Digital gear (CDP) can put a lot of digital noise into the AC which then can enter your other gear. When you had it pluged into the wall the gear downstream was really affected by the Digital noise. You have to look at at digital power cord as a two way street, one way the power is coming in but in the other lane you have a lot of garbage (digital noise) coming out back down the cord to the wall infecting the AC. So moving your plug to the other side, last in line helps. An Isolation Transformer will clean the power going in and stop the digital noise dead from going back to the AC line, it keeps your Digital gear totaly isolated from the rest of the gear. I use a Topaz Isolation Transformer which is one of the better brands. Check the archives for Isolation Transformer. It is best to get one say 3-4 times bigger than you need for more headroom. Say you Digital gear is rated at 25-50 watts ac, somewhere around 200 watt Transformer would be great. They can be found on ebay at some good prices and some not I even got one at the sally Anne once. Depending on your budget another way to go if your into a little DIY and understand ele. if you can open up your power strip you can install some parallel filters on your duplex in the power strip. I have used these with great success. I seem to be having some Computer problems right now, I will post later a few links to some very good DIY parallel filters which can be very good for digital + analog.
