Why does the VPI motor thump

The only time I ever had a thump is when the motor cap went bad. I don't have the problem with a variac because there is no turn on / off of the motor, just the switch on the variac. I keep the variac set to 0volts for turn on / off.

You don't have any thump because you're using SDS.

If a variac or SDS is used to manage the motor, there is no start up thump or pop.

I had the pop with both a TNT and an Aries motor. Currently using a variac on the Aries. Totally quiet start up and shut down. I turn on the variac when I turn on the preamp with the voltage set to 0v. I increase to 110 for start-up and and record brushing, then dial back to 60v for playback. When finished with a side, the voltage is doaled down to zero.

I like the very quiet background it provides compared to plugging the motor directly into the wall. Not sure I actually need something like a SDS because the speed seems OK.

String, you're using a SDS. That isolates the motor. No thump. So does a variac and performs the most important functions of a SDS (isolation and voltage reduction) though manually.

I don't necessarily think the tables are a bad design because they have a turn on / off thump. I usually judge a component by how it sounds when it's used as intended.

The thump is related to a capacitor required in the circuit. When used with a variac, SDS or other front end component to manage the voltage during start-up and playback, there isn't any problem.

But the design could be improved when not using some kind of voltage management device.

Have you discussed this with Harry?