Misused by guitaists and amp manufacturers, The "Gain" knob on an amp is really just another volume for a preamp or preamp stage, When most people hear an setting with a ton of pre-amp distortion, they think, Hey lots of "Gain", no it's just alot of pre-amp distortion, and it really doesn't take much to get that sound. To simplifiy this, just think of any control like volume, gain, Master 1, Master 2, etc.... as just a volume control that affects the next stage that it feeds into, feed a distorted signal in and the final signal out will sound distorted. Gain really is the difference between the input and the output, ie.. 104millivolt in, a 1.04 volt signal out, the difference is the gain of that device be it a effects pedal, tube or whatever. What Slash or VH are doing is cranking the amp into power tube distortion instead of pre-amp distortion which has that fuzz box sound, power tube distortion is much smoother sounding and this is where the tube amp is un equaled by the solid state amp, a non-master volume amp cranked wide open will go into power tube distortion, or by turning down the pre-amp and turning up the final Master volume you will get a similar result....... Man am I windy!