I've been out of the headphone game for some time now, focusing on my 2-channel speaker setup rather than headphones for the last two years. The last headphones I bought were a pair of ESW9 for $80 four months ago (audio-technica warehouse sale ftw). Though I have  been slowly but surely making my way back to headphone listening. I was browsing ebay and came across an auction with 5 minutes left for the K270 Studio dual-driver headphone. I was interested in owning a pair because of their rare design and for the sake of furthering my own headphone collection. I honestly didn't expect much in terms of their sonic capability, given the reviews for them are so polarizing. I decided to buy them, waiting until the last 20 seconds to place the winning bid for $65.
 
When I plugged them in and listened for the first time, I was pleasantly surprised. More full and musical than I was expecting. However, as the headphones warmed up from being on my doorstep all day, they started to really, really shock me. I started to become immersed in my music in ways I haven't experienced since I got into hifi equipment. I guess their sound signature just works for me. On the warm side, yet somehow detailed in its own way. The highs are a bit rolled-off, so if you are into hyper-detailed treble extension these aren't for you. However, this is where the weakness ends. The mids and bass response on these are among the best I've heard on headphones. Three days later and I still have the same impression.
 
Vocals sound warm, natural and placed right where they should be. Very representative of the recording. I am beginning to see what the famous "akg mids" are all about. The soundstage is large, as most people have stated. However soundstage isn't exaggerated unlike some headphones (k702 for me). It just seems accurate. Attack and speed are quite good, spreading the work between two separate transducers.
 
Bass frequencies are the most amazing part. These extend lower than any headphone I own, and seemingly without attenuation. Yet these are not "bassy" headphones by any means. They just have the ability to play back exactly what's in the recording. This makes me realize that many of my other headphones are clearly rolled-off in the low-end in favor of more forward mids and treble. Listening to large orchestras where double bass and bass drum are prevalent results in a skull-rattling experience. This may sound unpleasant, but it's definitely not. It's what you would actually feel listening to a live orchestra. Hearing the low-frequency echoes and vibrations of the venue is an incredible experience. On the flip-side, if a recording is not bass-heavy, these headphones will represent that fact. They will sound tight, agile and controlled.
 
The result is a (nearly) full spectrum of sound with extremely good separation and little distortion. Probably one of the reasons that I get so immersed in the music with these. Being able to hear every single instrument individually is part of what we audiophiles crave, and these truly offer it.
 
That's about it, just wanted to share my excitement and opinions on this headphone. Probably the best money I've ever spent on a piece of audio gear.
 
Nate

This is a mini review of the beyerdynamic dt220 400ohm.
 
Last year I stumbled upon a pair of dt220 on ebay for $75. I was unable to find information in regards to their sound but I bought them anyway. A true impulse buy. After hearing them, I bought another pair from the same seller. I could tell that I had found a special headphone, a true diamond in the rough.
 
Overview:
 
The dt220 is rare and information is hard to find. There are a few pictures and specs but very little in terms of listening impressions. Luckily I have two original boxes, so here are the specs listed for my pairs:
 
20-200000 Hz 400ohm
102mW = 122db = 6.4 V an 400ohm 260g
 
There is also a 20ohm version of this headphone which I do not own.
 
Judging by the phrase "a quality product made in West-Germany", I can safely assume this particular headphone was made, at the latest, in the late eighties. Though it could very well be from the seventies. As said before, little is known about production timelines.
 
My two pairs are identical, likely bought at the same time for the same studio, as I got them from one seller. The pads are very different from modern pads. They are made from rubber and filled with foam. The drivers are comparatively small compared to modern drivers. There is also a dense foam piece that surrounds the driver, which your ear rests on. This gives the bass a very punchy feel, just like Grados. It's a nice departure from my other headphones. My pairs feature single sided entry cable, which must have been implemented after some time indicated by this awesome beyerdynamic photo featuring a dual entry cable:
 
http://i13.photobucket.com/albums/a271/Metallurgic/DT220.jpg
 
This posed a problem, though. The depth of these headphones (thickness from front of pad to back of cup) is small compared to most beyerdynamics. This means that cup rotation is greatly hindered because of the cable entry/exit on top of the cups. You can even see where the aluminum cup brackets dug into the cable strain relief. Because of this limitation, the pads sat on my head at an angle which prevented a proper seal and removed what little comfort these headphones had.
 
To fix this I converted the headphone to dual entry using a sennheiser hd650 cable. I also removed the physical anti-rotation portion built into the cup hinge sockets and cup brackets. The result is perfect seal and the best comfort you're going to get with this headphone.
 
Sound:
 
My first listen was made using a TI class-D amplifier board modified to be a headphone amplifier. This little amp works great for all my other headphones but I feel that the impedance of the dt220 (400ohm) is well beyond its capability. Not knowing this, I still enjoyed this headphone immensely. The sound was the same as using it unamped out of my iriver h320. Bass was lean, mids a bit cold and treble sounded good. They seemed ruler-flat and took about any music with stride. Though, they sounded almost horn-like with some music. This was my impression of them for months, as I had taken a break from my tube amp.
 
Eventually I decided to try them with my SS Millet tube amp and the difference was night and day. Many people say amplifiers make no difference, but with this headphone the difference was overwhelmingly positive and far too large to be placebo. Instead of an overall cold/flat sound, music became warmer and closer. Bass can extend extremely deep and the physical feel of kick drums is prevalent. Mids are smooth, not recessed and clearly audible. Treble is slightly relaxed but not to the point of being hard to distinguish.
 
Overall the sound these headphones present just works. Warm, musical, yet somehow faithful to the recording. Faithful in the way that just about anything you play will be represented accurately and pleasantly. Some headphones just can't do that.
 
Practicality:
 
Comfort is where these headphones fall short. Granted, these were geared towards studio  monitor users so comfort may have been placed on the back burner. The main problem (with single entry models) is the limited cup rotation as stated above. Remedy this problem, and all you have left to complain about are the pads themselves.
 
The pads are foam coated with flexible rubber. The ear openings in these circumaural pads are rather small, which my small ears barely fit into. People with larger ears may experience untold discomfort. I can last a couple hours before I need a break.
 
Just beneath the main pad is a smaller pad made out of dense foam rubber. This smaller pad surrounds the driver and makes contact with your ear. This pad is interesting because its removal means loss of all warmth and bass. I believe the pad is there to limit the amount of dead air in between the driver and ear, as well as physically transmit vibrations to the ear. This gives a very punchy, physical bass experience much like supra-aural Grados. Remember, the driver in this headphone is actually very small, being around 30mm instead of beyerdynamics current 45mm. It doesn't move air quite as effortlessly.
 
Conclusion:
 
These headphones sell for relatively cheap as far as I can tell. I got both my pairs for around $75 and I consider that a great bargain. I have even heard of them going for well under $50. At any of these prices they are a great deal. They can compete with all my other headphones.
 
If you want these, consider proper amplification. It's even more important with these 400ohm headphones than it is with the k702. My tube amp brought out the best in these headphones, so try to have an amp on hand with specs greater or equal to the SS Millett.
 
That's it.