This file lists some possible mods to make on an Orange Dark Terror amplifier.
You should print the amp's schematic file for easier reference. I won't provide it since I don't know if it's copyrighted material, you should search for it yourself.
These mods will totally void your amp's warranty and are given for reference only. There's also high voltages involved, that can kill yourself, burn your house and rape your cat.
I'm not responsible for anything that happens to you, to whatever belongs to you, or to anybody.
Therefor, these mods are strongly discouraged and you should stop reading this immediately :)
The only difference with the Dark Terror's preamp is the 3-band EQ (instead of the Shape control).
Those parts will be reused once desoldered from the PCB, but you can buy new ones if you want.
Check that all caps are discharged, and remove the PCB from the amp.
Drill 2 new holes on the front panel for 2 more pots (around the Shape control hole).
Desolder the following components:
Build the new tone stack using the provided schematic (on a vero board, turret, whatever you like). You can reuse the 470pF caps you've desoldered: set them in parallel to replace the two 100pF in series (this will form a ~235pF cap that sounds fine).
Enjoy your new EQ :)
In summary, we will use the first triode for preamplification, bypass the 3 following gain stages and the EQ, and connect back to the FX loop. A relay will be used for channel switching.
Remove PCB from the amp, drill 2 holes on the front panel: one for the Natural volume pot, one for the Channel switch. Drill another hole on the back of the amp for the footswitch jack.
This builds the footswitch that toggles between the channels.
Build everything by following the provided schematic.