Just for fun, here is a PSpice simulation of an Ibanez Tubescreamer.
Simplified schematic used to simulate :
Bandwidth : (note the 700hz mid-hump)
Wave forms :
How to add post clipping boost (not more distortion but more volume)
Notice resistor R9 of 1kΩ. Let’s say we replace it with a 100kΩ (for instance, a log variable resistor, I assume) ; it could be done with a spdt switch to choose between 1k (standard tubescreamer resistor) and 47k to 100k with the variable resistor for a boost from 8 to 14dB …
Of course, these are PSpice simulations, to be prototyped.
When prototyped, we learn that R9 too high means a lot of parasitic oscillations, when highs are pushed to the max (and a lot of distorsion when high pot turned full clockwise !). In practice, 2k seems to be a good value for R9, not more.
Have fun !