I borrowed these from a friend as a trial and I can see why he likes them, unfortunately I do not share the same appreciation. Original review updated an extra half a star added.
Let me elaborate on this as it's no justification at all to dismiss these earphones because I have a personal preference. So with over 100 hours of burn in and a pain staking few days getting used to them I feel I can now review and asses the fx750's with brutal honesty.
Well lets start off with some positives:
Spacious is a word that I find myself picking as I write this. It is so odd coming from my Dunu 2000's which I now consider my reference pair as they have no significant flaws throughout the sound spectrum. Well that being said the 750 are certainly wider, the sound stage is open, the vented design I assuming helps this but I find it can be quite unrealistic. I am a big fan of musicality so a slightly out of head feeling is something I consider a positive. Unfortunately after being spoiled by listening to accurate reproduction through other earphones it makes me question why instruments are coming at me at all angles with no serious positional ques.
There is actually a copious amount of detail but I often found these earphones quite picky of sources there is no chance of me getting through an entire minute of music on my old ipod classic 5.5 amp or no amp. However in the spirit of perseverance I tried several other source finally settling on my laptop surprisingly enough. The sources used to try the 750s are as follows: Meridian Explorer, iPhone 6, ipod classic 5.5 with and without Neco V4 and finally Asus K55V straight from the headphone socket.
With all sources there seemed to be a lack of detail a hazy sound is the best way to describe it. There was always something missing significantly enough to warrant me pulling them out of my ears within a few minutes.
Bass these would like to be all about that bass, sometimes there's no treble. No seriously kidding aside the bass on these earphones complex me a little, I love bass especially bass done right. These are cannons which I can imagine some people enjoying, tons of mid bass which leaves a chasm of depth and texture to be filled. Don't get me wrong I've heard worse but when listening to these earphones you soon come to understand there is such a thing as quality and ergo lack off. I can understand what JVC are trying to do unfortunately it hasn't worked particularly well, I can only assume this was an effort to add warmth and character such a shame it didn't quite work out that way. I am listening to these again as I write this final sentence and there is still an over generous amount of mid bass but this however does add character and warmth to the sound, I am certainly not retracting any thing from what I have previously said but It is certainly not as bad as I lead myself to believe.
Transparency does exist and my sincerest apologies if that sounds sarcastic. There is with the right source a clarity to the sound particularly violins shine and shimmer through with some pretty great timbre. I have reevaluated the earphones in an effort to make sure everything is done in fair justice.
Mids and treble.... Well it isn't bad there is actually a substantial amount of detail here especially hidden in the treble it's just a little more subdued than I've gotten used to.
I would say due to the slightly recessed mid range there seems to be a lack of detail, but when doing some critical listening it becomes a little more apparent its only an effect. On the contrary there is about as much detail as I've ever heard from any dynamic driver. The mids are a marshmallow with metallic sprinkles for treble. With the right source and song the treble is actually presented rather nicely there is a natural tone to stringed instruments which I have missed many times listening on inaccurate sources. The mids are presented but take a back seat to the music and that ghastly, messy mid bass covers them when the bass line pumps. There are some benefits to this as it does lead to a warm rich sound. All in all these are not the strongest earphones for vocals but they do there best to not mess anything up.
Fit well the long and short is these were not built for my ears. These earphones have been a pain to get to seated. I've tried various tips ranging from the spiral dots to comply and back. If you are seriously considering getting a pair please try get a demo if at all possible. I only say this as a pre-warning as I know the frustration of having a beautiful pair of earphones made unlistenable due to comfort and fit issues.
The overall signature is warm with generous detailing, great timber and good transparency . I would love to hear it's bigger brother in hope it may be a more refined version with greater transparency, more control and a more accurate presentation. In conclusion these are not bad earphones its only due to hearing rivals in a similarly price category I can't whole heartily recommend them.
Let me elaborate on this as it's no justification at all to dismiss these earphones because I have a personal preference. So with over 100 hours of burn in and a pain staking few days getting used to them I feel I can now review and asses the fx750's with brutal honesty.
Well lets start off with some positives:
Spacious is a word that I find myself picking as I write this. It is so odd coming from my Dunu 2000's which I now consider my reference pair as they have no significant flaws throughout the sound spectrum. Well that being said the 750 are certainly wider, the sound stage is open, the vented design I assuming helps this but I find it can be quite unrealistic. I am a big fan of musicality so a slightly out of head feeling is something I consider a positive. Unfortunately after being spoiled by listening to accurate reproduction through other earphones it makes me question why instruments are coming at me at all angles with no serious positional ques.
There is actually a copious amount of detail but I often found these earphones quite picky of sources there is no chance of me getting through an entire minute of music on my old ipod classic 5.5 amp or no amp. However in the spirit of perseverance I tried several other source finally settling on my laptop surprisingly enough. The sources used to try the 750s are as follows: Meridian Explorer, iPhone 6, ipod classic 5.5 with and without Neco V4 and finally Asus K55V straight from the headphone socket.
With all sources there seemed to be a lack of detail a hazy sound is the best way to describe it. There was always something missing significantly enough to warrant me pulling them out of my ears within a few minutes.
Bass these would like to be all about that bass, sometimes there's no treble. No seriously kidding aside the bass on these earphones complex me a little, I love bass especially bass done right. These are cannons which I can imagine some people enjoying, tons of mid bass which leaves a chasm of depth and texture to be filled. Don't get me wrong I've heard worse but when listening to these earphones you soon come to understand there is such a thing as quality and ergo lack off. I can understand what JVC are trying to do unfortunately it hasn't worked particularly well, I can only assume this was an effort to add warmth and character such a shame it didn't quite work out that way. I am listening to these again as I write this final sentence and there is still an over generous amount of mid bass but this however does add character and warmth to the sound, I am certainly not retracting any thing from what I have previously said but It is certainly not as bad as I lead myself to believe.
Transparency does exist and my sincerest apologies if that sounds sarcastic. There is with the right source a clarity to the sound particularly violins shine and shimmer through with some pretty great timbre. I have reevaluated the earphones in an effort to make sure everything is done in fair justice.
Mids and treble.... Well it isn't bad there is actually a substantial amount of detail here especially hidden in the treble it's just a little more subdued than I've gotten used to.
I would say due to the slightly recessed mid range there seems to be a lack of detail, but when doing some critical listening it becomes a little more apparent its only an effect. On the contrary there is about as much detail as I've ever heard from any dynamic driver. The mids are a marshmallow with metallic sprinkles for treble. With the right source and song the treble is actually presented rather nicely there is a natural tone to stringed instruments which I have missed many times listening on inaccurate sources. The mids are presented but take a back seat to the music and that ghastly, messy mid bass covers them when the bass line pumps. There are some benefits to this as it does lead to a warm rich sound. All in all these are not the strongest earphones for vocals but they do there best to not mess anything up.
Fit well the long and short is these were not built for my ears. These earphones have been a pain to get to seated. I've tried various tips ranging from the spiral dots to comply and back. If you are seriously considering getting a pair please try get a demo if at all possible. I only say this as a pre-warning as I know the frustration of having a beautiful pair of earphones made unlistenable due to comfort and fit issues.
The overall signature is warm with generous detailing, great timber and good transparency . I would love to hear it's bigger brother in hope it may be a more refined version with greater transparency, more control and a more accurate presentation. In conclusion these are not bad earphones its only due to hearing rivals in a similarly price category I can't whole heartily recommend them.
. Who knows I may even change the title, I suppose the reason I chose it was because I had such high expectations and felt a little let down after inital listening began. 
After reading all available info on FX850 I was very close to get them, but then I stumbled upon a review on German headphone site where Gunther (I think he's also member here, would be great if he could chime in to this discussion) had directly compared 750 and 850 in the new JVC FX lineup.
It was a long-ish review, but in essence, in his opinion 750 and 850 are very close in their sound signature. He reckoned that "kick" bass on 750 is more "precise" (Google translator terms) and 850 although going slightly deeper can get a little boomy. Also he stated that with 750 he could detect slight frequency spike in 8-10kHz region.
According to his post he ended up buying 850 being overall more "stable" and great for slower and classical music whereas fans listening to "modern music and rock" may like 750 sound more as a matter of personal taste.
Price not being concern, but size, weight and previous negative experience with replaceable cables swayed me into buying 750.
I think I can proclaim myself as a basshead, but the bass must have certain qualities for me. Boomy, moody, ghastly, bloated will not do. Deep, but controlled. To my ears, my pair of 750 does just that. They sound the best paired with DX90 and Vorzuge amp (very good review of the amp, thank you), but not bad out of Fiio X5 at all. Woo Audio tube amp brings the best out of them, but these were bought for portable use.
I don't know why, but these are the best headphones I had or have for drums heavy music. As a former amateur drummer, I enjoy them so much. In this area they sound just phenomenal for lack of better word. Listening to Terry Bozzio, Denis Chambers, Mike Portnoy to name just few, is pure bliss. Another example is Tool's Opiate EP. The way it was recorded and mastered and how these IEM's portray drums and bass line attack send shivers down my spine. I have Ultrasone Ed9 as my reference cans, but even those will not deliver such an effect for this type of music/recording.
I never wrote a review, too lazy, and therefore I appreciate you people taking time and putting effort for the benefit of our community here. When I think about my previous comment, I think your disappointment with them has nothing to do with the source, as in hardware. You probably just prefer different sound signature and looking for different quality in the headphones than I do. And this is fine with me, we are all different listeners.
My review of FX750 would have title Musical followed with preamble that these are bass heavy, warm, very detailed, big soundstage, magic timbre, but not suitable for analytical listening. And I'd give them 5 stars.
Cheers.