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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
9 responses Add your response
tirebiter
16 posts
 
Is the app called RPM? If so, it is garbage in terms of precision and accuracy. It’s self calibrating mode simply does not work well and can see where you get readings all over the place. Try manually timing 100 revolutions with a stop watch, you will see what I mean.

I measure wow and flutter on my TNT with Analog Magik and get measurements below 0.08% (w/o SDS). The RPM app gave me much higher readings...in the range of 0.4-0.5%.

Find an app that measures frequency....with your test record, the phone apps seem to be accurate in that regard. From the readings you can calculate how far off speed is.
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. 
melm
1,075 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.
tre9901 OP
13 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.
noromance's avatar
noromance
9,769 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.

brf
1,715 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. 
bifwynne
2,206 posts
 
tre9901 - agree with Sturgis.  I own a VPI Classic "2.5" (sic).  I never checked the rotational speed or flutter of my platter.  That said, I agree with tre who advises that you check your speed with a paper strobe.  

Btw, is the TT perfectly level in all dimensions?  That's important. If you still believe there is a flutter issue, think about a new belt. That's the cheapest option.  SDS and/or a new motor is the next step ... and will cost bucks.  

As far as the motor is concerned, I was able to swap out the stock 600 rpm motor that came with my standard Classic for the 300 rpm motor that came with the Classic 3.  Easy as pie and soldering is not required. Just wire nuts.
miner42
709 posts
 
There there are very knowledgable members at the VPI Forum site who would answer your question to the most finite detail.  I enjoy that sire very much.
sturgus
68 posts
 
How accurate is the app? I think I would try a good printed strobe to see how it compares. Sometimes simple is better.
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