how do you level a turntable?

Get some shelf brackets or I used some old steel speaker stands cut up with lag bolts into the wall studs. Put threaded screws through the brackets, a piece of wood or porcelain and adjust away. Will sound much better. Pro-ject makes a wall bracket shelf like this that is adjustable for $160.

Make sure your 3/4'' mdf shelves aren't warped first. You'd be surprized. Run a level across them first.

Back in my youth when we wanted to level something we would either take it up to a third or fourth floor and drop it out the window or run a car over it. Guaranteed to level it.