there are three major tweaks that can be done to the rockmaster to improve it`s overall tone to get more gain, less honky mids and more tight gain, the preamp really comes to live with that small mods! 1. change the plate resistor (r13) to 200k! more agressive gain, more modern sound. 2. change coupling cap c14 to .0022uf! more tight, less honky mids, GREAT IMPROVEMENT! 3. change r33 and r34 to 4.7k. the preamp tubes voltage will raise from 260 to 320v! now the preamps really comes to live! there are some other small mods but these are the highly recomended and most effective mods available for the rockmaster! you will turn the honky mid based 80`s trash metal machine to an modern sounding new metal high gain preamp with the ability to dial in nearly every kind of sound and distortion you can imagine and with great imrpoved low end that will make your neighbours sick!