# Having trouble designing a Multistage Transistor Amp using JFETs and BJTs

#### Bordodynov

Joined May 20, 2015
2,500
ic(q1)~1mA, ic(q2)~5ma, Vbq1=Vbq2=1.7, Vbe=0.7 i(R12)=0.1*ic(q1) i(R14)=0.1*ic(q2) Vc(q1)=5 Vc(q2)=(10-1.7)/2+1.7 R10=10kOhm
R6=0 R3=56*

#### Raj Shah

Joined Mar 2, 2016
10
Could you please elaborate on this?

Thanks,
-R

#### Bordodynov

Joined May 20, 2015
2,500
For a fixed load (2KOhm), with an increase in the current through the last stage,
increasing its gain. But it is limited to the voltage at the collector resistor.
So I chose the current through the output transistor is equal to about 5 mA.
The larger current of the second stage, the greater the gain.
But it is quite acceptable to 1mA. This is not an optimal current,
but the total gain obtained sufficient. With the voltage across
the resistor and the current easily using Ohm's law, calculate
their denomination. The larger the voltage across the resistors,
the more stable the DC mode. But the more this tension,
the less remains for the voltage to the transistor and
its collector resistor. One volt is a compromise. This provides
sufficient stability and a large voltage swing. Selecting the mode of
the transistor quite arbitrary. Every developer, using its experience,
sets different modes of transistors. At the dawn of amateur radio (35 years ago),
I designed radios and amplifiers. Then I made up the equation for
the calculation of the gain. Is the optimal values of these modes equations.
I can offer my version of values of resistors. You can then replace them with your own.