Just tried these on my DT770pro/80 for a couple of days. It sounds pretty good, the stock DT770pro's are known for their extreme amount of bass that a lot of people can not handle and to them I have good news: I'd say these J$v2's clean up the lower end quite well. The deep sub-bass is still there, but way better controlled. Mid- and upper-bass have less impact and are better defined so I guess now it isn't as muddy anymore, like some people have referred its sound signature to (not me!).
It also positively affects the sound stage. This was the first thing that immediately caught my attention when I swapped the pads. It's so much wider now and very impressive for this closed headphone, when compared to the stock pads.
Overall I'd think these pads don't affect the DT770pro as much as they do the DT990/600. My DT770pro now sounds even better with metal, and as much as I had grown out of that genre, recently I've rediscovered my love for several classic albums, right now for example I'm listening to Fear Factory's "Demanufacture" album from 1995, and it sounds more brutal than I remember it was, during my high school years.
And finally, it also isolates better and leaks less (although the stock velour pads also did a pretty good job at this), which is good for when using these in an office environment or something.
Jeremy makes an amazing product and despite how much I love these pads I understand the negative comments towards him earlier in this thread and really hope he will make some changes in his (lack of) business attitude, so more beyer fans can hear what I'm hearing right now, which is an easy-to-install improvement well worth its money.
Tempted to buy another pair, because these will be going back to my DT990/600 soon, which like I said, benefit even a lot more!