[audiofil]

I need to say it from the very beginning - these headphones absolutely mesmerize me!
It was so unexpected and completely took me by surprise.
 
I've found these cans on ebay.de a few weeks back. The cable had problems and the pads weren't in the best of shapes.
I had no desperate desire of buying them nor any special interest in this particular model. I have the K701 for almost 4 years and K501 never represented more than a simple curiosity.
I've placed my bid and two days later I get the Ebay notification that I've won the auction at 58 euro.
The cans arrived 5 days later and the description was accurate - the cable was pinched somewhere near the jack and couldn't work in stereo more than a few seconds after a serious rattle.
The pads had serious signs of usage and were scratched and torn in a few places. Usable, but best if replaced.
 
I decided that it would be best to recondition them. After a thorough cleaning in went a balanced Mogami Starquad, a bit of Blu-tack on the back of the magnets and on the cups.
Searching for new K501 pads led me back to head-fi where the pad replacement has a few threads of its own. Long story short: they're compatible with k701 pads, which are locally available to me, so I bought a pair.
The K701 pads are said to improve the sound, especially in the bass, and extend the soundstage a little bit (as the pads are fatter on the side and angle the drivers a bit). I didn't listen much to the stock pads but I think there is truth in the above statements.
 
A few days later the K501 were reassembled and ready to sing.
I spent most of the day listening to them and only them. The initial plan was to compare them with K701, but I was so hooked by the K501 presentation that I gave up on that plan. The last week passed in the same way - once I've put the K501 on I completely forgot about everything else.
 
The K501 are, for me, sheer joy, energy and excitement. It's impossible to listen to them without a smile on my face and deeply connected to the music.
Technically they are not as potent as K701, especially when driven by the ROC, balanced.
But as soon as you put them on and press play these things disappear and leave you marvel at the life and energy they recreate.
There is a sense of freedom, light and air that I haven't heard at any headphone before, ever!!! Not even with K701.
 
The presentation is very airy and wide with a strong sense of space. The same can be said for K701, but there is an important difference: K501 makes everything sound rather near and immediate. The K701 put a bit more distance between the listener and the performance.
 
Dynamics are one of the greatest qualities of K501 and I feel it deserves a more detailed description.
They keep up even in the most violent passages of large orchestras without any sensation of strain or imposed limits in the sound. There is no rounding off the edges, no politeness, no slowing down nor an overenthusiastic poise that Grados present.
Micro-dynamics are rendered with a lifelike quality. Each nuance in the dynamic picture is faithfully reproduced. Solo string instruments have such a naturalness and texture to them.
There is a paradox in the K501 dynamics that I cannot explain or understand just yet.
They're obviously speed oriented headphones with clearly delineated and super-quick transients. The attack is very fast and I expected that decay times would be shorter too. But it's just not so. Oddly the decay is longer than logically expected and there is no rush in it's reproduction.
The K701 by comparison is just about as fast, but there is a sense of expedience in the reproduction of notes. It quickly jumps to the next, not leaving too much time for the last note to settle, sort of speak. So the decay is shorter.
So, is this a flaw? Well, I don't think so. The attack/decay "ratio" feels so natural that I cannot find any wrong in it, so it must be right!
 
Summing up, K501 are a real gem and really deserve a special place in the AKG line-up and the headphone world (which is growing constantly each year).
For me they're the most energetic and engaging can I've ever listened to.
In a way I regret not buying them sooner, but there is a chance that I would have failed to appreciate them as much as I do now.

 

[bluntman]

 

[helios]

Very well put and very true.

 

[Slaughter]

I had and sold the 501 due to the bass presentation, but other that that, I can't imagine any other headphone being much better. The 501 has so much life, energy and realism. It is definitely a special headphone.

 

[pataburd]

Nice review.  Thank you.  
 
You did fit the K501 with the K701 pads, correct?  So your text implies.  I tried that pad exchange, but felt that the K701 pads made the K501 sound honky and congested.
 
The K501 have a much more coherent, open and realistic midrange than the K701, IMHO.  (The K701 have an upper midrange glare/smear that destroys their coherency.)  My K501 are the "bass heavy" version, and with the venues I typically listen to (period, acoustic jazz, orchestral), bass quantity is ample, with bass quality well-balanced and well-integrated.     
 
If you get a hold of a pair of K501 pads, they will, I wager, bring out more of what the K501 already do so well, and accentuate what they already do better than the K701.

 

[Benaiir]

All the Kx01's besides the K701's are neglected. I own the K301's (Not to be confused with the K301 XTRA). Won them in an auction, all impulse. Love them. My favorite headphone that I've owned in terms of all-arounders.

 

[Justin Uthadude]

I bought a pair of these based in part on the recommendation of Patabird. (thank you) They are indeed excellent phones. I have replaced my pads with a new set meant for the K601, and find the increase in bass just right, with no discernable loss in any other quality. I am powering them with tubes and I love them. I welcome you to the secret club  =^)
.

 

[Don Quichotte]

Yeah, the K501 are indeed something special. I also love their musicality, so to speak, and agree on the wonderful dynamics, microdynamics in particular - the subtlest shades of intensity appear very clear and musically convincing through these cans. Also, the notes are very solid, there is some very nice impact to the sound - not weight, weight is somewhat lacking, but the sound is very tactile, a quality (that I love) K501 share with their bigger siblings K1000.
I think I have a bass heavier version (only 3 holes in the baffle, the other 3 are covered) and the bass is decent in quantity, if not particularly deep. The quality of the bass is excellent though, very detailed, textured and tuneful. I especially love the plucked double bass - it has excellent tactile qualities - and the piano - which sounds very rich and meaty to my ears, although depending on the recording it can sound a bit light.
 
What annoys me is that most if not all users seem to praise the treble performance of these phones, while I find the treble not so good, I think splashy is the correct word and with somewhat limited extension. Upper bass and midrange wise, K501 can sometimes hold its own (with a bit lesser detail) to the Stax 303 and K1000, but treble is miles better on the stats and K1000. Also, most speak of the speed and transients of K501, while I found the HD600 - generally described as a lazier phone - to have faster attack.

 

[burgunder]

I have the K400's which should sond a lot like the other cans from the Kx0x series, and I must say that I love them, actually I don't plan to switch to other cans anytime soon, but would like to upgrade but my EF2 and µDAC before I start thinking about any other. BUt that said I would love to hear the K50X one day, to see what the difference is.