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Stylus-Drag..Fact or Fiction?

Most audiophiles can't seem to believe that a tiny stylus tracking the record groove on a heavy platter could possibly 'slow-down' the rotating speed of a turntable.
I must admit that proving this 'visually' or scientifically has been somewhat difficult until Sutherland brought out the Timeline.
The Timeline sits over the spindle of the rotating disc and flashes a laser signal at precisely the correct timing for either 33.33rpm or 45rpm.
By projecting these 'flashes' onto a nearby wall (with a marker attached)....one can visualise in real-time, whether the platter is 'speed-perfect' (hitting the mark at every revolution), losing speed (moving to the left of the mark) or gaining speed (moving to the right of the mark).

RAVEN BELT-DRIVE TT vs TIMELINE 
Watch here how the laser hits the mark each revolution until the stylus hits the groove and it instantly starts losing speed (moving to the left).
You can track its movement once it leaves the wall by seeing it on the Copperhead Tonearm.
Watch how it then speeds up when the tonearms are removed one by one....and then again, loses speed as the arms are dropped.

RAVEN BELT-DRIVE TT vs TIMELINE
Watch here how the laser is 'spot-on' each revolution with a single stylus in the groove and then loses speed as each additional stylus is added.
Then observe how....with NO styli in the groove.....the speed increases with each revolution (laser moves to the right) until it 'hits' the mark and then continues moving to the right until it has passed the mark.

Here is the 35 year-old Direct Drive Victor TT-81 turntable (with Bi-Directional Servo Control) undergoing the same examination:-
VICTOR TT-81 DD TT vs TIMELINE 
128x128halcro
phoenixengr's avatar
phoenixengr
94 posts
 
"....why do you think VPI use trapezoidal commutation?
Surely this is not optimum if they want to minimize torque ripple."



The controller is made by Elmo Motion Control (Gold Twitter Solo), and while Elmo's PC control software is fairly comprehensive, I'm not sure if the controller is capable of sinewave drive;  it is not capable of sensorless operation (FOC) which would use sinewaves.  Sinewave drive is considerably more complicated and would result in smoother operation, but for whatever reason, VPI chose to operate the motor in the simplest mode available, as a DC motor which uses block commutation and Hall sensors. 


They do some other rather strange things:  The motor is designed for high power (500W) so the windings are 0.3R;  not the easiest load to drive especially from a class AB output amp.  The Elmo controller uses PWM output at 10kHz, which IMHO is a bad choice for use around a sensitive audio circuit like a cartridge pickup (especially MM).
testpilot
972 posts
 
I am getting a sneaky sensation that phoenixengr just might know a thing or two about TT motors.
mijostyn's avatar
mijostyn
8,570 posts
 
No kidding. Just for the record phoenix what turntable manufacturers drives do you like the best and why?
phoenixengr's avatar
phoenixengr
94 posts
 
Unfortunately, I haven’t had the chance to "look under the hood" on very many of them, but based on my limited exposure:

Belt drive: American Sounds AS2000. David Karmeli not only understands high end audio, he gets the physics and engineering part right as well. His design philosophy may be unique in the industry. Full disclosure: I had a hand in  designing the motor control for this table, based on the Eagle PSU and RR tach.

Direct Drive: I’ve not auditioned the new Technics tables and I don’t have a lot of technical info on them, but from what I can gather, they are doing some really sophisticated things in motor control and they have the engineering HP to do things right. It wouldn’t surprise me at all if they were doing FOC.

I’m basing my observations more on an engineering perspective than an audiophile one. YMMV.
atmasphere's avatar
atmasphere
11,977 posts
 
Anyway, who do you send the masters to for pressing?
@mijostyn I've found that if the mastering is done correctly most pressing plants can do a pretty good job. But QRP stands out as the best (their pressings have noise floors that easily rival Redbook), RTI is excellent and oddly enough we've had very good results from United. One of our projects was pressed in Holland, not sure which plant but all the US plants were 3-6 months behind at the time.
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