But is the AC line dector intended to be used for this? I have to wonder if the problem has been identified using the right tool for the job or not. I’d be more inclined to get the oscilloscope out and measure signal to grounds.
I’m not saying the OP is wrong. Just applying healthy questioning as to whether factors involved could lead to a false positive.
Fair point. The device i have is a PeakTech 1030. They also make professional oscilloscopes, so i assume this is a decent quality device. I am not inclined to spend a few hundred Euros to get an oscilloscope although my curiosity is nagging. Is there any other way you can think of, to check for a false positive reading?
My pondering was less about the quality of the device and more about the intended usage. And maybe it’s not a false positive.
But I can’t think of anything other than an oscilloscope that I would trust for this task. Maybe a friend has one? Just be careful. It’s easy to short probes against tiny rails and damage what you’re probing.
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I haven’t read all the replies since as usual they veer of course. I’d suggest getting or trying a good power line conditioner. The new-ish AudioQuest PowerQuest 707 is a very well made and comprehensive unit.
Would be interesting to try. I use an Audioquest 3000 with my music system, but there is no power conditioner where the router is (20 m away from the music system, though the router is on a linear power supply, SBooster), let alone where the repeater is (different room).
I think the problem can be solved without a dedicated power conditioner for the router/repeater, simply by modiying their cheap power supply.
I thought that by using a linear power supply with the router, i would be safe. I would not have thought that AC noise (or common mode noise) would travel all the way from repeater to router to music system through the ethernet connections. I would have also thought that devices such a Ifi Lan silences or the EE1 would block such noise, but they did not.
I recently saw that @Simon-in-Suffolk wrote extensively about this common mode noise problem.
Your router is 60ft / 20 meters away? Are you using 20 meters of Ethernet cable?
My advice such that it is is to use commercial grade switches that have inbuilt earthed power-supplies, and have your Ethernet cables connect to these switches. If there are excessive common mode currents, they are going to flow to earth. It might not remove the issue entirely, but should significantly help.
Having all your network devices powered by separate DC powersupplies, where the devices are not earthed is not sensible and will allow common mode currents to build and likely earth through your Naim streamer which is earthed!
Of course you could try and replace the main culprit.
One other option to help reduce the propensity of electrical noise in your network, is to consider Power over Ethernet enabled WiFi access points, and have them powered by your mains earthed PoE switch.
Very interesting suggestions. Thank you! Luckily both of my switches have their grounded inbuilt powersupplies ( a gustard n18 and a lhy sw6), so hopefully i have no common mode issues left.
It used to be a 20m ethernet cable. Now i have a 20m fibre optic connection from a gustard n18 (right next to router) to a second switch at the music system (lhy sw6). Very happy with it.
@Emrah - thanks for sharing your story, very interesting. I took my AC detector pen and first thing I did is check the USB-C cable coming from a power strip to my mouse. Am I crazy or there shouldn’t be any AC there? 
The hunt begins!
Bear in min the following:
This is a USB-C to USB-C with an Apple 20W brick plugged into my UPS power strip. Didn’t know there’s AC in USB-C power delivery.
Anyway, a surprise to me 
I hope we are not chasing windmills here. But the responsiveness of this simple detector to improved power supply is intruiging.
I think i am probably pushing this too far, but could not resist the temptation to share this:
Powercord comparison from left to right: regular powercord, Nordost Red Dawn, Transparent HighPerformance PowerCord, Audioquest Monsoon. Both regular powercord and Nordost have AC signal when you touch them or get near to them. Transparent and Audioquest have zero signal with the AC detector, no matter where you touch them (except at the plug, on the pos. mains side). I would say that either Nordost Red Dawn is not as well isolated as Transparent and Audioquest or, the latter two do not transmit any current
What is your pen measuring. Is it simply alternating field strength? If so just be mindful what it is showing you. But on a DC lead or a shielded lead it could show common mode AC currents if sensitive enough passing along thecshield. I suspect with double insulated products it shows leakage common mode currents on most connected wires?
Looking at some of the blown up images, it seems specifically for detecting 50~60Hz in the 200~300v range.
Hence, I haven’t disregarded the findings posted at all but cautioned several times against the possibiity of a false positive by virtue of using this device for something it was never intended for.
But it looks like the dog has it’s proverbial bone.
Thanks, it could likely detect leakage current (common mode noise) from double insulated devices then (ie many of those mains devices that don’t use a mains earth… like in many power supplies)
Great comments!. I am happy to sacrifice the last bit of respect that my family has towards my audiophile escapades and run around in the house with an oscilloscope to figure out what this thing is picking up. Is it possible to measure common mode noise with an oscilloscope?
With four probes, yes. Because to know if it is common, you would need to sample both poles to a separate ground reference and see which noise spikes are, well… “common”.
It’s non trivial. Common mode in the RF band will require a significantly more expensive device to measure and the knowledge to interpret the results and program the filters.
If common mode noise worries you, use ferrite chokes.
