source->pre amp->amp
pre amp->input stage of the amp which is the base of the transistor. as the pre amp voltage increases, the voltage seen on the base increases so the transistor conducts more, or becomes more forward biased..(this is shown in the video i posted) and this is why you can push the amp into cut off if the input voltage is to high, you will push the transistors into saturation(exceeding their normal operating permitters)...
the negative of the transistor, is often the common ground. which is also the (-) terminal on the amp. the (-) has to be an output, because you have to ground the speaker, and with the (-) as an output it puts the speaker ground or (-) terminal = to the amp ground.
as Chris stated the power supply is one of the most important sections of a home audio amp, that is where the power is.. so you can ONLY get the power that that power supply can provide... if you have a 500W power supply you will ONLY get a total of 500W out of that amp. even if the manufacture says each channel is "rated" for 500W..... this is why receiver ratings are misleading many times... the power supply for the receiver can not provide 135W X 7.. even though each amp in the receiver can product 135W, you WILL NOT get 135W to each channel simultaneously.
