Persistent hum on my connected phone
ProfTech:
As soon as I saw your post, it peaked my interest. I too saw this issue with a new Obi 200 recently. I had a 2 line phone with 1 line connected to the Obi and the second connected to POTS. If I had only POTS connected or only the Obi connected to the phone the hum was negligible. There have been lots of discussions about hum with the Obi 110 which has its own POTS connection so everything added up to the power supply that came with the Obi 200. Most cheap adapters that come with everything these days are of the "switching" type instead of being linear devices, meaning the switching adapters do not have a transformer. That is one of the things that make them cheaper. Long story short, I purchased a 12V Linear adapter from Jameco and the problem goes away. But they cost $15 and are heavy so shipping can be steep. Jameco part # 170245. YMMV
sailing:
Some background on "switching" power supplies. The isolated versions, such as the wall adapters, have a transformer. The incoming line ac voltage is rectified to dc then switched at a high frequency which is transferred through the transformer which is then converted back to dc. "Linear" power supplies transfer the ac through the transformer with a frequency of 50/60Hz (depending in US or Europe). The switching power supplies can switch at 100KHz and up. The higher the frequency, the smaller the transformer.
ProfTech:
That is good information and I stand corrected. I've heard rumors that some of the switching supplies could actually work but I'm not sure there is any way to know in advance which ones will work. It is true that the only linear supplies I've seen only work with 120v AC / 60hz due to the transformer.
*edited* I should have said the only ones I have seen with a transformer were strictly 120v / 60hz. I had no less than 3 of the "others" that I tried and none of them worked any better than the one that came with the Obi. Thanks
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