# Two stage preamp designing

#### *Neon23

Joined Mar 19, 2018
5
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?

#### Jony130

Joined Feb 17, 2009
5,484
Why are you using so many DC voltage sources? If only one is needed?
but is it acceptable that the No load voltage gain of the second transistor would drop to almost half when connected to a load?
Bad design. To fix this try to make Zo << Zin (Zin at least ten times Zout)

#### MrChips

Joined Oct 2, 2009
30,417
Use a single 12V source. Use this single 12V source to supply +12V
wherever it is needed.

Why do you need three stages. Get rid of Q5 stage.

Interchange 1st stage with 3rd stage.
Change C7 and C11 to 10μF.

#### *Neon23

Joined Mar 19, 2018
5
Why are you using so many DC voltage sources? If only one is needed?
Use a single 12V source. Use this single 12V source to supply +12V
wherever it is needed.
Forgot to simplify the circuit so that it has only 1 DC source.
Ill keep in mind to simplify the circuits before presenting in the future.

Bad design. To fix this try to make Zo << Zin (Zin at least ten times Zout)
Why do you need three stages. Get rid of Q5 stage.

Interchange 1st stage with 3rd stage.
Change C7 and C11 to 10μF.
Noted. Thanks for the feedback.
it is a requirement to have these three stages. Common emitter, common base and common emmiter respectively.

I'm a student right now and the design might be displeasing but it does help in figuring out flaws when designing. So thanks again.

#### Jony130

Joined Feb 17, 2009
5,484
So what goals you have to meet? Except three stages design.

#### *Neon23

Joined Mar 19, 2018
5
The design should be able to properly amplify the input signal without distortion and give it to a power amp which then goes to a speaker

#### Jony130

Joined Feb 17, 2009
5,484
The designs should be able to properly amplify the input signal without distortion and give it to a power amp which then goes to a speaker
But this tells me nothing. What "properly amplify"men? Is the gain 10x "properly enough"? Electronics is a strict technical discipline and you cannot use ambiguous words that say nothing.

#### *Neon23

Joined Mar 19, 2018
5
The over all voltage gain (loaded) would atleast be 300
Thanks for the lesson of being technical in this kind of field

#### Jony130

Joined Feb 17, 2009
5,484
Give us all requirements you have to meet with this project. Can you use global negative feedback?