Changes

Power amps are usually difficult to drive into heavy distortion and distort in a rough, somewhat nasty manner. Sometimes this is all you need to give your tone that edge that a smoother preamp doesn't provide. Unfortunately, it can be very difficult to control, requiring loud volumes to achieve. Many modern amps feature low or half volume switches, which allow you to drive the power tubes harder without getting deafening volumes. Also, distortion is frequency response dependent, but you don't have much wiggle room here. If you use the pre-amp's EQ or an EQ in the effects loop after the pre-amp distortion to prep the signal for power amp distortion, you may get the distortion tone you want, but the frequency response after the power amp may need some EQ tweaks. Yet it's impossible to EQ after the power amp and before the speakers. You ''can'' EQ post-mic'ing, but this won't help for practice/and many gigging applications, and you may have to rely on the house sound-man to do it for you where there may be differences of opinion in what constitutes a good tone. However, this doesn't matter if it's all emulated in a modeler, which is a big benefit of such devices. Power amp distortion can be affected by the type of tubes as well as how they are biased; however this can be very difficult to A/B and experiment with. Thus, a lot of these kind of tweaks rely on word of mouth, and there are tons of rumors about such modifications famous players performed on their amps. Hot biasing tubes can also decrease their life-span, leading to practical issues doing so. However, some amps, like the Mesa/Boogie ''Road King'' allow a lot of options in this regard...but it comes with a heftier price tag.