
Interesting bit from bcbox on the
adafruit (x0xb0x) forums:
"I found something very interesting... ok interesting to me at least! I recently stripped down an entire TB-303 mainboard I was doing some work on. When I got around to re-stuffing the PCB I found something curious. The legend for component C29 is backwards on the PCB, and in fact the component is installed backwards versus the schematic. I have verified this with pics from the dozens of 303's I have worked on, a few of which I show in some pics below...

The x0xb0x PCB is laid out the correct way, which would be like the schematic, so C29 is backwards versus an actual 303. This component is part of the circuit that makes up the recovery stage at the output of the filter responsible for converting the two outputs from the ladder to the single ended output at C14.
I also recorded some samples with C29 in both orientations. In each sample the first 2 bars is C29 as per actual TB-303, and the last 2 bars is C29 as per schematic."
This one in via David