It's my understanding that distortion pedals are customarily placed prior to an amp's "pre amp" stage. (As we know, doing this can affect the level of signal seen by the pre amp, causing the pre amp to clip more easily. Also, the character of the distortion can be changed). Is the purpose of this essentially to alter the pre amp sound, or is it to simulate a driven power section as well? For example, are the various "Marshall" or "Plexi" pedals that are meant to sound like Marshalls and Plexis (but actually don't) attempting to simulate a Marshall or Plexi with the power section cranked up? Also... If you have a master volume amp and place a distortion pedal in the loop, I could see it having some effect on the pre amp (by adding resistance to the circuit as a whole). I wonder, though, what effect this would have on a power section that is running clean. Would it cause it to break up at lower volume? Why are distortion pedals run prior to the pre amp? Is this an issue of simply wanting to influence the pre amp, and by extension influencing the power amp, or is there some other reason? thanks.