i am a student, taking an intro physics class in electronics - but the teacher always tells me to "go ask an engineer"..so i came here.

i have a working understanding of how differential amplifiers work in operational amplifier IC arrangements - but they seem to act very differently in a transistorized circuit. i am attempting to translate an op amp circuit into the transistor domain and failing at it.

essentially, i would like to take a bipolar sine (+/- 12v) and add enough DC offset so that only the peak of the sine would reach the output. then, i would like to use the other end of a differential amplifier and feed it the offset (without the sine), so that the peak would center itself on ground. Presumably, the circuit would look something like this: http://tinyurl.com/ycktghlg

but this circuit falls quite short. can anyone here help me understand what to do?