I modified a simple amplifier so its output power is as high as possible for a 9V supply and it has some gain. It is simple so it has about 2% to 5% distortion. Its distortion is less when it has more negative feedback but then its gain is low.

 

now which one among all the circuits is best???

 

now which one among all the circuits is best???

The one that satisfies your need.

I'm sure your professor has the link to this thread already.

 

My need is a low cost audio amplifier using transistor

 

My need is a low cost audio amplifier using transistor

If cost is the only criteria, then compute the costs of each design. The answer will present itself to you.

 

You really have to choose what frequency range you want to amplify to which gain.

 

I have got this one but doesn't know whether it will work or not!

 

Forum! wake up!!!

 

It will amplify the input, if that is what you want to know.

 

well in practical I guess there must be some noise as well so how I will remove that and I have no idea which mic and speaker to use so.................

 

You have a darlington transistor that is biased "do not ever bias a transistor like that" as we were told in university because the hFE of every transistor is different. It also has DC current in the 10 ohm speaker which is bad. Its voltage gain is only about 10 but for a mic as the input it must have a voltage gain of 100 to 200.