Had the chance to spend around 10 minutes with the HD660's on the Sennheiser Hdv820 using the balanced pentacon connection. Source was flac via USB from my Android. They put a stupid-smile on my face straight away - mainly because they do everything the HD650 does, and then some. They have DETAIL in the treble, punchy bass, and THAT mid-range we all know and love. Comfort-wise they're pretty much exactly the same, the pads maaaay have been a bit thicker? There was also an HD800s connected to the same amp via 4-pin XLR, meaning I could A/B test them directly. What amazed me was how well the 660s managed to keep up on terms of sparkle, whereas the 650 politely drops away at the top end. The soundstage was unsurprisingly less, but seemed on-par with the 650's.



These are going to be a bona fide smash hit, and I'll be getting a pair immediately. I didn't realise they were only 150ohm impedence until now though, so still think my 650s will be seeing plenty of use with my Crack and Speedball.