Re: Question about pots
AFAIK, there is no need to construct the Chapman Stick as left handed per se. The only changes required would be a reversing of the stringing, re-adjustment of the intonation and action, a left-handed belt hook and shifting the strap locking device from one edge of the neck to the other. (Four screws. Simple!)
Some might argue that wearing the Stick left-handed would put the jack socket in an inconvenient position. IMO, it cannot be any more inconvenient than it already is. My particular instrument has the additional complication of a Roland MIDI pickup under the Melody Strings. The triangular controller/connector housing hangs over one side of the instrument, well away from the playing area.
To be honest, even as a lefty, you might be better off playing Stick right handed. To get some idea of what this is like, strap your bass guitar on upside down and try two-handed tapping. If nothing else, this will increase your finger strength.
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Getting back to the pots for your modified bass guitar, if you are using a left-handed instrument, you should install either linear (B) taper pots or special reverse audio (A) taper pots.
Using RH audio taper pots in a LH instrument might explain why your mixed pickup tones were quieter than expected.
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P. S. - Do not be jealous of the Chapman Stick. It is just a big, expensive lump of GRP that sounds like a Harpsichord on acid. Fortunately, when connected to, say, a Roland VG-99, it takes on a whole new identity.