The v5i was provided by Burson for an honest review.

I have rolled some opamps before in various amplifiers. Although i think i hear a slight difference between each of them, its really hard to tell exactly what is improved or what got worse.

My thoughs on rolling opamps is that you cant properly A/B them for a straight forward comparison. Swapping opamps takes quite the time and your hearing memory is short. That said, i want to think that it makes a difference going from a really cheap chip to a rather good one..But the step above " a good one" is a lot harder.

I guess this goes with my overall thoughts on diminishing returns. The last steps to "perfect" is very expensive and most of the times not really worth it in the end anyways.

I don't claim to have perfect hearing, and i don't have perfect gear either. My gear is compiled of products i find interesting and are somewhat affordable. My gear is not compiled for the purpose of perfect sound. The purpose of my gear is to give me a variety of signatures and most importantly, to give me listening pleasure when i'm enjoying music, gaming and various tasks on my computer.

Gear used for this review:
Amp - Little dot 1+ with a matched pair of Mullard EF91 tubes
DAC - Korg DS-dac 100m
Headphones- AKG k240M, AKG K260 ( i'm in the middle of moving so majority of cans are in boxes at this time )

My little dot have seen different stages of "upgrades" during my time with it. First of all i have rolled some tubes. Mullard 8081, and Voshkod 6ZH1P-EV and finally the EF91.

The previous opamp was a OPA2107 from BB/TI and it was quite the upgrade to the stock "crap"

The V5i takes the overall sound quality to another level, or at least i want to believe it does. As i said earlier its hard to tell since the swap is complicated.

I really think the v5i is superior however.

The soundstage is the first thing that came to mind. It just sound much more spacious and open compared to the 2107.

The treble is also better extended and a bit more refined. The k240M is not a very bright headphone to begin with. It can sometimes sound a bit dark but at the same time i really love how mellow and organic they sound. The v5i ads a little sparkle to this setup.

The K260 is a quite rare headphone but it's newer than the K240 and does absolutely not sound anything close to the 240. Plugging these into the 1+ really brings out the details in the music. However compared to the more modern headphones these days they can be a little to unrefined in the treble and is not quite the match with the V5s extended detail.

The bass is tighter, or maybe its not as much as with the 2107..its really hard to determine this aspect of the opamps since i would need a proper A/B switch to get this settled. It's not worse its just a bit different and i would say that its tighter and faster with the V5i, but its

Overall the V5i is a good opamp..And for the price, it should be. If you replace a really cheap bad quality opamp with this, i think the results would be quite shocking. Burson did not put this together without doing the research, you just have to trust me on this one.

However if you are on a somewhat budget rig i would not spend the money on the v5i compared to let's say the 2107 in my case. But if you really want to ring the absolute best out of your amp, then why not? If you find the performance lacking at least you cant blame it on the opamp.

The v5i is a very simple install on the Little Dot.

The v5i to the left compared to a standard size chip to the right.
The first thing you need to do is to replace the awful super bright blue LED on the little dot amplifiers. I soldered an yellow/amper in place instead.

Let's start with the build since it is a hot topic on this headphone.
 
It´s not very confidence inspiring but it's chunky. Made out of mostly plastics and cast aluminum for the adjustment arms and probably aluminum or stainless for the hinges, this thing should be quite durable. However i don't see it lasting a lifetime. Since it's so heavy and the plastic seems to be of the hard kind that just cracks and shatter if dropped, i think that if this thing picks up speed during a drop, it's probably going to break. However, i don't usually drop my gear and i am a very careful person when it comes to my gadgets i personally don't see this as a problem, but it's worth knowing for some buyers.
Compare this to some much cheaper headphones from "headphone" companies like Beyerdynamic, AKG and some Sennheiser models or the undisputed heavyweight king of durability, the German Maestro 8.35-300 series headphones.The M4U is build "wrong" i would say.
 
Take note that this headphone isn´t new and it isn't (while sounding amazing) targeted at the pro-audio or headphone geek market. When the M4U2/1 saw the light there was an era of plastic fantastic cans with funky colors. If the M4U series was designed today, i bet it would look different.
The construction folds into a "portable" size. However when you unfold this thing of modern day "swag" the noise when the hinges goes into place, make you cringe. Not the kind of sound you want from a MSRP of 400 USD.
 
To summarize my rant here..It´s way to heavy for it´s own good. Instead of making out of durable plastics they added a lot of the shiny stuff to make it sturdier. I think it´s a shame.
 
Cable
 
It´s made out of a springy rubberish material. It´s not the worst but not the best. What is nice is that the plug is very small and sits flush with your device of choice. The microphone sounds rather good but it´s located to far down the cable. A mistake often seen on portable headphones. How hard can it be to make a proper cable? Either is it flat ( the worst thing ever! ) Or the microphone is way to low.
 
When the headphone is in active mode, you can press the little hump on the cable ( Where the microphone should be located btw ) This let´s the microphones for the noise canceling amplify outside sound to make it easier to hear without removing the headphones. Kinda of a nice feature.

 
Comfort? How does this massive contraption fit on your cranium? Well, surprisingly good.


 
It´s easy to find a good seal, the pads are of good quality and you get a replacement pair in the box, a nice touch! But nothing is perfect. Let me tell you what could be better.
 
The pads are to thin and to small. It's that simple. While the pads are soft and made of quality materials, when they get pressed around your ear they gets thin and your ear starts to touch the baffle. On my head ( and ears ) it's not really a big deal but i can absolutely see this an issue for people with larger ears or a larger head where the clamp get's the best out of these pads.
 
My favorite replacement earpads are the Brainwavz HM5. And they are too big, bummer! I have not found a replacement pad worth looking into since the main issue here is not quality, it´s depth.
 
Sound. Where it´s get interesting.
 
I did buy these cans without hearing them first, it's often how it goes down when i shop for cans. Part of that is the lack of demo units available around this part of the world ( Sweden ). Second, if there are cans available locally, the price is not nice! Heavy taxes etc yada yada makes this very expensive compared to the US for example.
 
Since i often buy cans like this, the first listen is something special. In this case i was pleased to say the least.
 
The sound out of this unimpressive thing made out of plastic is organic, vast and natural ( not neutral ) The headphone sounds damn good.
 
It´s a rather flat signature but with a warm tone that makes music and instruments sound pleasant and still with enough sparkle and detail to make it an interesting listen.
 
The bass is well weighted and goes deep enough but it can be a little honky and go up to the lower mid bass on some tracks. On the other hand this ads meat to guitar riffs and vocals. I would prefer more sub bass while still keeping the attack. Bass can be little lazy and honky but overall rather well tuned.
 
The treble is just enough. It´s organic and blends nicely in with the overall tone of the headphone. I would have enjoyed a better articulation in the treble though. A little bit more energy and crispness. However this is a dangerous area to enter when tuning a headphone. Specially something like this that has to be every headphone on planet earth at the same time. It´s enough treble, it sounds good. But it’s not magic.

 
Mid Range is well presented and not to forward. I think this is an important point to focus on. If mids are to forward people tend to not enjoy the overall signature ( speaking of the majority of the people here, not geeks like us ) Since the mid range blends a little bit with the bass it can sound a little hollow and honky. But hearing lyrics and detail from instruments like acoustic guitars are no problem here. It´s good and not tuned far back in the mix. It’s not magic, but absolutely good enough.
 
Soundstage is where it´s at with the M4U2. Really good surround feel and depth. Pinpointing instruments and details on a live jazz recording is a joy and really impressive for something “cool” looking like this. I’ve read that this headphone had good stage but i was not expecting it to be this good. Overall the presence blends together with the overall tuning and makes this a slightly warm and cosy experience. I think the soundstage is what makes this headphone stand out from the crowd.
 
Without soundstage and this organic flat-ish tuning the PSB M4U2 would be nothing. Nothing really stands out in the other areas of the sound signature. It´s the whole that is impressive. The bass is good enough, midrange and treble is also good enough, not fantastic. But when the “Room feel kicks in” you hear where it’s at.
 
Electronics..Yes! It´s powered by batteries and it’s why you should buy the M4U1 instead.
 
There is a built in amplifier which is great in theory but it’s to noisy. The headphone is easy to drive as is. It’s nice to have an easy to drive headphone that sounds this good.
 
There is also a active noise canceling funktion. This mode ads the noise of the amplifier plus the noise from the NC itself. However it does a rather good job with low frequency noise like engines, road noise etc. I can at least find a useful scenario to use this function compared to the amplifier. To bad you can't run the NC mode only without including that darn amplifier.
 
The active parts do NOT work on android phones..It makes me furious really. I know it’s apple only but it should not be. It’s a regular 4 pole plug on the cable, and the remote has one button only. Still when connected to any android unit ( nexus 6p, 5x etc ) all you get in active mode is static and ground issues. It´s all in the cable. A theory is that they somehow use the ground for the microphone on apple devices or the resistor or something like this to make it all work.
 
You can get it to work with a regular stereo source though. Xduoo X2, Sansa Clip for example.
 
To summarize this long review. The headphone sounds great but don’t pay for the active version, it´s not as good in drowning out noise as the Bose QC 25 and the amp is useless.
 
A great sounding headphone with a sound signature that appeals a lot of people. PSB tried to make this the only headphone you should buy, It got the “looks”, it “folds” it has “noise canceling” it even has a built in “amplifier”  and that's what's wrong.
 
Lucky you who can get your paws on the passive version of this called the PSB M4U1 it´s a much better overall experience since it’s a headphone, not a space craft.
 
I bought this pair used for about 120 USD, money well spent! However the best price for a new pair is 350 USD ( passive version not available here ) and for 350, i think you should look for alternatives.
 

To start this off, i did not pay for my pair of 315. If i had payed for them the disappointment would be vast. 
 
I have a pair of SE215 and while they are not my favourite iem, they have their place. Isolation is great, and the sound is warm and quite mid-forward and matches easy with many genres of music. 
 
The 315 is well, not as good. Simply put. 
 
I had high hopes on the 315, i really had. However upon first listen i though they sounded a bit strange. On some tracks like some 90s death/black metal or Bob Dylans earlier work they shine. Clear midrange and nice air and separation. Overall clarity and balance is a joy. 
 
But on some tracks there is a honky shrill in the midrange. Almost like a shout. It´s hard to explain but i think most listeners with some experience will notice this. To name some examples: Dream Theater, Soundgarden, Incubus, Ghost are not really enjoyable with the 315 just because of that honky midrange. 
 
If you want to monitor vocals and bass during a live performance, they will do a good job. But for a purely enjoyable listen, not so much. 
 
I am by no means a bass-head and i do like a forward prominent midrange and i absolutely like my treble. 
 
Oh i better say something of the overall design as well.
 
They have a very nice fit and good isolation. The connectors had held up well for me but i don´t remove the cables very often. The eartip selecton included should fit all users and are of very high quality. 
 
However the Cable on the 215,315,425 and 535 is crap. It´s to long and it gets very stiff over time, even more so if you live in a colder part of the world. I have bought a third party cable for my two pairs and i would suggest you do the same. There are many to choose from and the price is about 10-15 USD. 
 
Save your money and get the 215 if you want a pleasing slightly warm and forward sound signature. The 315 definatly have some tuning issues which is a shame. The single BA have some great potential here, but the tuning is off to my ears. 

When i bough these i had no id'ea how they would sound. I read some reviews but it is a iem that was flying under the radar and kind of hide in the shadow of the BA200 which is TDK's flagship ( was, i think it´s discontinued ) 
 
All plastic build, feels solid but not expensive. They do have a great fit and can be used both with deep or shallow insertion and a various amount of tips. Cable up can be bothersome. The isolation with a modestly deep insertion is impressive even if the housing appear to be vented. They leak some sound if you crank it up. 
 
Now instead of using a dual balanced armature the ie800 uses a dual dynamic setup. My previous experience with dual dynamics in this configuration stops with Nocs NS600 which had loads of bass, and a clear but rather metallic high end. Mids where recessed but well articulated. 
 
The ie800 looks to be using exactly the same setup. an 8mm and a 5.8mm where the 8mm is placed behind the 5.8mm driver. I don¨t know if it is the same setup but the sound is totally different and thats a good thing. 
 
Bass:
 
Speaking of bass the tdk does it just right in my book. I don´t like bloated elevated bass and i prefer a fast tight solid bass that can keep up with the rest of the music. And here it is. i can´t really say much more then it´s the best bass i have ever heard iem or full size. It´s just so well balanced and controlled. there is a slight bump in the midbass. Maybe that´s why a good miked kick drum sound so damn good here Now this is not for everyone and i understand that. Keep in mind that it´s not a bass monster and if you want something with more oomph there is plenty of iems out there you should pick over this. 
 
Mids:
 
Oh the mids! Vocals sound so damn good! Detailed with a great detail and air. Not ever have i thought that it lacked midrange or that vocals sounds nasal or recessed. Metal, rock, jazz, singer/song. all sounds good here, and everyone is welcome. Works with every genre and always gives a great presentation. Really impressive!.
 
highs: 
 
I do like treble, that said i do not like very peaky treble that is just there to try and present something as "detailed" when it really just sound unbalanced and annoying. Examples of iems i do not enjoy is Vsonic vc02, Brainwavz delta and vsonic vsd5 in some cases. The treble on these mentioned iems is just to hot in a bad way to my ears.
 
The ie800 has a very smooth, yet extremely detailed treble. It really picks out different instruments with fantastic precision. Never sibilant never in your face or presented in a ways that it is just "there" for no reason. Even old recordings sounds good here. From Meshuggahs furious instrumental magic to the most brittle jazz vocalists it never seems to be out of place. How they tuned this iem this ways is beyond me. Rarely is there a iem that suits all my needs ( hence the collection ) But every time i go back to the TDK i instantly know what i have been missing out of. The amazing treble. To me this is great..Absolutely fantastic. 
 
Now reading this review it probably sounds like this is the best iem ever..But it has flaws.
 
What i dont like:
 
The cable. It is cheap, thing and very prone to microphonics. It lacks proper strain reliefs as well. Handle with care! And don´t use them when you are running. 
 
The size. They are big.. Big as in they stick out of your ear alot big. 
 
The impedance. 10 ohms.. This has caused some issues for me when pairing with portable players. An ipod classic won´t work at all here and they sound drastically different ( to the worse ). You need something with really low output impedance. 
 
Some what hard to drive:
 
Picky with source gear.. first there is the impedance, then there is the power. Now a sansa clip for example sounds good enough but it does lack a little bit of power. This however can be placebo from my end. But i just have that feeling, that i think i hear a difference I have the same feeling that the Xduoo X2 makes this iem shine. It´s a dap that has alot of grunt and brute force. 
 
To sum this up. A great sound in a not so great shell. 
 
There are still some out on the web. and if you find them for a bargain price ( which i did ) It´s an absolute treat! And a overlooked ugly duckling to have in your collection ( cause there is always room for another iem in the collection ) 
 
Listened to with my ears with my preference when it comes to a good sound. We don´t always agree, but that´s okay!

The housing has a rounder shape then the vsd3/5 and i much prefer it this way. While the shape and looks is simple, it does not feel very cheap. The diamond cut shape on the vsd3/5 seems a little bit gimmicky to me. The fit is very good and comfortable. Very negative fit so it does not stick out of my ears at all.
 
The cable is also very good. It is thin, but feels sturdy enough. However i would like a angled jack like on the vsd1s and vc02 for example. They have the jack, why not put it here as well?
Also the cable lacks strain reliefs, a common “problem” with v-sonic iems and probably one of the most common defect. The cable is NOT removable which i think is a good thing. The mmcx style connector they used on the vsd3 is horrible anyway.
 
Bass is well balanced and kind of warm and smooth. However it is not very bloated or bleed into the mids. Plenty of heft for most ears i think. However, it is a rather balanced iem over all so if you want loads of bass.. This is not the iem for you.
 
Mids is taking a step forward in the mix. Again, the character is still rather warm and easy to listen to. guitar riffs sound great with both crunch and detail. The overall vocal presentation is good. Not as good as my reference the TDK ie800 but it´s enjoyable.
 
Compared to the vsd1s which it replaces. ( i think )  The vocal presentation is taking a step forward. My ears found that the vsd1s was a more recessed and brittle midrange then the vsd2.
 
Now the hot topic when speaking of vsonic iems. The treble.
 
Previous versions like the vsd1,3,5 has a forward treble. Now i do like treble and i have quite the tolerance for sibilance but the treble tend to be quite “hot” on vsonic iems and if you want something more smooth and less fatiguing the vsd2s is a great choice.
 
It is toned down quite a bit compared to the vsd5 for example, but i don't feel that is it is lacking really. For long or easy listening sessions. It´s well balanced. And i find this a good change in the iems from vsonic.
 
Overall i think it´s a very good all round iem with great fit, good cable and a easy likeable sound for most people. If you own the vsd3/5 i think this is a good iem to have to balance them both out. Another great argument to add another iem to the collection isn’t it ?
 
Here is a spontaneous ramble if you like to waste 7 minutes of your day