I have had very good luck with Topnisus clip on ferrites from Amazon you can order the diameter that fits your cable. They can be removed with your finger nail no key required and they are reasonably priced. Some argue that without published specifications beware Ferrites are cintered ferric oxide (rust) my guess is given a physical size and shape they filter about the same. I also recommend Clearer Audio digital cables their top of the line is the best I’ve heard
An update on my ferrite-fi journey:
A couple of weeks ago, I ordered 13 x 8mm ferrites to fit my USB cable from Amazon uk for under £7 including delivery (high end pricing gone mad!). But I hadn't anticipated that the delivery was to be via a slow boat from China,so whilst still waiting for that, I ordered various size Topnisus ferrites, which cost a a bit more, but were delivered from UK within 2 days. These to be added to my ethernet and power cables (no Topnisus sizes were ideal for my USB cable thickness). There seems to be all sorts of brand names for these cheaper ferrites - my guess is that they all come from much the same mass production lines in China.
So, to my existing setup of 8 Wurth ferrites on each of my USB and ethernet cables, I added a further 8 Topnisus ferrites on my ethernet cable (total now 16), plus 4 ferrites to DAVE's power cord (in addition to the 2 ferrites built-in to this Clearer Audio power cord). I wasn't sure if further ferrite improvements were possible after my last Wow moment, but I was pleasantly surprised to find that the improvements were immediately apparent: yet more focus and detail whilst at the same time more natural and effortless. Apart from the extra weight and clunkiness on my cables, there is no downside to this SQ improvement. I'm now a full ferrite convert and declare these little blighters to be the best VFM upgrades of all time. Ever. Previous title holders were audiphile fuses and later my Supra CAT 8. But pound for pound, the ferrites easily take over that title. Can't wait for the slow boat from China to arrive.
As my system has improved recently (including the ISORegen still in place and mR v1.4 clock upgrade), my reaction to some DAVE functions has shifted:
1. I'm a big fan of the cross-feed function, particularly for HEK V2's, my preferred setting being CF=2, and I never quite undesrtood why some eminent headfiers liked CF=3. Well now I prefer CF=3 as well, although any CF value is miles better than none at all for the HEK V2's
2. I've always fussed over the Phase switch. Now I don't worry about it so much. I can still tell which phase is which, but the wrong phase doesn't now bother me as much, because both ways sound better than they used to. BTW, my albums are now tagged at over 10:1 in favour of Positive phase.
3. I've always preferred HF Filter Off, and I still do, but now I'm less bothered by the slight dulling effect of Filter On, and might even prefer that on my brightest recordings.