This review originally appeared on Head-fi.org. It was my view about the so much talked Yuin earbuds: the PK1, PK2, OK1, OK2 and OK3. Since most (if not all) of these models are still around, and among the most interesting earbuds available, I wanted to give a refreshed view here.

Presentation Yuin is a chinese brand of earphones, designed to provide better to much better than average sound quality, in the earphones realm. The first series, the PK series, mostly gave a shake for the PK1 model, much bigger sounding than expectable by a earphone, and often compared to Grado SR225 headphones. The Yuin OK series came out as a follower series, being much better looking, and going towards a more neutral, leaner sound signature shared consistently across the three models (OK1, OK2, OK3, in order of importance). This is in opposition to the PK1 versus PK2 sound signature, where the PK1 sounded warmer, more thumpy and aggressive than the PK2, and a lot bigger sounding. I feel the OKs start sharing a similar sound signature to the PK2, improving it.

PK2 vs OK3 I find these earphones very similar. The most noticeable difference between them is sensitivity. The OK3 are a bit less sensitive than the PK2, needing a bit higher volume on the mp3 player. The two earphones are otherwise extremely similar, they have a neutral sound signature, clean, with not very powerful (nor muffled) bass; the midrange is very clear (offering clear vocals); there are hints of sibilance occasionally (especially with sharp vocalists as Freddy Mercury), and the sound is pretty small.

OK2 vs PK2 The OK2 share the same sound signature as the PK2, bith in bass quantity, midrange tonality and slight treble forwardness. The biggest differences between the two, come out when comparing the soundstage. The OK2 are widely out of the head, in the same league as the PK1 and the OK1. The PK2 (as well as the OK3) are in the head and don’t give the same feeling of using a small full size headphone (like the SR-60) that the other three give. The OK2 is a PK2 on steroid.

OK1 vs OK2 The OK1 sounds like bettered OK2. The OK1 improve in bass presence, upper treble precision and soundstage (especially height and depth). The two have the similar lower treble midrange response, with hints of sibilance when using not very good recordings. The OK1 give better sense of refinement in instrument placement and resolution. The OK1 do require an external amplifier over the average mp3 player, in order to actually sound better than the OK2. They are very high impedance (150 Ohm), and the power output of a regular mp3 player wouldn’t be enough to drive their impedance across the frequency spectrum.

PK1 vs OK1 PK1 are warmer, with thumpier midbass, but not much bloat as the SR-60, which makes for a gradoish sound compared to the neutral OK1. The PK1 also reach lower frequencies compared to the OK1. Vocals are fuller with the PK1, mostly due to a midrange emphasis (probably around 2kHz, adding vocals presence and sweetness, and part of acoustic guitars body), but without the same crystal-clarity provided by OK1. Soundstage is wide in both cases. The PK1 have slightly wider soundstage, the OK1 have better instrument separation and placement, which sounds cleaner as the midbass doesn’t get in the way, but also because treble seems more extended and to have more quantity in the cymbals region. The OK1 are more transparent, and certainly do better with classical and jazz. The PK1 sound more “effortless” with rock, thanks to the stronger (but not bloated) midbass energy. The PK1 share the same external amplification requirements the OK1.

Conclusion When evaluating a earphone among the Yuin line, I’d consider their usage, at first. If I were to be using a Pico amp/dac out of a pc, for transportable usage, then I’d surely jump on either the PK1 or OK1. Same, if I wanted to use any other interface for transportable computer audio (like Halide DAC HD and a portable amp of choice); also, I’d be doing so if I were to be using one of the chinese audiophile players which have come out lately (Hifiman line, iBasso DAX1000 or Tera Player). If using a regular mp3 player output, which some wrongly say “going unamped” (which is very wrong, since an mp3 player has its own amplification circuitry), I’d either go for the Yuin OK2, or consider alternatives. Based on the above, the following considerations follow: The OK1 are very transparent and not as colored as the PK1, and for this reason they might appeal a different range of people. Rock sounds “effortless” with the PK1. I think the PK1 color the music more, adding similar tone to many albums, but on the upside, they are pleasurable and more effective at conveying the message. The OK1 make themselves less noticed, but thin recordings can feel a bit cold. Both PK1 are more neutral and refined than Grado SR-60, for example; while I haven’t heard the Grado SR225 (arguably the more balanced in the lower end Grado line), often mentioned in forums when speaking about PK1, I heard the SR-325i (outside the scope of this comparison, totally different price range), and while if was technically very capable, I found its sound very hard to listen to and treble heavy, unbalanced. The OK2 are very similar in sound signature to the OK1. They don’t sound as big as the PK1 and the OK1, but they are close. The OK2 are a really good choice for going unamped, more so than the PK1 or PK2. In my opinion, lower choices are price dependant. Often, there are earphones that sound similarly good but are harder to discover (for example, earphones that came in bundle with Kenwood HD20GA7 mp3 player and successors, are as good as Yuin PK2).

Tony