I'm reposting the pic for easy reference to the functions im talking about
To give it a quick overview...
The knobs
Presence drive - this adds a bit of treble, but mostly adds distortion to the "treble.
Amp drive - this is the main distortion control, works like any distortion pedal would
Output - Simply an output level control. It's notched at around 2 o'clock, or what would be 7/10 to allow you to neither boost nor cut
High - This is a high cut or boost. below 12 o'clock it acts a bit like a low pass filter, removing a lot of highs. above 12 it can add quite a lot of treble
Already you can see that you can shape the distortion by balancing the "presence drive" and the "high" knobs
Side Switch
These are really just EQ switches, but the change how the other controls react a bit. For example you get less distorion on the fender mode.
Lead (Marshall) - This adds a little bit of high frequency, and some mids. You can also get the moost gain in this mode
Normal (Mesa Boogie) - The EQ here is pretty much flat.
Bass (Fender) - Gives a bit of a bass boost, and lessens the gain a little
Mini Switches
1 Mid Boost I
2 Mid Boost II - These are similar, but slightly different mid frequencies curves.
3 Low Drive - According to the manual, when off it cuts the bass, rather than boosting when on. Basically this gives you quite a full sound, driving the low frequency a little harder than usual
4 Clean Amp - Kinda like the fender switch, you get much less gain with this switch on
5 Bright Switch - The higher the amp drive, the less you hear this, but it adds quite a bit of treble. From memory, if you turn 1,2,3 and 5 on its fairly flat thought not entirely
6 Vintage tubes - takes a little bit of treble out of the signal, mostly from the distortion part of the circuit
7 Speaker edge - the manual says this adds extra presence, but its a bit lower than your standard presence control, kinda high mids
8 Close Miking - Does the opposite of speaker edge, adding a bit of low mid to emulate a bit of proximity effect
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I had to look in the manual to cover some of the detail, but most things do 'what they say on the tin' so to speak. Switches like the one of the sideare obvious when you use them, and even then the names good enough really.
You can see its basically all just an over the top EQ and gain circuit, but it gives you a lot of options for shaping your tone and distortion. It has some preamp circuitry in it which the manual claims works when the unit is bypassed. Some people might be against this, but i quite like the sound of it turned on when the settings are fairly neutral, so i don't imagine it's doning many bad things to the sound. That said i've never bothered to compare the sound with it in the chain but turned off to with it not in the chain at all.
