how do you level a turntable?

...if neither the TT nor the table same sits on have feet which are adjustable?
You need a bubble level and some shims to insert under your TT feet. I've used layers of electrical tape with good results, but anything will work. It just needs to be thin so you can gradually increase the height.
If you can remove the TT feet, you can replace them with adjustable ones. If you can't remove them, maybe you can use some other form of adjustable isolation. There's also TT wall shelves.
I used 'Post It Notes'
Just take a pad of Post It Notes and start peeling off layers... place a few here or there under some feet and after a little fiddling you too can have a level turntable.
If you have a turntable with soft feet, the above methods would be fine. If you have a turntable with hard feet or cones, using soft shims may affect the sound of the table. I use a 3 1/2" thick maple platform under my turntable. To level the platform, I installed brass 1/4"x 20 threaded inserts. Then, I used a short length of threaded brass rod to install Black Diamond Racing footer cones. Each corner can be adjusted very precisely.
I use pennies dimes and nickels
Depending on your stand's legs, but many can have a threaded foot retrofitted. If hollow steel square tubing is used most Ace hdwe stores have adjustable feet that will fit. If there are wood legs they can be drilled and have a metal threaded endcab/footer installed.
hello glenn could you email me directly re. the erato pre? thanks dan
It wasn't cheap, but I had my Thorens TD-166 Mk II modded by a local guy. He removed the stock feet, and replaced them with threaded bolts, terminated with rubber balls glued into inverted cups, which act to absorb vibrations. I now have a couple of inches of adjustable leveling range, which I need due to my very uneven basement floor. Email me if you want info on this modder - he is in New Jersey.
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.