Since a cap behave as a short ckt. for mid freq. range, then even though I use it before the pot(with my connections), the collector would get gnded?
Or else, how it works?
??????????????????
We use a common collector config. for impedance matching( ri/p very large & ro/p in Ω). Whereas here, in the 3rd stage CE config. is used( ri/p= 1k-3kΩ & ro/p=40k-80kΩ). Why?
The reason why a common-emitter configuration has been used is because we only have 1.5v rail and this is very little voltage to play with.
We could have used common collector (emitter follower) for the output transistor but since the third transistor has to be connected to the collector of the second transistor, we have to look at the voltage swing on the collector of the second transistor.
This voltage swing is not very much and the transistor is sitting at approximately mid-rail. Suppose this is about 0.7v This means the swing of the emitter of the third transistor will be 0.7v less than the swing of the collector of the second transistor. If we put headphones onto the emitter we will get almost no output.
That's why a common emitter stage has been used for the output.
The collector of the second transistor will swing nearly 1v and thus the output transistor will swing almost 1.5v but it will have about 100 times more “current” to drive the earpiece and achieve the greatest volume.