Stylus Drag

In any motor, AC or DC, if the load increases the current in the motor will increase too. This provides a feedback mechanism that functions well even on open loop systems. For an AC motor that runs off the line, if the motor has any torque at all it will be able to compensate for stylus drag with ease (the voltage of the AC line contributes to torque while the frequency determines the speed) as it might just draw a little more current to stay on speed and with the AC line, there is essentially an infinite supply.

With a DC motor (open loop- not sure if that is the right term as many DC motors have internal electro-mechanical speed controls) the limitation *can* be the stability of the power supply. There are a lot of variables here depending on design so calling out generalizations can be risky.

I have an older VPI MKIII with the stand alone motor assembly. Stylus drag is exactly what tells me when my belt is getting too stretched out and the motor needs to be re-positioned.

It is especially apparent when there is a loud sustained line (kraftwerk or other electronica). The pitch sags when the volume increases. This is the 9lbs platter btw.

I do agree with Dover......that the better your TT becomes at maintaining accurate and constant speed under heavily modulated passages.....the more you tend to hear the imperfections of the record pressings such as off-centre holes?
For every solution.....another problem is revealed :^(

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.