[v1rt]

   
I'm not a super expert on the past versions of the HE400i, but yes there is one general difference: past versions used to feature twist-to-lock F connectors in the detachable cables. Now the HE400i uses the more traditional (and more practical) 2.5 mm jacks.
I think there were also versions along the way with differences in the grill, though I can't begin to tell you how, when, and what differences it makes. I only have the new version with the 2.5 mm jacks, none of the other past iterations.
Hope I've helped!

 
Looks like the one I saw in Amazon is screw based? https://images-na.ssl-images-amazon.com/images/I/51aD4mpRrqL.jpg
Is that screw based? The pic is bit blurry so I can't tell if that is a new model. I took that pic from https://www.amazon.com/HIFIMAN-HE-400I-Full-size-Magnetic-Headphones/dp/B00MULH672/ref=cm_cd_al_qh_dp_t

 

[drwlf]

 

   
I'm not a super expert on the past versions of the HE400i, but yes there is one general difference: past versions used to feature twist-to-lock F connectors in the detachable cables. Now the HE400i uses the more traditional (and more practical) 2.5 mm jacks.
I think there were also versions along the way with differences in the grill, though I can't begin to tell you how, when, and what differences it makes. I only have the new version with the 2.5 mm jacks, none of the other past iterations.
Hope I've helped!

 
Looks like the one I saw in Amazon is screw based? https://images-na.ssl-images-amazon.com/images/I/51aD4mpRrqL.jpg
Is that screw based? The pic is bit blurry so I can't tell if that is a new model. I took that pic from https://www.amazon.com/HIFIMAN-HE-400I-Full-size-Magnetic-Headphones/dp/B00MULH672/ref=cm_cd_al_qh_dp_t

With 99.9% certainty a "real" vendor on Amazon is selling the 2.5mm newer version, and just using the older stock photos with the SMC connector.
I highly doubt any vendor receives a mysterious batch from pre-late-2015 production any longer to their stock/or has it in stock.
 
Related:
http://www.head-fi.org/t/791185/new-he400i-driver-housing-design-or-just-a-mixup-with-he400s-drivers
or search for "backplateless" from this thread, if you're actually interested.
 
As a new buyer, I wouldn't pay *any* attention whatsoever to the older SMC model, unless you're buying one used.

 

[Deoee]

It doesn't really matter except when you want to change the cable because 2.5 will be cheaper.
 
The screw ons are super easy to apply too, takes ~10 seconds for each side to make a solid connection.

 

[drwlf]

  I found this neat comparison:
 
http://imgur.com/a/Xjo22
 
Anyone has something to add to especially the HM5 ones used in the album?

Audeze ones are 120€ here which is way way too much

I actually mentioned that in Feb, but couldn't find the url.
http://www.head-fi.org/t/698974/hifiman-he-400i-impressions-and-discussion/11640#post_13268053
 
Otherwise, search is your friend:
http://www.head-fi.org/t/572327/mission-replace-the-hifiman-ear-pads-with-other-brand-ear-pads/540#post_12665489
http://www.head-fi.org/t/711824/hifiman-he-560-impressions-discussion-thread/17025#post_12886234

 

[drwlf]

 

  Been there, done that. Ditched focus pads.
Pleather pads is the answer.
 

​Tried the pleather pads again, it does bring the bass up a little but it also makes brings the mids too forward and the highs have a bit of harshness

 
Which ones you used? HFM official protein rounded leather ones?
I found the angled Brainwavz HM5 pleathers to increase the sub-bass a tad, tame some sizzling highs, move the soundstage a wee bit towards your head and having either an illusion of squishing/or actually squishing the soundstage a minor/negligible albeit a noticeable amount. Similar to @James Myers measurements here earlier.

 

[drwlf]

  The more I listen to these, I notice the bass less and less. Whats a good way to increase the quantity slightly?

So yeah, as you might've noticed, you've got some options.
Outright EQ, software-based being the cheapest and most hassle-free, or a hardware equalizer.
Or physically altering the headphone, via cheapest/most hassle-free pad-rolling, or mods in general to tweak the headphone.
There's a lot of differences with the pads, due to their shape, size, distance from the ear, ranging from cavity dimensions to reflecting materials, and even the materials inside the reflecting surface (read: material) of the pads. @zolkis' posts, measurements and dabbling with various Foster/Fostex variants' pads has been a joy to read for example.
And if you're actually interested in modding the headphone itself, reading HE-6 mods threads' (as it's the most extensively researched/modified from the HiFiMAN-line), followed by 560/500/400 threads', from various websites, if you're super into it.
 
Oh yeah, and sorry for the annoying followed posts, trying to head off for brunch. Typing replies and thinking between showers & getting ready. Annoying!

 

[drwlf]

And yeah, If there's any backplate versions with 2.5mm connectors, or SMCs without the backplate floating around, (haven't seen a single sighting of one, just some speculation about them), they must be some late 2015 production change refurbishings, but don't quote me on that.

 

[SoundTown]

   
Looks like the one I saw in Amazon is screw based? https://images-na.ssl-images-amazon.com/images/I/51aD4mpRrqL.jpg
Is that screw based? The pic is bit blurry so I can't tell if that is a new model. I took that pic from https://www.amazon.com/HIFIMAN-HE-400I-Full-size-Magnetic-Headphones/dp/B00MULH672/ref=cm_cd_al_qh_dp_t

 
I'm sorry, I'm vision impaired so I can't help you there. Screw-on should be the F connectors, but I reckon, like other users are saying, it is highly unlikely the stock Amazon / distributors are holding on to would be units using the old system. It's just more convenient to use the older photos. If you buy one brand new, it is almost certain it'll sport the 2.5 mm jacks.

 

[peter123]

Been listening to the new Kendrick Lamar album with the HE400i today (Burson V2+ > Project Ember II > HE400i) and the bass impact is excellent. Anone feeling that the HE400i lacks bass should try this album and if they're still feeling that there's not enough bass I'd suggest buying some other headphones

... or a more powerful amplifier.....

 

[DavidA]

   
Which ones you used? HFM official protein rounded leather ones?
I found the angled Brainwavz HM5 pleathers to increase the sub-bass a tad, tame some sizzling highs, move the soundstage a wee bit towards your head and having either an illusion of squishing/or actually squishing the soundstage a minor/negligible albeit a noticeable amount. Similar to @James Myers measurements here earlier.

​The official HFM, the one that came with my HE400.  The foam is also on the harder side so I think it causes the mids to become too forward and the highs to get harsh being reflected of the hard surface.

 

[v1rt]

  It doesn't really matter except when you want to change the cable because 2.5 will be cheaper.
 
The screw ons are super easy to apply too, takes ~10 seconds for each side to make a solid connection.

I wasn't really worried about the screw ons. I had a feeling that if the batch was the one with screw ons, this batch might not be up to par with the newer versions if HiFiMan made some changes on the internals. I noticed(on few articles/threads I've read) everytime a headphone company comes up with a new model, they usually tweak configurations. I just want to make sure I'll get the latest one when I buy. Looks like based from the earlier responses, I'll get the latest one. Thank you.

 

[DavidA]

  I wasn't really worried about the screw ons. I had a feeling that if the batch was the one with screw ons, this batch might not be up to par with the newer versions if HiFiMan made some changes on the internals. I noticed(on few articles/threads I've read) everytime a headphone company comes up with a new model, they usually tweak configurations. I just want to make sure I'll get the latest one when I buy. Looks like based from the earlier responses, I'll get the latest one. Thank you.

​I think there are more QC issues with the newer 2.5mm version and after hearing a few of the newer ones I like my older one with the back plate better, the bass goes a touch lower and its not quite as bright, but with all things YMMV

 

[v1rt]

 
​I think there are more QC issues with the newer 2.5mm version and after hearing a few of the newer ones I like my older one with the back plate better, the bass goes a touch lower and its not quite as bright, but with all things YMMV

Oh wow. Thanks for the heads-up!

 

[Kermeli]

Hello,
 
Im gonna buy little dot mk3 for my hifiman he400i's, iv never had a tube before. What dac would suit well? Im currently using O2 + ODAC combo, DAC-budget at 300€ ~ i think i saw dacmagicplus for little over 300€ used, would that be good buy?

 

[raband]

Not sure with that setup, but from what I've read the planars don't usually pair well with tube amps?