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Vinyl Asylum: REVIEW: VPI Industries SDS Accessory by Bruce from DC

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REVIEW: VPI Industries SDS Accessory

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Model: SDS
Category: Accessory
Suggested Retail Price: $1000
Description: turntable (or cd player) motor speed controller and a line isolator
Manufacturer URL: VPI Industries
Model Picture: View

Review by Bruce from DC on February 24, 2007 at 19:11:48
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for the SDS

There are two ways to spin a turntable with an electric motor -- using AC electricity and using DC electricity. AC seems to be the favored method on the western side of the Atlantic; DC on the eastern side. The attractiveness of using AC is that an AC motor locks on the frequency of the power it's given and spins at a constant speed, more or less independent of load and more or less independent of the voltage it's fed. Of course what this means is that the speed accuracy of your AC turntable is only as accurate as the frequency of the AC supply . . . which is pretty accurate, since your friendly power company's interconnected system of different generators and loads would come crashing to a halt if there were signficant variations in the frequency or phase relationship of the various generators that are strapped together from different parts of the country to drive the load. This property of AC is what allowed people to have reasonably accurate household electric clocks (more accurate than most mechanical watches or mechanical clocks) for decades before the advent of cheap quartz-crystal controlled oscillators.

Which is where the SDS enters the picture. The SDS is nothing but an AC power supply controlled by a super-precise -- and adjustable -- quartz crystal oscillator. This means that you can speed up or slow down your 'table by increasing or decreasing the frequency of the AC that is driving it. It also means that you can run the table at 45 rpm without moving belts to a different pulley, etc. Just flip the switch on the SDS. Finally, the SDS has some sort of current sensing device, so once the table gets up to speed (and is drawing less current), the SDS reduces the voltage supplied to (on my unit) 84 volts. Since the strength of the magnetic field radiated by the motor and the power cord to the motor is a function of voltage, reducing the voltage reduces the radiated magentic field, and therefore the induced 60 cycle hum in the tonearm cable and interconnects between the 'table and the phono stage (a good thing).

An indispensible accessory product (IMHO) is a strobe disc with a strobe light that is not timed by the domestic AC power supply but by its own power supply. (What's the point of using the suspect frequency of the AC mains as a reference to calibrate your down-to-the-nearest-one hundredth -of-a-cycle SDS?) KAB Acoustics makes one that's about the size of a pack of cards and comes with a 10" strobe disc that dispenses with the little radial lines but has numbers, either "33" or "45" instead. When the right number stands still, you're speed is exact. Anyway, using the KAB strobe as reference, an indicated 60 hz on the SDS spun the table at precisely 33 1/3 rpm. The fun comes in that you can put a 12" record on the table, with the 10" strobe disc on top. Then you can see how much stylus drag slows the table down. (It does!) On my table, with a record with loud band music on the outer edge, an adjustment of the SDS to 60.04 Hz was required to compensate. But, before anyone gets too excited about this, remember that the stylus drag is not constant. It's a function of how loud the music is and where the stylus is on the record. Although a record turns at a constant angular velocity, the linear velocity seen by the stylus is not constant. It's greatest at the outer edge of the record and slowest as the stylus approaches the dead wax near the label. So the drag of the stylus is not constant, either; and, therfore, its kinda silly to compensate by four one hundredths of a cycle and think you're really doing something.

Now, what's the theory here? Well, before reviewers stopped measuring turntables (unfortunate, since turntable measurements do mean something), there were 3 basic measurements: "rumble" (low frequency noise from the bearing; the less the better), "wow" (relatively slow changes in pitch, usually caused by some eccentricity in the pulleys in the driving mechanism) that modulates what's supposed to be a constant pitch and make it sound like "wow"; and "flutter" (which is very rapid changes in pitch that are not really audible as such). The much maligned "Stereo Review" made a test record in the early 1970s that I bought which, among other things had three different solo piano passages with increasing amounts of flutter recorded in. The only way I can describe it is that increasing amounts of flutter result in a sort "sick" or "sour" sound to the piano. It's subtle, but insidious. So, what the SDS does, I think, is keep the dailed-in frequency accurate over a much shorter periods of time, than your friendly power company, which may do an accurate 60 Hz if you measure over a second, but may wobble a bit if you measure it over a tenth of a second.

The SDS will work on any AC-powered turntable.

So, what do your ears get for about $850 street price?

If you listen to a lot of acoustic piano music, you get a much better-sounding piano. The piano seems to have more sparkle from the right side of the keyboard and more impact from the left side. Its no accident that the Stereo Review guys used piano recordings to illustrate the sonic effect of increasing amounts of flutter (present, by the way, in tape recordings as well).

The second noticeable effect is a much better-defined bass. For example, in "So What," the first cut on the A side of "Kind of Blue," Paul Chambers bass seems to kind of mumble along indistinctly in a sort of low growl during the introduction. The SDS adds some definition on those notes. Transients are cleaner, sharper; and this is particularly noticeable in the standup bass and bass drum in all jazz records.

The third noticeable effect is a more "locked-in" sense of where the musicians are. This is noticeable on KOB, again. (By the way, I've never liked the sound of the piano on KOB; it sounds muffled, almost as though its some sort of electric piano. The SDS makes it sound a little less muffled.) This effect is not always terribly welcome, especially on some early stereo recordings. For example, "Midnight at Mabel Mercer's" one of the few recordings of hers that is in stereo, sounds pretty dry, with Mable on the right. You're wanting a little reverb or little "fuzzing up" of the location of Mercer's voice, and what you get is a "mic's-eye" view instead . . . almost like someone is singing in your ear. Immediacy can sometimes be too much of a good thing! On the other hand, the piano accompaniment in that recording (sorry, forgot the pianist's name) is just delightful and SDS adds just enough "sparkle" to the pianist's right hand ornamentation to make it a bit more prominent in the mix. So, the totality of the effect is that you're in the front row of the club in New York where Mercer performed, and there's definitely a directness and immediacy that you don't get in a more processed studio recording. (That said, I'm not sure that this wasn't done in a studio; but if it was, the technique was minimalist.)

I couldn't begin to say whether or not whether the SDS is cost-effective. The concept is almost meaningless when it comes to vinyl. The SDS certainly does something . How much "something" vs. how many dollars, I am unable to talk about. The way I looked at it, it seems like SDSs sell very quickly on audiogon at not much of a discount; and, were I to upgrade my table in the future, the SDS would work with the new unit as well. So that was my rationale for spending on the SDS about 50% of what I spent on the table and arm itself (used).

Product Weakness: For the money it costs, the packaging (case, front panel, controls) is strictly utilitarian.
Product Strengths: Does what it promises; is easy to use.

Associated Equipment for this Review:
Amplifier: BAT VK-600SE
Preamplifier (or None if Integrated): NONE
Sources (CDP/Turntable): VPI HW-19 Mk 3; JMW 10
Speakers: Joseph RM -7si
Cables/Interconnects: Mostly Goertz Triode Quartz
Music Used (Genre/Selections): jazz, classical, bluegrass, vintage rock
Room Size (LxWxH): 14 x 10 x 11
Room Comments/Treatments: no special treatments; built-in bookshelves (filled) cover two walls; upholstered furniture, rug; room sounds very good
Time Period/Length of Audition: two months
Other (Power Conditioner etc.): Equi-tech 20 amp Q balanced supply
Type of Audition/Review: Product Owner

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Topic - REVIEW: VPI Industries SDS Accessory - Bruce from DC 19:11:48 02/24/07 ( 31)