Over the last few years, we’ve seen DAC dongles and portable DAC/Amps explode into the audio world, seriously elevating the level of convenience for audiophiles to enjoy their sonic pleasures anywhere. We’ve seen some impressive units take over the scene—some claiming true desktop sound on the go, others boasting ultra convenience. Cayin has established itself as a powerhouse in the DAP and amplifier space for many years, with the N6iii being one of our most popular DAPs and the HA amp series a community favorite—not to mention their $7,500 flagship masterpiece, the Soul.
We just got their newest offering in stock: the RU9. RU9 is a portable DAC/Amp with tubes, multiple filter options, and… MagSafe capability? It’s only been in the office for a few days, but I finally managed to fight everyone off and get some extended listening time—and it seriously impressed me. In this article, we’ll break down what makes the RU9 so special and why I think it’s one of the best portable units you can get your hands on today.
Build and Design
The RU9 has a pretty sleek design. It’s lightweight for its size, though not exactly a small DAC dongle like we’ve seen from iBasso or Astell&Kern (think DC07 Pro, DCE/Nunchaku, or HC4). But that doesn’t seem to be what Cayin is going for here. The RU9 features a rectangular build: about 4 inches long, nearly 3 inches wide, and roughly half an inch thick. It kind of feels like a wider iPod. It’s super lightweight, but a bit too large to qualify as ultra-portable. That said, it’s still very portable and can easily fit in your pocket.
On the bottom of the unit, the RU9 has two output jacks: a balanced 4.4mm and a standard 3.5mm, along with a coaxial output on the far right. There’s a switch to toggle between battery mode and direct current mode, plus two USB-C ports—one for power only and one for audio/data connectivity.
On the right side, you’ll find the power button and a “Timbre” button, which cycles through the unit’s three sound modes (we’ll dig into those in the sound section). On the left side are the playback controls: play/pause, and track forward/back. The volume wheel sits on the front next to the display, featuring a smooth scroll-style adjustment.
And of course, I can’t talk about the RU9 without mentioning what might be my favorite feature: MagSafe. As an iPhone user, the convenience and compatibility of MagSafe is such a treat. I took our RU9 unit home this past weekend and used it daily—around the house and out on walks. It is a bit bulky to have on the back of your phone, but with an L-shaped USB-C cable, it offers a new kind of convenience that’s honestly just fun to use. Sure, there’s a practicality to pocket-sized DACs, but MagSafe just feels right. Cayin is innovating here in a really cool way, and I hope we see more of this kind of integration across other brands in the future.
Sound
I'm going to try and be analytical and objective here, but as always, let me get my personal bias out of the way first: I really enjoy the RU9. I especially appreciate its MagSafe convenience and portability. It sounds great, and while I wouldn’t call it my all-time favorite portable DAC purely in terms of sound, it's seriously impressive and emulates a true desktop setup remarkably well.
For my testing, I used either my iPhone 16 Pro or MacBook as the source, streaming from Apple Music. I listened to Xenns Tea Pro, ZiiGaat Arcanis, and Thieaudio Valhalla, all paired with Eletech Baroque ear tips. I also spent some time with the HiFiMan Arya Unveiled. With that out of the way, let’s dive into the sound.
The RU9 features three distinct sound modes: Classic (C), Modern (M), and Solid-State (this option on the device looks like a 0). Solid-State does exactly what it says: it bypasses the tubes to deliver a cleaner, more reference-oriented sound. Classic provides more of a stereotypical tube signature: warmer, more musical, and incredibly engaging. Modern is a hybrid of the two, delivering technical accuracy with a slight warmth. It’s a great middle ground. Each filter has its own appeal depending on your IEMs, music genre, or personal preference. Personally, as a self-proclaimed tube fanboy, I spent most of my time on the Classic setting.
Sonically, the RU9 is impressive, and it's got solid power, too. For a device with tubes, it leans surprisingly neutral and clinical, especially in Solid state or Modern mode. The Classic setting brings warmth, but it’s not as lush as something like the HA-2A or the Nunchaku. Instead, the RU9 balances technical precision with just enough musicality. It delivers a large soundstage and impressive detail, helping bring out the best in your IEMs.
While I did test the RU9 with headphones like the Arya, it shines most with IEMs. It drives them beautifully and with authority. What I love most is that the RU9 doesn’t dominate the sound. RU9 lets your IEMs do what they’re designed to do. With its natural, laid-back presentation, it highlights the unique qualities of each set rather than coloring the output too much.
In short, the RU9 handled everything I threw at it: budget sets and multi-thousand-dollar flagships alike. It scales beautifully, making it an ideal all-around portable solution no matter where you are in your audiophile journey.
Comparison - Nunchaku, Earman L-Amp
Comparisons can be tricky—especially when different portable DACs and dongles are clearly aiming for different things. I picked two other tube dongles to compare here, despite the big differences in presentation and purpose between them.
Compared to the Nunchaku, the RU9 has a more transparent and reference-leaning sound. Nunchaku leans heavily into warmth and gives you that classic tube sound many people expect. However, the RU9 offers noticeably better build quality and has no microphonic issues. Nunchaku’s biggest drawback is its tube ringing, which can happen if you're moving around or the device gets jostled in your pocket. While the Nunchaku is incredibly portable and compact, that sensitivity makes it better suited for stationary listening—like at a desk or while relaxing. If you're after the most “pure” tube sound in a dongle and plan to use it while staying put, Nunchaku is a solid option. But if portability, usability on the go, and convenience are key for you, the RU9—with its MagSafe design and robust construction—is the better fit.
The EarMen L-Amp is probably the closest competitor to the RU9 in terms of overall design and tuning. It also has a warmer tone but with a more incisive edge, similar to RU9. Both use a rectangular form factor, but the L-Amp is slimmer and lighter. It’s also the more budget-friendly option, offering a streamlined tube sound for listeners who want simplicity. That said, the RU9 outshines the L-Amp with its extra features—like selectable sound modes, MagSafe compatibility, and superior overall sound quality. The L-Amp is a great unit and has been a hot item, but if you’ve got an extra $100 in your budget, I’d confidently recommend the RU9.
The Bottom Line
The RU9 is, in my opinion, a truly market-breaking device, and I think we’re going to see it become a popular choice for the foreseeable future. It’s versatile in both power and sound signature options, and it stands out with its unique design and MagSafe integration. It performed beautifully at my desk during work hours and was just as easy to use on the go—whether on walks or doing chores around the house.
Practical, powerful, and genuinely fun to use, the RU9 delivers excellent sound that will appeal to tube lovers while still offering a solid-state mode for those who prefer a more reference-style presentation. It’s a great fit for just about anyone in the audiophile space.
If you have any questions about it, hop into our live chat or send us an email—we’d love to talk more and help you decide if it may be right for you.
