JVC HA-S680 Over Ear Headphones - Reviews
Pros: Soundstage, Comfort, Moddable
Cons: Read Review
This isn't a detailed review.
If you are still an S500 user and prefer it's sound, get the S600, to see why, read below.
I'm still kinda shocked nobody has voided people from these.
Burn In Times & Changes
If you don't believe in Burn In, ignore this. But be aware you're missing out.
These cans can't be burned in by just listening sessions, Constant Burn In required.
10h Mark:
Bass will loosen a bit, headphone sounds more spacey.
12h Mark:
A little change, Mids were getting lost in the Lows, but the famous S500 Shiny Highs start to show their faces.
20h Mark:
Bass begins to hit a bit harder, and if you use low bit rate files, bass comes off muddy.
30h Mark:
Same differences, no real change.
50h Mark(Final Mark! These only need at least 50h)
-Highs became even more prominent, yo basically begin to get S500 style Highs that the S500 would get after Burn In times.
-Bass Response Tightens.
-Bass loses a bit of flooding Mids issue.
-Soundstage increases, Bass detail is more prominent.
So all that being said, there isn't a huge Burn In time, the headphone has more Soundstage and icreases rapid response and Bass Detail.
Bass isn't as mushy as S500, it's more tight. 
Cotton Mod - Apply bits of cotton inside inner shell to reduce echoing in Bass punches.
EDT250 Pads - Bass loses rapid response, but increased comfort.
I thought they were pretty good as well, until I got the Creative Aurvana Live. The CALs sound MUCH better than the HA-S680
JVC or Meizu HD50?
Pros: great value for your money, great sound and good comfort.
Cons: long burn in, at least 50 hours in my experience.
Before I had the 680, I used my s500, which I realy liked and considerd them great value for 50$.
But now, the 680 have ruined the s500 for me. They sound way more alive, and much more real than my s500, and comfort is way better.
At 70$, I consider them a better buy then my s500.
Out of the box they sounded very disappointing so I let them burn... after a little over than 50 hours I can only say wow!!!
The diffrance was huge, Suddenly I had a realy nice pair of headphones in my hand.
My first impression about the build of this phones was that it feels a little flimsy, they are just so light... but I think that
won't be a problem after I handled them for a while, and they simply feels great on my head.
The cable is the exact same cable as on my s500, which is a great cable.
In conclusion I must say that this headphones, for me are very good value for my money, i'm not claiming that they can
compete with 150-200 dollars headphones, because I never listened to any.
But I can say for sure that in it's price range and perhaps a little higher, those are one of best headphones that you can buy.
I also have noontec zoro which are considerd very good headphone's for the price, but they sit on my table unused,
by me and also my brother which now use the s500 over the zoro's. i also happend to listen to sony mdr v55, and think the 680 is way better.
I can definetly say that I highly recommand this headphons for any one who's looking for a headphone a little over 50$, you won't be disappointed!
Pros: Monster soundstage; good lows (though, when un-EQd, can be overwhelming); good highs; good build-quality; thick, high-quality cable; angled plug
Cons: Recessed mids; quite closed-sounding; bass will be overwhelming for many non-bassheads; quite veiled-sounding when un-EQd
Initially I was completely turned off by the sound signature of this 'phone. The warm, bassy signature bothered me. I did expect them to be colored, but not to this extent. However, eventually, with a bit of listening, I became accustomed to the sound signature—to an extent. After a while I just knew I'd have to EQ them in order to get fully lost in music played through these. I personally tend to stay clear of very colored headphones and speakers since a far from neutral sound signature can remind me too much that I'm listening to 'phones / speakers which can make it very hard for me to get lost in the music. But, thanks to EQ, all is now well and my brain is no longer reminding me that I'm wearing 'phones when listening to music through these. There are, however, times when the odd song, usually of the rock genre, will sound like utter crap through these and I'm reminded that I'm listening through 'phones. But, fortunately, nine out of ten songs I play through these sound great so it's not a huge problem. I've realized for a while now why some songs sound like crap through them: it's due to, I think primarily, recessed mids. Due to recessed mids, some music (mostly rock and metal, though definitely not all rock and metal) sounds like crap through them. But when the right songs are played through them—including songs of the rock genre—they can sound jaw-droppingly amazing and make me think "Holy Hell—these cost just $70?!" For some reason most classic rock I've played through them (Led Zeppelin, The Doors, The Velvet Underground, The Beatles, etc.) sounded great, and even beyond great, through them. Yet the vast majority of modern rock I've played through them (The Church, Wilco, etc.) has sounded subpar and, at times, barely listenable through them.
Apart from the recessed mids, I find the bass quite excessive but that "problem" (it's a problem for me, but certainly won't be for many people) was easily fixed with EQ. These 'phones do sound a bit closed and claustrophobic (they are, after all, a closed 'phone), but I expected that and it doesn't bother me much. The recessed mids bother me far more than the somewhat closed, claustrophobic, sound of these. Initially I thought the highs were recessed, but after much listening I've found that to not be so. The highs are actually, for the most part, great—though a tad shrill at times. I think that when these were unEQd the powerful bass is what made it harder for me to properly judge the highs (or, perhaps, the highs were indeed recessed due to the cans not yet being burned in yet?).
Aesthetically, these 'phones look great. They're quite a bit smaller than they look in photos and the box they come in is so small that, upon receiving my parcel, I was convinced I was sent the wrong 'phones; I thought for sure they must have sent me the HA-S400 or HA-S500. Additionally, the build-quality of these 'phones is great. Yes—they're made of plastic (as you should expect them to be considering how cheap they are). But the plastic is thick and I'm sure could sustain quite a bit of abuse. The cable also is of high quality (finally: a portable 'phone with a cable built to last! The cable is thick enough to assure me that I don't have to perform any mods to it to prevent it from fraying, something I hate having to do) and has an angled plug. Comfort-wise . . . they're fine. They're apparently a huge step up in comfort from the 400 and 500—two 'phones I've never heard—but they're not the most comfortable 'phones I've worn. I find the clamping force a bit too strong, but I was able to make it ever-so-slightly less strong by placing a few books between the pads and leaving them like that for a while.
Overall, these are a good bang-for-your buck, well-built 'phone that are now my go-to portable can. My go-to closed 'phone for general use is currently the CAL! (but may soon be the NAD HP50) since it's highly consistent and handles all genres nicely; in fact, I've yet to hear anything sound bad through it. But if the 680's mids weren't recessed they'd likely get more listening time from me than the CAL! I absolutely love the monster soundstage, smooth sound and almost everything else about the 680. But those mids . . . where are they hidin' at?!
If you're a basshead and listen primarily to rap or electronic you'll love these. But if you, like myself, have a more eclectic taste in music and aren't that much of a basshead, you'll probably from time to time be disappointed with the way they render your favorite songs. Unfortunately, some of my very favorite bands sound like crap through these, so if these were my only 'phone I wouldn't be too happy. But they compliment the CAL! well and when the right songs are played through them they sure shine!
I give these four out of five stars. I docked one star for their recessed mids (which makes them inconsistent and prevents them from being an all-rounder), their somewhat closed sound (I realize that they're closed but there are closed 'phones out there that don't sound closed; the CAL! is a good example of a closed 'phone that doesn't sound closed), their (rarely) shrill treble and their at times overwhelming bass (which, fortunately, is easy to tame with EQ).
I hope JVC will eventually release a portable carbon nanotube 'phone with less prominent bass and more pronounced mids.
Pros: Fantastic comfort, great sound, incredibly easy to drive, very very light.
Cons: Not the strongest feeling headphones (super light), Sound terrible out of the box, Very long burn in period (36+ hours).
The S400 and S500 are incredible quality bargain headphones, but these even at several times the cost are more refined and more worthy in every way. If these cost $120 i would still recommend them, they have made that much of a impact.
Out of the box they sound pretty bloody bad, everything was muffled and the bass sounded like it was coming through a wall. That's just the way these JVC's seem to ship, after 48 hours though these are a whole other beast, one worthy of your time and money, at least as a travel pair.
Pros: Very clean and balanced sound, tight bass, non-sibilant yet present highs, vocals are engaging, airy yet intimate soundstage, resolving, comfortable
Cons: Limited availability, intended for Japanese market.
The review thread is here: http://www.head-fi.org/t/690493/the-jvc-ha-s680-s400s-and-s500s-big-brother-is-here
JVC HA-S680 is the next generation of HA-S400 and HA-S500, with the carbon nanotube technology.
Just like them, it's not meant to be sold outside of Japan

Nevertheless, here we are!

They utilize a 40mm driver, but it's not the same driver as in S500 - it is the next generation!
Output sound pressure level: 102dB/1mW
Playback frequency: 8Hz ~ 26.000Hz
Impedance: 32Ω

S500 is louder (106dB/1mW) and has 1 Khz less extension at the top.
I own S400, so I will be using it for comparison.

Sound Quality - upon receiving them, I gave them a short audition. They sounded nothing special, but I had good reasons to believe they would improve:
1) It took me over 200 hours to fully burn-in my S400s, and they didn't sound great until the process was finished.
2) These are Japan-only headphones, and Japanese usually keep the best stuff to themselves
3) SQ was scaling up with better sources - always a good sign.
So I started burning them with this noise:
12 hours in - Small changes here and there
24 hours in - Oh my god, did they burn in already? All the frequencies sound so much better,
                      especially the bass. I compared them to S400, and it became clear that there
                      was still a long way to go - the bass wasn't as tight and vocals weren't as emotional.
48 hours in - Now this a clearly superior headphone to S400.
                      Sound is balanced, similar to S400's sound signature, but the bass hits harder
                      (although just as tight) and the larger pads helped improve soundstage and
                      imaging. Instrument separation is better too. The vocals are very engaging.
72 hours in - No audible differences.
This is where I believed that this is a new improved driver, and not just an old repackaged one.
The old driver took over 200 hours to burn in, but they perfected the formula and the new one is done in 48!
There are a few significant design changes in S680 - 1) Bass ports 2) Larger pads

The bass ports are necessary for the harder hitting bass, what surprises me is that the bass is still just as tight as before, despite increase in volume. There is no leakage into the mids either.

Comfort - the larger pads increase both soundstage and comfort. For some people, especially women, these may be around-the-ear,
for me they are still on-the-ear. However, they are much more comfortable then S400, because they press on the more remote parts of the ear.
I've tried the Shure HPAEC840 pads - they are too big, may need to be modified to fit properly.
BrainWavz HM5 pads are a perfect fit, but have the same effect as on S400 - soundstage improves, but the bass becomes a little boomy. The HM5 look like they were made for S680, on S400 they looked monstrous.

Isolation - the larger pads make it better, but the bass ports make it worse. They are OK to use in an office, but not on a mass transport. Sound leakage is minimal, can be used in a library.
Overall, this is a fantastic portable closed phone, my new #1, ahead of HA-S400 and ATH-ES700.
They scale well with better equipment, but aren't hard to drive.
They also make a decent desktop speaker - I can put my NFB-11.32 on high gain and volume at 1-2PM - the sound fills the room

Price - I have bought it from White Rabbit Express for 96$ including shipping.
I've asked one of my Japanese eBay sellers to list it, and he listed all 3 models for 80$ including shipping!!!
I guess the pioneers always pay a price...
The black one is here:
The red one is here:
The white one is here:
I've bought some audiophile items from him before, he's really good.
Also, you can buy them directly from Kakaku for 65$-75$ depending on color and your location:
Other users' impressions:
Painful Chafe:
The burn-in procedure:
1) Use https://www.dropbox.com/sh/rnrj5g0mmbldj58/ZhYIByMYOE/White-Pink-Brown%20Noise%20%28For%20burn%20in%29.wav
2) Adjust the volume so that the middle noise is too loud for comfort
3) Take the headphones off, and add another 20-30% volume
4) Keep burning 24/7
5) Give it at least 48 hours
6) Once burn-in of the driver is done, please let your brain burn-in as well - it will take a few days for the brain to adjust to
    the sound. At first, the brain will refuse to process the soundstage and clarity that HA-S680 can produce, but it will give in
Oh, I see. So that's why Amazon kept marking only the red ones "Japanese import".
I wonder if the same distinction exists in s680.
If you like S400, you are pretty much guaranteed to like S680.
The problem with SZ2000 is that it is a 350$ headphone, and in best case scenario it will sound like one. With S680 at 81$, you have an unlimited upside and you can spend the rest on a DAC/Amp or your girlfriend.
JVC or Meizu HD50?