VPI SDS speed issue

As far as I know, the SDS's ability to adjust line frequency in Hertz is not due to instabilities in line frequency coming from the wall, as this is usually very stable, but rather to fine tune deficiencies in platter, or pulley diameter, or other anomalies in the table's drive system itself.

Which brings me to this suggestion for the original poster.

First, find out what your ramp down voltage is set to. If 72V, this may perhaps be too low a setting for your particular table, and drive system.

That using Idler Pulleys, ultra heavy Platters, etc, 72V may not be sufficient voltage. You may need to select a slightly higher voltage?

Just a thought, and worth trying first, before condemning the unit as faulty. Mark

Make sure that your motor pulley isn't slipping. I had a similar problem a while back with my Aries.

As pointed out by myself and Brf, the output of the SDS is independent of fluctuations in frequency of the mains line. The SDS output wave is produced by an adjustable oscillator driving an amplifier. I would not expect much oscillator frequency drift from such a setup - and if it does vary slightly, it won't be related to mains frequency drift.

I understand about having to make small frequency adjustments on the SDS from time to time. I suspect this may be more due to mechanical fluctuations with the motor/bearings/belts etc. This is no big deal. Since we're talking about small changes over long periods of time, it should have little sonic consequence.
If you are having more frequent issues, the top suspect would be worn drive belts IMO.

Actusreus,
What I've noted with my own VPI SDS, that I've owned a good 4 years, ans use to power my HW-19's Motor, is that doing repeated periodic checks, there has never been a need to have to continually fiddle with the line frequency settings.

Even after lube maintainence of the MK-IV Platter's Bearing, via KAB Strobe Disc the exact speed is always spot on. Evidently a testament to just how stable line frequency in Herts usually is. Voltage, that's another entirely different matter, but fluctuations in voltage does not effect Platter Speed.

Only when I more recently changed to the newer VPI HW-19 SAMA, with its fine stepped Pulley, versus the older (Junior model) two step pulley, was I then able to even more accurately get exact speed, with a bit closer setting of the SDS to the line reference 60.00Hz setting.

As an example, with the Junior Motor-Pulley, I was at 60.17Hz. With the SAMA I am now at 60.07Hz. This tells me the SAMA's stepped pulley, all on its own, permitted much better truth of 33.33 speed, minus the SAMA in the Circuit.

Good point brought up about the Motor Shaft Pulley possibly being loose.

Another, is what Motor Run Capacitor is being used on the Aries? Harry has mentioned that certain value Capacitors can play havoc with the SDS's proper operation.
Even if it is found that the Existing Cap is the correct value, it could possibly be faulty?

Hope this helps. Mark

While I was sorting things out with my set-up I used grease that was too heavy, To trouble shoot, you can eliminate the step-down voltage drop quite easily. Try that and see if the speed remains constant. Then you can try the different drop down steps until the speed becomes unstable. For instance 72 volts is too low for 45 RPM but it works fine at 84V. Basically, I agree with Marc51 above on reading his post more closely.