Furman IT Reference 20i - Buzz/Hum

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I have three Furman Power 'Conditioners'. Two IT Ref 20i's and one 2400-IT, all output balanced power. I installed these to lessen ground loop hum and protect my equipment.

I live in a house with several dedicated 20 amp lines and was built two years ago in a new community with apparently "clean" electrical supply.

One IT Ref 20i makes an audible hum from the unit itself heard easily in a room from 10-15 ft away. This occurs whether or not there is a load. I checked the DC offset from the wall with my multi-meter, it was extremely low. I then tried using the Emotiva CMX-2 before the Furman and this made no difference. I plugged it into a dedicated 20amp line feet from the circuit panel. It still hummed/buzzed. When I plugged in speakers, I did NOT hear any additional buzz/hum and I did NOT hear any buzz/hum through the speakers with my ear to the driver.

I decided to move the Furman Ref 20i from this location where it was not in a cabinet to one in which it was in a cabinet to decrease my ability to hear the hum/noise. The Furman continued to hum/buzz in the cabinet but could not be heard with the doors closed. So, I plugged in my preamp and amplifier and fired them up. Low and behold, I know had a buzz/hum from the speakers as well as the unit itself. I then unplugged the amplifier (Parasound halo 5 channel) and left the preamp (Marantz 7703), and plugged the amp directly into the wall (same circuit as the furman) and the hum stopped from the speakers.

Can anyone explain what is going on? I presume it is a problem with this unit (but have not substituted the other Furman's in to test this theory since each is mounted and 90lbs).

I have tried to contact Furman (Nortek) several times and they are non-responsive and recently included the sentence on their website that says (I am paraphrasing) 'we no longer accept/perform out of warranty repairs and recommend replacing non-functioning units). This policy seems ridiculous to not support your 3-4k equipment, but that is for another place to discuss.

I would appreciate any thoughts on what could be happening with the unit and how to fix it.

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