VPI Analogue Drive System

cleeds,  Do you dispute what I actually wrote, in essence, that you can set platter speed with the SDS or the Walker?  I did neglect to mention that the motor should be of the AC synchronous type, but that wasn't really the question.  Most turntable motors fit this category, to one degree or another. Also, I don't know how you can say that current has no effect on platter speed, but frequency does.  "Current" has the property of frequency, which as you say does determine the speed of an AC synchronous motor.  I have read conflicting statements about the degree to which AC line frequency is tightly or not tightly controlled by power companies. Most sources say it's "pretty good" with small variations over short time that average out to 60 Hz over longer time periods.  Is that good enough for most audiophiles? I don't think so.

Jerry, Stylus drag is definitely NOT constant, by the way.  It's constantly varying across the surface of an LP.

I moved my motor drive belt up to the top slot on the motor drive pulley which effectively lowered my 3150 test tone from 3160 to 3149 on my PlatterSpeed app.  There was a significant improvement in sound quality with all my MC cartridges (I have 4 of them).  This obviously didn't cost me anything and I should probably have done it awhile ago, but I've just started paying attention to this tweak.  So far I'm not running out to buy anything yet.

Running your TT at the right speed (or nearly so) is not a tweak.  It's just a very basic thing everyone should do, like leveling the platter.

Melm:

Sorry.  Wrong word.  At this point I'm almost ready to take your advice not to buy anything and maybe the DIY components that Phoenix Engineering used to make will be available again.
So far no one who has bought the ADS has responded as to how great it is.

All the "speed control" fanatics are completely missing the point and the REAL issue.  Speed control is NOT the issue.  It is VOLTAGE control.  At wall voltages, the motor will generate pulses that are carried to the table through the belt (or drive).  Reducing the voltage will reduce the magnitude of the pulses and fix the noise issue.  THAT is the reason to get one of these units.  A variostat will do the job at a fraction of the price of a "speed control."  Start the table at full voltage then reduce to 70 volts or so when it's time to drop the needle.