Cayin RU9

Introduction to the Cayin RU9 Review

Cayin is a Chinese manufacturer of audio components, mostly known for its tube-based designs; however, they also have plenty of non-tube offerings in their range, like the N7 DAP or RU series of dongles, up until the RU9, of course. Cayin’s products cover a wide range of price points and types of devices. My first introduction to Cayin was trying the C9 at Audio Video Show Warsaw 2021, together with the N8ii DAP and Noble Audio Kublai Khan IEMs. I was stunned to say the least, and that experience immediately solidified Cayin as one of my favorites at that show. Cayin also offers a wide range of full-size tube stereo amplifiers. Since I only review headphones and headphone-related gear, I am not very familiar with their offerings in that range, but positive impressions from friends make it seem like an option worth trying.

Another important aspect of Cayin’s product range is their full-size headphone amplifier range. I don’t recall ever listening to a bad one, from the HA-1A, through HA-300MK2, all the way to the latest constructions like the Cayin Soul 170HA. It’s important to note those achievements, because I consider the RU9 to be a product that bridges the gap between the portability of their mobile devices and the performance that seems to go way beyond that, crawling into the full-size territory. In my opinion, reviewed Cayin RU9 sets a new standard for mobile DAC/Amps thanks to its form factor, functionality, power, and sound. It’s a fascinating device, and ever since I got to try it at High End Munich 2025, I knew I needed to review one. Let’s get right to it.

Packaging

The unboxing experience of the tested Cayin RU9 covers all bases that are necessary with this kind of product. The packaging itself is not over the top in any way, but it’s neat and elegant, with a design closely reminiscent of Cayin’s other portable offerings. What’s important is what’s inside. Apart from the RU9 itself and the usual paperwork, there is quite an array of essential accessories, which, in this case, are essential for a good user experience. There is a leatherette case with magnets installed, protecting your device from scratches and maintaining the MagSafe functionality. It also seems to provide a slightly better grip on the device, which is quite important, seeing how often it ends up in your hands during use. 

Among other accessories, you will also find a magnetic ring with double-sided tape that you can stick on a device without MagSafe functionality. It’s a good nod towards versatility, and I think the magnetic attachment is one of the RU9’s best features. If I had to keep only one accessory, however, it would be the 90-degree USB-C-to-USB-C cable. It is the perfect pairing for a device that attaches to the back of your phone – all the straight-angled cables just can’t compare to this slim, barely visible cable when it comes to the comfort of use. It’s quite crazy to see how much such a seemingly small addition can change, because it changed the way I view comfort when using the reviewed Cayin RU9. Great addition!

Design, Build Quality

Cayin RU9 is noticeably larger than your usual dongle DAC/Amp. However, it more than makes up for it in form factor. A MagSafe device like this has become my favorite way to listen to music with a portable device, apart from using a DAP. Comfort-wise, it easily beats any dongle or mobile DAC/Amps like the EarMen Angel. The RU9 is not very heavy – at 150 grams, it doesn’t add that much to the mix, but the device that it gets attached to will be bulkier – now your phone won’t fit as easily in your jeans pocket, but still fit in your coat pocket nicely. The chassis is CNC-machined from aluminum and gives a very solid impression – there is no “give” anywhere on the flat chassis, and the parts are fitted very tightly. 

Reviewed Cayin RU9 has a display with all the necessary information present – sampling rate, volume, timbre mode, battery, etc. It is also used to change settings with the use of the TIMBRE button, which I will mention later. The volume knob, in my opinion, is one of the weaker parts of the system. It’s a stepped encoder meant to adjust the volume first and foremost, as well as change the settings. For the latter, it’s completely fine, with each distinct click taking you up or down in the settings, but for the volume control, not so much, as you have to wiggle your finger quite a bit to adjust the volume by 20 steps. However, I like the golden accent next to the volume knob. Below that, you will find the tube vents. The tubes light up when you plug your headphones or IEMs in. Cool!

At the bottom of the device, you will find all the ports. Two analog outputs, 3.5mm and 4.4mm that can also act as line outputs, two USB-C ports, one for power and one for data, and a coaxial output. Above the power port, there is a switch between DC and Battery mode. The DC mode changes quite a lot in the mix, because it raises the maximum power output from 420 mW at 32 Ohms all the way to 1000 mW at 32 Ohms, taking a decently powerful IEM driver and turning it into a device that can power many modern full-size headphones. I have done some listening in that configuration as well, and indeed, the RU9 has what it takes to make headphones like the HEDDphone D1 sing.

On the left side of the tested Cayin RU9, you will find the previous/pause/next buttons, which got the least use in my case. On the right side, there is the power button and the TIMBRE button. The power button, to the great surprise of many, is used to power the device on, as well as turn the screen on or off. The TIMBRE button is way more interesting. There are three timbre options to choose from, similar to something like the N3Ultra – Modern Tube, Classic Tube, and Solid State. I am surprised to report that I don’t think it’s possible to pick a clear favorite, but I’ll explain more down the line. For some extra functionality, you can press and hold the TIMBRE button to access the settings. There, you can pick your source, inputs, outputs, gain, USB version for your console, as well as some display options. There are no filters or EQ profiles built in, and I think that’s completely fine, given how good the timbre modes are.

Tech

Cayin RU9 features one of XMOS’ latest creations, the XU316 decoder. Also, interestingly, this device features Bluetooth 5.1, as if the seamless USB-C connection wasn’t enough! That is handled by Qualcomm’s QC5125 chip. Available codecs include LDAC, aptX HD, aptX Low Latency, as well as SBC and AAC. The DAC chips used for this construction are dual AKM AK4493SEQ, able to handle DSD up to DSD512 and PCM up to 32bit/768kHz. The amplification circuit is based on a total of 6 Toshiba 2SK209 JFETs and TI OPA1662 op-amps. And finally, in my opinion, the star of the show – KORG’s 6P1 Nutubes. Those components are used in different ways depending on your choice of timbre setting, making them way more than just digital EQ filters. 

The tube implementation is particularly interesting here. Reviewed Cayin RU9 is designed to mitigate vibration and shock as much as possible, leaving the usual unpleasantries of tube use behind. The tubes don’t hiss or crackle when warming up. One gripe I have with the RU9 is its battery life, and I think this is the weakest point of the device – you can get 4 hours with change at best, and above 3 hours when using the balanced output. Battery life also depends on the volume and impedance of headphones, so your mileage may vary, but I’d love to see it go higher than that, even if it means a heavier battery.

The sound of the reviewed Cayin RU9

This is the best and the most important aspect of the Cayin RU9 in my humble opinion. Remember how I said that it’s impossible to pick a favorite timbre setting? Well, it’s true, because each IEM or headphone is better suited to different settings. Given how easy it is to just switch, you can even use different songs for each setting. All of them sound different; the differences are quite significant, and down the line, I will go through each. The sound performance of the RU9 has a common denominator – every preset shows great handling of dynamics, a balanced timbre, and impressive separation. All of that, combined with the easy customization of sound through DC and Battery mode, as well as the timbre modes, of course, makes it hard not to call the RU9 my daily driver from now on.

Classic Tube

This is the mode that I found the most enjoyable with headphones like the HEDDphone D1, as it brings some lushness and a slightly laid-back character into the mix. I would describe the music as the softest in this setting, with the bass hits and subbass rumble losing a bit of sharpness, but remaining more prominent and present than with the Solid State mode. That being said, the balanced nature of the sound is maintained, just softened overall. Another aspect of the sound that seems a bit tamed is the highs. They are the least lively and sparkly among other timbre modes. They still carry plenty of information, it’s just not thrown into the front row as much. The mids are more intimate, with textured instruments and voices becoming lush, inviting, and slightly warmer. It’s a great mode to be used with neutral or analytical headphones to add some richness to the mix, but it also works great when you want to double down on the warmth.

Solid State

This mode is the closest to neutral, adding balance to warmer headphones and IEMs. It equips such devices with prominent dynamics and textures, and overall makes for quite an even performance. I wouldn’t call this mode entirely transparent or neutral, though – maybe it’s the fact that I’m comparing it against two modes that color the sound in their own way, but with headphones like the D1, I felt like the highs stood out a little bit compared to the rest of the mix. Apart from that, it is a largely neutral presentation, filled with micro-detail. The sense of space and air is especially prominent here. Switching to this mode from the Classic Tube mode is like removing a tiny bit of fog from your glasses, but when used with neutral headphones and IEMs, I miss the bit of lushness that the Tube modes have to offer. If your IEMs or headphones suffer from slight muddiness that you want to help eradicate, or if you are someone focused on neutrality and transparency, you will find yourself using this mode often.

Modern Tube

The Modern Tube mode is something of a mix between the two previously described modes. It is the mode where the total frequency extension shines the most, and I think it’s the mode that can be described as the most universal. It’s a mode where the highest of highs and the lowest of lows are accentuated, but also, interestingly, the vocals specifically seem to be put more forward. They are not overly intimate or in-your-face – they sound larger and more prominent. That being said, the Modern Tube mode doesn’t output as much warmth as the Classic Tube mode, and doesn’t lose the sharpness of the lows and sparkle of the highs, at the cost of a bit of lushness and richness. It is also more engaging and universal than the Solid State mode, but it is not as neutral or analytical, if that is what you’re looking for. Overall, I would consider the Modern Tube mode to be a good match for most listening devices and tracks, and it’s a good starting point. Want more warmth and coziness? Go Classic. Want more neutrality? Go Solid State.

Pairings

HEDDphone D1

I decided to take advantage of the power output of the Cayin RU9 and test it in DC mode with something that is next in line for a review – the HEDDphone D1. It’s a largely neutral headphone with professional use in mind, so I consider it a perfect companion to test what the RU9 has to offer. And, just like I thought, it was a great match, putting every timbre mode’s characteristic on display. I am often surprised by how much detail retrieval this headphone is capable of, and I am glad to say that the RU9 does not hold it back in any way. I especially enjoyed the HEDDphone D1 in the Classic Tube mode, making the listening sessions more relaxed, and more suited to my taste – I’m not someone too fond of crystal clear neutrality. Great pairing, no matter the used timbre mode or the music you choose.

Craft Ears Omnium

The Omnium has to be one of my favorite IEMs of all time. Its sound signature is largely similar to what the Modern Tube mode has to offer – amazing speed and dynamics, but the love for an engaging midrange is also there. This pairing has been my pairing of choice for some time now when it comes to IEM listening. It’s truly a perfect match, and each of Omnium’s strengths is accentuated by what the Modern Tube mode has to offer. The soundstage is vast, and the instruments placed on it are lifelike and dynamic, despite the fact that I wasn’t using the RU9 in DC mode – I wanted to save some battery for on-the-go listening. Overall, this is my favorite IEM and DAC/Amp pairing right now.

HiFiMAN Svanar

This IEM shares some traits with the beloved Omnium and is also one of my all-time favorites as far as IEMs go. However, this time, there is more warmth and richness in the midrange. I wanted to further the speed and clarity in the mix, and the Solid State mode was perfect for that. The warmth wasn’t removed at all – god forbid – but the dynamics were even sharper and clearer for the entire mix. Imagine an intimate vocal performance, but served with greatly refined dynamics, all plated up on a vast soundscape. With the Classic Tube mode, things got a bit too dull in the highs for my taste, but still remained palatable, and I feel like the vocals are already accentuated enough. That’s why my pairing of choice for the Svanar would be the Solid State mode.

Comparisons

FiiO BTR17

Two mobile DAC/Amps, with completely different form factors. Both are powerful, Bluetooth-capable, and with a volume knob. Both do their own things right and are simply amazing at their respective price points, but I have a clear favorite here.

The tubes, timbre modes instead of EQ, and a shockingly convenient form factor make the RU9 the winner of this showdown. I have enjoyed my time with both, but the simple flexibility and the MagSafe features made me come back to the RU9 more often. The sound also feels more refined and detailed overall. Thanks to the customizability options offered by the RU9, it felt like the more versatile contender.

The BTR17 is no slouch either, with a clearly superior battery life, a smaller form factor and less than half the price of the RU9. But even in a dollar-for-dollar comparison, I prefer the RU9, and I think it redefines what mobile music devices should be like.

Cayin RU9 – Summary

Cayin RU9 became one of my favorite mobile offerings the moment I came into contact with it at High End Munich 2025. After some testing, I can comfortably say that it is one of the best mobile DAC/Amps currently on the market. Despite costing 499 USD, which is not a small amount, it still manages to punch way above its price point. 

One significant downside of the RU9 is the battery life – 3 to 4 hours is simply not enough. But during that time, the RU9 proves itself to be a perfect match for any IEM and most headphones on the market, thanks to simple but effective customization options via the timbre setting, as well as a significant power headroom of 1000mW at 32 Ohms. Add to that the MagSafe compatibility, lightweight yet solid construction, tremendous functionality, and most of all, amazing sound, and there you have it – one of the strongest contenders for mobile DAC/Amp of the year.

Wildly Recommended.