# 2 Stage Amplifier Help

Discussion in 'The Projects Forum' started by Assassin_Sharks, May 25, 2008.

1. ### Assassin_Sharks Thread Starter New Member

May 25, 2008
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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.

2. ### thingmaker3 Retired Moderator

May 16, 2005
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What are your values for Vin and +V?

3. ### Assassin_Sharks Thread Starter New Member

May 25, 2008
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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: May 25, 2008
4. ### thingmaker3 Retired Moderator

May 16, 2005
5,072
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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?

5. ### Assassin_Sharks Thread Starter New Member

May 25, 2008
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50mVpp sorry for missing all these these details >.<

6. ### thingmaker3 Retired Moderator

May 16, 2005
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So your distortion is peak clipping, yes? The output wants to swing 13Vpp, but can't can't quite get to even 10vpp?

7. ### Assassin_Sharks Thread Starter New Member

May 25, 2008
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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.

8. ### thingmaker3 Retired Moderator

May 16, 2005
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When you say you've checked "all components," does that include your breadboard? (Assuming a breadboard is being used, that is?)

9. ### Assassin_Sharks Thread Starter New Member

May 25, 2008
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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 >.< .

10. ### thingmaker3 Retired Moderator

May 16, 2005
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So your symptoms change with each build? I would definitely try a different breadboard.

11. ### Assassin_Sharks Thread Starter New Member

May 25, 2008
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k thanks for all your help.

12. ### logicmind New Member

May 20, 2008
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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..

13. ### Audioguru New Member

Dec 20, 2007
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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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14. ### cumesoftware Senior Member

Apr 27, 2007
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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.