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Well, my curiosity got the better of me so I opened the case. You wouldn’t believe it but when I got the case open I found that it was grounded! I also tested that all the inputs and outputs were isolated from the case correctly and got impedances of 100K – 1Mohm.
I disconnected the GND wire and the buzz disappeared – almost – completely.
I’ve put up a new video to show the effect. It was quite dramatic. There is still a slight hiss but it is inaudible from more than 30cm away from the speaker and could be caused by all the fluorescent lights in my workshop and a noisy mains power source.
I’m not sure if this indicates that the power points in my house aren’t grounded, or if there is another problem somewhere, but I am very happy with the board as it is.
I bought this as a cheap option, conveniently preassembled, to see if it would be worth buying more expensive original boards from a reliable supplier, and if the ‘real’ ICEpower boards are even better sounding than this clone then I am very keen to get my hands on some!
Thanks for your help with this! Much appreciated.
