With HDVD800 as amplifier I bought HD650 (6 years ago), HD800 (4 years?) and HD820 (1 year?) (All HD8XXs use the official XLR Sennheiser -3) . Overall experience has shown that the HD800 performs better than the HD820. So my conclusion is that if you don't use a headset in a noisy environment, the HD800 is a better choice. Perhaps the HD820 is better suited to an office environment.
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