turntable speed control

You’ve claimed that " belt creep does exist and it is measurable." That’s another rather odd claim. How have you measured this phenomenon?

Are you denying that belt creep exists? That’s not only an odd claim, it’s counterfactual. Without belt creep, elastic belt drives could not transmit torque to the platter; it is undesirable, but necessary for these systems to work.

AC synch motors operate at 2 different speeds: 100.00% of rated speed determined solely by the drive frequency or 0% when the cogging torque is exceeded and the motor stalls. There is nothing in between. If you even lightly touch the platter while it is moving, it will drop in speed, yet the motor maintains its speed at 100%. How do you account for that if there is no belt creep, a phenomenon that is well documented in physics?

It’s trivial to measure the difference in platter speed caused by stylus drag (if you have the right equipment i.e. a tach with 3 decimals of resolution; a hand-held tach with 1 decimal is a poor indicator, strobe discs are even worse). The difference in drag at the beginning of a record is even different than when the stylus is closer to the spindle. Anything that creates drag on the platter, including changes in bearing friction, will increase the torque demand on the drive system, increase belt creep and reduce platter speed.

If I let the platter speed stabilize at 33 RPM for several hours where little or no correction is applied, switch to 45 RPM for even one side of an LP, then switch back to 33 RPM, the speed will be 0.15-0.2RPM higher while using the exact same frequency as when I left 33 RPM. The difference is due to changes in the belt and bearing.

I’d suggest you do a little more research before you decide to debate how these systems work. You seem to have little understanding of the physics involved, yet you "know" so much.

As far as measuring the consistency of turntable platter speed - I have found nothing better than the Timeline form Sutherland Engineering, its a device that emits a laser beam pulse at very precise time intervals.  This is placed on the spindle of the turntable and a dot appears on the wall of the room the turntable is placed in.  If this dot does not move the speed of the turntable is exact - and I have yet to find any belt drive turntable thats been able to hold the position of the spot over the entire length of a LP playback.  I have run many VPI based tables with and without a SDS unit and while SDS certainly makes it a lot more speed stable it simply cannot hold absolute precise speed.  I have not tried the Phoenix unit but will some time in the future.

However, once you get a Direct Drive turntable it becomes very obvious that these are far better at maintaining the correct speed The Denon drives which we retrofit,  rebuild and sell are quite precise.  The Technics SP 10 MK2 and 3 are exceedingly more accurate in maintaining correct speed.   And by accurate I mean the laser dot emitted by the Timeline does not move on a wall 23 feet away from the turntable.

Halcro whom posts on this site frequently posted a video on youtube a while back indicating the speed accuracy of his Victor TT101 Direct Drive turntable to indicated if Stylus Drag is an issue on a Direct Drive Table
The results of this are quite obvious.


https://www.youtube.com/watch?v=RE52bsIh_ZA

  
Good listening

Peter

phoenixengr " ... I’d suggest you do a little more research before you decide to debate how these systems work. You seem to have little understanding of the physics involved, yet you ’know’ so much."

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.

Not incidentally, the question isn’t only, "Is it measurable?" but, "Does it create an audible effect?" I say that because we can measure some things that we cannot hear.

" If you even lightly touch the platter while it is moving, it will drop in speed"

Not necessarily. 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.

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.

"Not incidentally, the question isn’t only, "Is it measurable?" but, "Does it create an audible effect?" I say that because we can measure some things that we cannot hear".

More importantly, I believe, we can hear things that we cannot measure.  That is why, despite the great (industry approved) measurements from relatively inexpensive direct drive TTs, most careful listeners know that belt drives (which may measure worse in some respects) sound better.

""If you even lightly touch the platter while it is moving, it will drop in speed"
Not necessarily. A light touch to a 22-pound platter doesn’t effect speed"

Well, I have a 20 lb.TNT platter + a flywheel and the reduction in speed when given even a very light touch is undeniable to all who can hear . . or measure.