I transitioned from electrostats to the Avantgarde Duos almost seven years
ago. Quieting the system was a major effort, but yielded enormous
rewards. I agree with the above remarks about trying to find the source of
the hum. At a certain point, mine was not pronounced, but I wanted the
system to be dead quiet and worked further on the following things, some
of which you have done:
1. dedicated AC and subpanel
2. running a noisy compressor for my tonearm into an isolation transformer
3. identifying noise inducing appliances that contribute to low level hum on
the system- even dedicated lines don't really 'isolate' the system power
from the rest of the household electrical system. For example, a hi-
intensity, low voltage spotlight over a kitchen sink 3 floors away will induce
hum. Solution- when I am listening, we don't turn on that light. Ditto on a
room humidifier in one of the bedrooms. Finding the source may thus not
even be 'in the system' in my experience.
4. Cable and equipment layout, as others have mentioned.
5. Playing with grounding solutions- for a while, I used that Granite Audio
Ground Zero- a sort of external star grounding system that allowed you to
change impedence on various grounds (these are not a substitute for the
ground to power receptacle but in addition to it). It worked for some system
set-ups, but I'm now at a point in my evolution where I don't need it.
6. Others with more technical experience can weigh in here, but as I
understand it, different components may have different internal grounding
set-ups. That may contribute to the problem.
7. Alot of this is simply time consuming and mind-numbing, frustrating
experimentation and fiddling.
8. Positive note: it can be done! My system is extremely quiet. And the
results are worth it, not just for avoidance of hum, but to yield more
information coming through the system.
9. Anecodotal observation: The Avantgarde Duo is tricky in the extreme to
really nail. A lot of folks critical of it have heard it set up badly. I'm not
suggesting that it is the 'best' or 'better than' anything, but I can get an
extraordinary amount of music out of my system.
