There's something that's been bugging me about (normal - not MOSFET etc.) transistors. It's been ages since i've done any of this stuff, and i've forgotten most of it, but in school I was taught that in order for the transistor to do anything the voltage has to be over the Threashhold voltage ( ~ 0.7volts) on the base, the same way a diode won't conduct unless it's above a certain value (if you use the " two diodes" analogy for the transistor)
but the output of a guitar is well less that 0.7V peak, And even if it wasn't, the signal is a wave, So wouldn't the circuit simply cut off any part of the wave less than 0.7v?

The only solution I can think of, is, You could possibly mix the guitar input with a constant 0.7V D.C. but this is obviously not how they do it.

So how do they do it?