The Superdongles: Cayin RU7 and L&P W4

Cayin RU7

I have a real soft spot for Cayin, even though I haven’t owned a Cayin music player since my very first DAP, the Cayin N3, several years ago now. I briefly flirted with Cayin’s RU7 predecessor, RU6, given my preference for ‘analogue’ R2R DACs, but found it redundant alongside the more powerful R2R DAPs I used at the time (and still do), nor the most resolving dongle I’d heard with my IEMs. 

When Cayin first introduced its N7 DAP earlier this year, I was intrigued by the inclusion of a discrete 1-bit (DSD) DAC in a portable player, a first of its kind. Well, Cayin has done it again, only this time shrinking its 1-bit DAC design even further for the dongle format. 

It’s a sign of the times that you can now get native DSD audio up-sampling from a low-power portable dongle the size of a matchbox – a feature that was previously the preserve of some serious desktop computing hardware. 

RU7 ships in an small, understated box with a matte black satin finish and a glossy silkscreened image of the dongle from two different angles. Inside the box you’ll find the dongle in a custom foam tray, and separate tray with a USB-C to C cable and USB-C to A adapter. 

There is no USB-C to Lightning adapter or cable included, Cayin opting to sell its $20 CS-L2C cable separately for some reason. Cayin does include a protective green leather case as standard, however, along with two matching leather stick-on magnetic patches to connect the dongle to a smart device in case you want to stack them.   

Unlike the chiselled, angular W4, RU7 is a more ‘conventionally’ rectangular design, coated in a silky-smooth matte-black aluminium finish with a glossy glass top. A small OLED screen is built into the glass panel, offset to the left of the player rather than centred in the frame.

There are three slightly raised buttons on the topmost long side of the dongle, two volume toggles and a menu/function button. Outputs include 3.5mm single-ended and 4.4mm balanced headphone ports, which double as true line-out ports for connecting RU7 to external amps without double amping.

One usability issue I have with the input buttons is that they’re flush with the case, and although the case is slightly indented around the buttons, I often end up lowering o raising the volume when I want to do the opposite, or accidentally changing the volume when I want to change settings. It’s not a biggie, but I find W4’s ALPS wheel more user friendly and tactile.

Overall RU7 is really well-made, and looks very classy in its green leather case. The screen is brighter than on W4, though information on the squashed screen format isn’t as easy to read as W4’s elongated 2-line display. These are all hair-splitting differences, though, with both dongles being best-in-class in terms of form factor, usability and design. 

Specs

  • DAC: 1-bit discrete resistor fully-balanced 4-channel DAC
  • Volume control: discrete resistor 100-step linear volume control
  • FPGA: No
  • SNR: 114dB (3.5mm) 112dB (4.4mm)
  • Power output: 160mW (3.5mm) 400mW (4.4mm)
  • THD+N (32-ohm): 0.006% (3.5mm) 0.008% (4.4mm)
  • Dynamic range: 115dB
  • Screen: 0.91-inch OLED
  • Audio formats (PCM): 16/24/32-bit 44.1-384KHz
  • Audio formats (DSD):  DSD64-256
  • Dimensions: 66mm x 24mm x 12mm
  • Weight: 25g

Settings

  • Gain: choose between low and high gain, for sensitive to less sensitive loads.
  • All to DSD: choose between up-sampling PCM audio to DSD64, 128 and 256.
  • Output: choose between PO (headphones out) and LO (line out).
  • Backlight: choose between permanently on, to auto off in 10-second increments between 10 and 60 seconds.

Notable features

World’s first dongle-based 1-bit discrete resistor DAC. Made up of 128 pieces of 0.1% 25ppm high precision thin film resistors, the custom-made 1-bit DSD DAC features an All-To-DSD engine that up-samples incoming PCM signals to DSD64, DSD128 or DSD256. The higher the setting, the more precise the conversion with higher resolution. The up-sampling level also has a perceptible effect on tonality. 

Since the DAC is based on 1-bit topology, all incoming PCM signals must be converted into DSD format for playback . This is the key difference between the DACs in the RU7 and W4.

Parallel dual phone amplifiers. Cayin has implemented dual parallel amplifiers in the RU7, boosting amplification current by as much as 80% from the RU6. They’ve done this without significantly increasing the noise floor of the amplifiers, resulting in a near-silent noise floor with all but the most sensitive IEMs. 

Shared line out ports. It’s rare to find a line out function in a dongle because of the limitations on the hardware needed to provide a separate line out circuit. Cayin circumvented this limitation by folding line out functionality with the headphone ports. 

This does limit line out quality and output levels – 1.2V for single-ended and 2.4V for balanced (compared to typical 2V and 4V outputs in dedicated DAP line outs), but it’s apparently a user-requested feature and so Cayin made it happen. 

Be warned – selecting line out is not automated, and the dongle won’t switch back to headphone mode after a line out session, so be careful when you use this feature to switch back to PO, especially when using sensitive IEMs. 

Discrete digital volume array. RU7 uses three banks of resistors and switching relays to provide 100 steps of precise volume increments.

Separate digital and analogue circuits. The digital and analogue sections of the RU7 are split into two separate PCBs, shielding the analogue amplification signal from digital clock and DSP noise. 

Continue to RU7 sound impressions…

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ABOUT AUTHOR

Picture of Guy Lerner

Guy Lerner

An avid photographer and writer 'in real life', Guy's passion for music and technology created the perfect storm for his love of portable audio. When he's not playing with the latest and greatest head-fi gear, he prefers to spend time away from the hobby with his two (almost) grown kids and wife in the breathtaking city of Cape Town, and traveling around his native South Africa.

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