Thursday, September 30, 2010
A Visit with the VPI SDS turntable motor controller
Accurate analog production with a turntable is a tricky business. There is the cartridge, which produces millivolts that have to be amplified up to line level. Then there is the arm, which requires rigidity, vibration dampening, the ability to ride warped and off-center records all while adding nothing to the sound. The turntable body itself is another source of vibration, especially if the AC motor is clamped to the plinth. On top of this, we have speed inaccuracies and vibrations from the motor which can be transmitted to the rest of the turntable system. It's amazing that records can sound as good as they do.
VPI created the Synchronous Drive System (SDS) in order to help correct turntable motor issues. It is essentially a turntable motor controller and line isolator through the use of amplifier with a semi-adjustable quart crystal sinewave generator. This allows the user to dial in the exact frequency for their AC turntable motor, resulting in a locked 33 1/3 rpm. It also has a current sensor to adjust the amount of voltage to the motor, allowing 115VAC as the platter spins up to speed and then it tails down 20-30Vs for normal operation. This has the effect of reducing motor vibration.
I bought mine used via Audiogon and through the use of the KAB Speedtrobe, adjusted the AC frequency down to 59.69Hz to achieve an almost perfect 33 1/3 rpm on my VPI HW19 Mark III turntable.
Sound differences are hardly earth shattering, but more of a baby step towards that impossible goal of achieving audio perfection. Music has more of a "locked in" feel as images are rock steady. Bass sounds slightly deeper as does the soundstage depth. Pitch control is excellent, reminding me of the solidity of the compact disc. I'm very happy with the changes and can't wait to purchase the VPI SAMA outboard motor and a new tonearm.
preamp: Threshold FET-10/HL
phono preamp: Audio Sector Phono Stage
amplifier: Threshold S/500
analog: VPI HW19 MkIII - Rega RB300 with Incognito wiring - Denon DL-103R
speakers: Magnepan 1.6/QR with Sound Anchor Stands
speaker cable: Kimber 4PR/8PR Bi-wire with banana jacks
Interconnects: Cardas Cross and Cardas Quadlink 5C