Audio Amplifier. Which class should I use?

[Shayaan_Mustafa]

Thanks a lot godfreyl. I was hoping that you would reply to me.

Here is my attachment as you said. I changed frequency to 5000KHz from 20KHz

godfreyl if you see I need help and goldsmith is offline or you can see if I must know this thing then you please help me. I am very great full to you for this.

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@godfreyl can you tell me why law about biasing BE of class AB is important. Can you give me explanation about this? post#144

 

[goldsmith]

Hi shayaan
Congratulations ! increase the step to see a better waveform . and remember that your circuit need bias for base-emitter junction too .

And about BE biasing : as you probably can see in the out put shape , it has crossover distortion . it is due to the BE junction . those diodes are not on . and your signal should be able to turn them one . hence if you don't bias them with enough DC voltage , your out put will have crossover distortion . you understand ?
Best Wishes
Goldsmith

 

[Shayaan_Mustafa]

And about BE biasing : as you probably can see in the out put shape , it has crossover distortion . it is due to the BE junction . those diodes are not on . and your signal should be able to turn them one . hence if you don't bias them with enough DC voltage , your out put will have crossover distortion . you understand ?

Nice explanation. Thanks sir.

So Now I should connect bases of the two transistors with diodes. Right?

 

[goldsmith]

With diodes and resistors ! can you remember the solution for CC complementary amp ? ( trough two resistor and two diodes ?)

 

[Shayaan_Mustafa]

I think I should use diodes across BE junction of each capacitor or may be use diodes to connect bases of the two transistors.

 

[goldsmith]

I think I should use diodes across BE junction of each capacitor

What ?????
BTW : you'd better to use a resistor in series with the common mode ( emitters ) to the ground to provide a little negative feedback to reduce THD.
You should create a DC path for diodes .
A guidance : in parallel with BE junction . BTW : don't forget to add that feedback resistor .

 

[Shayaan_Mustafa]

Sorry not capacitors. I mean transistors. LOL

 

[goldsmith]

So , now exert things that i told , and show me the result of your simulation .

 

[Shayaan_Mustafa]

Here is attachment.

 

[goldsmith]

It seems good , but why you forgot to increase the step of simulation ? do you know how to increase the step ? if no i can explain it .
And the other thing : why you forgot to add feed back resistor in emitter ?

 

[Shayaan_Mustafa]

1) No I don't know how to increase step of simulation. What will be its benefit?

2) And does adding feedback resistors decrease THD? How?

3) And I have added collector to base resistors. Did I do right this?

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Here is attachment. I have added feedback resistors. But I don't see anything different. The waveform before adding these feedback resistors and after them is almost same. What difference should I notice there?

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Here is attachment. I have added feedback resistors. But I don't see anything different. The waveform before adding these feedback resistors and after them is almost same. What difference should I notice there?

 

[goldsmith]

3) And I have added collector to base resistors. Did I do right this?

of course it is correct . you made me hopeful ! my friend .

2) And does adding feedback resistors decrease THD? How?

There is a node that emitters connected together and then this node connected to the ground . you should use a low value resistor between that node and ground . ( such as 10 ohms ) this action will reduce the gain but it will increase BW and decrease THD as well .

1) No I don't know how to increase step of simulation. What will be its benefit?

It will help you to see higher quality , results .
See below ,please :

What is the value of maximum step size in your simulations ? ;-)

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Here is attachment. I have added feedback resistors. But I don't see anything different. The waveform before adding these feedback resistors and after them is almost same. What difference should I notice there?

Is that feed back resistor ????? see what i told .

 

[Shayaan_Mustafa]

Here is my both attachments i.e. resistor at node of emitter to ground and simulation profile. How to change steps?

 

[goldsmith]

Shayaan , are you designing an audio amplifier ? if yes i don't think that there is any human available that can hear 5000KHZ ( 5MHZ ) ! change it to 20KHZ if you don't want make a transmitter ! .
And change your alignments to these :

 

[Shayaan_Mustafa]

OK thanks goldsmith. I have changed frequency.

But I am still getting cross over distortion. And at 5V amplitude I was getting clipping. So I changed amplitude to 3V. I am attaching both with 5V and 3V results so that you could see difference and could know why I changed 5V to 3V.

But what about cross over distortion?

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Also I have increased steps according to your suggestion and provided image.

 

[goldsmith]

Use 1n4148 instead of those diodes and use these transistors : BD135 and BD136

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Use 1n4148 instead of those diodes and use these transistors : BD135 and BD136

 

[Shayaan_Mustafa]

Sir I don't have 1n4148 diodes instead I have D1n4148 in library diodes.
And don't have BD135 and BD136 in library bipolar.

Do you have these components in libraries?

 

[goldsmith]

did you added all of the libraries ? if yes , type this : D1n4148 and BD136 or BD135 . i think i told you how to add all of the libraries ? didn't i ?

 

[Shayaan_Mustafa]

Yes you told me and I have added all libraries. And I searched parts. But they are not found. Is there not any alternative?

And kindly tell me which version are you using of pspice?

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Yes you told me and I have added all libraries. And I searched parts. But they are not found. Is there not any alternative?

And kindly tell me which version are you using of pspice?

 

[goldsmith]

9.2 . add them again and retest . and tell me the result .