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Furman IT Ref 20i - Hums/Buzzes

Hello,
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.

Thanks
rxhurley
jea48
4,425 posts
 
rxhurley Said:
I have three Furman Power ’Conditioners’. Two IT Ref 20i’s and one 2400-IT
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.
First you can not check for DC on the AC mains with a regular multi meter. The meter needs to be connected to a low pass filter that is connected to the AC mains.

Imo the mechanical buzz you are hearing from only one of two of the IT Ref 20i units tells me the problem is not caused by the AC mains power of your home.

Because of the size (VA rating) of the toroidal isolation power transformer in the unit I would think the thing has a DC blocker installed ahead of the primary winding of the transformer.

Unplug the unit from the AC wall outlet. Let it set for about a half hour or so.

Pull the top cover off the unit and then plug the unit into the AC wall outlet. Turn on the unit. Try to isolated, listen, exactly where the buzzing sound is coming from. I would imagine it is coming from the toroidal power transformer.

Turn off the unit and unplug it from the wall outlet. **I don’t know it the unit has any capacitors for power factor correction but just to be on the safe side let it set for about a half hour or so before sticking your fingers inside......


Inspect the toroidal transformer and its support mounting.
Make sure the transformer is seated properly on the bottom side of the transformer. Make sure the supporting round top plate is seated properly on the top of the transformer. Make sure the bolt/nut is securely tightened. Do not over tighten.
(If the alignment looks off, out of wack, loosen the bolt/nut enough so you can realign, the transformer, transformer top plate, and bolt/nut support. Re-tighten nut to securely support the transformer.)


Photo of the transformer.
https://www.crutchfield.com/p_756ITREF20/Furman-IT-Reference-20i.html?awcp=1t1&awcr=105211333043...


Jim

.
erik_squires
16,056 posts
 
I'm sad to hear of a Furman doing this. Usually it IS DC on the line.

Take it to another home and see if the problem magically disappears. :)

Best,

E
rxhurley OP
6 posts
 
Thanks everyone, I will try out the suggestions and let everyone know.  I will also post to gearslutz about the new Furman/Nortek policy.  It is baffling.Rob
rxhurley OP
6 posts
 
Update - Furman/Nortek responded. They said 'some of these hum/buzz'. Clearly not an answer anyone would accept, when I pushed they said simply 'return it to a dealer' and sent the general Furman/Nortek website link.

They confirmed they do NOT repair or support their equipment post-sale. They only refer you to a dealer to see if they can help. Bizarre approach to the sale of equipment that costs >$4,000. They did offer a discount on a new Ref 20i, but it is tiny and I can't see why anyone would purchase another piece of equipment from them when they acknowledge they won't support or repair it after the warranty.

To many of the answers on this and other sites - yes, it could be DC on the line, still haven't been albeit determine; however the reality that I have two other Furman units (ref 20i and 2400-it) on the same power (also using dedicated circuits on the same 120 leg) which do NOT hum or buzz (the unit itself).  I am pretty much resigned that it is the Furman IT ref 20i itself that has failed or is faulty.
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