Need help with BOSS HM-2 clone

[kzl666]

Well, everything is described in this thread: https://www.reddit.com/r/diypedals/comments/4tec17/need_help_with_boss_hm2_clone/ please read it. Also, there is some videos to watch that can help understand the problem.
Short version: something is wrong with the gain knob. When it's in the lowest position, the sound is kinda gated and when I turn the pot there's scratching noises, but the pot is 100% fine and brand new. There is some DC going on the pot when I turn it up and down, I think it is related to scratching noises.
And judging by videos of HM-2, my device has noticeable less gain, but the sound itself is OK.
Substitutes I've used:
BF244 instead of BF245
2SA733/2SC945 instead of 2SA970/2SC2240
Д9 russian GE diodes instead of 1n34a (diodes has nothing to do with that gating stuff, tried shortening them)
TL072 op-amps
Please help me, I'm out of any suggestions what might be wrong, checked everything I could with no luck. Something is wrong with a first part of schematic (transistors and 1st op-amp stage). Everything past it works as it should.

EDIT
The issue is solved:

You wouldn't believe what was wrong. It's a @#$%ing 10mF tantalum cap (C31). Changed it to normal electrolytic one and everything works as it should, no more gating and scratching. God knows why I thought it would be a good idea to use tantalum one.