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 
F047e6d3 4ab4 4f0d 81a3 1d06afd11319halcro
"Dear friends: I would like to know if each single LP was recorded/cutted at exactly/accurated 33.333..rpm and if for any reasons exist tiny deviations from 33.333..rpm accuracy why or how can we or not detected through an accurate TT that spins at exactly 33.333...rpm during play time of LPs?"



The most popular motor for the cutting lathes is a Technics SP02 direct drive motor which is quartz locked for speed accuracy and weighs ~110lbs with plenty of torque.  W&F are rated at 0.0084% RMS.  In terms of absolute speed accuracy, it should be more accurate (and more stable) than most of the DD tables playing the LP it cuts.

http://pspatialaudio.com/lathes.htm

of course, this is a natural selection problem. far beyond numbers or instruments. my son-in-law is a physicist working for the Allen Institute. they do brain research. he assembles big data for the neuroscientists.

he said in maybe 10 years they will be able to replicate a cubic cm of mouse brain tissue. but right now it’s too much data to replicate. he does not think he will live long enough for them to be able to do that for a cm of human brain tissue. just too much data.

so when we think that we can measure what our senses have evolved to sense, we are kidding ourselves. and not just the hearing part. the whole body is involved in whether we think something is fake or real.

which is why getting as close to absolutely steady as possible means more to our musical sensibilities than what we view as corrected speed. there are no naturally occurring servos.

In general, accurate rotation is obtained by servo-control by negative feedback, but at the micro level, if it rotates or becomes faster, it detects it and slows it, and repeats the operation to make it faster if it gets slower. If you try to measure a period with a small level, you cannot measure the instantaneous state, so you should measure the average value. Therefore, fine vibration generated by servo-control cannot be measured by the measuring instrument, it depends on the human ear.

Mike.
Exactly. This is what I was trying to say with respect to dynamic speed stability, (steadiness)
The level of granularity we use to measure TTs is simply too crude to show us what is going on in real time under dynamic conditions.  

But we sure can hear it.


Hi @lewm.

... No matter how much I search on that last topic, I have never found a satisfactory treatise on the subject of coreless motors vis a vis cogging, but most talk about coreless motors as if they are free of it. ...

Here's a few links that may be of interest;  cannot say if they count as satisfactory. 

Comparison of Slotless and Slotted Motors. The article does discuss cogging.https://www.celeramotion.com/applimotion/support/technical-papers/slotless-vs-slotted-motors/

Brushless, slotless, and cogless (1999)
https://www.designnews.com/content/brushless-slotless-and-cogless/60538412940113

Very interesting thread.  As I read through these responses, I have to wonder if the original recording mechanism, the record lathe that cuts the master from which the molds are made, is equally subject to modulation induced speed variations.  Plowing a new field, so to speak, would seem to take a bit more energy than playing an existing groove.  How does the record lathe overcome this?  And if it doesn’t, perhaps stylus drag speed variation in the playback system mirrors the speed variation in the recording process........