Cayin RU6 Review: First of Its Kind

  • Analog sounding
  • Very clean background
  • Provides excellent extension on both ends of the spectrum
  • Two different flavors through the NOS and OS modes
  • Hardware volume control

  • Steep price
  • Occasional stutter when adjusting the volume (this is due to Cayin's self developed discrete resistor array for volume control)
  • Tempered glass panel prone to smudges and needs extra care if you don't use the leather case

Cayin is a well-known brand, originated from China, that offer broad range of products in both the portable and desktop categories of the audiophile hobby. They produce solid state and vacuum tube amplifiers, digital to analog converters, digital audio players, and even in-ear monitors. The RU6 is Cayin's first attempt at the very popular dongle DAC segment of the market, and it is a special one. The discrete R-2R DAC is nothing new, but the RU6 is the very first dongle DAC to use this architecture. The RU6 currently retails for 250 USD, and was provided to me at a discounted price by Cayin in exchange for this review.

Specifications taken from Cayin's website :
Poco X3, Poco M3, Redmi Note 7 Pro, Redmi Note 10 Pro, Lenovo IdeaPad 110

Gears paired with the RU6:
Koss Porta Pro
Koss KSC75X
thinksound ov21
SIVGA Phoenix
KLH Ultimate One

In-Ear Monitors:
Audiosense DT600
Audiosense DT300
Hisenior FE3U
Kinera Freya
NF Audio NM2
BQEYZ Autumn

VE Monk+
VE Monk Lite 120
VE Monk SM
Astrotec Lyra Mini
HZSound Bell Rhyme
DQSM Z&W Panda

Test tracks:
Africano - Earth Wind and Fire
Dark Necessities - Red Hot Chili Peppers
Gurenge - Lisa
The Chain - Fleetwood Mac
Monsters - All Time Low
Ours - Taylor Swift
Stay - Mayday Parade
Snuff - Slipknot
Yesterday Once More - Carpenters
So Slow - Freestyle
Aurora Sunrise - Franco
Attention - Pentatonix
Blue Bird - Ikimono-gakari
You're Still The One - Shania Twain
Anyone Who Knows What Love Is(Will Understand) - Irma Thomas
Salamin - Slapshock
AOV - Slipknot
Hey Jude - The Beatles
The Way You Make Me Feel - Michael Jackson
...and a lot more.

Unboxing and Accessories:
The RU6 comes in a medium sized rectangular box. Upon opening, you will see the dongle DAC resting on a thick piece of dense foam. Underneath, there is a small envelope that contains the instruction manual, a USB C cable used to connect the RU6 to any device with a USB C port, a female USB C to male USB A adapter, and a silica gel packet to keep everything dry.
Cayin also sent the CS-L2C which is a USB C to lightning cable to connect the RU6 to Apple devices, and the leather case. The leather case comes with a large silica gel packet and two magnetic pieces, about the size of a coin, with adhesives on the back side that you can stick to the back of your phones to keep the RU6 at bay. Both the case and lightning cable are sold separately and doesn't come with the standard package of the RU6.
The frame of the RU6 is made of anodized metal. There is a small OLED screen under a tempered glass panel that shows the volume level, gain setting (high or low), sampling mode setting (NOS and OS) and current sampling rate. At the side, there are the volume up and down buttons, and the mode button used to change the different settings like the gain, sampling modes, and backlight timeout. Up top is the USB C port, and below are the 4.4 mm jack for balanced output and 3.5 mm jack for single ended output. The included cable has flexible rubber insulation and USB C plugs enclosed in a metal housing.
Initial sound impressions will be written using the Non-Oversampling mode, and will be later compared to the Oversampling mode.

Now let's get to the sound.

The lows receive a very slight emphasis. There is a very small boost in the thickness of the subbass, and the decay is slightly more extended than average. Even then, the reproduction still feels very natural. The smoothness of every bass note is outstanding, with the additional warmth reminiscent of tube amplifiers, without the hint of darkness that some of them have.

The mids maintain a neutral position. The warmth of the lows carries through here. Upper and lower sections have an extra weight, that is much more noticeable in male vocals and acoustic tracks. That being said, vocals still sound organic. The resolution of the mids is exceptional but to a certain degree, the warmth definitely has an impact to the overall resolution.

The highs have a smooth presentation. Same with the lows, decay is also nicely extended here. There is sufficient reach in the treble but upper portion can be a bit tame on some tracks. Despite that, clarity is still very good and instruments, especially cymbals, never sounded grainy nor lacking in body.

Soundstage and Imaging:
The stage is averagely sized in both the depth and the width. Imaging has excellent transparency and accuracy. Layering is very good and there is adequate air in between instruments.

Oversampling Mode
Switching to the oversampling mode gives subtle but noticeable changes. The lows become tighter. Subbass decay shortens a little bit. Midbass moves slightly forward with a slightly heavier impact. Mids also become forward and sound a little colder, resulting in partially improved clarity. The highs become more refined and the reach is partially increased. Overall clarity and detail retrieval are also improved in this mode. Soundstage narrows down a bit but the quality of the imaging and other technicalities are retained.

Cayin RU6 in NOS Mode (Discrete R-2R, 250 USD) vs. FiiO KA3 (ES9038Q2M, 90 USD)
The KA3 sports a brighter, more balanced timbre and tonality. The lows in the KA3 is more neutral. Subbass and midbass are more linear, as well as a slightly tighter and quicker attack. The RU6, on the other hand, has tiny bit more rumble quantity. Mids have thicker note weight in the RU6. While the KA3 has a flat approach, the RU6 still manages to exhibit better midrange clarity. The KA3 has more body in the highs, as well as slightly better reach. Level of decay is extremely close, but the RU6 has a small edge. Imaging is clearer and has better resolution in the RU6, but the KA3 has more space in the soundstage.

The R-2R digital to analog converter has been around for ages now. It has been implemented in a few digital audio players recently, but never seen before in a dongle form factor. Cayin made a very bold decision when they launched their very first dongle, and they have made it unique and extra special in a way that anyone would want to try it immediately when they see the specsheet. The RU6 may not be the most portable dongle due to its size, and can be quite tough to acquire due to its price, but for the sound, it is surely one of the best.

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