@Andyaka I have changed the voltage values so all of them are the same. I believe I have mentioned what is my input voltage level and what I require at the output.

@DaveTweed, I knew it would be inefficient but not as much. Is there a better circuit that I could use to amplify the input ? besides using high voltage op-amps.

@user_1818839, Yes I forgot to include that in my calculations, Thank you. but it doesn't solve the problem.

@DaveTweed, No It's not homework and I'm not a student. I'm trying to build a high power Class AB amp and I have made it and tested it with my scope the only problem is that my Class AB amp requires the input signal voltage to be amplified since it is a emitter follower.

@Colin, Thank you for helping and recommending the book. I'll try to make one out of discrete components. and update the post with results.

@Oli I don't think I understand your input signal source. It's not likely to be a true voltage source with a 10 Farad input capacitor. I gather you already have a class-AB ready to go that does what you want and that it just needs a driver. But that's very strange to me, as class-AB stages are usually integrated into an overall design (they have two inputs to deal with, typically, and not a single input that could come from a single-ended stage like yours. I think I'd need a lot more info on the class-AB stage and whatever is driving the whole system.

@Oli This looks an awful lot like you've hung your hat on a single approach that you are trying to shoe-horn into a service where it's probably not even closely appropriate to handle. It doesn't make sense to design something like this without knowing what it stands between, in detail. And, finally, this kind of stage is almost never actually used in practice. It's an educational tool more-so, these days. And back when it might have been used, the BJT choices were expensive, not good performers and placed into bad power supply regulation systems, so other additions were made, too.

@jonk, I had totally forgotten, those are supposed to be 10uF not 10 farad. My bad, I will fix them right away. I'll also update the post with class-AB stage schematics.

@Oli Willst du mich verarschen?!? That's the class-AB output stage??? Seriously? Okay. Calm down.... What are you driving with that output stage, exactly? What's the desired delivered power and what's the load? Also, you aren't sourcing it at all correctly (the left side is a disaster and needs an emergency surgical operation to revive it.)

@Audioguru, I'm not using the class-A because of the distortion. There is no negative feedback because there is no driver stage for my class-AB Amp.

@jonk, I know it's bad which is why I'm asking for help, sorry if it's terrible but somehow it works. My load is 2x2 ohm subwoofer at 800W RMS, and I have tested it with all the frequency range at max power and there is no distortion.

@Oli Well, the first thing is to work out the class-AB output stage. It's not right. Then, once that is figured out, the rest can follow. Sure, with those resistors and the adjustable POT you can "make it work." But really, not over a wide driving range as the resistors are supplying the base current and when the voltage nears the rails those resistors will just run out of juice, so to speak. So it is really a very very bad arrangement and it needs repair, first.

@Jonk, How can I fix the problems? This is my first amplifier design. Can you point me in the right direction ?

@Oli Sure. Start with what in the heck you are driving with this beast. What the transducer at the output??? Why do you need such a wide ranging output voltage? What kind of power is required? Details. Is this really just a woofer seriously at 800 watts??!! Because that is major ...., you know! Not minor hobbyist back-room, off-the-cuff on the back-of-an-evelope design. That kind of power is serious crap.

@jonk, Thank you. I am driving a 2 x 2 ohm subwoofer at 800 Watts, I need +- 32 volt at output to be able to push the current through 2 x 2ohm coil of the subwoofer. I have written them in question too.

@Oli This is where I need to stand down, I suppose. You are looking in the face of advanced output driver design -- likely class D or well above. And that's out of my bailiwick.

@jonk, I'm trying to do it with a class-AB amp. I have looked at my other of the shelf amp it also works by using a AB output stage

Hi. Yeah. This is way beyond my ability to advise. Class-AB is going to be less than 50% efficient. This means that you are going to dissipate more than 800 watts just to deliver 800 watts.

That's a whole other space. There are lots of techniques used to provide multiple voltage rails for class-AB designs on this scale.

But the complexity is impressive.

Also, most audio is only about 1/5th or 1/6th of the maximum capability. So you want a system that can automatically arrange different rails as the output increases. This makes the class-AB driver (if you go that way) far more complex.

And it is bad enough without that.

@jonk, Okay Thank you for letting me know. The voltage rails of the of the "of the shelf amp" are provided by it's own DC-DC converter which converts 12 volts to +- 32 volts.

A class-AB can do it. But a simple design, one that we could discuss reasonably on this site, would dissipate like crazy.

I just wanted to make something that "works", Apparently it's not gonna happen :(

If you are looking at paralleling two 2 Ohm speakers (for 1 Ohm output), then the sqrt(2*power*ohms) yields +/- 40 V rails (with 100% perfection, which won't happen.)

At 2 ohms, that's +- 57 volts.

And it doesn't count any of the necessary overhead.

Your Darlington chain of BJTs may work okay on Spice simulation, but there is no possible way you'd want to use that in practice.

Besides, your resistors to the rails aren't the way to supply the necessary drive currents.

You need a current source, for that.

One that works well.

As I said it doesn't need to output full power all the time, as long as it sounds good and loud, it'll do the job. I guess I'll try my stupid design with a high-voltage op-amp as driver stage with negative feedback and see if it works.

I don't mean to cast aspersions. Don't get me wrong.

I'm just saying that this isn't "simple."

Also I have built the AB stage physically

It takes some thought.

I know don't worry

Did you drive that stage? It should have serious problems as you near the rails.

As this is my first design of an audio amplifier I was expecting it to be bad

Yes I did and it worked really good with no problems near the rails

well it did have some problems near the rails at first but after adjusting the pot it got fixed

In practice? I'm surprised.

YES

me too :D

I can upload scope screen shots if you need

As the drive voltage nears the rails the resistors cannot any longer supply the necessary base currents.

It's as simple as that.

That's because the voltage across those resistors decreases until it is neglilgible.

I'm only saying what I saw on my scope

And therefore the current isn't sufficient to drive, anymore.

no that happens when there is no input connected

I'll upload some screen shots of my scope so you can see it your self

there is absolutely no distortion any where at any frequency from 1Hz to 20kHz

also gain of each BJT is around 50 minimum

I've seen brute force designs on youtube. But I'd not use one. In any case, there's a need for current limits (to preserve your circuit and power supply) as well as many other protections. That said, I won't argue with your success. If you want to keep that output stage, fine. You should want a 2-quadrant driver for it. But given what you are willing to accept, I'm not sure anymore.

I know I'm forcing it do what I want, but I really don't have much option other than buying one. I am a beginner when it comes to amplifier design or even analog electronics

I'll just suggest that you consider the fact that a class-A stage, as you are proposing, doesn't source well. It sinks good, but sources poorly. So it won't drive your output stage well. But if you are willing to accept crazy-minded low values for the collector resistor, it might work.

I'll use an op-amp

I didn't want to because they are really expencive

Most opamps won't deliver more than 20 mA. But some will do fine at that level and even much more. Just look for something that can deliver some serious output current compliance.

but seeing how complicated it is to drive it otherwise, I'll go with an op-amp

I have got this one OPA454AIDDA

Well, it's a lot less complicated if your output stage is well designed. But that is a very different issue, I gather.

I need to head off, now. I have learned something from the discussion. Thanks for that. I'll leave you to work through this early design process. I kind of get where you are coming from and I don't want you to stop. Keep at it. But it is a little out of the area where I want to advise, in any detail.

someone in the comments recommend a book by Douglas Self about audio amplifier design. I have started to read it, and I think I'll need way more study to be able to design a "standard" high power audio amplifier.

Thank you so much

His book is worth reading.

I have learned a lot too

He also has a small signal version book, as well. Also worth some time.

Thank you, I'll read that too.

Also look up Bob Cordell.

Sure, thanks for helping me out.

No problem. And best wishes. Seriously.

Have at it!!