Performance

To do a fair comparison between the different earphones I own I used the same source and matched the volume of them as close as possible before doing A/B testing. The sources I used for the review include the following: Octavart The One DAC & Amp, Cowon iAudio i7 both with and without a Go-Vibe V6 as amp. As far as earphones go I used the following as reference: Yuin OK1, Yuin OK2, Yuin OK3, JVC Gumy, Sennheiser MX500, Head-Direct RE1, LiveWires T1.

Since the Yuin PK1s are earbuds they provide absolutely no isolation, a bit of distortion at best. The Yuin PK1s are anything, but ordinary since they require both an amp and plenty of burn in before they sound their best. I have an old pair and it was not until they had been burning in for about 200 hours that they sounded their best. The same thing goes for the new Yuin PK1s. Straight out of the box they are pretty lifeless, weak bass, sibilant highs and a quite grainy midrange. Definitely not the kind of performance you would expect from a pair of $159 earphones. After the first 100 hours the sibilance is almost fixed. The bass comes into play after the 150 hour mark and gains presence and depth. The frequency response is very odd to begin with, but settles down over time. In the beginning you will notice a lot of odd note decay and some strange response in the upper midrange. Being fed with pink noise at a high listening level for a very long time seemed to cure all of the major issues regarding the sound quality. Of course it would be best if they sounded their best right from the start, but like we see with many high-end headphones, burn-in is needed to get them to perform.

After the burn-in the PK1s sound way better. The bass is pretty tight with very little distortion compared to the amount of it. The mids are incredibly precise and airy when amped. The PK1s are quite the beast when properly amped, the highs sound sparkly without being overly sibilant and the extension is quite extreme for a pair of earbuds. With the proper amp these earphones will undoubtedly be able to compete with some of the way more expensive IEMs sound quality wise.

The bass has a lot of presence and authority. The PK1s strike me as being aggressive and speedy in their presentation. Even when the music becomes very complex, the PK1s still maintain their precision and speed. Percussions sound really good on the PK1s because of their speedy and forward presentation.

The Yuin PK1s are a very articulate pair of earphones almost on par with the OK1s, but lack a bit of finesse. On a high end amp you tend to notice the small difference more. On the Octavart for instance you can clearly tell that the OK1s are far superior when it comes to detailing and treble extension. Also the sound stage is a little more immersive on the OK1s, but not by much. You would hardly notice these differences when used on the move because of the background noise and possible lack of amplification. Compared to earphones such as the LiveWires and other high end in-ears it is clear that the earbud form factor has an advantage when it comes to sound stage, the PK1s loose on all accounts when it comes to details, but their tonal balance and sound stage makes up for it. The midrange is medium warm on the PK1s, and is incredibly textured when paired with a good amp and source.

The Yuin PK1s have a slightly bloated bass region that has a tendency to make some nasty distortion on some tracks. With my home amp this did not seem to be that much of a problem, but with my Go-Vibe V6 which has a slightly elevated bass and midbass this problem becomes so much more apparent.

The PK1s are very comfortable to wear and I still find myself switching back to them when it gets hot or when I do not want my hair messed up by a big pair of headphones. They are a good alternative to big cans when you are on the move because they are easy to tug away in a shirt pocket or bag unlike its bigger rivals.
The only real problem with the high end Yuin earbuds is that they need an amp to sound their best.

Durability

The build quality is generally good with the Yuin products. The only minor problem present is the finish. It is a bit rough compared to a lot of the other earbuds on the market. In return for the more brutal finish you get a more solid product. I think that the tradeoff is a good one, I much prefer a solid earbud rather than a pretty looking one.