Sennheiser's redoubtable HD580 precision is a group of possibly 5 headphones, none of which are identical in sound to the other precision models never mind their HD600 or HD650 models. Because of silent changes the group might be the following:

HD580 precision, flat plate, made in Germany, 1st version
HD580 precision, flat plate, made in Ireland, 2nd version
HD580 precision, raised plate, made in Ireland, 3rd version (dark driver screen)
HD580 precision, raised plate, made in Ireland, 4th version (light driver screen)
HD580 Jubilee
The most produced versions are probably the 3rd and 4th version. If you purchase a HD580 precision today you will most likely receive one of these with the 'HD580 precision' written on a raised nameplate rather than one of the (less produced ?) earlier versions with it printed on. My first HD580 precision was a 3rd version, next after much searching was a flat plate (printed HD580 precision) made in Ireland 2nd version and finally a Jubilee. In each version there will be many Sennheiser designed variables:

grille (different for flat plate/raised plate)
plastic earcup that mounts the driver
driver version
driver screen colour, fabric or paper
foam disc
earpads

each one will affect the sound properties, some more than others. These headphones give a quite neutral sound and depending on which one you own the design intent will be closer or less close to neutral. The 3rd version that I owned I found a significant improvement over the HD595, however as I had a warm amplifier at that point it overall sounded too warm (for me I prefer near to a cold sound) and some recordings suffered as a result. Next was the 2nd version. With a more neutral amplifier this headphone was an upgrade, delicate, natural, precise and like the newer version it did contain a little warmth in its upper frequencies (these were I found out later, dark because of the driver's age. Replacing them with a HD600 driver (only) brought back the missing treble that made them feel slightly dark)). Like the HD650 these headphones have an exquisite sound. They are of course exquisite in different ways but once 'tuned in' to the headphone they deliver an experience close to the source but with a little warmth also. Like the HD650's wonderful tonality these offer a more modest sound image but in a similarly charming way. The HD580 Jubilee from 1995 (not the 58x) is an analytical headphone even more than the 2nd version. Since it's a 'blank' headphone it doesn't have a sound signature and it just gets out of the way without any warmth at all. In the world of headphones this is rare like the Jubilee itself. It's a little bright but nothing like a Beyerdynamic's mass produced DT880 (600Ω). If you can put up with bad recordings or even recordings that assume the listener's equipment is inherently coloured then this is for you. Otherwise the non-selection of a sound signature may be confusing. It's not for everyone but the Sennheiser HD580 precision is a class act. Unfortunately they are fairly rare now and mostly only the later versions.

This is a review of the Colorfly’s (C4) occasionally compared to Nationite’s (S:Flo2) Tekmod. This is my impression of the two players (without using switching/volume matching equipment) through Sennheiser HD595 headphones. I have never used either of these players as portables with IEMs and this comparison relates to only home use. I won’t compare the build quality, as the C4 is a far more expensive player than the S:Flo2 ever was. In their user interfaces both have several issues, the cheaper S:Flo2 suffers more in this respect than the C4. The C4 presents files in memory as a simple folder structure but forgets to select anything (either a folder or a song) by default. So you need to press up/down/left/right arrow to select something. If an artist only has one album any key will select it, for multiple albums right/down arrow select the first album and left/up select the last album. Not very intuitive. However when you go back from the play screen the song/album are highlighted (selected). Once you exit the play screen the only way back is the long way round to the root menu. At least it has the `up one level’ button that would transform the S:Flo2’s interface. I found the buttons on the C4 often unresponsive and the volume slider lacking in precision. The C4 does load up quickly from cold and both devices are quite quick once you get used to their quirks. The C4 is an unusual player using engraved wood, having allen key heads to enable dismantling and 3.5mm and 6.25mm headphone sockets. Then theirs the rocker switch to set the EQ or bit rate/sample rate on the front panel. Perhaps the most unusual decision was not to include a line out but rather have digital in/out instead. One thing that surprised me about the C4 is that for such a big player it only has a 2000mah battery, smaller than the S:flo2’s 2500mah item. The S:flo2’s size is dwarfed by the C4, which is not very portable; their weights are 259g and 133g respectively. The S:flo2 has been modified by burnwayGTA4 a former member of Headfi from Russia. The mod is quite extensive and relates to the HO (headphone out). He modifies the internal amplifier to use TI’s LM4562 and THS4222 Opamps in place of the Philips TDA1308 as well as replacing many other components, capacitors, etc. Two media players virtually never sound identical usually because the hardware is often different and its implementation is always different. The C4 uses the Cirrus Logic CS4398 DAC and the S:flo2 uses dual Wolfson WM8740 DACs. The music files were flac 16/44 and EQ set to normal on C4 and User (flat) on S:flo2. Both players are fairly neutral the S:flo2 being more so. The C4 produces a thicker more full sound than the S:flo2 and is also a bit brighter. The C4 has more colouration than the S:flo2 making it the warmer of the two. The C4 sounds much like a CD player plugged into a headphone amplifier. The main difference between the players is in their presentation. The C4 sounds similar to listening to speakers whereas the S:flo2 and all other players I have heard sound like headphones. How the C4 produces this `3D’ sound I don’t know. The C4 tends to separate instruments more than the S:flo2 (not R/L separation: which makes it sound more physical or live than the S:flo2. The listener is further back in the audience with the C4 than on the stage with the S:flo2. The downside to this however is in order to achieve this `3D’ effect some of the detail and texture that the S:flo2 produces is absent. On the C4 there is no way to turn off this effect, which is more noticeable on some tracks than others. The S:flo2 is more intimate and gives a more accurate rendition of the recording. Many however will prefer the earthy speaker-like sound of the C4. Both players make poorly recorded material sound unpleasant; naturally the S:flo2 is more ruthless than the C4. Bass frequency extension is lower on the S:flo2 but the difference is slight. The level of bass is a little higher on the C4, the player gives a little more of everything but in a refined likeable way. The C4 is a bit like the unmodified S:flo2 but with an enhanced soundstage. My ideal player would have the construction/durability aspects of the C4, an upgraded C4 user interface and the electronics of the modified S:flo2. The price of the C4 at £540 makes it a considerable expense compared to the S:flo2’s price of about £120 plus the mod at £100 plus £50 postage to and from Russia, so approx. £270, half the cost of a C4. Most non-audiophiles (and even some) would much prefer the C4 in this comparison. Which you prefer will have a lot to do with whether you think soundstage should be a function of the recording/headphones or whether you include the media player also. Also whether you are a more is more person (C4) or a less is more person (S:flo2 Tekmod). I find the C4 likeable in a similar way I suspect people like Grado headphones more than accurate and natural ones. There is also something alluring about burwayGTA4’s modification also.
 
For:
Solid construction
Sound quality
`3D’ soundstage
Power to drive 300ohm headphones
Both 3.5/6.25mm headphone sockets
Unique design approach
 
Against:
Expensive
User interface needs subtle tweaks
Slight colouration to sound

The Nationite S:Flo 2 is a media player that is no longer manufactured. It is a larger memory version of Teclast’s T51 player with extra storage (on the 16GB model) and different firmware graphics but the same UI. This player has a rare dual mono architecture which mirrors rack CD players. There are two DACs and two pre-amps, one for each channel. The advantages of this are supposed to be lower noise, less distortion and better separation. However this architecture has not generally been adopted (except for the Astell & Kern AK120) and most Hi-Fi players tend to utilise one DAC. An obvious disadvantage of this method is power consumption. This means the 2500mAh battery will last for a maximum of 10 hours playing mp3’s and less for flac files. Also because the line out (LO) and headphone out (HO) are connected irrespective of which one is being used the battery life is lower overall. It has been estimated you might get 20 hours continuous playback from the HO if the dual TI OPA2604 op-amps were not active. One way you can increase battery duration when using the LO is to set the volume pot to zero. Fortunately the batteries are quite durable and can be replaced by opening up the player, but conserving the battery has not been given the design priority that most other players have. A nice feature would have been a connector for a power supply, as many will use this player as a substitute for a CD player at home. Going outside Apple’s eco system often means lower grade interfaces and the S:Flo 2 suffers from this. It has this strange ‘File Align’ by time, name or type option that affects behaviour. Most people want files arrange alphabetically by artist. If you align by name then artists with multiple albums will have them mixed with track 01 of the first album and then track 01 of the second album etc. If you align by time then artists with multiple albums will have them separated, tracks 01-10 then 01-07 etc. but not in separate folders. Lastly if you align by type they seem to go into reverse order! 09-01 but not in separate folders. There is an unusual selection under title, which puts every single song in its own folder. The albums selection is as expected. There is also a directory section which shows the contents of the onboard memory and any trans-flash (TF) cards inserted. Unlike the selection of artist earlier mentioned, in the directory selection multiple albums are in separate folders. You don’t have the integration of onboard/TF storage like the artist selection (although artists are still grouped A-Z onboard storage and then A-Z TF storage) and there is the extra step of specifying onboard or TF storage. The user interface is chaotic and overly complex but it is surprising how you get used to it. Having two distinct methods of finding artists/albums etc. is not ideal. Multiple artists aren’t sorted alphabetically either in the artist or directory selections. If every artist has only one album this player becomes much easier to use but effectively the UI handles multiple albums rather poorly. There is also another difficulty in that once you have played a song on an album you are stuck in that album, the alternative being to start from the beginning selections again. To select another album using the artist selection takes 4 key presses and 6 using the directory selection. Apple players require 2 presses to change album. This player has some unusual other features: a dictionary, a calculator, a stopwatch and 4 games. The player supports mp3, flac, ogg, wma and the unheard of ape format. It won’t play Apple’s aac or m4a formats. This player can be used with full sized headphones with excellent results. Compared with many other players the S:Flo 2 has a few differences: the balance is quite neutral; it seems clear and fairly cold in presentation. The lack of colouration makes this player rare as lots of players have significant colouration. Compared to Apple’s iPod Video 5G the S:Flo 2 has more pronounced and nicer bass, is brighter and clearer overall compared to the iPod’s slightly duller and darker tone. Detail and soundstage are about the same. Through the HO using the Philips TDA1308 amp the S:Flo 2 has more attack compared to the slightly warmer and mellow sound of the iPod. It is never harsh though. The S:Flo 2’s character changes using the LO, which unlike some players seems to make quite a difference. The use of TI’s OPA2604 combined with an amplifier produces a sound with a little less attack that seems like the bit-rate of the file has been increased. Many elements are enhanced; bass has greater range and is more defined, as is the midrange. Critics have said the sound signature is too bright, it did seem a little like that with my Sennheiser HD555, but with my HD595 it seems less noticeable. My impressions were with the equalisation set to ‘user’ and flat. The ‘normal’ setting I find does not give a flat response and as its level is also higher this can occasionally cause distortion. This player has a few firmware defects and some quaint characteristics. Things like the screen randomly goes to maximum brightness occasionally or it ‘forgets’ the last song that was playing when you last switched off and selects another one. Sometimes after plugging into a PC it thinks the TF card is empty until you restart the player. Due to the heavy-duty electronics you will hear thuds through your headphones entering and exiting the playing screen. When playing through the HO you might notice noise which ceases when the display goes off. But for all its faults it was and still is a great player. There have been several audiophile players that cost more than this one did that simply do not provide as good sound quality. There are also ones that cost much more than this that may only give a relatively small improvement in sound quality.
 
For:
High HO sound quality
Wonderful LO sound quality
Low cost
High quality screen
Durable
Short battery life
Expandable storage
Hardware volume control
 
Against:
UI could be improved
Not a great video player
Short battery life
Limited onboard storage
Display noise through HO
[size=12.0pt]Some less refined traits[/size]