Sharp smells

[Pugdog1]

Hi all first post Here but have been reading for a little while, I recently (5 months or so) bought a turbo 500 still kit and since i bought it I have done about 5 runs (all different recipes) I generally get about 3L of 93-94% out of a run and when it's at the 93-94% it smells sweet and doesn't burn the nose, however as soon as I water it down to 40% It gains a very sharp smell especially when air rated, any ideas what could be causing this?

Thanks for any help