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I AM SO ANGRY for not doing this design first.  Well done!

Update: working.  It always ends up being something dumb.  R21 was 100K, not 1M like it should have been.  Missed it during my first part check pass.  Works like a champ now. 

Next stop: partyin' on the Mothership.  WHEEE 

This thing drove me crazy. I tried to build it two times. Then one day I was pokin around at it and disconnected wire 8 from the mode switch and it started working fine. I'm not to sure why but it worked for me. It's worth a try

Didn't work for me, unfortunately.

Shelving this for now.  Bought some CA3080s from Smallbear to swap in for the cheap eBay ones, will see if it solves the issue.  After that... well, best not to dwell on it.  Haha.

Either way, appreciate the assistance from all--thanks!

If you can desolder easily, try removing C6 then temporarily run a wire from the round pad to your breadboard. Then connect a 4u7 polarized cap with the negative end to the wire and the positive end to +9v to see if it corrects your problem. I can try this on my build too to see if there is any difference (I may have already done this when I prototyped it but I honestly don't remember) but probably not until tomorrow.

Thank you for the suggestion!  Unfortunately, no difference either way--sounds the same +9v as into ground.  Also swapped out the J201 in Q2 w/ no change.  Everything else seems to check out: transistor values & positions, resistor/cap values, no cuts or cold solders, etc. etc.

Is it possible to be tripped up by the CA3080 ICs?  I've heard tell of how cheap eBay purchases of this chip have led other builders into trouble w/ other projects.  (Guess where I got mine?)  Or is that just paranoia? 

So I got a new Sharkfin pcb and tried this again and have the exact same problem. I double checked all values before soldering. The only thing I used from the old board was the charge pump and the 2 CA3080s. The only thing I can think of is the J201s I got from Tayda. I just saw the thread stating a lot of these are fake. Could this be causing this problem? Would the Sample/Hold still work if so?

I've built several projects but this one by far is the biggest pain. Any help would be very much appreciated.

In fact, I am having this exact same issue.  Mine Sample/Holds like a champ with a full range of tone, but the Filter mode is just a cocked wah.  It quacks a bit, but only with ear-shrieking treble, no matter how you dial in the controls.  So, not so good.

Does anyone know what voltage readings I should be seeing in T1 and T2?  Are there specific parts to the Filter section of the schematic I should be scrutinizing?   Not quite confident enough in my skills with this one, alas.