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Speed Stability

I have been fretting about the speed of my vpi for about a week now. I do not have a test LP or a strobe mat but I feel that if there is a speed issue. I am hearing the pitch fluctuate up and down on notes that are held out. I have compared some recordings to a CD version and have gotten mixed results. For instance:

On the first track of John Coltrane Quartet Ballads, I noticed that the ending note on the the first track tended to sway like an old VHS tape compared to the solid pitch of the CD version.

a first pressing of Dark side of the moon compared to my anniversary CD copy resulted in no significant changes in pitch that I could hear.

I guess what Im trying to get at is could that be a issue with the speed of the pressing itself, or could it be that some records show off a problem with my rig more than others. I hope it hasnt just started to be a thing thats just in my head. I think my next step is to take the Coltrane over to my fathers direct drive technics and see if the pitch continues to sway or not.

I would appreciate any input on the situation. Thanks

Darren
macd
tonywinsc
583 posts
 
Then it would stand to reason that the position of the record relative to the platter can affect playback quality. What I mean is, if the turntable has a certain rhythm (wow and flutter characteristics) then it must be possible to turn the record relative to the platter, ie say in 10-15 degree increments and effectively match, or optimize the record's eccentric hole tolerances to your turntable and find the best playback position. Sounds like an interesting experiment. Has anyone tried this?
dougdeacon
3,338 posts
 
Very true. Eccentric rotation alternately accelerates and decelerates the velocity of the groove past the stylus. Varying groove velocities necessarily cause pitch variations, think Doppler effect. These variations may or may not be audible depending on their severity, the qualities of the whole system and the acuity of the listener.

Rotational eccentricity also alters the balance of lateral pressures between stylus and the two groovewalls. This will affect channel balance and crosstalk and may impair clean tracking.

If a TT has an eccentric spindle or platter, the solution clearly is to repair or replace that table. Mounting LP's off-center just to fix an eccentric table would be the worst sort of band-aiding. (Sorry if I misunderstood, but that's what I thought you suggested.)

OTOH, if you're asking about off-center record holes as the cause of speed variations, Nakamichi used to make a table with an eccentric/adjustable spindle to compensate for this. Pretty complex, pretty expensive, no longer available new. I never used one and don't know of any other tables which address this.

Simpler just to ream out the record's center hole and clamp it in place at the appropriate rotational position to get it centered.
tonywinsc
583 posts
 
We are well beyond eccentric platters here. The experiment is based upon matching the noticeable to unnoticeable eccentricity of the source (the record) to the wow and flutter and surely the unmeasurable runout of the turntable platter. The theory is that a record should sound better at the optimum position relative to the platter. Has anyone ever noticed that sometimes a record sounds really good and at other times just so so? Could it be related to the record's random placement on the platter?
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