Turn table speed variation question

[/quote] 12-19-13: Halcro
When I listen to acoustic guitar on my Victor TT-101 DD turntable with unequalled speed accuracy......an off-centre record hole will be mercilessly exposed. :-(

Halcro - you are ready for the next big upgrade......
Nakamichi TX1000 - direct drive and self centering for eccentric records - perfect sound forever, almost as good as digital.

Using high compliance cartridges on heavy arms will exacerbate the problems of eccentric records as well.

When you have these wow/flutters variations in your turntable is time to update some points in your system.

I also recommend you a tool similar to Dr Feickert platter speed program and Adjust+ LP to check changes on values.

I usually improve these values taking care a lot the belts. You should move your non direct drive turntable everyday to avoid any kind of belt deform.

You also need to re-oil your turntable bearing.

If yo have an AC motor you need a good frequency generator to control Hz fluctuations. If you have DC there is nothing to do.

Indeed you can buy an outer ring to improve the moment of inertia, trackability and effective platter mass.

All of these points are interesting if you are a vinyl lover

Using high compliance cartridges on heavy arms will exacerbate the problems of eccentric records as well.

Some evidence or proof for this statement would be illuminating?

However, you are quite correct about original instrument recordings being an "acid test" for speed stability. But, IMO, the main reason for this is what I pointed out in my previous post; the presence or absence of vibrato.

Excellent point, Frogman.

Thanks for confirming my impression of the difference in harmonic structure between modern and older instruments. I spent 8+ years getting my system to the point where it can play (nearly) all my authentic intrument recordings without distracting levels of distortion. It requires a speed-stable TT of course, and much more. Densely packed waveforms in complex harmonic structures are ruined by almost any sort of distortion, anywhere in the system.

Well, since someone brought up the timeline again... For sure DD turntable owners like to brag about how stable the laser line stays on the wall even when dropping a tonearm or two on the record. DD tables have closed loop speed control systems. Short of dropping a brick on the platter, the speed will stay constant under varying loads. The thing is, what happens between those laser flashes is just as important. Closed loop speed control systems have their own issues, like cogging or low frequency hunting that will affect the music playback. I'm sure some of the better DD tables minimize this; but the only way to know how well it does requires a scope.
Belt drive turntables sound more musical to me. Sure the speed stability is not as good as a DD under varying loads. And I know too that my belt drive has to run 5-10 minutes to warm up in order for the speed to settle in. That is because a belt drive turntable is typically an open loop speed control. If the load changes slightly, the speed changes. So it can be expected to have to adjust speed while playing a record if you want speed to be dead on. Once the bearing and motor warm up the speed is good and stable. The belt drive turntable sounds sweeter because the motor isn't hunting around a set point. The belt drive turntable also has many more options for isolation and vibration dampening over a DD turntable. As far as torque variation while playing a record with loud passages, I showed those calculations before. With the massive platters on most belt drives, the minute torque changes have little affect on speed. As others have already noted; the center hole is the big issue with vinyl playback. Speed control on any good turntable is easily an order of magnitude better than the affects of the center hole tolerance.

And on the subject of pianos- I agree with some of the insightful comments here. I have heard live pianos sound like they have a Wow & Flutter problem. I wondered about that and I think some of the comments here answered that.