2 Stage Amplifier Help

Thread Starter

Assassin_Sharks

Joined May 25, 2008
6
Hello, I'm doing a project for school and need some help with finding values that work for getting 260 gain or more with out distortion. (roughly 48.3dB)

I have tried a couple times to make this circuit but it either did not work or it had a lot of distortion. So i was wondering if any one had values that they knew worked. I also have the equations to calculate all the values but i was wondering if some numbers work better than others in the real world...

I'm using 2 npn bjt(2n2222a). I'm also putting up a schematic that I'm going off of.


 

Thread Starter

Assassin_Sharks

Joined May 25, 2008
6
Vin was about 1v to 50mv. V+ was about 10v. These can be changed if needed.

I also forgot to mention when i calculated my little r'e it was a micro ohm so i threw in a resistor on both circuits to make a little r'e of 100 ohms. This can also be changed.
 
Last edited:

thingmaker3

Joined May 16, 2005
5,084
260 * 0.050 = 13.

13 > 10.

Also, is that 50mVrms, 50mVp, or 50mVpp? In other words, will your output be 13Vrms = 37Vpp, 13Vp = 26Vpp, or 13Vpp?
 

Thread Starter

Assassin_Sharks

Joined May 25, 2008
6
Actually it wasn't clipping the wave as much as it just looked like a bad sign sign wave. It was also getting only about a gain of 10. I had 2 of my classmates check over it and then the instructor. They all said my circuit was hooked up right it just wasn't doing what it was supposed to. I have checked all components to make sure they were still good.

I was just hoping some one might have a better idea of what values to use.
 

Thread Starter

Assassin_Sharks

Joined May 25, 2008
6
Yes I am using a breadbroad. I didn't check it while having this issue but i have built other circuits on it they day before that worked. It also seems at times that when i rebuilt it one stage was amplifying while the other wasn't. I've rebuilt it countless times >.< .
 

logicmind

Joined May 20, 2008
9
Yes I am using a breadbroad. I didn't check it while having this issue but i have built other circuits on it they day before that worked. It also seems at times that when i rebuilt it one stage was amplifying while the other wasn't. I've rebuilt it countless times >.< .
try using different slots on the breadboard other than the ones u are already using, sometimes the slots are damaged inside or has a broken connection. It happens to me a lot, i just move my stuff over to another slot..
 

Audioguru

Joined Dec 20, 2007
11,249
Transistors have very high distortion when the output level is high, there is no negative feedback and the input source impedance is low. The voltage gain of two transistors with the emitter resistors bypassed is about 40,000 and the distortion is at least 40% like this:
 

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bloguetronica

Joined Apr 27, 2007
1,372
You could use negative feedback loops, one for each transistor. I can see that the Q points of both transistors are stabilized, but that may not be sufficient to reduce distortion. So use lots of gain and reduce the gain of each stage using the negative feedback loops.
 
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