Bests & Worsts Reviews from Amazon

The description on Amazon claims that this thing "Filters unwanted low voltage from ground line that cause ground Hum" without bothering to explain what that is. The description on the package actually mentions ground loops specifically. I thought that maybe it had chokes that might help with high-frequency interference from some devices. It did not make a difference in my case. As far as its ability to eliminate ground loops, I was very skeptical, since it does its magic "while maintaining ground connection" (which is a good thing). By the way, in my case an audio isolation transformer solved the problem, as I knew it would. I wanted to try something different and it didn't work. For consumer audio (250 mV line level) I would recommend JK Audio Pureformer, which costs just a few $$ more than this thing -- pretty inexpensive for a good audio transformer. I'm not affiliated with JK Audio. Before returning the "hum filter", I got curious and made some I-V measurements. Here's what I found (all measurements made between the respective terminals of the plug and the outlet of the mysterious device): hot-hot - 5 milliohms cold-cold - 2.5 milliohms (yes, I can do that) ground-ground - looks like silicon diodes in inverse-parallel, so at low voltage the resistance is relatively high, and at about 0.6 V they begin to conduct. Actually, at first I used an regular ohmmeter, and it looked like the ground had a high resistance, which would make it unsafe, so I used a sourcemeter and got the above (correct) results. This is not a filter at all, and it's ridiculously overpriced. The good thing is that the diodes can sink at least 3 amps, which is as high as my sourcemeter will go. That's not enough for a really good ground connection, but at least it's not obviously unsafe, and if they burn, they will probably just short out. The bad thing is that this won't always make a difference in terms of noise. What this device does is a sort of "safe ground lift". So if you have two devices that form a ground loop only though the ground pins of the power plugs, and you power one of them through this thing, then it will work. That won't always be the case, especially in a complicated setup with multiple signal lines. In some (although probably rare) cases, if there is a leak from the power line to the chassis, this device could make the noise a lot worse. And the possibility of leaks is of course why there is a need for grounding. They write on the package that the device should not be used on an ungrounded outlet, which is true, of course, because then it really won't do anything. This information is currently not on the product description page on Amazon. This would have lifted the mystery fog a little bit.