Review: VPI Industries SDS AC filter

Category: Accessories

The folks at VPI certainly produced another stellar product for their range of turntables.

Years ago I used the first generation of this type of unit from VPI called the PLC. While this was a decided leap in the right direction in getting clean power to the turntable motor and being able to control the line frequency being fed to the turntable, most impressive for the time.

However this third generation of line filter units from VPI has emerged and set the bar quite high. The performance of this unit is astonshing to say the least.

The VPI SDS is connected to a VPI HW19 MkIV turntable.

Set up is as about dirt simple as it gets. Basically if you can read and follow simple instructions included with the unit, it is a breeze to set up and use. The SDS weighs 10 pounds on my postal scale. Measures 16x3x12 and will fit most anywhere ventiliation is not a major concern, but do avoid tight fit cabinets as air does need to circulate around the unit.

Music Used For Evaluation:

LP Playback:

Bob James - Hands Down (Columbia FC 38067)
Hiroshima - Self Titled - (Arista MFSL1-525)
John Coltrane - Blue Train - (Blue Note BST 81577)
Wes Montgomery - Bumpin' - (Verve V6-8625)
Rickie Lee Jones - Self Titled - (Warner BSK 3296)
Wynton Marsalis - Live Blues Alley - (Columbia PC2-40675)
Eric Gale - Forecast - (KUDU Records KU 11)(CTI Records)
Kenny Burrell & Grover Washington Jr - (Blue Note BT 85106)
Earl Klugh - Finger Painting - (Blue Note MFSL 1-025)
Larry Carlton - Friends - (Warner 23834-1)
Sadao Watanabe - Autumn Blow - (Inner City IC 6064)
Doobie Brothers - Minute by Minute - (Warner BSK 3193)
Santana - Zebop - (Columbia FC37158)
Pat Metheny Group - American Garage - (ECM 1-1155)
Frederick Fennel - Cleveland Symphonic Winds - (Telarc 5038)
Paul Desmond/Jim Hall - Complete Recordings - Mosaic(MR6-120)
Time Out - Dave Brubeck Quartet (Columbia CS 8192)
Paul Desmond - Self Titled (Artist House AH - 2)
Ahmad Jamal - But Not For Me - Argo LPS 628
Bill Evans - At The Montreux Jazz Festival - Verve V6-8762
Bill Evans - At Montreux II - CTI 6004
Sunken Cathedral - American Gramophone - AG 361
No Bass Hit - Concord Jazz Label - CJ-97
Oscar Peterson - Night Train - Verve V-6 8538
Gerry Mulligan Reunion Chet Baket - Pacific Jazz ST 90061

This is just a representative sample of the many LP records that were used for evaluation of the VPI SDS.

While I was expecting a marked improvment of the previous VPI PLC, I was not prepared for the WOW factor. This time VPI clearly swung for the fences with the SDS and more than delivered a product, that must be considered as a must have for the analog maven.

Living here in Florida with the Hurricanes of recent years has challenged the electric utilities in their abilty to deliver clean power. Here in my house the output voltage from the wall varies from 112 to 126 volts and is a constantly changing. It has become better, since a new transformer was installed in the neighborhood, but still remains far from a constant from the wall outlet.

The VPI SDS clearly resolves that problem by managing rock steady voltage and the ability to fine tune the frequency range the motor sees.

It matters little how adept a turntable is at isolating its associated arm/cartridge from both external vibrations and those generated from within the analog playback system itself. It is all for naught if the motor and the platter fail to rotate at the correct speed. Distortions resulting from erroneous motor speed, which includes incorrect, and, in the worst case, continually varying pitch. This prevents the faithful delivery of the grooves with in the record. On some of the finest analog playback systems, sustained piano notes,and other string intruments tend to have less stable pitch than their digital and live music counterparts.

Inconsistent motor speed can result from several factors, but the most common is the input AC signal whose frequency varies, either permanently or periodically, from the desired 60Hz. Since a motor's speed is directly proportional to the frequency of its incoming AC signal, variations in said signal result in speed fluctuations, therefore, audible distortion in the frequency domain. Without some form of compensation, the performance of a turntable will suffer at the hands of an input AC signal which, in most homes, rarely complies with the 60Hz specification.

Although VPI has previously attempted,with much success to address this problem with their series of Power Line Conditioners, such as the PLC, their latest effort, the Synchronous Drive System (SDS), is an all-out attempt at delivering the purest form of AC to the company's Hurst-sourced motor drives.

The frequency of the signal available at the typical wall outlet cannot be relied upon for little more than its unreliability. The SDS utilizes a quartz crystal oscillator, whose initial frequency is adjusted to within 0.005% to synthesize a new waveform, with a precise frequency, suitable for driving the motors used in VPI's turntables. It is not sufficient, however, for a turntable motor speed controller to simply synthesize a 60Hz signal and assume that this will, by dumb luck or divine intervention, cause the coupled platter to rotate at exactly 33 1/3 RPM.

According to VPI's Harry Weisfeld, factors such as aging motor and platter bearings, which can cause an increase in drag on the turntable's belt, and changes in heat and humidity which affect the belt's performance can account for incorrect platter speed even in the presence of a pure 60Hz input signal. So rather than hard-wire the SDS for 60Hz operation, certainly compromising the performance of its turntables in the process. VPI has equipped the SDS with an output frequency control which allows for fine-grain frequency adjustments to the tune of 1/100 of a cycle, a similar, and less sophisticated, control is also available on VPI's PLC. Using this control, the output frequency of the SDS can be adjusted throughout the range 52-66Hz and 71-90Hz for 33 1/3 and 45 RPM operation. The SDS stores the selected output frequency in non-volatile memory so that the setting is retained when the unit is powered off.

Cosmetically the beveled front panel of the SDS hosts a rocker-style power switch, and three flush-mount push buttons: one to select platter speed, either 33 1/3 or 45 RPM, indicated by a small, green backlit display, and one each for increasing or decreasing the unit's output frequency. All push buttons are of the stainless-steel dome variety and, according to VPI, have a 1 million cycle life. To the left of the output frequency controls are two green-LED digital displays, which indicate respectively the frequency and voltage of the synthesized output waveform.

In order to overcome the platter's inertia upon startup, or when switching from 33 1/3 to 45 RPM operation, the SDS will step up its output voltage to allow the motor to consume more power. Once the platter is up to speed, the voltage is automatically stepped down to minimize both motor vibration and the generation of RFI. The digital output voltage display provides visual confirmation that the SDS is, in fact, adapting its output voltage as specified.

As well one can source the calibration mode in the SDS to manually adjust several parameters for additional control. By removing the turntable plug in on back of the SDS, this feature is accessed by pressing both up and down arrows, while powering on the SDS. This will take you to the calibration side of the SDS. Some of these features should not be adjusted such as C-1,C-2 and C-3. However C-4 does allow for the change of voltage from the steady start position of 115 Volts. One can set 115,108,102,96,90,84,72
Based upon my VPI table I have chosen 72 Volts as my preferred setting after the initial ramp to 115 Volts.

C-5 is the procedure as above for 45 RPM speed. A very nice added touch for those of you that use 45 speed records.

My opinion is very positive on the SDS. If one is really into jazz trio and jazz quartet genre of music, the SDS will let you hear music that you have never heard from those grooves before. For the classical music maven, the WOW factor is spectacular. All this being a given that your record collection is in good playable condition. For the contemporary rock n roll fan, to my hears did not make much of a difference, although that form of music did benefit from the SDS.

After some 50 years in this hobby I generally view items such as this and tweaks and accessories as little more than snake oil. The audio landscape it literally littered with gizmos that claim one improvement after another. Most are failures generated as cash cows for the so called inventor.

After having this for awhile now, the SDS is not snake oil by any stretch of the imagination. The claims made to the SDS are valid and its use in an analog system makes a decided improvement in what you hear from your record collection. I am impressed beyond my wildest expectations.

Final conclusion is, if you have a turntable with an AC
Synchronous motor,the SDS will take it to a level you did not think possible. Works with all VPI tables and other brands with an AC Synchronous motor.

I have removed the SDS from my system to evaluate without it. After about 10 minutes out of the system, the SDS was back in and will remain in use. The SDS is not a lateral move but a quantum one that will put that big silly grin on your face. Although a bit pricey, nonetheless delivers the promise and thats what in the final analysis we as audiophiles look for - THE PROMISE.

Like I said earlier in this review, if vinyl playback remains an important part of your audio system, then the SDS is an absolute, hands down must have.

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Good review. I will be getting one eventually as I have become a VPI dealer again after a lapse of 14 years. I am using on of the [second generation?] PLCs, the one with two knobs. I used and sold the first two or three generations of the 19 and had a TNT 1 with a few upgrades in my own system. I thought I knew the VPI sound, I have just set up my first new table, a Scoutmaster with the standard arm. I even took out an original AT OC9 that I had used in my TNT. It sure doesn't sound like I remember VPI sounding; or like my Basis Ovation with SME arm. What are other members reaction to the new solid plinth VPIs VS the suspended tables?