Copper Sleeve over IEC

Ouch,
Sorry it did not work out for you. No, it's not you or your system. If you CAN hear differences by switching ICs or speaker cables then the problem is not you.
Are you kidding? I've not heard it in person but people think the pair of your Krell Revolution speaker is top notch details. Now, I'm rasing my eyebrown not understanding why it's not working out on your Rotel?

Well don't take it personally Nasaman! In actuality, I really did not give the copper coupler much of an evaluation. I simply slid it on and off during audio/video playback a few times and I really couldn't discern any differences. I'm going to leave it in place though. You know, I spent hours - days actually, tweaking my stand, and I employ a number of other tweaks (e.g.: weights/damping on the chassis of all the equipment, dedicated AC line/outlet, after market power cords, etc.), all of which I really can't discern much difference. I suppose it all adds up though (that's what I'm sticking with). As I mentioned above, I can actually hear a difference after I elevated my listening position by 1.5 inches; that, and I most certainly can hear a difference in late p.m. listening sessions compared to other times of peak power consumption. Those last two "tweaks" being free! Another freebie is speaker placement tweaking. For me, very slight changes in positioning have yielded big returns - in fact, I’m sure that I have not found the optimal position yet, but it’s a pain in the %@#!, so I keep putting it off

Here is my feedback FWIW:
I bought a few copper couplers - 1-1/4", 1-1/2" & 2". One side of my power cord is less fat than the other side hence I need a 1-1/4" on 1 side & a 2" on the other. I put copper couplers on the CDP power cord, power cord to the PS300 unit & on the RGPC 400 Mk1.
I've had just one reasonably long listening session & so far the conclusion is - no positive effect & also no sound degradation (whew!). In the back of my mind I really did not expect anything much to come out of this tweak as I live in a fairly RF clean environment + I believe that my CDP does not splatter much digital noise. Additionally, I have several other tweaks - dedicated lines, damped rack, damped chassis, elevated cables, Faraday shields over the magnets in my power cords, etc. All these items did make improvements & they've added up each time I tweaked.
All-the-same, I'm going to leave the copper couplers in place & listen more. In my system this seems to be a subtle tweak & subtle tweaks take time to settle in & time to discern.

Agree, let's keep the copper ON for few days of listening until you totally get use to the sound from your gear (WITHOUT modding or tweaking any thing), slide the copper away from the IEC plug, or yet, completely remove the copper from your system..... keep us posted.

I just said it because I could not think of any other posibility. The copper tweak works out for me, instantly.

Did anyone try the double copper shielding like I have? Please report your findings. Very curious what you are hearing compared to a single coupler.

Thanks