You don’t happen to have a spec for that Solution Turntable rack by any chance ? I’m not much good at diy but I know a man who is ...!
No not a spec. Its pretty simple really. Its mostly cast concrete. The hardest part is making the mold. That is how you get the size and shape you want for the shelves. I like the gentle curve across the front and radius matching the legs at the corners. You could simplify it to be square. Either way you make one mold and use it for however many shelves.
On mine the top and bottom shelves have a sand bed cast into them. Use styrofoam or whatever to create the depression during casting. Also cast some threaded inserts into the corners.
The legs are ABS. Use sandpaper and xylene or other solvent to clean the ABS, then buff it to a shine. Fill with concrete, with bolts and/or threaded inserts. Do it however you like. The idea is the thing is modular. Because each part is very heavy, this lets you wheel each part in and assemble on-site. The bottom shelf has stub of pipe cast into it. Put a pipe cap on the stub and you can level by turning the cap.
Couple things I would improve if doing it again. One is instead of filling all the legs with concrete I would use a spring, at least in the top one, to suspend the turntable shelf. Another is instead of granite I might go with something like a couple inches thick shelf of butcher block. Either way the key will be to use springs between the shelf and the turntable.
One trick with a sand bed, mix the sand with a little mineral oil. Just enough to eliminate dust and help hold the sand together. This way you can pack it down and it will support footers so you don’t have to cover fully with a shelf unless you want to. Look real close, its hard to tell but the bottom shelf of mine is just sand with the phono stage on squares of MDF, and the top shelf of granite is sitting on a sand bed with only barely 1/8" space between the granite and the concrete.
If you look close you will see the sand and the pipe caps. I drilled and tapped the pipe caps and screwed BDR Cones into them, which is why they appear to be floating on the carpet.
This rack works great. When the turntable was moved from the floor to the rack it actually sounded better on the rack. That is hard to do, be better than the floor.