Chopped OC2 Questions

[mattoverse]

Well after 6 failed attempts to breadboard the U-Boat I breadboarded Aron Nelson's Chopped OC-2 and it worked the first time!  I used this schematic: http://www.aronnelson.com/gallery/main.php?g2_view=core.DownloadItem&g2_itemId=9449&g2_serialNumber=2

I have noticed that at the extreme ends of the potentiometer travel for both the direct level and sub-octave level there is a bit of weirdness.  For example if the direct level potentiometer is fully clockwise, the sub-octave is cutoff, the same effect if the sub-octave potentiometer is fully clockwise.  I also have a similar issue when either pot is all the way down cutting the signal completely.  Both of these problems are eliminated when you move the potentiometers a hair a way from either clockwise or fully counter clockwise positions.  I have tried putting 100ohm resistors in series and that seems to help a bit, this is not a big deal, but I am very curious as to what is causing it?

Additionally, the schematic has pin 1 of both the direct level and sub-octave level potentiometers going to the Vr line vs. just going to ground?  Why is that? 

This leads me to my third question, what is the purpose of the 2n5088/2n3904 at the output.  I hear no change if it is removed and the center pin of both the sub-octave and direct level potentiometers simply go to + leg of C11?

Final question is how sensitive is it to exact capacitor values, specifically the smaller pf caps.  I have the right value caps, but since they are ceramic they very by as much as 20-40pf from the designated value?  Just trying to determine if it is worth my time to measure my whole stock and select those with the value closet to the printed value before doing a physical build?

[merlinb]

I also have a similar issue when either pot is all the way down cutting the signal completely. 

Sounds like you don't have R59 and R60 instaled?

Additionally, the schematic has pin 1 of both the direct level and sub-octave level potentiometers going to the Vr line vs. just going to ground?  Why is that? 

It saves a few parts because it means the output transistor can receive its bias voltage through the pots.

This leads me to my third question, what is the purpose of the 2n5088/2n3904 at the output.  I hear no change if it is removed and the center pin of both the sub-octave and direct level potentiometers simply go to + leg of C11?

It's an output buffer, to ensure very low output impedance. This gives better hum rejection in noisy environments, and allows the pedal to drive difficult loads more easily.

Final question is how sensitive is it to exact capacitor values, specifically the smaller pf caps. 

Probably not very sensitive. C20 might be, though.

[mattoverse]

Thank you so much Merlin!  I very much appreciate your time and insight.  I was failing to read the schematic correctly and had omitted R59 & R60.