Stylus Drag

Stylus drag is defined by the coefficient of friction between the stylus and the vinyl groove multiplied by the normal force (tracking force) of the stylus. I found some old technical papers that measured and evaluated the coefficient of friction of vinyl records comparing different vinyls as well as cleaners and lubricants. Surprisingly, the coefficient of friction can vary quite a bit. They showed numbers ranging from 0.2 to 0.4. Multiply that by your tracking force, eg. 2 grams and the stylus drag can range from 0.4 to 0.8 grams. That drag is what generates the skating force component on the tonearm. So your anti-skating setting is an indicator of just how much stylus drag you have- less bearing friction in your tonearm. As an aside, if your tt sounds better with no anti-skating applied, then perhaps the tonearm bearing has some significant friction.
As for speed control: I have shown some calculations in other threads for information and inspiration purposes. Observations with the timeline show that the speed shifts on some tt's when the needle is dropped onto the record. That doesn't mean it is a bad tt. Any external force applied to a platter must be reacted to by the motor/speed control system. Dropping the needle onto the record can add about 0.011-0.021 in-lbf (120-240 g-mm) of torque to the platter. How much that changes the speed, if any is dependent entirely on the tt.
So let's say someone using the timeline with a 500mm radius to the wall observes a 2mm shift in the red line when they drop the needle onto the record. At 500mm that is a 0.06% change or 0.02 rpm shift. If you were playing a 3150Hz test tone, that would cause a 1.9Hz change. Now what I thought I read was that the red line on the wall shifted one time as the needle hit the record but then did not drift while playing the record. What is wrong with that? So the speed shifted ever so slightly due to the torque change. The motor/control system compensated and the record platter speed remained stable afterward. Seems fine to me. The timeline accuracy is good to three decimal places and almost all turntables are good out to two decimal places. Record runout is good only to one decimal place. Ref my calculations in the other thread. I can hear record runout. That is the real problem. I cannot hear my turntable's 0.02%/0.03% Wow and Flutter- not even in the soundstage or other subtle cues. And my analog soundstage is superior to CD.

As far as stylus drag's affect on speed control, let me also explain that platter mass is part of the entire speed control system. The speed control system is designed around the motor and platter inertia. Turntable designers, especially belt drive tt's use platter mass for dampening. Mass is commonly used for dampening. Your car engine and even your car body has mass dampers to minimize the vibrations that you feel and hear in the car. A massive platter requires more torque to control speed- and so belt drive tables use the small motor pulley and large platter outside diameter as a torque multiplier. A direct drive tt has a relatively low mass platter and as many on this forum will attest, also has excellent speed control. The speed control system is different for the low mass DD tables as compared to a belt drive table. DD turntables simply use a different control system for the lower inertia platter. DD turntables were originally designed for DJs so they could stop/start the platter quickly. My personal preference is the massive platter on a belt drive table because the mass doesn't just dampen torque variations, but also external vibrations from the floor and the air. The massive platter makes a great sink for the record. DD turntable users have to admit that they must work hard to isolate their DD turntables and platters from vibrations.

Even in a closed loop system some speed variation will occur. An error must exist between the setpoint and actual before the system will react. A certain deadband around the setpoint exists or else the sytsem would hunt, ie. cycle about the setpont which would be much worse. That is the theory. I do not know the details of the actual tt design. It is analogous to the cruise control on your car. You are at a set speed and come to a hill. Notice the speed drops one or two mph as the engine increases torque to compensate. The same happens as you go down a hill; the speed increases one or two mph as the engine torque decreases. But in the case of our high end turntables, I think the designers have the platter speed held to within 2 decimal places under moderate load variations due to needle drag.

I had used my little strobodisc for years on my turntable. When I used the 3150Hz tone and the iPad app, I found that my speed was low by a few Hz. I didn't hear it as a pitch change, but as a rhythm and pace improvement. I'm hearing all of my records as new just from getting the speed dialed in correctly. That was a learning experience; don't rely on the little stobodiscs. I hear a pitch variation only when playing a pure sinewave. The record runout causes a small but noticable warbling in the pure tone. Improving record runout (filed the hole out and centered the record on the platter) directly reduced the pitch variation.

It occurred to me re-reading some of these threads that no one has mentioned some turntables have closed loop speed control systems while the rest are open loop. That means if you put your finger on the rim of the platter ever so slightly just to add some drag and you hear/see the speed drop and stay low, then your tt is an open loop speed control. A closed loop system has a speed sensor and the control system will add/subtract torque as needed to maintain the set speed. If you touch the rim of a closed loop table you might see/hear the speed change momentarily but then correct itself. My turntable is open loop. I have a speed dial to adjust the speed and I adjusted it while playing a record, but any changes in load on an open loop turntable will affect the speed of the platter. If the friction varies from one record to another, then our open loop tt's will have slight variations in speed. Probably too small to notice, but it is there. I don't know which tables are closed loop design vs. open loop, but I think just about all DD turntables are closed loop. The timeline device probably seperates out the closed loop tt's from the open loop systems. That's because the closed loop tt's are going to maintain a constant speed by adjusting torque as the needle is dropped onto the record and as the friction/drag varies while playing the record. Again, I don't necessarily hear it as a pitch change but more as rhythm and pace.

Peterayer, the SME table embodies to me, everything a turntable should be- massive platter, state of the art speed control, great sound and great looks. If I had the means I'd let SME spin my records. Happy listening.

I call it record runout. Runout is the periodic side to side motion that can be seen in the record and even the tonearm as the record is spinning on the platter. It is caused by the centerline of the record hole being offset to the centerline of the record grooves. When it is visible with your eye and in many cases even the tonearm is seen swinging side to side, that is near the maximum tolerance; but still within tolerance! In the other thread I posted the industry tolerances for the center hole position and its impact on WoW & Flutter. The higher quality pressings I found, have pretty low runout but some old Columbia pressings from the 70s are probably the worse that I have seen. Ironically, my stereo test record had pretty bad runout which I corrected by filing the hole out; but now I have to center the record on the platter.

I meant to also say that the outside diameter of records are not always round. You really have to reference the grooves to find the true center of the record. I'm guessing that they trim the OD of records with a knife to remove the flash, if they trim them at all when they come out of the die. That's typical in most molding processes. So you can't count on the OD of the record to be concentric to the hole or the grooves either.