Hi Paul
I just added a Clearaudio Ovation to my system this week and I to am having some feed back issues. Needless to say I am very disappointed, but it is what it is. Mine seems to be feeding back approximately at 30hz and 120hz at volumes ranging from 85 to 95 db.
Some of the contributing factors that I think are helping cause my issue is my listening room is very small at 14 x 10 x 9, located on the second floor of a 122 year old house and I have the turntable sitting on a very cheap fiberboard end table along an outside wall about 3' feet in front of my left sub.
I placed some anti vibration pads under the feet of the turntable (available from amazon for about $10 to $15 for a four pack) which helped reduce if not eliminate the feedback at 30hz and added a little more detail to the recording. I use an active crossover to integrate my subs that has a digital graphic eq built into the inputs that I used to reduce the 120hz output of my system thus eliminating the feedback.
My next move is to build a prototype table out of 2 x 4 pine so I can relocate the turntable so it is above and slightly to the rear and left of the sub. If this works I will then have Saluda River Audio Stands build me a permanent table out of maple and walnut.
Also when you said that all hell broke loose when you switched polarity on your sub I believe that was when your subs were actually in phase, at least with the turntable.
