# Two stage preamp designing

Discussion in 'Electronics Homework Help' started by *Neon23, Mar 28, 2018.

1. ### *Neon23

4
0
Mar 19, 2018
Currently I'm designing a preamp for a project. And requirements would be having common emitter as an active mixer, the first stage of the Pre amp would be a common base and finally the second stage of the preamp would be a common emitter

and I appreciate some advice on this matter.

Here is an image of what I already have

Second transistor is a First Stage of the preamp (Common Base)
200 = AVNL (No load voltage gain)
98 = AVL (With load voltage gain)
23 ohms = Zi (Input Impedance )
3.3k ohms = Zo (output impedance)

Third transistor is a Second Stage of the preamp (Common Emitter)
10 = AVNL (No load voltage gain)
3.2k ohms = Zi (Input Impedance )
3.3k ohms = Zo (output impedance)

by the way
I have no problems at the first transistor (active mixer)
but is it acceptable that the No load voltage gain of the second transistor would drop to almost half when connected to a load?

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2. ### WHONOES

856
206
May 20, 2017
What are you trying to achieve?
Have you tried simulating it?
It would be a good idea to draw your circuit a bit more conventionally with the + power rail at the top as this makes it a lot easier to read as well as not having to include all those 12V cells on your sketch.

3. ### *Neon23

4
0
Mar 19, 2018
I'm figuring out how to maintain appropriate voltage gain at the second transistor even if it is loaded.
Yes I tried simulating it and the voltage gain from the second transistor is not even half of the unloaded voltage gain.
Okay thank you I'll do that for the current circuit and circuits I'll present in the future.

4. ### Cannonball

184
49
May 6, 2017
You need to turn your coupling capacitors around. They look like electrolytic caps and they are polarity sensitive.

Your collectors will be more positive than your bases.

5. ### Audioguru

2,790
633
Sep 24, 2016
The high impedance collector output of the first transistor is extremely overloaded by the very low emitter input impedance of the second transistor. The second transistor should not be a common base type.

Your schematic will be easier to read if you turn off all the Chicken Pox dots.