Orange Squeezer - error in Mark Hammer's mod?

[alextdel]

On generalguitargadgets.com, (http://www.generalguitargadgets.com/diagrams/orangesqueezer_marks_variable.gif).
Mark Hammer's gain, bright, level mod to the OS shows a 10k pot (R13) going straight through R15 / R16 into the op amp. This causes the voltage at the input pin to the op amp to be very low due to the 10k pot wiper being in parallel with the 330k resistor. Should there be a de-coupling cap between R13 and the junction of R15/R15? If so, how do you work out the best size of cap ?

I have tried a bigger pot (500K) but I have the feeling this unbalances the C9 P2 R14 network.

My present build is very scratchy and unstable and I think the cause is this or something related.

Thanks for any help

[Processaurus]

Good eye, you're right.  Funny, I was just working on an OS and was going to try these mods.  I'd guess a .47uF cap would work fine in there, without cutting any bass.  Thanks for the correction. 

[Mark Hammer]

You're right.  My bad.  Too busy on pushing those posts up to 5000. 

Should work fine with that change, though.

[alextdel]

thanks Mark and thanks for the email reply.