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Questions about VPI Turntables and rotational speed

I've noticed that my VPI Prime Scout is not as good as I'd hoped at rotational consistency.  This has been measured by two different iPhone apps on my X.  Now, I can get it to stay around 33.33 RPM, but it seems to have a fair bit of flutter.  My thinking is that this could be caused by the relatively heavy weight of the iPhone X in a relatively small part of the turntable, whereas vinyl would produce relatively light weight, in across the entire platter.  Does this sound right, or is the weight of the iPhone probably inconsequential?

That said, I know there are devices made by VPI (i.e. the SDS) that will cause a more optimal signal to the motor.  However, I also know that speed may be varied fairly significantly by moving the motor closer, and further from the center of the platter.  So, given this non-fixed ratio, how does the SDS serve to make a better signal for the VPI?

Thanks!
tre9901
brf
1,699 posts
 
I believe what you are experiencing and measuring is the uneven distribution of mass around the axis of rotation caused by putting an iphone on a balanced platter. 
noromance's avatar
noromance
1,780 posts
 

Yeah, the phone can only do wrong. Can you hear instability when playing a recording with piano?
The SDS simply recreates a clean version of the voltage waveform needed by the AC synchronous motor.

tre9901 OP
10 posts
 
Thanks all.  So, when playing a 1kHz test tone, it does not feel like a very pure note.  Granted, I'm comparing to a pretty high end digital rig, but I would have expected it to be pretty close in this price range.
melm
309 posts
 
You may be measuring speed inconsistency (which comes in many different varieties), but I don;t think you are measuring flutter.

A relatively easy way to HEAR ordinary flutter is to play a recording of a solo acoustic piano and listen for the notes as they trail off and decay.

The VPI SDS and ADS, as well as similar units from other manufacturers, improve speed consistency by cleaning up the power going to the TT motor and by lowering the voltage after start-up.  They do work.  What also works is the addition of physical flywheels, and the replacement of bearing (and motor) lubricant when required.
invictus005
597 posts
 
App is a nonsense and completely inaccurate. You’re wasting your time. I hope people who use these apps have enough respect to not call and bother turntable manufacturers. 
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