turntable speed control

Mr. Creeds, 

not it trying to offend but I own the Phoenix control and tach unit for my VPI Prime. I know for a fact that if you even lightly touch the platter the tach rpm drops instantly. Also - before I powdered my belt - on start up the tension side of the belt was taught but after the belt passed the pulley you could visibly see the band vibrating due to the slack. This was only obvious for a second until the platter speed stabilized, but I would still think this is happening albeit to a much smaller degree once the platter is up to speed.  Wouldn't this be some indication that belt creep is happening to one degree or another?

All i I know is that the system works flawlessly and tach reads 33.33x where x fluctuates up or down .001+/- rpm.  And I definately hear very stable sustained piano notes. So belt creep aside, it does a magnificent job at keeping the platter stable and at a significantly lower price than the SDS. 

Cudos to PE!

last_lemmin"not it trying to offend but I own the Phoenix control and tach unit for my VPI Prime. I know for a fact that if you even lightly touch the platter the tach rpm drops instantly."


No offense taken! I guess what's at issue here regarding speed deviation is what defines a "light touch" and, of course, variations between different turntable platters. I can certainly slow down my VPI platter by touching it - I can make it stop, for that matter.

I've heard nothing but good things about the Phoenix motor control and tach, so I'm not questioning those products at all.

When phoenixengr asked how I made my measurements, I responded and the answer is above. But when asked how he substantiates his claim that " Belt creep does exist and it is measurable," he becomes argumentative. Of course, he’s trying to sell something here, and I’m not. Perhaps that accounts for the difference in our attitudes.

Wow, you managed to get just about everything wrong on that one; from your straw man argument about my sales motive to the lack of understanding of even basic physics. You deny that belt creep exists, yet you can blame speed variations on "some other" mysterious force? If you reread my post above, you will see that I did answer your question. Belt creep manifests itself as reduced speed, and I measured it with a digital tachometer. But even simpler than that, you can do as melm has indicated and just listen when you touch the moving platter while a record is playing.

Not incidentally, the question isn’t only, "Is it measurable?" but, "Does it create an audible effect?"

Yes. See above.

A light touch to a 22-pound platter doesn’t effect speed - the force of
the touch is insignificant compared to the moving mass of the platter.
But phoenixengr already knew that.

You are wrong on both accounts. Inertia will only affect the rate at which it slows, but it will slow down. And, I know the opposite of what you said to be true. Apparently you not only know what you know, but now you claim to know what I know.

phoenixengr, your products are highly regarded by many in the audiophile community. I’m sorry to point it out to you, but you’re really not helping yourself with the illogic you’re using here.

There is nothing illogical about my posts. Everything I've posted about the operation of belt drives is correct and easily verified not only by application of simple physics, but also by empirical testing (listening) and simple measurements.

I guess what's at issue here regarding speed deviation is what defines a "light touch" and, of course, variations between different turntable platters. I can certainly slow down my VPI platter by touching it - I can make it stop, for that matter.

Semantic arguments aside, if you put a digital tach on your 22 lb platter you will see that the speed slows down even when the stylus makes contact with the record (I'd consider 1.75 grams to be a light touch).

As far as the rest of the tables that do drift over time, would you agree that constant platter speed is better than a slow drift upwards in speed?

You still have never answered this question.

phoenixengr
  " Wow, you managed to get just about everything wrong on that one; from your straw man argument about my sales motive to the lack of understanding of even basic physics. You deny that belt creep exists ...  you can blame speed variations on "some other" mysterious force? ...  You are wrong on both accounts.... Apparently you not only know what you know, but now you claim to know what I know. Semantic arguments aside ...  "

You're funny, phoenixengr. I certainly never stated that belt creep didn't exist. To refresh your memory, here's what I wrote:

" How have you measured this phenomenon? How can you be certain that whatever speed issue you may have detected is attributable to 'belt creep?'"

You seem to enjoy vituperative exchange. Have fun! I'm not interested.
 

The problem on these (and all audiophile) posts is that too many people think they know it all. What these pages should be is a forum of people’s experiences and beliefs in their own systems and others’ that they know well. ....a friendly exchange of experiences ..delights, and disappoints. There are few absolutes in audiophilium.