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

After going through a complete overhaul of an AR XA I've been tempted to take a step further back in history and restore an old Rek-O-Kut idler turntable. Can't remember the particular model number from Craigslist, but it seems like it may be an interesting project and far more customizable than the XA, especially when it come to the tonearm. The one I'm looking at comes with the original tonearm, but my guess is that it's even more garbage than the stock XA 'arm and I'd certainly replace it!

However, I don't generally become invested in something if it doesn't pay off. So if the sound is going to be dreadful because it's an idler, then I'll steer clear. But if the sound is bitchin' then I'll jump on the opportunity!
128x128mjperry96

Showing 2 responses by decibell

decibell
69 posts
 

Since you obviously enjoy restoring vintage equipment I expect you will enjoy the idler restoration project as well. These tables are in high demand and prices for a Rek-O-Kut or Garrard 301 will very likely not come down - so your project should be a good investment. Once you experienced the sound characteristics of a good idler drive you will not want to give them up again. And you will be able to listen for these qualities in other designs. Either way, you can only win. I did the same with a Garrard 301 and learned a lot about the importance of the drive system in regards to sound. Even though I ended up replacing the Garrard, I knew what sound characteristics I was looking for. But you may very well stay with your Rek-O-Kut, if the weaknesses of the idler drive system don’t bother you. I’d say go for it!

decibell
69 posts
 
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 ... 
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