using a stock Lenco L75 Turntable

the 75 and 85 are both first class performers, i have heard stock and modded with huge plynths, but they sounded pretty much the same.

Well, it's listenble - that's the best I can say for it. mainly due to a decent Grado cart.

The Lenco arm wasn't good in any scale, and now - they are all peaces of junk. When you change the arm, you might as well upgrade the whole thing...

The 85, I think, is a belt drive, so probably not relevant. I would agree with the idea that the 75 tonearm is problematic, but I think you can get very decent sound out of the stock setup, competitive with a lot of more expensive stuff. The tonearm bearings have often collapsed due to abuse; someone out there can repair them and/or replace those bearings for a nominal sum, IIRC.

The Lenco original arm has a metal edge resting on a rubber base. this wasn't a good combination at any time, but now, after 25 odd year, the rubber in ALL lenco arms, has already dried up, and eroded, so there are no more arms in a decent state, and there is almost no supply for replacement parts.

the plinth in not part of the problem with this turntable - it can be tuned to be VERY quiet in it's original form. The arm, it's mounting and wiring - is!