Vintage DD turntables. Are we living dangerously?

Halcro,
No one has yet to provide a provable theory how or why a mat works?

This stuff might seem like rocket science to you or I, but it's not. The record/platter interface is understood, but platters are made differently and people bring their preferences to the evaluation table.

If you read the literature describing the Acromat, you know that its mechanical impedance is trying to match that of a record so vibrations are drained unimpeded. The bubbles are to prevent the vibrations from reentering the record.
Apparently this works, at least to some extent. Some people are getting good results. This approach is taken directly from Pierre Lurne (physicist). He devised a platter that was (I believe) 10mm of lead sandwiched between methacrylate slabs. Lead is extremely affective at slowing vibrations and the methacrylate was formulated to match the record. The formulation of acrylic and methacrylate can be varied to different hardness.

Rubber or sorbothane is good at damping, but generally isn't a rigid platform - it gives.
A leather top mat can soften the blow so to speak, between the record and a hard platter - metal or glass. It too will give, but if it's thin and LP is hard clamped, it might not compromise detail? You can say the same about sorbothane, but IMO that only goes so far.
With that said, I just ordered a thin leather/suede mat. I'm still going to make a lead mat. I have to figure out how to do it and what to use on the outside. I always liked the Goldmund mat, but they're pretty much gone.

The notion that JVC had this figured out 35 years ago, is akin to burying your head in the sand. Look at all the statement tables back then, NONE had a great mat or platter, at least the interface.
Regards,

In medicine, it is said that a "specialist" is someone who knows more and more about less and less, until he knows everything about nothing.

Soft mats do have their appeal, but not soft rubber mats. Do you consider Delrin to be "soft"? I've never had one in my possession. TT Weights sells some, I think, and I've been tempted. However, I always thought of Delrin as one of those materials that attempts to mimic the characteristics of vinyl, so as to minimize impedance to energy transfer from the LP, i.e., I thought Delrin was "hard" (in the way that vinyl LPs are hard) vs soft.

Is there anyone here who adheres to the notion of elevating the LP in space, a la the old Transcriptors turntable platter and the new "Resomat"? It's the total opposite philosophically of what we've been discussing.

I just landed a Luxman PD444. Does anyone here have personal experience with this table? Also, a pointer to the service manual would be much appreciated. There is nothing on Vinyl Engine or anywhere else via web search.

Assuming that it arrives in good working order as advertised, I suppose the first step will be to re-cap the electrolytics and attempt to inspect the condition of the bearing. This may be a challenge, as a poster has written that the bearing is sealed.

It's an interesting design. Luxman literature indicates that its slotless DC servo motor somehow levitates 4/5 of the 2.5kg platter weight without resorting to a permanent magnet around the bearing. Here is an extract from the owner's manual:

"The PD444 employs a slotless, flat DC servo motor that offers a small amount of torque ripple from theoretical viewpoint as well. It is so designed as to obtain an even torque regardless of the rotor position, thanks to the brushless structure with hall elements which detects the rotor position.

In addition to conventional speed control by means of a frequency generator circuit, a so-called "Quartz Lock" system is employed utilizing a PLL system...crystal oscillator. Therefore, the open-loop gain in DC area becomes infinite, which helps suppress external load variations in low frequencies. Also, the rotation speed is locked to the... crystal.

The QL system is effective in the suppression of external load variation from DC area to 1Hz. To reduce those load variations of relatively higher frequencies(5-10Hz), the flywheel of the (heavy) platter is effective.

But coupled to these advantages are such problems as shorter life of the bearing, and longer rise and decay time. Our exclusive "Load-Free Spindle"...solves these problems. The phono motor itself offers the repelling power to the spindle to float the platter, unlike conventional magnet-float systems.

The driving current to the motor is small, and such characteristics as S/N ration and wow and flutter are improved."

Lew, I use a Resomat and prefer it to direct coupling on my L07D and VPI TNT. However, the Resomat can sound a bit light and tizzy without a clamp or record weight to bring the LP into full engagement with the two full circles of vinyl cones on the mat that mate with the record lead-in and run-out sections. Too much weight or pressure becomes counter-productive, cupping the LP away from the outer circle of cones. To prevent cupping I stack rubber washers on the spindle above and below the Resomat. When the record weight is applied the perimeter cups down.

All of this may seem like too much trouble, but it's really no big deal.

Lew, re: elevated LPs?

This seems to be popular in Great Britain, I believe the source of the Ringmat. And that company may or may not have produced an earlier version utilizing a number of cork dots (smaller than a quarter) to suspend the record.

Also, B&O made at least one table with radial plastic supports on the platter to suspend the LP.

So I must ask, as I have with other "out of the box" ideas, if it was truly successful would not nearly all manufactures have adopted something similar by now?