PS Audio Noise Harvester

I have a couple, tend to use them as a detector vs. eliminator.

Nothing that physically small can do any real filtering at the noise frequencies that concern us most.

What frequencies concern you most? I realize RLCs capable of handling 120 V+ rms and working into the audio range will be large, but I suppose they could be using some sort of active circuit. However, IME, the marketing copy is technically misleading at best. Passive filters reject noise, preventing it from reaching the component, or shunt across the line and again prevent it from reaching the component. Some types dissipate energy in the filter, some do not. Dissipating the energy in a LED or resistor does not matter to the component, nor does simply rejecting the incoming noise instead of dissipating it directly. "Returning the noise to the neutral" does not matter to the component if it does not see it, and since an LED works by current flow technically they are doing exactly the same thing, just frequency-shifted if they are filtering and using the resultant LF/DC current to power a LED. Current is a loop, it does not come from one side and magically dissappear; the LED is drawing its power from across the line.

Dave Collins was talking about this the other day and actually did some measurements...... no change!