To reduce or even eliminate cogging, try using a variostat between the wall outlet and the turntable. For turn-on, use full 120v (or your local wall current). Once the platter reaches speed, reduce the voltage to just above the minimum required to keep the motor spinning the platter. I don't know how effective this will be with a quartz-controlled dd table, but for AC synchronous motors, particularly VPI motors. It's a LOT cheaper than a VPI SDS or other motor controller and just as effective.
