There are four known iterations of the 303 that came to market during its short run between 1981 and 1984: types A, B, C and D. More information on that subject can be found on the Analogue Renaissance website.
On this particular test bench are two Din Sync RE-303 models alongside two originals. One of these is a type C, while the other is unknown and carries what appears to be a very early serial number - a prototype, perhaps?
Check out the video below for the full rundown. Paul is very keen to stress that this is by no means a scientific comparison, but it’s plain to hear that there is something very different going on with the envelope in the ‘unknown’ model.