Amplifier with direct coupling. 3 stages.Problem with gain level

Thread Starter

Виктор Борщёв

Joined Nov 2, 2016
11
I stucked on this schema,i got some voltage gain, but it isn't enough. So i recalculated a billion of times the values and i guess i do this wrong.

Attach some screens with info and schema.

So that is schema in Proteus
Schema with values


that is schema from the book(i changed diodes with resistor)
from book


in book used very old transistor MП-40(PNP) and MП-37б(NPN)

in proteus schema i used 2N2222 and 2N2907

this is signal level simulated, Yellow - out, blue - input.
signal


i ask for some help in calculations or if u can give me a direction where to move :)

Thank you for answers
 
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crutschow

Joined Mar 14, 2008
34,280
Your circuit design has a low designed gain (I simulated about 7).
For example the second stage (Q3) has a design gain of less than one (emitter resistor is larger than the collector resistor).
How much gain were you expecting?
 

AnalogKid

Joined Aug 1, 2013
10,986
The book schematic has an emitter follower in the 2nd stage, but you have a common emitter gain stage in your schematic. This adds another signal inversion, so the feedback resistor no longer is an input bootstrap. It would be a gain reducer if there were enough gain.

ak
 

Thread Starter

Виктор Борщёв

Joined Nov 2, 2016
11
The book schematic has an emitter follower in the 2nd stage, but you have a common emitter gain stage in your schematic. This adds another signal inversion, so the feedback resistor no longer is an input bootstrap. It would be a gain reducer if there were enough gain.

ak


well, i calculated a bit and got a bit more gain, but if i change a value of resistors for example one of them with +20 or -20 ohms, it give a big distortion of signal, its normal ?



changed R8 from 600Ohm to 580
 
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