Readers,
I don't know if anyone is still checking this thread. Nonetheless, here is the result of my conversation with Sumiko.
According to Sumiko, to get rid of the hum on an EAD Powermaster 1000, connect the "black" lead to any inexpensive RCA connector, and then use available RCA connection on the preamp. Make sure you connect the "black" lead to the RCA connector's ground signal (outer portion). I haven't tried it yet. But the ultimate suggestion was to leave the amp on, which is better for the amp any way.
I hope this helps. If anyone tries this method, please share your experience with the group.
Ken