SDS or phono stage

Just for the record, and speaking only for myself, I discussed the SDS only because that is the unit that Arsh asked about. What I said about the SDS is only hearsay. I personally do use a Walker Audio Precision Motor Controller, which does pretty much the same thing as the SDS but without some of the less useful SDS features. All my experience of the beneficial effects of a Motor Controller has to do with the Walker. Some, who have tried both the Walker and the SDS, have found the Walker to "sound" a bit better, but with a VPI tt, I assume the SDS would be a great match. There is no savings associated with purchasing the Walker vs the SDS. Used or new, I think the typical prices are about the same.

As to use of a laser tach and other similar gadgets, that's fine, but they do not address the issues at hand, and they suck up funds otherwise available for the nitty gritty solutions. The KAB strobe is the most accurate and cost-effective device for checking tt speed and speed stability, IMO.

I owned both the Walker and SDS and I could not tell any difference between the 2 units. I sold the Walker only because I had a friend who wanted it. I would have been happy with either.

Lewn, have you tried the Platter Speed? At a cost of $35, it is easy to use and hard to beat.

Has anyone actually compared the sonic output of a variac vs. the SDS? From what I have read technically, the SDS is designed to control the speed of the motor by varying the FREQUENCY of the AC current where a variac is just a glorified transformer outfitted with a wiper to adjust the voltage by adjusting the effective number turns in the secondary.

Mcbuddah, The SDS and the Variac are not equivalent devices, as you seem to know; the SDS is an active device whereas the Variac is passive. One small error: the Variac is an autoformer, not a true transformer. Since the primary and secondary of an autoformer have one connection in common, an autoformer does not isolate the primary side from the secondary. So an autoformer will not either block noise on the AC line or prevent tt motor noise from going back into the AC line. (I think this is true; perhaps Al will jump in and correct me, if I am wrong.) On the other hand, the SDS synthesizes "new" AC and both voltage and frequency can be varied. So the SDS can control a motor by varying either of the two parameters and will ameliorate noise, etc. I have a feeling you know all this. Bottom line: I have tried using a Variac, not to control a tt but to reduce bias voltage on an ESL panel, to "rest" the diaphragms when the speakers were not in use. For some reason, I found that it introduced a very objectionable coloration to the sound from the speakers. I don't know whether the same effect would be audible if Variac is used on a tt motor, but my Variac is now occupying a dark and dingy place in my basement.

Brf, What is "Platter Speed"? Since I've spent about ~$100 on the KAB Strobe, why would I want to spend $35 more on a device that does the same thing, or does it? By the way, that's "Lew M". You are not the only one who finds it hard to read "Lewm" and thus calls me "Lewn". On the other hand, I am a bit Lewnie, for sure.

Lew M, sometimes it is better to ask questions than to shout out answers, only to find out the world has moved on. All the variacs I have ever used or even seen have been of below par construction for audio use. I think most are used to control motors in certain kinds of factory production and OEM usaes in the same role, where critical adjustments are either not necessary or are supported with gauges or a servo mechanism. The speed precision needed to properly replay records far more important due to the sensitivity of our ears to even tiny speed inaccuracies. The KAB device used with VPI's SDS is capable of both setting and holding the speed steady, something else that the Variac likely does poorly in that it is set by mechanical means, whereas the SDS resolves in .01hz increments.