What is this trimpot for...?

[AdamB]

Hey,

I'm in the middle of working on my second axis face, as my first one was ok but not good enougth to warrant boxing up or anything, just wondering tho what is the use in the 50k trimpot in the following layout:
http://www.indyguitarist.com/torchy/Distortion_Overdrive/Axis%20Face%20-%20Si/Axis_Si.gif

I know the 10k is for getting 4.7V from or whatever but what about the 50k one? Is it to do with biasing Q2 or something, I've yet to get my head around biasing...

I'm guessing this is from an earlier revision of the axis face too, as there are parts missing from this circuit that are on fuzzcentral, so I was gonna add the bits like the capacitor going from input -> ground and the diode going from input -> ground and the capacitor in parallel with the 1k2 (or in this layout 330R for some reason?) resistor as shown on the circuit diagram at fuzzcentral. However, where did that 2u2F capacitor come from? Shouldn't that be a 0.22uF?

Cheers,
-Adam

EDIT: Typed in wrong resistor value (300R to 330R)...

[no one ever]

input gain is my guess.

[spudulike]

Isnt that the rev 1 schematic ? Philips site has a rev 3, and the first trimpot is the "Smooth" control innit ? Depends how old the layout is I suppose.

[formerMember1]

yeah i think that is the smooth pot/ bias pot on '69 fulltone,..just now phillip  uses a 100k not 50k like original,..

great pedal BTW

[AdamB]

ok, so if I change the 300R to 1k2, put in the cap in parrallel with the 1k2, add the diode and resitor that go to ground, change the 2u2F to 0.22F and wire a 100k pot where the 50k trimpot is, take out the bias pot completly (just connect the R7-1 to R7-2&3 with a wire), I should have the rev3?

-Adam