now this is my new ckt. pls. check and in last post you said for calculating input capacitor R1//R2 is taken in formula, but what about Emitter bypass capacitor, pls. tell it also.

Thank's..!!

 

I increased the input to 1V peak to show that your transistor is wrongly biased so the bottom of the waveform is severely clipped.
I changed your 15k resistor to 18k so that the waveform is not clipped.

I reduced the value of the input coupling capacitor so that it still passes all audio frequencies.

You add an emitter bypass capacitor and see what happens.

 

now, i have a capacitor in emitter, pls. tell how to calculate it and in last i post you were saying for calculating input capacitor C=1/(2*pia*R1//R2)
but here you have not mention about hie (parameter) how to calculate it or not??

 

Well well Rritesh, I see you're actually trying to learn some things from the beginning for once - good for you!

As far as an emitter bypass cap I'd guess that anything between 10 uF - 47 uF would be fine, when in doubt multiply the input capacitor by 10.

 

Well well Rritesh, I see you're actually trying to learn some things from the beginning for once - good for you!

As far as an emitter bypass cap I'd guess that anything between 10 uF - 47 uF would be fine, when in doubt multiply the input capacitor by 10.

you are saying for calculating bypass capacitor it should be multiple of 10 of input capacitor value, why??
and what about the hie,,... value in expression!!

 

For calculating bypass capacitor use this equation
Ce = 0.16/ ( Fc* re )

re = 1/gm = 26mV/Ic

 

you are saying for calculating bypass capacitor it should be multiple of 10 of input capacitor value, why??
and what about the hie,,... value in expression!!

Because it's simple and works just fine in most non-critical circuits.

If you want exact I see a formula was posted above.

Sometimes you've got to take the engineering out of things and play around with values until a circuit works the way you want it to. I've seen so many engineers go through 4 or even 6 years of college then have trouble designing a simple transistor amp stage because they insist on having 19.294K resistors here and 4.4734 ohm resistors there. A EET would know to try a 20K or 22K and a 4.7 ohm or if they're really lost they'll just put in pots and adjust them until the circuit works the way they want it, measure the value the pots ended up as and get the closest to that.

Point is don't try to microanalyze everything.

 

What is the matter with this website? Half the time it doesn't open and many of my posts do not work. I just made a post and it gave an error that the website cannot be found.

I added an emitter bypass capacitor that has a high enough value to produce a response that is -3db at 50Hz. Because the gain is very high I reduced the input level.
Because there is no negative feedback then there is severe distortion.
I forgot to increase the value of the input capacitor because now that the emitter resistor is bypassed then the input impedance is much lower.

 

Missing from my last post was info that was deleted when my first post didn't work.

The hie of a 2N3904 is shown on a graph on its datasheet. The hie (input impedance) is the hfe (AC current gain) x the internal emitter resistance re when the emitter resistor is completely bypassed. The re is about 9.7 ohms in this circuit and the hfe is about 165 so the hie is 1600 ohms. Of course R1 and R2 are in parallel making the input impedance of this circuit 974 ohms.

 

Mr. Kakkar, you may be able to get more help from this web site; http://riteshelectronics.webstarts.com/index.html

 

Try the same simulation with a 22 uF cap for the bypass

 

If the emitter resistor's bypass capacitor is only 22uF then the frequency response will be -3db at 727Hz so bass frequencies will not be produced. If 330uF is used then the frequency response is -3db at 49Hz.

 

For calculating bypass capacitor use this equation
Ce = 0.16/ ( Fc* re )

re = 1/gm = 26mV/Ic

Sir, what is Fc??

 

Fc is the cutoff frequency where the output level is -3dB (0.707 times).
My 330uF emitter resistor bypass capacitor produces an Fc of 49Hz with the 10 ohms internal emitter resistance (re) of the transistor.

 

I didn't realize we were trying to come up with a high fidelity amplifier with a simple 2N3904 here, if so there's a lot of changes that need to be made. It's kind of hard to cover the entire audio range with a single transistor amp unless you're not shooting for much gain at all.

 

Rritesh, Fc is usually an abbreviation for the cutoff frequency commonly considered to be -3 dB when dealing with audio.

You best try and read this: http://en.wikipedia.org/wiki/Decibel

 

I didn't realize we were trying to come up with a high fidelity amplifier with a simple 2N3904 here, if so there's a lot of changes that need to be made. It's kind of hard to cover the entire audio range with a single transistor amp unless you're not shooting for much gain at all.

The bandwidth for a single transistor is no problem if the capacitors are the correct values for good bass.
The problem is severe distortion when there is no negative feedback (when the emitter resistor is bypassed).

 

Fc is the cutoff frequency where the output level is -3dB (0.707 times).
My 330uF emitter resistor bypass capacitor produces an Fc of 49Hz with the 10 ohms internal emitter resistance (re) of the transistor.

Pls. tell how you have calculated Fc of 49Hz with 10 ohms internal emitter resistance (re) of the transistor.??

 

Rritesh, I guess he either used the math formulas &/or his simulation software.

Try not to rely as much on the formulas except to get you fairly close, get a feel for the way things work by experimentation.

Son, I don't know how well you are as far as funding goes but you really need to set up a small lab in your home with some basic test equipment and an oscilloscope is really a necessity for an experimenter. If you look hard enough you can find an absolutely outstanding Tektonix analog scope for next to nothing as most of the big companies have moved to the new digital ones. Get on your phone and call any and everyplace related to electronics to see if they've retired any. Explain that you're a student in need and they might even give you one for free along with who knows what else they have sitting around gathering dust.

A good day or two on the phone and you might hit a bonanza उपहार with a ton of test equipment and parts to help you stock up.

 

I have small lab in my home which contain almost all small equipment, is there any software from which i can connect output directly to computer??