Im not new to beatmaking, but new to the 303. I dont have the manual and Ive been learning everything on my own. So my only question is:

When I add drums/samples or anything else and I apply the Vinyl Sim, for some reason it tunes down the sample. Why does it do this for and how do i fix it?

This is like the only thing that is stumping me with this machine...

It sounds like it is being compressed. did you mess with the fx knobs when vinyl sim is lit? Is the sample to hot?

try turning knob 3 all the way to the left

knob 3 "Adjusts the rotational irregularities that occur when playing an analog record."