changing output high pass filter on electric mistress

[Wounded Paw]

I'm building an Electric Mistress but want to alter it for use on bass.  My question is about the capacitors on the output.  There's a lot of stuff going on right at the output and I was wondering which components are forming the high pass filter on the output.  There are pots for feedback which are connected to ground and there's also a 510ohm resistor going to ground through a cap and this is all after the pair of capacitors on the output signal.  How do I calculate and change the cut off frequency for the output's high pass filter?
Here's the schematics
http://www.woundedpaw.com/pedals/9V_Mistress_schem.jpg

[Wounded Paw]

So no one wants to take a look at this? 
I have another question now, the un-affected signal that takes the send-return path (I'm using a jumper) would seem to have it's own high pass filter setup with the .22u cap and 510 ohm resistor to ground if I ignore the 13K resistor.  This gives me a cut-off frequency of 1419 Hz which is way too high for bass.  Will it affect things badly to change that 510 ohm resistor to something significantly bigger?  Or should I just put in a larger cap for C16?
and what is the purpose of the 47n caps C18 and C17?
You can't actually have high pass and low pass filters inside of each other can you?  (probably a dumb question)

[Paul Perry (Frostwave)]

I don't know exactly what is going on - but any BBD circuit is a compromise, trying to prevent clock noise coming out. I expect some of the filter complexity derives from that.
I doubt that there is much in the way of trying to cut out bottom end.
Though one problem with BBDs is the narrow dynamic range - you have to keep signal level high to get out of the BBD noise level, but it's awful if you overdrive them - you can see some bass rolloff at the input, since the lower notes are typically higher level.

Would it be useful, in general, to reduce bass gain at the input to some effects, and boost it at teh output? I don't know, but maybe worth considering at times.

[Wounded Paw]

I did change the input caps, subbing in one .1uf for the combo adding up to 39n.  I figured that was a small enough change to not affect the bbd functioning.  I think I'll just have to socket some things on the output and see what I can do.

[Paul Perry (Frostwave)]

I think I'll just have to socket some things on the output and see what I can do.

That's a very good idea, because all these things are a matter of compromise, and the compromise that is best for YOU, may not be the same as for someone else.
This is why DIY is great - custom tailoring vs off-the-peg.