https://www.google.com/search?q=wurth+ferrite+150+khz+8mm+12.5mm
I have a lot of 8 mm and only one or two of 12.5 mm (two audio systems, two powerstrip).
What devices do you want them for? What problems have you detected?
I detect no problem in my power line or in my power cables, but I've changed cables and I've got better sound, so I thought may be I could try some Split Core Ferrite to see if they make a difference, as they are cheap.
I believe Nord amps, like almost any other class D amp, are very sensitive to AC power quality. I've installed a dedicated AC line and I've upgraded the power cord and both made a good improvement. So, maybe spending about $30 won't be much of a risk.
What do you think? would you recomend trying some Split Core Ferrites? What differences have they made on your system? where (in the cable) do you recomend to place them? on what cables (power, interconnects, etc)?