Audio Amplifier. Which class should I use?

[Shayaan_Mustafa]

With diodes D1n4148 I have this result. As I said I couldn't find BD135 and BD136.

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With diodes D1n4148 I have this result. As I said I couldn't find BD135 and BD136.

 

[goldsmith]

It is impossible that you couldn't find them . would you like that see the result of my simulations ?
see below , please :


Good luck
Goldsmith

 

[Shayaan_Mustafa]

Can you tell me the library of transistor in which you found BD135?

 

[goldsmith]

simply ! i added all of libraries ( selected all of them ) and the i pressed P and then typed : BD135

 

[Shayaan_Mustafa]

OK I will give you result by tomorrow. Thanks for great help. Thank you very much.

 

[goldsmith]

So , good nigh my friend oh no , good morning my friend !!!! :-D

 

[Shayaan_Mustafa]

Good afternoon sir.

Now as you know we have completed complementary CE. I have tried this circuit on other simulator and its working like your circuit. Now I will convert it to CB and then post result.

Have a nice day.

 

[godfreyl]

Now I will convert it to CB and then post result.

Before you do that, did you notice that there is a very big problem with this circuit posted by Goldsmith. If you build this circuit, it will not work as you expect.

In your simulation, look at the current flowing through C9 or C10. Do you see that the current is flowing mostly (or only) in one direction? That means the capacitors are slowly discharging.

After a few seconds, the output voltage from this circuit will be much smaller, and very distorted. You can not see that in your simulation because you are only looking at the output for a very short time.

If you want to see the problem, set the simulation "Run to time" to 5 Seconds, the "Maximum step size" to 0.0001 seconds, and the signal frequency to 20Hz.

This is obviously not the sort of circuit Goldsmith wants you to use in your amplifier. I think he is just showing it as a bad example - what not to do. If you simply change the circuit from CE to CB, you will still have the same problem.

View attachment 75547

 

[goldsmith]

In your simulation, look at the current flowing through C9 or C10. Do you see that the current is flowing mostly (or only) in one direction? That means the capacitors are slowly discharging.

Hi Godfreyl
Why you said that ?
Why you didn't say that in class A amplifier ? ( i'm talking about coupling capacitors ! )
I changed the time as high as some thousand usec . see below : why the result , is good ? ( still ?)

Respect
Goldsmith

 

[godfreyl]

If you look at the current flowing in each transistor, you will see that it is not a class A amplifier. It is a class AB amplifier.

If you look at the currents flowing through C9 and C10, you will see that those capacitors are discharging.

You are still only looking at the output for 50mS. If you look at the output for 5 or 10 seconds, you will see the problem.

 

[goldsmith]

Gorfreyl
What is the benefit of current through , Capacitors ? are those really important ? of course no . we are just looking for out put waveform ( voltage across the load ) .
And if you think this circuit after some second will cut the waveform , what will happen ? nothing special ! because the voice that each human can hear is around 20HZ up to 20KHZ . but some second is pretty higher than that . because our signal will have very fast changes ? BTW : at class A amplifier , we have a capacitor in out put too . but it will work fine ! why that capacitor isn't important ? though we can say , things that you told are not important for our signal amplification .
however , i didn't refer to this circuit , my mean was completely different . but it is good , too .

 

[Shayaan_Mustafa]

@goldsmith so I should convert the existing CE into CB configuration?

@godfreyl thanks for this post. But I want to know what would happen if capacitor discharge slowly or what distortion through speaker I received?

I say both goldsmith and godfreyl to answer this so that, I could ask some more questions from both of you experts. I want to make my ideas clear like glass.

Thank you experts.

 

[goldsmith]

Hi shayaan
Good night my friend .
The CE would be good for your aim . now you can start i think ! so you'll need a CC ( class AB ) arrangement after this circuit . right ? so , can you design one CC at class AB configuration ? show me , if yes .

 

[Shayaan_Mustafa]

Why CC? Why not CB (Common Base) ? We were designing CB before but for easiness I chose CE. Now you are saying CC. Why is it so?

While CC has unity voltage gain. Isn't it?

And yes I can construct CC in class AB. Its easy. I will post it.

 

[goldsmith]

Shayaan . CC after your CB or CE . CC to provide high value of current gain . you understand my friend ?

 

[Shayaan_Mustafa]

Oh OK OK.. I got. So you mean CB is to provide high voltage gain and CC is to provide high current gain.

Right?

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Here is hand made sketch of CB complementary.

Here transistors are BD135 and BD136.
Diodes are D1N4148 both.

Is this circuit right?

 

[goldsmith]

Oh OK OK.. I got. So you mean CB is to provide high voltage gain and CC is to provide high current gain.

Right?

Hit to the point !

And about your circuit ! i prefer that you simulate it ! show me the result of simulation .

 

[Shayaan_Mustafa]

OK you please wait until I do.

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Here is my CB complementary.

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If it is right. I mean until now if everything is right then I have some questions. Which I think I must know. But first tell me is everything with my circuit is right up till now?

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Sir Now I am leaving forum. I waited you. Good morning. TV have a nice day.

 

[godfreyl]

What is the benefit of current through , Capacitors ? are those really important ? of course no .

No, it is not important. But if you look at it, you may learn something. If you look at it, you may understand why there is a problem.

we are just looking for out put waveform ( voltage across the load ) .

Yes, this if most important. Did you look at the output waveform for 5 or 10 seconds to see what happens?

And if you think this circuit after some second will cut the waveform , what will happen ? nothing special !

The music will become very distorted. That is special. I think Shayaan will want to listen to music for longer than 2 seconds.

though we can say , things that you told are not important for our signal amplification .

The things I said are important.
Why do you not do the simple tests I suggested?
Do you not want to learn anything?


One more problem:
Did you look at the voltage on the transistor collectors? If you do you will see that there can be more than 60V between the collector and emitter. So why do you use BD135 and BD136? They are only rated for 45V. BD139 and BD140 would be better.

 

[goldsmith]

Hi

Do you not want to learn anything?

of course i want . but you forgot to answer my question ! why in a CE class A amplifier you didn't say that ! is there any path to discharge the capacitor ? of course no ! if we use two stage as a chain , adn the other stage with Zi = pretty high .

Did you look at the voltage on the transistor collectors? If you do you will see that there can be more than 60V between the collector and emitter. So why do you use BD135 and BD136? They are only rated for 45V. BD139 and BD140 would be better.

Quite right . but i didn't say that to shayaan because i wanted that he understand this issue that the specifications of transistor are pretty important . such as HFE and VCE and IC and vcesat and vbe ( reverse ) . and GBWP of current . and ....
Be patience ! i don't want confuse shayaan . i want he be able to see some problems in practice . as i told , i didn't refer to this circuit . it is completely difference with thing that is in my mind . but we can optimize it . so you can tolerate .