VPI SDS Calibration Gurus?

Hi all, Having recently acquired a new SDS, I had noted that upon power-on of my SDS, it reads 72v. Upon power on of my HW-19Jr with MK-IV Platter, it will ramp up to 115v, but then only at first ramped down to 84v.

I searched the Audio asylum, and found that there is a calibration mode for the SDS. Nothing of this is mentioned in my manual. I toyed with it a bit, and did eventually set the calibration of voltage to then again ramp down to 72v after platter reaches speed. (perfect speed for me with stylus drag included is 60.11hz with the KAB Strobe) Would this be the optimal voltage setting for me? (72v)

Can someone please comment, and perhaps please post the calibration instructions here for me? Thanks in advance, Mark
Hi Mark. I'm just guessing here, but it seems to me that theoretically the power cycle tweak is to make up for slight deviations in equipment geometry from ideal and the voltage tweak is to provide enough power for a steady speed. I.e., if the voltage is too low, the platter won't get enough power to spin at a constant rotation. In the limit, the difference in the amount of needle drag between loud passages and quiet passages would be enough to cause wow distortion, despite the smoothing effects of a weighty platter. My guess is that the VPI factory settings imply that 72 volts is sufficient for no record and no needle, and 84 volts is enough to overcome essentially all effects of varying needle drag. (Of course, there is always the secondary effect that needle drag may cause some change in geometry -- belt stretch for instance -- that would require a power cycle adjustment also.) In any case, unless there is a strong reason to cut the record playing voltage to 72 volts, maybe keeping it at 84 volts would be prudent.
Hi Jameswei, Thank you again for your help, as I'm sure you've helped me with avice here in the past.

I hadn't considered what you've said about the SDS in relation to the various VPI (or other Tables), in which owners wished to implement the SDS into thier Analog arsenal.

I had assumed-considered that perhaps in some instances, the ramping down to 72V after the Platter reaches speed would be insufficient, and hence, the reason perhaps VPI incorporated this feature.

It was my thinking, (and hopefully correct thinking) that one should-could try to use the lowest voltage one could "get away with" to provide sufficient voltage to properly run the Turntable, and also assumed that the lower the Voltage supplied, the lower noise that the AC Motor would produce? Is this thinking flawed perhaps?

I've yet to audition my Table at the lower 72V ramp down setting, but will do so this evening, and will hopefully report back with my findings.

Since the KAB Strobe Disc I have is slightly smaller than a 12" LP, I believe I do have the ability to check again, my speed with stylus in play (to account for Stylus Drag) for the first few minutes of play by just placing the Strobe Disc on top of one of my less than stellar LP's?

I do understand that there is a word DOC on the VPI site for SDS Calibration, but being a webbie user, I cannot open these attachments. I reckon I'll have to use a friend's computer, or the Library's, and print myself a copy of it. If you'd further like to comment about what I've said James/All, please feel free to. Thanks, Mark
My SDS cycles down to 72 volts for playing. I've also got the KAB strobe and the TT's speed is rock steady while playing.

Hey, email VPI about their word files on their website. I sent them an email about this a couple of months ago. I told them I'm a web developer and no one should be using Word files on their website to distribute documents. And that they should convert all of the word docs to PDF format. I even created a PDF of their price list for them and sent it to them.

I got back a snotty "go away" email from Sheila saying that they knew more about the web than I did and that everyone LOVES their website and they didn't need any suggestions. Pretty much a "piss off" email and all I was trying to do was help them.
Just a quick update, that after dropping the ramp down voltage from 84v to 72v, what I had noticed, was that again, the Platter was running just a slight hair slow again, and needed to compensate, by raising the frequency from the originally needed 60.11hz, to 60.17hz.

From what I can see, by careful examination again with the KAV Strobe Disc-Strobe Light, all appears just fine, with the speed staying rock stable even with stylus in play, and the sound which I sampled last night for a good hour, or so, sounds very good indeed.

Soon, I'm about due again to yank the Mk-IV Platter-Bearing for some fresh oil-lube, and I suspect this might again mean a minor adjustment of the SDS's frequency to compensate. Mark
Sounds like you've got it!