to get. ibb.co/brmM8tZ shows the FFT with a third harmonic of -53dB compared to the signal. This is absolutely ok for me. ibb.co/ZdGrNqW shows the linear FFT plot. The output voltage at the 3rd harmonic is 22 mV compared to a 10 V signal. It is impossible to hear this contribution.

When you use a MOSFET output stage ibb.co/TKcDc0N you can make the circuit very linear. ibb.co/zFb30Jt shows the FFT. The THD is considerably lower. The 9th harmonic comes with the highest level leading to a distance of -59 dB.

Hi thank you for your comment and sorry for the late replay. Indeed if the load you are driving is purely resistive then yes the maximum power dissipation on the output transistors does occur at an output voltage that is lower than the maximum output amplitude the amplifier is capable. But as can be seen in the video, the amplifier is driving a complex impedance that has an inductive component and as such, the maximum power dissipation occurs at the maximum output amplitude. I will demonstrate this behavior in a video shortly. Stay tuned.

@@gkdresden Although common emitter output stages can give nearly rail to rail outputs, they are highly unstable (there is whole host of reasons why this is the case and I might discuss it in future videos). Therefore it is best to stay away from such circuits.

Go back and re-watch the video...the answer is there ;) I will give you a clue... It has something to do with zero crossing of the voltage across collector and emitter Vce(t) and collector current Ic(t). (Also think about what will happen to the power dissipation in the transistor if the load is only an inductor...)

@@SmithKerona Thanks. Much appreciated.

no

@@AndrewTa530 explain

"What happened to the day's when people just built an amplifier just going by the look and feel of the components and worried about the math later...." I'd imagine you only get that good having done the calculations many times, having built those circuits so many ways, and having had a deep grasp of the underlying mathematics. As in software engineering, any other trade or performant art, you can only sensibly abstract away the technical details to think at the architectural level after you've mastered those technical details.

If you take a step back and consider that what you begin with are mathematical descriptions of something both physical (electronics hardware) and intangible (i.e., frequency) and what you end up with is something that works as you've predicted (i.e., a bomb ass high fidelity speaker -- or an airplane that doesn't fall out of the sky because some controls engineer somewhere did his math homework), it's quite miraculous. The system of symbols and abstract models, on paper, mimic reality! The science of it is much more interesting of a strategy than some guy who picks up a random capacitor and tells you to put it in your circuit and observe whether it blows up.

Minh Tran you can throw a capacitor in your circuit anywhere and if it blows up, then don't put it there again unless you found out that you actually enjoy blowing things up LoL... Maths on the other hand just takes the fun part out of electronics... All that you need is some basic numbers that are available from datasheets and basically just have fun experimenting, Your test equipment will tell you what's happening and also give you the math that you may need... I think that if I started with mathematics first before I did anything else, then that's clearly saying that maybe I'm in the wrong industry... Whatever you are into, you should have already have plenty experience because you already know what isn't going to work because you have already thrown that capacitor into the same circuit before and you definitely know that it won't work without any mathematics.... And yeah I get it that some people develop an erection while doing maths and I'm okay with that, I'm just not one of those people.... I can just look at the circuitry and see what is wrong with it and where I haven't thrown a capacitor into it yet! But the real beauty of it is that I can do it all in my head. If what you are doing is fun, then you must be passionate about what it is that you are doing but if it isn't fun, then it's just a job and you don't have the passion to make a difference in the world. As an employer, I'm not really interested in your schooling qualifications... I really just want to see the passion in your eyes and hear it in your voice... That's the difference right there!

Minh Tran Oh and as for coming up with something as predicted! You are better off reading some service manals and fixing some tv's... hopefully you will achieve something as predicted!... But please don't tell me that you are going to do some mathematics and come up with a prediction that you are going to come up with something that no one else has done before! So basically the Wright Brothers went and did some mathematics and came back with the answer that they are going to be able to make a contraption that will definitely be able to fly! Or maybe you might think that they just made a frame and threw some capacitors at it to see if something comes out of it? if something did come out of it then I'm sure that they would have busted out the mathematics to work out why it worked... But if it didn't work, I'm sure that they would have tried something else based on their simple observations of what happened when they threw the capacitors at it... No point in doing the math for something that clearly didn't work... Because while you're doing mathematics, someone else is on the verge of inventing the next world changing idea, he can worry about the math later because everyone else is going to do it for him.. and that could potentially be you!

‘But please don't tell me that you are going to do some mathematics and come up with a prediction that you are going to come up with something that no one else has done before!‘ Math is a vast and terribly interesting subject on its own but engineers use it as a tool of analysis. Specifically, it allows us to describe, model, and simulate the behavior of physical components and systems (i.e., dynamics of sound, flight, fluids, electricity). It is a design aid, like a saw to a carpenter. Mathematical models help us design and understand complex circuits. Edison, Tesla, Franklin, Joseph Fourier, Bernoulli, Newton, Einstein, Currie, Feynman, Maxwell, Alan Turring, Marconi, Von Neuman ... to name a few, were pioneers of novel technologies who were renown for their mathematical prowess. Do you think they had a manual for what they were doing? How do you think we describe and observe things beyond human perception - Black holes, gravity waves, light, atoms? We we express their properties in mathematical equations and refine them. To reiterate, math is a tool.