New Turntable Advice

@richardbrand.

"Once set, it applies a constant drag, against which additional drag from highly modulated passages is pretty insignificant.  Hence the music does not seem to slow down!"

Precisely!. It will be slowing down but much less that if there was no predrag .

You described, much better than I, the efficacy of predrag. Of course the motor must be of good quality such that it doesn't become noisy when loaded thus. This is where torque ripple can be a problem as it is a function of current draw , torque output. 

In the Garrard's case the mechanism which sets the correct speed has the lovely positive side benefit of making the drive stiffer. The result, more startling transients, greater apparent dynamics. some may even call this "slam" My guess is that the technicians designing it knew about this

@lewm

What can affect speed of idler TT is wear on the idler wheel and stuff like that

Uniform wear on the idler wheel should have no effect on the platter speed - the idler just transfers its rim speed from the motor pulley to the platter rim.  This assumes it does not slip, and has no wear flat spots.  In normal use, the idler wheel is retracted until the table is switched on, which also mechanically engages the idler wheel via springs.

Provided the platter is not forcibly restrained while running, the hard rubber tyres on idler wheels should last for decades.

Wear on the motor pulley is more likely, though I think very uncommon in normal use.  Changing motor pulleys and idler wheels is straightforward unless you also want to change the idler wheel bearings!  The lower bearing housing is fixed with rivets made of unobtainium

@richardkrebs 

My guess is that the technicians designing it knew about this

By the time they got around to the 301, Garrard had been building turntables for about 35 years, starting with clockwork mechanisms.

The more I poke about, the more I appreciate the hidden engineering details.  For example the control knob for fine speed adjustment is mounted on the chassis, but the magnet it moves is pivoted on a sprung assembly.  To minimise unwanted vibrations between the two, the linkage is split into two, with an outer ring connected to an inner hub by three radial springs.

Turntables were just a sideline for Garrard, who for centuries had been the UK's leading jewelers, by Appointment to successive Royal Majesties!  Precision manufacturing indeed!

@richardbrand 

Yes, and if you want to advance the state of the art, dissect the older designs and take their learnings. Then apply them to the materials, manufacturing and tech capabilities we have today.

One example. A plain bearing should not have a highly polished shaft. It needs a tiny amount of roughness to ensure an even oil film. This is common in my industry, hydraulics, but is rare in the audio TT world. EMT knew this and when you look at the shafts of their classic TTs they appear dull...by design. This is engineering done properly. 

cheers.

Porter - Dobbin - Galibrier all recognised for their Plinths and adopted methods for improving mechanical interfaces. All potentially got their early information from Lenco Heaven. From their starting out designs changed and in some cases, TT Models worked with have been expanded on.

There is very little that these Bespoke Services do that can’t be found on Lenco Heaven. 

More than enough info is Public and enabling for another to use to produce their version with a successful  finish. 

Even High End TT manufacturers have adopted the materials discussed on LH that have been used to great effect when ovrrhauling a Lenco TT’s Bearing Assembly. 

Rigidly coupling a Bearing Housing on a Lenco TT has been seen carried out as a design for numerous years. 

My own endeavours commenced before LH was a Forum, but the detailing of the used designs that are shown on LH are a fast track to intensive learning and successes with one’s own adaptations being realised. 

I can easily add an ID TT for the OP, I’m sure they would really enjoy the experience, I myself have a long period behind me of enjoying the experience. 

The OP should be let know that their concerns about Speed Fluctuation, when considering a ID or BD TT is usually best improved by a Off Board Purpose Produced Device. 

Certain devices that are recommended can comfortably be costing more than a JVDD TT, that if functioning without issues, is far more reliable for Speed Control. 

When this Costing for Speed Control becomes known, the JVDD TT, does become an attraction. 

Commonly available Vintage ID TT’s can easily cost $3Kish+, versions with a modernisation, can be double the cost.   

and Vintage BD TT’s can easily match and surpass the costs for ID TT’s. 

Each of the above will be likely to need a Off Board Speed Controller to give their optimised control of speed. Such Off Board Devices can easily cost $1.5K and ascending in cost. 

A JVDD TT Model - Aurex SR 510, is able to be everything the above drives can be for 40 - 50 x less as the purchase price. For 30 x less cost other JVDD TT’s can be a slight betterment for Speed Control over the 510.

Note: Much of what is discovered on Lenco Heaven to improve mechanical interfaces, is totally transferreble to the DD TT.

Add to this the use of a Resin Impregnated Densified Wood Board as the Plinth Material, and this will surpass any historical Plinths used and be a competitor in it’s performance  for any Plinths produced by so called Plinth Guru’s offerings where $2K get one on a waiting list, and enabled to dicuss the final asking price.