VPI SDS speed issue

The SDS is not a power line filter it’s an AC power regenerator (like a mini PS Power Plant). The SDS first converts the incoming AC to pure DC voltage and then digitally regenerates its own clean AC signal.

The SDS is designed to work with the AC synchronous motors. The speed of a synchronous motor is determined by the frequency it is fed. Logically, a device whose speed is based on the AC line frequency will function better when a stable consistent frequency is delivered.

Right, but this still doesn't answer my question regarding Tobes' post. Does the SDS need to be adjusted based on the fluctuations in the wall current frequency? I believe yes as otherwise there would be no need for the frequency adjustment on the unit. Tobes' first paragraph seems to suggest otherwise.

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.