Ground source hum

Are both amp and preamp on the same circuit? If not, put them on the same circuit. Have you tried changing the preamp>amp interconnect? If not, try this. Are you sure it's not cable? Have you disconnected your main incoming cable line?

BTW, I think if I had to float a ground it would be on the amp, not the preamp.

Good luck,
John

I assume this is too your Orions. I had a problem with hum also. You may have already done this, but since you've ruled out the cable, check your outlets for proper grounding. It's not uncommon, even in newer homes, for the wiring to be incorrect. Also, how far away is the ASP from the amp or other electronics? It is sensitive to EMI, you may need to keep it several feet away. I had both of these problems in my old home. After I moved the problem was the cable and the only fix was an isolation transformer on the cable.

BTW, love your version of the Orion—stunning!

Turns out the fix was a little more straight forward. I use a Power Wedge 116 for power distribution. I had the Pre and Amp connected to the same outlet section. Switching the pre to a different outlet dropped the hum by at least 75% (only noticeable at less than 12" from driver). I suspect the remaining hum is as Ojgalli suggested, EMI between the Amp and crossover. I will try to move those further apart and see what happens but even as is, the hum is fine.
Thanks for the compliments Ojgalli