This one has been a bit problematic and is very picky about the optocoupler (which is why it has been discontinued).
I have some alternate component values from another member that might help.
R7 - 1M
R8 - 4K7 (Guitar) | 10K (Bass)
R9 - 6K8
Range - B100K
Level - A100K
IC1 - TL022CP