VPI Synchronous Drive System
No matter how adept a turntable is at isolating its associated arm/cartridge from both external vibrations and those generated from within the analogue playback system itself, it is all for naught if the motor (and hence the platter) fails to rotate at the correct speed. Distortions resulting from erroneous motor speed, including incorrect, and, in the worst case, continually varying, pitch, can prevent the faithful delivery of the groove-embedded analogue signal. While I’ve been loath to accept the compact disc as a truly high-end playback medium, its pitch stability has always struck me as superior to that of analogue media. Even on some of the finest analogue playback systems, sustained piano notes, in particular, tend to have less stable pitch than their digital and live music counterparts.
Incorrect or inconsistent motor speed can result from several factors, but the most common is an imprecise input AC signal whose frequency deviates, 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 and, 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 exactly with the 60Hz specification. Although VPI has previously attempted (with much success) to address this problem with their series of Power Line Conditioners (PLCs), 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.
Since the frequency of the signal available at the typical wall outlet can 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’s 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, almost 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, if 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 respectively. The SDS stores the selected output frequency in non-volatile memory so that the setting is retained when the unit is powered off.
I was fortunate enough to receive one of the first full-production samples of the SDS, sporting neither a serial number nor a user’s manual (VPI’s Sheila Weisfeld informs me that units after serial number 10 include complete user documentation). Measuring 19″ x 3½” x 8½” (WxHxD) and weighing approximately 12 lbs, the SDS is physically deserving of true component status – no mere accessory, this. Dressed in basic black, the unit’s chassis is fashioned from magnetic steel to prevent EMI originating within from interfering with nearby components. Power entering the SDS via its detachable IEC power cord is double filtered to prevent both line noise from infiltrating the unit and internally-generated noise from contaminating the power source of other system components. The SDS is, in effect, both a motor speed controller and a dedicated power line conditioner for VPI’s turntables. Price is US$1,000.
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 appropriately.
Clearly, someone at VPI has put him or herself in the customer’s shoes and anticipated their every need. When I purchased a JMW tonearm recently, I was pleasantly surprised to find that it was accompanied by a one-point cartridge alignment jig and a Shure stylus pressure gauge – virtually everything required to get the arm and associated cartridge mounted correctly. Such forethought and consideration, especially in the analogue world, is all-too-rare in my experience. In similar fashion, the SDS was accompanied by a VPI-branded stroboscopic disc, necessary for dialing-in platter speed via the output frequency controls.
Not surprisingly, the SDS’ default output frequency of 60Hz (selected upon initial power-up) caused the platter of the VPI Aries to rotate at the incorrect speed – ever-so-slightly fast, in fact. Reducing the output frequency to 59.78Hz locked the platter speed firmly at 33 1/3 RPM.
Having spent but a fortnight with the SDS, I’m prepared to share little more than first impressions, which, I will allow, are highly favorable. The Classic Records reissue of Sarah McLachlan’s The Freedom Sessions (perhaps, in MTV-speak, more aptly titled McLachlan Unplugged) has seen much platter time of late. The track entitled Hold On finds McLachlan in vocal recital with solo piano accompaniment, a simple soundscape in which even minor fluctuations in pitch are readily laid to bare. The SDS revealed what I thought to be vagaries of the recording (namely a tendency to two-dimensionality, and blurring of piano and vocal lines) to instead be artifacts of inconsistent platter speed. Along with the SDS came a considerably more dimensional and sharply defined presentation, McLachlan’s voice possessing a tangibility heretofore unheard, a piano with a newfound sense of tonal purity, and a black background of celestial proportions (bettering the already impressively low noise floor of the Aries alone).
I have long admired the abundant, yet underrated, talent of jazz pianist Michéle Petrucciani, his musical accomplishments all the more extraordinary in light of his physical handicap. Petrucciani has made some consummate recordings during his career, none of which, to my ears and sensibilities, outdo his effort on Power of Three (Blue Note BTC 85133) alongside jazz luminaries Wayne Shorter and Jim Hall. I have however, on occasion, been cognizant of what sounds like subtle shifts in the pitch of Petrucciani’s piano during sustained notes and chords throughout this disc. Determining that neither my tonearm nor cartridge were in any way geometrically challenged, I decided to lay the blame at the foot of the recording, pressing, or, perchance, the piano tuner. With the arrival of the SDS, it became abundantly clear that the blame, in fact, lay squarely at the foot of the turntable’s source of power. Not only was the pitch of Petrucciani’s piano remarkably more assured with the SDS in the playback chain, but the piano’s attack and decay too were rendered more faithfully and completely.
Although I hesitate to draw any conclusions after what has been little more than a preliminary audition, it would certainly appear that VPI’s Synchronous Drive System is yet another successful attempt by Harry Weisfeld to elevate his arguably world-class line of turntables to hitherto unrealized levels of performance.
Further information: VPI Industries
