#1
Hey guys,
Trying to get my head around the OD-3 schematic. I've modded quite a few pedals but they were all clipping, tone stack kind of mods. On this pedal I'm noticing quite a few transistors. It seems that there are 7 JFETs, 1 NPN and 1 PNP. Does that look right? I want to put a trim pot in place to manually bias the trannies but I'm not sure where that would come in. I know there is usually a resistor that can be taken out and replaced with said trim pot. I'm having trouble locating where those would be.

If someone could point me in the right direction I'd greatly appreciate it.

Heres a link to the schem:
http://www.freeinfosociety.com/electronics/schemview.php?id=2299
#2
20k trim set as a variable resistor for R43
10k trim set as a variable resistor for R50
5k trim set as a variable resistor for R52
5k trim set as a variable resistor for R55

The other transistor stages are either acting as switches (q9 and q4) or voltage followers (q8, q10, q1) In addition, you might wanna play with the diodes and capacitors in the feedback paths of q15 and q11.
#3
Wow. Thanks so much! Caps and diodes are a definite.
Heres how I'm making sense of it: Q9 and Q4 are going through diodes to ground and that is how you know they're for switches.
Not really sure how you tell the voltage followers from trannies that are gain/tone related.

And all of the resistors that get replaced with pots are going to ground from the source. That sound right? I'm wanting to replace fixed bias with trim so I can adjust it and get some underpowered sputtering sounds. Does that seem like it will make sense?
#4
They are actually hit with a signal, but the signal is basically DC, it's either some positive voltage or ground, the voltage of the gate with respect to the source determines the resistance of the drain-source channel, this turns the effect on and "bypassed."

If the high impedance electrode (drain/collector) is going to a power source directly, and the low impedance (source/emitter) is connected to the opposite power source via resistor, and a capacitor is used to move the signal from the transistor to the next stage, pretty safe bet that it's a follower. Followers can be used to alter tone by causing them to distort, but I've never seen it in a stompbox.

Correct, this allows you to set the idle current for the stage, allowing you to set the idle drain voltage where ever you like. The drain resistor, the drain, the source, an the source resistor are all in series, the current through one (for the most part) is the current through the others. Therefore, the voltages across each are proportional to the resistances.