VPI SDS speed issue

Go to the VPI website and download the SDS calibration manual. If your SDS goes from 115v => 84v => 72v then something is wrong because the SDS is only programmable for a single step down voltage i.e. 115v => 72v. The step down voltage can be programmed by the user. Depending on the age of your SDS, the factory default is set at either 72v or 84v. Try recalibrating your SDS and report back.

There is a PDF file on VPI's website on how to access the calibration mode on the VPI SDS. This file was not included with the standard issue owner's manual.

But, to me, it sounds like you have some sort of problem with your Unit?

Yes, the SDS should initially start up upon turn on to 115VAC, then drop to a selected lower voltage, and the factory default setting was said to be 72V. Then it should stay at that prescribed lower voltage setting, and not change while the unit is in use.

Not until it is then shut off, and turned on again, will it again go through the same process I mention above.

I'd definitely get ahold of the folks at VPI, and describe your problem. I'm not knowledgeable enough to troubleshoot your problem, which could be a fault with the SDS itself, or perhaps some other problem, such as a wiring, or Capacitor problem with your Aries Table?
Mark

Input line voltage/frequency fluctuations to the SDS should not change the output frequency - that's the whole point of the unit, it synthesizes a stable output frequency independent of the line.

When I was experimenting with using dental floss as a belt material, belt slippage caused all sorts of problems. As slippage got worse I had to keep increasing the frequency to get proper speed.
Try some replacement belts and it may cure your issues.

Regarding SDS output voltage. While the factory setting after startup is 72V, I actually run my SDS at 115V all the time (set per the procedure in the manual). I find this sounds punchier in my setup - but I use the original heavy TNT lead/acrylic platter with the single motor/flywheel, which is not a stock setup.

Tobes,
If I'm reading your post correctly, I'm actually confused on this issue. My understanding is that the SDS allows you to adjust the current frequency so as to obtain a correct platter speed, but what that "correct" frequency is is itself dependent upon the stability and frequency of the power supply in your wall. Since the frequency in your wall current fluctuates, you might have to adjust the output frequency on the SDS to get the platter spin dead on from time to time. I agree that if your wall current is relatively stable, once you find at what frequency your turntable reaches the most accurate speed, you might not have to adjust the SDS often, but since the current does fluctuate in most homes, occasional adjustments might be necessary. In my experience, I get the platter on my Classic dead on for 33.3 at 59.95 Hz, but have gone over 60 Hz a few times.

If the SDS knew precisely what frequency to feed to the table based on the current going into it, it seems there would be no need to have the function to adjust it on the unit.

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.