I don't understand the need of amplifier stages if i want for exmple to amplify a small AC signal. Sure i get that it is used to improve the gain, but isnt an RC transistor amplifier made in such a way, that the collector voltage is equal to half Vcc in order to have maximum swing. If so, why do we need more than one amplifiyng stage? To get bigger current? Here's what i know about that: When im building a light sensor for example, i form a voltage divider with a photoresistor and another resistor to ground. The output is connected to the base. I bias it in such a way that the base current is 1/4th of the whole current through the photoresistor and sometimes this doesn't give large enough collector current. This is when i use something like amplifiyng stage. I either use another transistor to increase the gain by connecting them like darlington transistors, or i use the main weak signal to turn off a transistor, which in turn will allow for another transistor to turn on, giving me high enough output. And this is all i use amplifier stages for-to increase a weak current. Is there anything else i dont get here?