Obi110 and corded phone results in ground loop hum, how to get rid of it?
Lavarock7:
Years ago I would have just headed down to Radio Shack and bought a cheap isolation transformer (120 v to 120 v). They are not that plentiful or cheap anymore.
MurrayB:
I miss those days of trotting down to Radio Shack or another store or ordering from the Allied catalog. I saw this on E-bay:
http://www.ebay.com/itm/150W-120V-Isolation-Transformer-for-Vintage-Tube-Radio-Television-Amplifier-/321041150947?pt=Vintage_Electronics_R2&hash=item4abf8b33e3
sailing:
AceE3
I made an assumption that a Lynksys or medical grade power supply would work based on other posts and an assumption on my part.
I don't have a clear vision of what your setup is but if your setup, without the Obi, doesn't have hum and then with the Obi inserted in the setup, does have hum, it probably is the Obi.
Another check would be to have the Obi setup. Unplug all phones. Then plug one corded phone in that does not use a power adapter. If the hum is present, it probably is the Obi. If you plug a single line phone directly into the Obi, I doubt there will be any hum. Another indication it probably is the Obi.
An isolation transformer, as mentioned on the previous two posts, would probably reduce or eliminate the hum. Unfortunately they aren't easy to come by and they aren't cheap.
Lavarock7:
I searched yesterday before posting the isolation idea and saw that same ebay listing. It is a two wire (no grounding lug) and may work. The other idea I had was that in my case, I would investigate using two back to back transformers since the unit doesn't draw much current. Something like a step down and a step up transformer. It doubles the cost but still isolates the output. Regulation may not be great as the 120 fluctuates.
Here is a possibility: alliedelec.com model Triad Magnetics N-68X
http://www.alliedelec.com/search/productdetail.aspx?SKU=70218526#tab=specs
a single one at $11 and you use the 120 v taps on each end. Then again, you have to assemble and put in a case.
sailing:
Here are isolation transformers I would recommend, if you want to try this.
http://www.digikey.com/product-detail/en/171A/171AHM-ND/459365
Digikey part number is 171AHM-ND
The plug and outlet are already wired in.
http://www.alliedelec.com/search/productdetail.aspx?SKU=70218525
This isolation transformer requires wiring. It is a better choice then the other post recommends.
By the time you get done buying components to wire the one from Allied in a safe manner, the cost won't be that different. Considering the time and effort required to wire a transformer, I would go with the Digikey transformer.
Disclaimer: Although an isolation transformer should eliminate the hum problem, I have not tested it so I make no claims. I only post this to make it easy for someone to try this. If you do, please post your results.
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