The Cayin RU9 is a revolutionary portable tube DAC/amp, defying expectations with its surprisingly lightweight and compact design. Weighing only around 155g, it’s significantly smaller than its predecessors in the RU family, yet boasts impressive power and features, including a built-in battery and Bluetooth connectivity. Its secure MagSafe connection ensures effortless integration with smartphones, making it the perfect companion for on-the-go audiophiles. Despite its diminutive size, the RU9 delivers exceptional audio performance, leveraging dual AKM AK4493SEQ DACs and a unique tube configuration for a rich, detailed listening experience.This review delves into the RU9’s performance, examining its sound signature in both solid-state and tube modes, its impressive power output capable of driving demanding headphones, and its battery life. We'll compare its capabilities against other leading portable DAC/amps in the market, assessing its strengths and weaknesses to determine whether it truly earns its place as a top contender in the portable audiophile landscape. Discover if the Cayin RU9's combination of portability, power, and sonic excellence justifies its price point and whether it lives up to the hype.
Pros And Cons
- Battery-powered
- Bluetooth connectivity
- Dual Gen 6418 tubes
- Inferior performance compared to RU9 (at least 10% worse)
- Lightweight (155-156g)
- Bluetooth DAC/amp functionality
- MagSafe connection for secure attachment to phones
- Compact and discreet USB-C cable included
- Powerful: 310mW per channel at 32 ohms (single-ended, high gain), 620mW per channel at 32 ohms (balanced, high gain), up to 1000mW per channel at 32 ohms with external power
- High power output even with high-impedance headphones (e.g., Sennheiser HD600)
- No floor noise, even with sensitive IEMs
- Intuitive controls (rotary volume, play/pause, forward/reverse)
- Dual AKM AK4493SEQ DACs
- Uses NP61 tubes (similar to Cayenne N8 MKI)
- Good battery life (4.5 hours in solid state mode, ~3.5 hours in tube mode)
- Option for trickle charging from phone for extended runtime
- Good performance in Bluetooth mode (approx. 90% of wired performance)
- Classic tube mode offers a warm, organic sound
- Modern tube mode offers a balance between solid state and tube sound
- Short cable is prone to RF interference
- Battery life reduced in Bluetooth mode
- Gets hot during use (though max temperature is relatively low at 38°C)
- Powerful, comparable to desktop amps
- Similar sound signature to Cayenne RU9 (especially in classic tube mode), but perhaps more analog and warmer
- Larger, heavier, and thicker than the RU9
- Similar battery life to RU9 in tube mode
Read more: Fiio K11 R2R DAC/Amp Review: A Worthy Upgrade or Redundant Luxury?
Lightweight Design and Functionality
The Cayin RU9 boasts a surprisingly lightweight design, weighing in at approximately 155-156g. This is remarkable considering its size, as it's the largest in the RU family, significantly surpassing the smaller dongle-style RU7 and RU6. Unlike its predecessors, the RU9 incorporates a built-in battery and functions as a Bluetooth amplifier.
Its compact size and secure MagSafe connection to smartphones make it ideal for portable use. Even with the included protective case, the MagSafe connection remains secure. The included USB-C cable is exceptionally compact and discreet, further enhancing portability.
Portability vs. RF Interference
The RU9's short cable, while contributing to its portability, makes it susceptible to RF interference, a common issue with high-performance devices like R2R or tube-based DAC/amps. Using a longer cable would mitigate this but compromises portability.
The 2000mAh battery provides approximately 4.5 hours of playtime in solid-state mode and slightly less in tube modes (around 3.5 hours). Charging from 1% to 100% takes about 1.5 hours using a PD 3.0 charger.
Thermal Performance and Battery Life
As a tube amplifier, the RU9 does get warm during use, but impressively remains below 38°C. This is lower than many tube amps which operate closer to 40°C. The device offers a trickle-charging option via the connected phone to extend battery life.
With trickle charging enabled, the RU9 can operate for significantly longer than 4.5 hours. However, this method also drains the phone's battery, reducing overall playtime (approximately 12 hours).
Sound Quality and Performance
The Cayin RU9 features dual AKM AK4493SEQ DACs, similar to the Cayin N3 Ultra. It utilizes a unique tube configuration (NP61) also found in the flagship Cayin N8, resulting in exceptional sound quality.
In tube mode, the RU9 delivers a warm, organic, and detailed sound signature, particularly in classic tube mode. Solid-state mode provides a neutral, analytical, and highly resolving sound, comparable to top-tier DAC/amps.
Power Output and Headroom
The RU9 delivers impressive power output, rated at 310mW per channel at 32 ohms in single-ended high-gain mode, and double that in balanced mode. With external power, output increases to around 1000mW per channel. This power allows it to drive high-impedance headphones like the Sennheiser HD600 exceptionally well.
Even at high power, the RU9 remains remarkably clean, with no noticeable floor noise. This is consistent across various headphone and IEM impedances.
Controls and Features
The RU9 features intuitive controls including a rotary volume knob (100 steps), play/pause, and track navigation buttons. A simple button allows switching between solid-state and classic/modern tube modes.
The device offers Bluetooth connectivity, including LDAC support for high-resolution audio streaming. USB connectivity provides the best sound quality.
Comparisons with Other Portable Tube DAC/Amps
Compared to the XDuoo XD-05T, the RU9 is smaller, lighter, and more portable, though the XD-05T offers slightly warmer sound. The RU9 provides slightly greater transparency and accuracy.
Against the Cayin N3 Ultra, the RU9 provides a superior tube experience, with a more airy soundstage. Compared to the iFi Hip DAC, it offers more power and a more prominent tube character. Against the Muse HiFi M5 Ultra, the RU9 is considered superior overall (by at least 10%).
Conclusion
The Cayin RU9 represents a significant advancement in the portable tube DAC/amp market. Its combination of portability, power, and exceptional sound quality makes it a top contender. The RU9 excels in both solid-state and tube modes, offering a versatile listening experience.
While slightly more expensive than some competitors, the RU9's superior performance, especially in tube mode, makes it a compelling choice for audiophiles seeking a high-quality portable solution. It is significantly more portable than similar high-power options, making it a strong contender in the portable market.