Since my two DD-12 Plus are working fine I haven't visited Velodyne Acoustics GmbH in a while.
Early on they had links to internationally located service providers who seemed to have changed over time. It appears they're now using the RMA form method to begin service concerns.
@rwwear You have to make sure the amp is for your model because they have to be programmed for different DD subs. The DD-15 and DD-18 use the same amp but different programming. And they all look alike.
The fellow who helped me during my visit to Morgan Hill mentioned something about different model programing within the same series.
To my knowledge DD Plus is the only processing were its Sweep Tones are played through both the main speakers and the sub/s as Auto EQ develops the subwoofers digital parameters to support the main speakers analog timbre and low frequency output all within the room. Afterwords the user can make further presets adjustments to taste.