I have just bought a Slim Phatty and I noticed the following problem:
Dependig on the patch I play, the C4 ( or the C2 depending on the patch) plays a different sound. It doesnt sem to be a ring or mod issue or a detuned oscillator, as the sound is the same in different patches.
I have already a rebot and a system restore, but it is still the same.
I would guess that the patches that exhibit this behavior have filter or volume velocity enabled and the controller keyboards “C” key is wearing out, thus sending different velocity behavior than the other keys. Just a guess.
It sounds like that C key is not tuned properly. Go to system utilities and perform the note calibration under the calibration submenu.
I suggest you to take a loot at the manual and perform all the calibrations. There is an specific order but don’t remember which. This has been commented in the forums.