Wanted to share with you all my history with modding these.
 
FIrst, I saw the kramer mod and figured I could do a little bit better. (easier and than drilling a lot of holes)
I decided to fully open this puppy up. 
I went to the dollar store and got a stainless steel sink strainer. This woudl become the new baffle.
I removed the original black plastic baffle from the headphones.
I cut circles of metal sink strainer and epoxied them to the front of the headphone.
Now the speaker had a uniform opening to breath.
 
After doing the above mod, I put the foam ear pads back on. They were quite a bit brighter than I wanted. So that is why the original Kramer mod is the way it is!
 
Next, I bought some knock of sennheiser px 200 ear pads. I figured these move teh speaker a bit away from the ear. Better sound balance and sound stage I thought! I installed these and they were much better balanced and soundstage might be a little better a little deeper. BUT the midrange now has a honk.
 
Time to modify the px200 pads. I realized that the pleather was covering 3 very large side vents on the back of headphones. I cut a bit of the ear pads to unblock these vents and bam. They sound superb now. I would suggest for anyone wanting to mod the pads to perforate the pleather. maybe stabbing it a lot with a needle? micro hole punch? These pads are a lot larger then the stock foam, you will probably need to bend the ear hook to accommodate. 
 
Finally, if after doing the above, they are still too bright for you, you could always install the foam ear pads underneath the px 200 pads. let me know how that goes for you.  
 
Silly Side Note: I admit I am crazy. Before I made these modded Koss, I bought some hd6xx, fostex ebony (stock, zmf and brainwaves hybrid pads) and schiit jotunheim  w/ DAC. I did not like the hd6xx at all with the jotunheim, sold them. I liked the fostex and the effortless bass. The stock ear pads suck because uncomfortable, the hybrids also suck because treble peaks, the zmf pads work nicely. Yet still, I am selling the ebonies and the jotunheim. As of now, I am perfectly content with these Koss and my LG V10. It's just a much more simple setup. I am planning on getting some custom iems to supplement the koss because these things are so ugly I won't go outside with them. For biking and working out I have the se215 on a westone mmcx bluetooth cable. 

 
Costing me only £16, these are one of those bang-for-your-buck kind of items in the audio world.
 
Build Quality, Fit & Comfort
 
The packaging reflects the budget-fi nature by looking like something hanging on a checkout aisle at a Walmart somewhere. The build itself is expectedly not stellar, the cups are made of hollow plastic with holes. The foam is not particularly soft but not particularly rough either. The cable is another issue, being really flimsy and rigid. I would not recommend being too rough with the cable or headphones, as it does feel like it’s prone to fraying – and generally being one caught door handle away from being pulled out of the socket.
 
Because of such build materials, these are extremely light and do not weigh down your ears. They stay in place quite well too thanks to the clips, but don’t expect the wearing experience to be one where the headphones disappear on your head – I’m always aware that they’re on me due to how they sit, balanced on nothing but your ears.
 
Sound
 
The main draw of these headphones is the price-to-performance ratio. The sound is very, very impressive for its price range and form factor. The bass is punchy and has impressive extension for being such a seal-less and light fit. While I can’t say that I preferred EDM with the bass performance, it was certainly stellar for rock and metal music – with kick and double kick drums ringing out clearly in the mix along with the bass guitar, when it came to the low end. I would not characterize the bass as bloomy either, it does not overstay its welcome in more delicate genres of music. However, because the bass is of this nature, and also because there’s no real seal, wearing these in public makes the bass quite anemic – with it becoming a substantially brighter headphone.
 
The midrange is very, very clear and impressive. Listening to Simon and Garfunkel’s The Sound of Silence, the original acoustic version, shows off just how clean vocals can sound on the KSC75. Quite the contrary to the more forwarded mids on some headphones, the midrange of these are actually a little recessed – leading to a remarkably effortless transition from the bass to the midrange, something that I found lacking in both the Sennheiser Urbanite and Beats Solo 2 – which are both headphones that are several times more expensive. However, despite the impressive nature of the Koss in this regard, do not expect a very “natural” or full-bodied sound from the midrange – it actually has an artificial nature to it and a bit of grain. But, for its price, it is the best I have heard yet in open-back on-ear headphones.
 
The treble is probably the most impressive frequency of these headphones to me. I usually prefer a bassier and more mid-forward sound, but I could not deny just how much these headphones breathe. Stringed instruments such as acoustic guitars and violins have so much air around them – with the treble being very well extended without reaching immensely problematic peaks. Due to this extension and the slightly subdued nature of the mids, I would actually say that this headphone is bright overall – despite the punchy bass. However, as with the midrange, the treble is more metallic sounding than natural – but again very satisfying and impressive for its price. I will admit that I do prefer using the Ibasso DX80 digital-audio player, with its slightly warmer and treble-rolled sound signature, with the KSC75 rather than my SABRE DAC based AUNE M1s, which is a bit brighter. I also tried it with my VE RunAbout Plus portable headphone amplifier, but headphones do not really need to be driven as they can sound great out of a smartphone.
 
Another quirk of these headphones is that the soundstage is not very large by any means – which surprised me a bit due to how little they isolate and how punctured and open the cups are. The imaging is largely a miss, with the emphasis of sound reproduction being squarely from the left and right channel instead of projecting in a larger space. Due to this, songs with a lot more layers, tracks and tones can find themselves without enough room to truly shine on the KSC75 – but most songs are not of the nature where it would truly bother a listener using these for what they are intended, which is casual listening.
 
Conclusion
 
Probably the biggest compliment I can give these headphones is that I am critiquing them as if they cost above £100. They go neck to neck with many headphones several times the price on a purely sound quality basis – and even leave some more premium offerings in the dust in the same regard. I personally love when I encounter anything with this price-to-performance ratio in any hobby that I have – not just audio. With that in mind, I can strongly recommend these to anyone reading this review.
 
One final thing though, I did notice that it said on the bottom of the packet that some chemicals used in the construction of these headphones can cause severe health problems, such as cancer, according to the state of California’s regulations. However, I am told that Californian requirements are very strict, and the state has a long list of chemicals that receive this classification – deservedly or not, so make of that as you will.
 
 
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Had these, but sold them when I got a pair of KSC50, which gave me a much more enjoyable and clear sound.
The KSC75 had very little bass impact, cut-off early in the treble, poor detailing in the sound.
Both the KSC75 and KSC50 have a problem with comfort over a longer time of use, the clips make my ears tingle and hurt!
But for a short listening session when I want some "open" sound on a vacation, the KSC50 is usable.
They do provide the bass and detail that the KSC75 does not.

I bought these after reading so many positive reviews and I must say it's disappointment for me.
I tried them on Lenovo X3A40, Xonar ST and Xonar ST + Dispre v4. Many people says they are balanced with nice voals, highs and not so good bass. Well bass is ok for me. Not too much bass like Porta Pro (which I own too). Mids are slightly behind bass and trebles in compare of my AKG 701, Yuin PK1 and PK2, Ety ER6i, Hifiman RE-0. Highs are there for sure. They are sparkling but it sounds soooo rattling. Specially percussions, cymbals. Highs are worst part on these headphones for me and I like trebles. I like lot of trebles, I like sparkling trebles or even agressive trebles are not big problem for me but those from KSC75 are just ... yuck. Wierd thing is they sound good in rock music but are horrible in electronic music or classic music. Vocals sounds like placed into higher frequencies but overall they are nice. Soundstage is not big but separation is OK. I don't like sibilance on KSC75. For so cheap headphones KSC has a lot of details. Also balanced sound is not what I imagine when I'm listening KSC75. Isolation is bad but that's no surprise. Guitars sound nice in KSC75. Porta Pro has more energetic sound, more enjoyable except those bass.
Overall KSC75 are fine headphones but not for me. I like smooth detailed sound like PK1. These sounds more like PK2 with rattling highs, much smaller soundstage but better bottom mids.
I was listening to Faithless, Redhots, Dire straits, Lenka, Die Antwoord, MDK soundtrack, Fatboy slim, Daft punk and something more from Tidal after 12-15 hours burning.
PS: graphs about Audio Quality, Comfort, Design and Value are not like I set so don't look on them.

I am gonna start this where it should. These are the best thing in audio I have found at the price-point. I recently took all the headphones I have access to, and basically did a shootout. For audio quality, these came in third out of about a dozen. The Koss KSC75 came out ahead of the Sennheiser HD558, G4me Zero, G4me One, Monoprice 8323, and some others. Purely objectively, these are crazy for the price. (The two ahead of it were the Philips SHP9500, and the Superlux 668b).
 
The Koss KSC75 are quite comfortable for a clip-on. They weigh about as much as you would expect. The ear-touching thing is not nearly as objectionable as I had guessed it would be. As others have said, switching to a headband style would not be difficult at all. My only complaints with comfort and fit are how the clips dig in a little after a while, and they are a bit odd to center on your ears. This is entirely due to being clip-on.
 
The build quality is low, This is to be expected with anything at this price point, but has to be noted. The plastic backing is cheap, the foam padding is cheap, The cable is comparable to that of an old Walkman charger. The cable is awful. The cable, however, is a good length for portable use, and does terminate in an angled 3.5mm jack, which is good. The ear clips are cheap, and are just plastic. The wire supporting the clips are slightly different sizes on mine. One clip sticks out, and back a bit further than the other. The Koss KSC75 passed the shake the head around, jump, run test as well. These do not fall off my ears, but keep in mind my ears give plenty of surface area to hold on to. Overall, It is what you should expect for the price-point.
 
Now for the sound.
As mentioned before, these beat out some Sennheisers in my audio quality shootout. The sound is inviting enough that fatigue is not much of an issue. The clarity is great. Highs and mids are fairly well balanced with a few peaks and valleys. Vocals are great, but don't stick out so much that it becomes a problem. The bass is entirely dependent on environment and positioning. Overall, I neither find it lacking, nor overwhelming. The is not particularly loose or tight either. Soundstage is good, and the Koss KSC75 passed the CS:GO test with flying colors. These are extremely open. They get the double in the open catagory. Not only are they on ear, they are open backed, and use thin foam pads. The sound signature I would describe as similar to the SHP9500 with a bit more bite.
 
I figure I should start picking a song for each pair of headphones I review to give an idea of what sounds good with them.
Feature song: human - Christina Perri
 
 
Conclusion: The Koss KSC75 are hands down the best (imho) for their pricepoint. The Superlux 668b/ Samson SR850 is objectively better, but is much less inviting, and more cold. Still, I prefer the Sennheiser hd558 sound to any other option I have tried as of writing this. If you are addicted to headphones, or just need something open, cheap, and sound quite good, I highly recommend these.
 
I do all my testing with a FiiO e10, and all kinds of audio files. Please feel free to leave feedback, suggestions, questions, and especially recommendations. All these lower price headphones are a bit of a gateway drug to the world of audio. 

Read the others

 

eargasm

First that all, I called them Pieces of ****, because they look incredibly cheap and ugly, but they sound really good. They remind me a lot to the 668B, both have a fast bass that lacks Sub-bass (On the KSC75 that lack is worse), both have a sort of dry timbre, and both have great highs (Depending on your tastes you might find 668s highs a little bit too bright). To be honest, I find the KSC75 highs a little bit lacking. xD

Soundstage is very good, it is a step back of my 668b's soundstage.

Their clips are comfortable, but It takes a while to put them on. However, you can buy "Parts Express Mini Stereo Lightweight Headphones" on Amazon and use its Headband on KSC75s.
Overall, for 15$ You wont believe how good they sound.

Edit: I´m updating my reviews, I have to add that my KSC75 died (6 month ago) I´ll try buy a pair or even two pairs next year. Also I had the opportunity to try others portable headphones like HD202 and UE4000, and really, the KSC75 destroy the HD202s in almost every way and its on pair with the UE 4000.

UE4000s destroy the KSC75s on timbre and Sub-bass, However soundstage is wider and bass is faster on the KSC75. (I think this comparison is a bit unfair because you can buy almost 3 pair of KSC75 for the price of one UE4000).

Really, even after 6 month without them I cant still believe how good they were, and their biggest problem is how my KSC75 died, the died because their drivers themselves died (Not the outer cable) (It seems that the internal thin wires of the drivers broke up due to knocking).

I was looking for some headphones under $50, went through hell lot of reviews here n got confused about everything. Then somehow the browser showed few auto suggestions n I found these gems.
I read in almost every review that these are the cheapest n best earclips in the market. Well they are best but not that cheap in India especially when the exchange rates are so high. I got them for $25-$26 shipped to India through ebay.
Packaging:- The packaging was good, simple, nothing much to talk about.
Build:- They look flimsy n build quality is questionable. The cable is so thin n so ordinary, I have to be very careful while wearing them.
Comfort:- When I first wore the , I felt they are loose on my ears, so I tried to adjust the clips by slightly bending them. It takes time to adjust them in the beginning but after a while you get used to it.
Sound:-
Bass:- When I first listened to them I found the bass bit muddier. After burning them for 20-25 hours they opened a bit. I would say the bass is soft n punchy at the same time. You cannot listened to them on high volume as they start to rattle. I think these are made for soft listening levels.
Mids:- Some say they are recessed but I don't completely agree to it. Its true that they don't have forward mids but they are not recessed for sure. Mids are very clear, airy n pleasant for my choice.
Treble:- Highs are the most beautiful things on KSC75. Yes they are grainy but in a positive way. They are crisp,clear n I'm loving them. Highs have got nice extension.There is no sibilance whatsoever. In fact after listening to them I started feeling my Soundmagic E30 are bit sibilant too.
Isolation:- KSC75 are open back earpads, so you cant expect isolation from them. They are nice to wear at home or at gym but certainly not for wearing them on the streets if you live in noisy places like Mumbai. I tried wearing them in trains but i was completely disappointed (Don't compare trains in Europe with Mumbai local trains)
Conclusion:- KSC75 are the best deal out there for the price for sure. Sometimes I prefer them over my RE262 just for the love how energetic they sound even at low volume.(RE262 lovers please don't kill me for that, I love my RE262 a lot too, and quality cannot be compared)But it's just the characteristic of KSC75 that you fall in love with them. They look funny on the street. I look like a character from 1970's science fiction film. But I don't care about it as long as I'm enjoying the sound of it. As almost everyone said earlier, they are must have headphones and everyone should own these at least once in your life.
 

 
 
My simple tiny set-up-Cowon C2 + Fiio E6 + Koss KSC75:-

I bought these KSC75 clips because I lost my modded Koss UR55 and I read oodles of praise for them online. At first I was skeptical because they are very flimsy looking and they are often compared to the Koss PortaPro which sounds muddy in my opinion. So I tried them on and I was immediately impressed by the overall balance and airy sound. Everything sounds so natural and forward, and it's really easy to separate vocals and instruments. I really like these with pop and rock music. The KSC75 crush the PortaPro. However, I must say that the treble feels grainy at times, especially with shimmering electric guitars (typical in post-rock). Another complaint would be that they look super dorky on your head, especially next to the PortaPro which is very stylish. 
 
I think that the KSC75 would almost better the Grado Sr60i, if it weren't for that grainy treble. They are that good.