Do preamps actually make the signal louder or is it just more fine tuning?
The Pre amp just shapes the signal of the guitar and then outputs it at line level to the power amp.
What about for mics? I need to make my mics louder becaouse my pa is allthe way up and the goitar and bass are way down.
Get a mic preamp. It will raise the volume of the Line Level signal.
After the preamp, the guitar signal is shaped (most tone, effects,) but it is not loud enough to hear very well, the power amp amplifies the signal to hearing level.