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.
Have you checked the consistency of your voltage from the wall? Does it vary a lot?
You may find plugging the SDS into a power conditioner helps stabilize it.
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?
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.
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 its 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.
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.
How does one change the voltage on an sds?
Mine seems permanently set at 72 and only adjustable options are for frequency and changing speed from 33 to 45 rpm.
MR M- Go here: ( http://vpiindustries.com/manuals.htm ) Right under the SDS Manual listing; you will see, "Calibration Mode for SDS." Either open or save that file, for the info you seek.