class AB amlifier.

[yasir_ali]

@ Audioguru

one 2 last things about this biasing technique is that,
1- is it fine to use this biasing technique? because if you zoom on Oscilloscope, you'll find that the upper peak is clipping a bit.

2-that i am a bit confuse or interested to know when to use this resistor biasing technique and when to use that virtual ground creator technique.?

 

[yasir_ali]

@ Audioguru

one 2 last things about this biasing technique is that,
1- is it fine to use this biasing technique? because if you zoom on Oscilloscope in picture in my last post , you'll find that the upper peak is clipping a bit.

2-that i am a bit confuse or interested to know when to use this resistor biasing technique and when to use that virtual ground creator technique.?

 

[audioguru]

@ Audioguru

2 last things about this biasing technique is that,
1- is it fine to use this biasing technique? because if you zoom on Oscilloscope in picture in my last post , you'll find that the upper peak is clipping a bit.

The oscillator circuit is too simple. It is missing parts that keep the output at a constant level that prevents clipping. Many years ago a light bulb was used because when the output level increased the light bulb would get more voltage which made its filament hotter which made its resistance higher so it stopped the output level from increasing more. If the output level drops then the opposite happens. New circuits use a Jfet to control the output level.
You can reduce the voltage at the (+) input of the opamp a little so that the clipping on the simple circuit is symmetrical.

2-that i am a bit confuse or interested to know when to use this resistor biasing technique and when to use that virtual ground creator technique.?

Since the input resistance of an opamp is very high and uses an extremely small current then the resistors can bias it. But a circuit that uses a high current from the "half the supply voltage reference" needs a virtual ground circuit that can supply a fairly high current without its voltage dropping.

 

[yasir_ali]

@ Audioguru
today i have downoaded the new version and replaced old 741 with TL071. now please tell me how to calculate the output current and how to get 40mA(RMS) current at its output.? still its very low to put it in the base of Class AB amplifier.


Thanks

 

[audioguru]

The minimum supply for a TL071 is 7V but you have only 5V.
Your 'scope shows that it is clipping like crazy because your extremely simple oscillator is missing a circuit to stabilize its output level.

40mA RMS has peaks of 56.6mA which is impossible from a TL071 and most other opamps. With a peak output of only 2.5mA the output voltage loss from a TL071 and most other opamps is a max of 5V peak. You don't want a voltage loss.

 

[yasir_ali]

@Audioguru

Hello, Today i've tried using a Common emitter Amplifier with my oscillator to amplify its current But i am having very bed result. i think it is because of the low input impedance of the Common emitter Amplifier. am right.? Now if i try to increase the input impedace, other parameter will be disturbsd (hfe=60, Ic=50mA, Vcc=9v for inclosed picture).
1- now please tell me , what should i do.?

2- or you tell the way to amplify the current of my Oscillator to 1A. you can send me the block diagram.

Thanks

 

[audioguru]

You do not have a power amplifier in your circuit. The little transistor is shorting the output of the opamp and is getting hot.

1) Your oscillator is too simple so its output is clipping with high distortion.
2) The input impedance of the transistor "amplifier" is only 64 ohms which the opamp cannot drive.
3) Only the high frequency harmonics of the clipping distortion from the opamp pass through the input capacitor that is much too small.

Why don't you design or buy a power amplifier?

 

[yasir_ali]

At first i was going to design the class AB power Amplifier. But as you said my OScillator uses 2 battery and because i needed 1 so i decieded to design Oscillator with one battery with your help. Thanks.
And look at the Rf in last post when i did not used common emitter Amplifier, i have used 400KΩ resistor instead of 360kΩ that's why the output was clipping.

And now it's time to amplify the current to 1A. now please you tell me how can i do that.
Can i use class AB amplifier directly? or i must use some small signal amplifier to drive the class AB amplifier?

 

[yasir_ali]

At first i was going to design the class AB power Amplifier. But as you said my OScillator uses 2 battery and because i needed 1 so i decieded to design Oscillator with one battery with your help. Thanks.
And look at the Rf in lasts post when i did not used common emitter Amplifier, i have used 400KΩ resistor instead of 360kΩ that's why the output was clipping.

And now it's time to amplify the current to 1A. now please you tell me how can i do that.
Can i use class AB amplifier directly? or i must use some small signal amplifier to drive the class AB amplifier?

 

[audioguru]

The 400k resistor in your oscillator sets its gain. If its value is slightly too low then the oscillator will not oscillate. If its value is slightly too high then the opamp clips the signal.
Your extremly simple oscillator is missing a circuit to control the output amplitude so that the opamp oscillates properly but does not clip.

A good simple class-AB power amplifier has 3 or 4 DC-coupled transistors. You don't need much gain so the amplifier can have plenty of negative feedback for extremely low distortion.

Why doesn't your teacher teach you about this stuff?

 

[yasir_ali]

i am not in any institute but a lover of electronics and found no one in my area who can help me in this regard. i just get some time to learn electronics and thank God i found people like you. that's my be the reason that i am slow in learning.

 

[audioguru]

Sorry,
Most of us learned electronics in university. There are a few teachers here who might help you learn about the fundamental basics.

 

[yasir_ali]

@ Audioguru

Hey! i am not asking you to teach me the who electronics But i am justing asking you to help me what i am wanting to do. and you helped me a lot up till now. and your help was very very helpful for me. And now you cannot leave me in between like this please

 

[yasir_ali]

@ Audioguru

Hey! i am not asking you to teach me the whole electronics But i am justing asking you to help me what i am trying to do. and you helped me a lot up till now. and your help was very very helpful for me. And now you cannot leave me in between like this please

 

[audioguru]

@ Audioguru

Hey! i am not asking you to teach me the whole electronics

But your oscillator is distorted because it is too simple and your "amplifiers" are hopeless.

I like talking about new and fairly complicated circuits, not the old basics.
Maybe somebody else can teach you the basics of electronics.

 

[yasir_ali]

ok. you please send the block diagram of the whole circuit like if you were to built the circuit what you would have been using?

 

[audioguru]

A block diagram has no details. Here it is:

 

[yasir_ali]

Hi, I've got all the things except this "Level control circuit". is it the circuit you were talking about to stablize the amplitude of output of OScillator.?

 

[audioguru]

Hi, I've got all the things except this "Level control circuit". is it the circuit you were talking about to stablize the amplitude of output of OScillator.?

Yes.
Your simple oscillator has the opamp increasing in level until its output saturates and clips the signal. As I explained before, a light bulb was used many years ago since its filament changes resistance with the amount of signal in it and a Jfet circuit is used now.

There are many tutorials about Sine-Wave Oscillators on the internet and you should look in Google for them.

You do not have a good class-AB amplifier circuit.

 

[yasir_ali]

ok. from today i am start working on "Level control circuit" then i'll come back to the Class AB amplifier. and i have read some notes about this class AB amplifeir. and amoung many forms of class AB i'll use class AB with Vbe multiplier amplifier. which does not require matching diodes and has many advantages over diode biase class AB amlpifer. But first i'll start working on output stablizer.

Thanks