I don’t think I’ve seen anyone open up either of those pedals. Would be interesting to see, but knowing Fortin it’s probably something very vanilla or just a straight copy of some else’s modded 808.
I think the marketing copy of the Maxon fortin OD9 mentioned red LED’s as clippers so that’s a start. I used red LED’s in a tubescreamer I made a few years back. I had stock 1n4148 pair, and red led pair on a switch but I only used the LED’s so I took out the switch. You get a good volume boost because of the higher forward voltage on the LED’s, vs 4148’s.
if you want a tighter and more metal sounding tubescreamer, modding the low pass filter in the op amp negative feedback loop is a good place to start. Swapping the 47nf cap for something smaller will cut more bass, but this overall lowers the pedal output also.
you can also decrease the value of the 4k7 resistor instead/as well to cut more bass, but this also affects the gain.
what I did on my tubescreamer clone (along with the LED clippers mentioned above) is get a 50k pot and 1k resistor in series, then put that in parallel with the stock 4k7 resistor. So all the way down the pedal is more or less like a stock ts9 but with LED clippers (51k in parallel with 4k7, is like 4k3 but close enough for me), but all the way up the resistor is about 830r, so the low pass filter corner frequency goes way up so more bass is cut, but also the gain is increased significantly so it doesn’t really sound like the pedal got any quieter. End result with the pot all the way up is a really brash and tight tubescreamer that sounds great in front of a loose amp, like a recto. But doesn’t sound so good in front of much else so the pot is useful for dailing I’m tightness.
take a look at the schematic of metal-oriented tubescreamers like the precision drive / dwarven hammer, and compare that to a normal tubescreamer to see where they differ.
these are also great resources that break down the various parts of the circuit and describewhat they do:
Schematic, JFET Bypass Switching, JFET Switch Operation, Toggle Circuit Operation, True Bypass Alternative,Power Supply, Input Stage, Input Impedance Calculation,Input Buffer Gain Calculation, Clipping Amp
www.electrosmash.com
