What's the deal with idler turntables and do they have a place in modern HiFi?

Thanks for the kind words, Charles.

We all continue to learn, and the untapped "goodness" in idlers certainly caught me by surprise. That Dagogo review is beginning to look dated, although I stand by my comments that rigid belt coupling gets you a large part of the rim drive sound.  Direct and idler/rim drive are definitely not for everyone (what architecture or product is?), as they have a different set of virtues and drawbacks.

larryi:

bdp24, 

As I stated above, I don't know why the idler tables I heard have the kind of "drive" that they do have, but, I suspect it has to do with the high torque motors employed.  I have heard the same sort of sound from the three motor Audio Note table and it is a belt drive table, but, it employs three massive motors, each of which supposedly is a 2 hp motor (three massive power supplies are also used to power the motors).

It would be interesting to hear what a modern idler table sounds like. I would love to hear the Galibier table.

Since my experiments began with identical drive systems (motor,  controller, bearing and 33 Lb. Gavia platter), I can safely say that it's not about massive torque (relatively high, but not massive). 

The first thing that jumped out at me was the difference in time that it takes for the platter to lock speed (observed with both Feickert software as well as a Sutherland Timeline).  The idler locked in much more quickly.

It's pretty clear that we're hearing control of the braking motion - what would be the "back" or "slack" end of the belt that the idler idler is grabbing control of, but which a belt isn't capable of doing.  If you buy into the concept that both acceleration and braking need to be controlled (or alternatively, that a drive system needs to be immune to both of these forces), then none of this should come as a surprise.

Given how we've learned that a stylus tracking at 2 gm. can modulate the speed of even a massive platter, we shouldn't be surprised that some speed control benefits could be gained.  

Of course, the questions remain as to how audible this is, how it's perceived, and how musically significant it is.  From initial auditions of late stage Eiger prototypes, people are noticing the differences in presentation, and are definitely split in their preferences.

I'm really excited to return to the Eiger, and as soon as I get my head out of the NiWatt amplifier design (Labor Day?), I'm looking forward to returning my focus to the Eiger.  There's a lot of untapped potential, and it's been patiently awaiting my attention. 

Cheers,
Thom @ Galibier Design

thom_mackris

Given how we've learned that a stylus tracking at 2 gm. can modulate the speed of even a massive platter ...

I've seen this claim before, but never seen any proof of it. I've measured the speed of my turntable with it 22-pound platter as it plays an LP and never detected this sort of speed deviation.

I believe it is safe to say that maintaining absolute platter speed in the presence of an ever changing load (friction from needle tip) is physically impossible! One can try to minimize speed fluctuations - but will never eliminate them completely! 
Regulating designs need to measure a speed change first in order to correct the speed. 
Unregulated TTs like the Garrard try to minimize speed changes by employing high torque motors. The speed-torque curve of the motor needs to be as steep as possible to minimize speed fluctuations from a changing load. 
The over all flexibility of the drive system is another important factor. That's where idler drives have their strong side! 
The flexibility of any drive system can be measured by applying a defined torque to the platter while locking in the shaft of the driving motor. The resulting angular movement of the platter allows to determine the flexibility of the drive system. Belt drives with very long and flexible belts allow more platter movement - idler drive systems with direct coupled idler connection and stiff motor support allow very little angular platter movement with same amount of torque applied to the platter. 
These thoughts lead to the conclusion, that a high torque motor with steep speed torque curve plus a drive system with little flexibility between driving motor and driven platter is a must - no matter if speed regulated or not. Not all modern TTs follow these principles - but some do. And I believe that some modern designs are able to achieve these goals even without employing an idler drive arrangement. A short and rigid belt driving a small sub platter follows the idea of little flexibility in the drive system. In combination with a high torque motor the result will minimize speed changes from the ever fluctuating load caused by the needle tip ... 

Hi Cleeds,

I’ve seen this claim before, but never seen any proof of it. I’ve measured the speed of my turntable with it 22-pound platter as it plays an LP and never detected this sort of speed deviation.

I stand (partially) corrected ... primarily because I didn’t want to blow my own horn. I’ve seen stylus tracing induce speed instability on some turntables but not on Galibiers. Mass absolutely helps.

Cheers,
Thom @ Galibier Design

decibell

I believe it is safe to say that maintaining absolute platter speed in the presence of an ever changing load (friction from needle tip) is physically impossible!

Please explain how the speed of a 22-pound spinning platter can be altered by a stylus whose force is measured in grams.

Please tell us about the measurements you've made that support your belief.

Belt drives with very long and flexible belts allow more platter movement - idler drive systems with direct coupled idler connection and stiff motor support allow very little angular platter movement with same amount of torque applied to the platter.

There's no "angular platter movement" on my belt drive table. It's a VPI.