STEREO GUIDE verdict
+ Natural, powerful sound even with sophisticated hi-fi headphones, even on cell phones
+ even balanced wired receivers can be connected
+ useful display
+ magnetically fixable on the back of cell phone cases
- goes to Lasen the battery life of the smartphone
Practice / Connectivity9.5
The Cayin brand is actually known for its tube amplifiers. But the Chinese manufacturer, which is currently celebrating its 30th anniversary, has meanwhile also made a name for desktop and especially mobile audio at the highest level. A particularly interesting audiophile gadget is the Cayin RU7, which has just been introduced and has already been put through its paces by us in a review. This USB mobile headphone amplifier has just the dimensions of a pack of gum. But it is supposed to perform like a big one and thus spur even a high-quality passive headphone to musical peak performance. No matter how compact the USB DAC/Amp dongle may be. In terms of price, it definitely competes with the heavyweights among mobile headphone amplifiers, which are already not so easy to put in a jacket pocket, let alone a pants pocket.
To ensure that the tiny DAC doesn’t get lost in the process, its designers have come up with something. But before we dive deeper into the amazingly sophisticated technology of the Cayin RU7, we would first like to discuss the technical benefits. Finally, this high-quality vest-pocket digital-to-analog converter is also very interesting for many music fans who can do absolutely nothing with classic tuning table HiFi jargon. Some simply expect more than the headphone outputs of smartphones, tablets or laptops are capable of. Bluetooth is also limited in this case, because the resolution does not meet the extreme expectations of many Hi-Res fans, especially since the integrated amplifiers of wireless headphones do not have a high resolution. Not to mention the cost of such devices.
Small, fine upgrade for the smartphone
With the Cayin RU7, you can not only elicit more dynamics from a wired headphone than with a cell phone. Its sophisticated transducer technology, in conjunction with the powerful output stage, also promises more resolution and precision, especially in conjunction with Hi-Res audio. And let’s not forget: Many headphone aficionados swear by the sound benefits of balanced headphone connections. This is not possible at all with a smartphone, tablet or PC. There, the 3.5 mm mini jack has prevailed – partly via adapters, like in the iPhone. The Cayin RU7 also has a corresponding port. But it also enables the balanced connection via a 4.4 mm jack. This increases the flexibility and sound potential of a high-quality wired headphone in equal measure.
Tiny with format
The D/A converter supports FLAC, WAV, AIFF, ALAC, APE, WMA Lossless, DSF and DFF lossless file formats. In addition, the RU7 copes with MP3, WMA, Ogg or AAC. The maximum resolution is 24 bit/384 kHz with the PCM format, DSD256 can also be played back with it. By the way, iPhones now also support FLAC audio playback without additional apps. A very convenient way, assuming fast data connection, is to access these files via its iCloud storage.
But back to our test object. The extremely compact design of Cayin’s DAC dongle, which weighs 25 grams and is only 1.2 centimeters high, left no room for a battery. The RU7 scrounges its operating voltage from the smart device or computer. Therefore, its developers paid attention to the highest efficiency, but you can already notice from the waste heat even at the USB connection that some current is already flowing… Cayin specifies a power consumption of 100 to 110 milliamperes.
For iOS and Android smartphones and tablets
You can use the mini D/A converter with Android devices and iPhones. However, the latter requires an optional Lightning adapter, which Cayin offers under the name CS L2C for 24 Euros. A short USB-C connection cable and a plug adapter from USB A to USB C for laptops and desktop PCs (Mac OS or Windows 7/8/8.1/10) are included with the RU7. But the coolest addition is green leather: the cover makes the DAC/AMP look even classier and protects its shiny surface from scratches.
An integrated magnet in combination with adhesive metal plates allows the smartphone to be fixed to the back of the smartphone or its case. The small monochrome OLED display with a resolution of 128×64 pixels can be read through a cutout on the top. The buttons on the back for volume control and switching the oversampling modes of the Cayin RU7 can be operated through the cover and are highlighted from the leather for recognition.
The display proved to be useful in the review. The feedback is so much better than many other DAC dongles, which only indicate the operating status via LEDs. The Cayin display shows the sampling frequency of the input audio signal and the volume level, as well as the oversampling mode, which can be controlled via a dedicated button.
Convertible D/A conversion
Non-oversampling (NOS-DA) mode feeds the digital audio data directly to the D/A converter without conversion. In contrast, the oversampling mode performs an upsampling that upconverts the sound files to the maximum possible 384 kHz. The finer resolution speaks for this solution. One argument against them is that jitter or rounding errors could creep in. This mainly affects songs ripped from CD, because their sampling frequency is 44.1 kHz – i.e. not an integer divisor of 384 kHz.
As far as conversion is concerned, Cayin makes an astonishingly high effort, especially considering the extreme compactness. For each of the two stereo channels, the RU7 uses four 1-bit converters in differential mode with a downstream R2R network of four groups of 32 discrete thin-film resistors each. This is particularly unusual because even most home hi-fi DACs and CD players simply rely on a highly integrated chip for D/A conversion. With this effort, Cayin aims to increase conversion precision.
The brand from the coastal province of Guandong already recently relied on this recipe for the 2,000 euro N7 high-res player. But it can’t even begin to compete with the tiny RU7 in terms of miniaturization and lightweight construction. The very fine volume control with 99 levels built with discrete resistors is also one of the positive consequences of the comparatively high effort. For connection to the HiFi system, the analog stereo output can be switched to fixed output level “Fixed”.
Surprise in the listening session: The tiny one sounds like a big one
In the listening session, we were curious to see what the peck would do on our iPhone. With the Lightning adapter, it offered effortless plug & play. But for the RU7, we had borrowed a headset that would make it anything but easy for him. The Focal Clear is a high-resolution, ultra-precise diva that places very high demands on the headphone amplifier. But Cayin’s flyweight not only really breathed life into it. Besides the dynamic qualities and the easily attainable listening level beyond integrated output stages of smartphones or tablets, tonal balance and precision were also convincing.
As for the classification of the playing pleasure and the maximum volume, one should consider the Focal over-ear headphones’ impedance of 55 ohms. This is actually too high for mobile use. For listening to music on the go, 32 ohms or even lower is considered desirable. So when the Clear really takes off on the Cayin RU7, with impulsive drive and gripping dynamics, that already says a lot about its sense and usefulness. Such playing pleasure could not even be achieved with standard 32-ohm mobile headphones on smartphones. Thus, the RU7 not only gets more out of the usual on-the-go solutions. This means that you can use your hi-fi headphones, which were originally intended for your living room, when traveling and have access to a wider range of headphones.
Not affraid of big headphones
The deep, rich bass reproduction also fits into this thoroughly positive picture. With a headphone like the Focal Clear on a smartphone with a tiny dongle, that’s quite an announcement. In this respect, it is unnecessary to mention what is possible on the Cayin RU7 with a high-quality low-impedance in-ear, such as with the Beyerdynamic Xelento 2. We reviewed the wireless version of the handset from Heilbronn. But it can also be operated passively without its electronics module. That’s where the tiny Cayin DAC really gets things going.
Conclusion and alternatives to the Cayin RU7
With the Cayin RU7 we open a new category of headphone amplifiers/DACs. There, it establishes itself surprisingly high on the score scale, where we had many headphone DACs known to us in mind when evaluating it. These include the Aune BU2, which is a bit cheaper, but much larger and thus less mobile than Cayin’s DAC dongle.
Cayin RU7 technical data
- Manufacturer’s suggested retail price: 350 Euro
- Type: USB headphone DAC
- Dimensions (W x H x D): 6.6 x 1.2 x 2.4 cm
- Weight: 25 g
- Special features: Powered by USB, OLED display, leather case, magnetic fixation on smartphone case by stick-on metal plates.
- More at: cayin.com