The SDS provides higher voltage on turn-on, then reduces the voltage to 72 volts. The turntable motor needs more power on start up, to accelerate from zero up to 33 rpm. After achieving 33 rpm, less power is needed to maintain speed (i.e., to overcome friction, etc.). The voltage is managed so as to meet these power requirements. VPI apparently believes there are benefits (either sonic or better motor longevity) to using lower voltage when possible.
