Little lost trying to find some resource on determining explaining an impedance mismatch between amplifier stages.

I get a 2 stage common emitter to output +-3V, a vbe multiplier biased push pull output stage providing current gain, join them together and no more gain. I lower the collector and emitter resistors in the common emitter amplifiers by a factor of 100 and the voltage returns.

How would I caluclate this? Determine the output resisatnce of the common emitters which is Rc and internal resistance Ro, hybrid pi model which is easy to find. But when it comes to vbe push pull...struggling to find much. Do I attach two common collector hybrid pi models together?

 

Little lost trying to find some resource on determining explaining an impedance mismatch between amplifier stages.

I get a 2 stage common emitter to output +-3V, a vbe multiplier biased push pull output stage providing current gain, join them together and no more gain. I lower the collector and emitter resistors in the common emitter amplifiers by a factor of 100 and the voltage returns.

How would I caluclate this? Determine the output resisatnce of the common emitters which is Rc and internal resistance Ro, hybrid pi model which is easy to find. But when it comes to vbe push pull...struggling to find much. Do I attach two common collector hybrid pi models together?
View attachment 355226

Hi,

Isn't it obvious?
If the output transistors do not get enough input current they will not be able to drive the output load enough.
The emitter current Ie of a transistor is roughly Beta*Ib, and if Ib is not large enough then Ie is not large enough. If you want to be a little more exact, then:
Ie=(Beta+1)*Ib