You probably mean differences between the 1 and the 2. These are actually spelled “i” and “ii”. (82Zii). As far as I can remember: plastic resonators versus metal resonators, one piece bell versus two piece bell, front F adjustment screw. The differences are pretty small. Yamaha uses lower-case letters for smaller improvements or changes. Larger design changes are indicated when Yamaha uses new model numbers. For example 52, 62, 82.