30 ft rca run too long for a phono to preamp?

I designed a shelf for my table, and emailed it to a local welder, then today while awaiting a reply, I decided to make one myself, just to make sure it would work. It did. I used 2" Mahogany, 4 1/2" stainless screws, glued, clamped and screwed. It's not fine furniture, but it is solid, goes with the equipment stand and room, and best of all it was free as I had all the materials on hand. I can jump up and down right in front of the turntable and it does not skip. My son and I tested it out well.
I tried the Hi-fi news test lp again, and It tracked the torture track with only the slightest distortion from the right channel, best yet. I moved the speakers into the room a bit, and while I don't have my super deep bass right now, I can play as loud as I want without audible feedback distortion. Depending on what the quote from the welder is, I may just keep my version and spend the rest on records. I am now looking to put a slab of granite, Mango wood, or a poured concrete slab ( like a countertop) and probably a sandbox, with the galibier metal inserts into the sand, and I think I'll be done for a week or so.

Thanks for all your help.

Mike, is your suspension on the tt working properly or is it getting hung up? I seem to remember the 147 as a sprung mount suspension.

I am using a 15 foot IC between my phono and amp and I don't use a preamp at all. I have used a couple of phonos; Pass, Herron and a couple of home rolled tube units w/o a hint of a problem.

Hello again,

I thought I'd post an update. I replaced the repaired woofers in my speakers and now have the full bass again. I built the wall shelf, placed the table ( I got a vpi scout during this whole process ) on a slab of granite which is sitting on isoballs, moved a couch, spread out the speakers, and I have no problems with footfalls or feedback at any volume level. Life is good.
Thanks for all the help.

Mike