I analyzed RU6 sound with various IEMs, including Oriolus Traillii which I’m intimately familiar with and use in my critical sound analysis while playing a variety of my favorite test tracks, such as Agnes Obel “The curse”, Sandro Cavazza “So much better” (Avicii remix), C-Bool “Never go away”, Ed Sheeran “Shape of you”, Alan Walker “Darkside”, Galantis “Hunter”, Iggy Azalea “Black widow”, Indila “Boite en argent”, Dua Lipa “Love again”, Counting Crows “Big yellow taxi”, David Elias “Vision of her”, and Michael Jackson “Dirty Diana”. RU6 had about 100hrs of burn in before I started with my analysis.
I found RU6 to have a neutral sound signature with a smooth natural fuller body analog tonality which doesn’t compromise on resolution or retrieval of details due to its lovely treble definition. So, RU6 has a natural wet analog tonality with a touch of organic warmth and very good retrieval of details. Plus, its neutral sound signature keeps the bass and the treble balanced, without any exaggeration. Often, some manufacturers want to sweeten the sound with extra boost in bass or to give higher resolution with extra sparkle in treble. RU6 with many IEMs I tried had a very natural dynamic balance without any exaggerated boosting.
The technical performance, regardless if you are listening to singled ended or balanced outputs, is the same and has a very wide soundstage expansion and nearly 3D holographic imaging. That was probably the first thing that stood out for me every time I listened to RU6, how the soundstage wrapped around me and how well sounds were separated and positioned in space. I found that to be quite impressive considering this dongle has a single ended architecture with a balanced power boost. The impressive vertical dynamics expansion and extra sparkle in treble also helped with layering and separation of sounds, giving more air between the layers.
3.5mm vs 4.4mm.
As I already mentioned, I hear the identical sound sig, tonality, and technical performance. The only difference is in power output where I had to adjust the volume by about 5-6 clicks to match output between single ended and balanced.
NOS vs OS.
I had to listen very close to pick up any difference. With NOS I hear a wider soundstage, literally spreading wider left to right. Also, with NOS I hear a smoother and softer mids/vocals. To my ears, with NOS the sound is a little more relaxed, while with OS it is a bit faster (faster transients) and a bit more aggressive.
Source pair up.
Out of curiosity, I decided to compare RU6 connected to my Galaxy S9 vs connected to other DAPs like Cayin N6ii, Hiby RS6, and even a budget $99 Hiby R2. In my comparison between my Galaxy phone and other two Android DAPs, using HibyMusic app (with Exclusive HQ USB audio access enabled and USB Audio performance mode set), I found the sound to be nearly identical. And, the same with R2, using it as a digital source for RU6 yielded nearly identical sound performance.
USB-C interconnect cable pair up.
One question I have been asked a lot lately was if other usb-c to usb-c interconnect (IC) cables make any difference in sound with RU6. I tested and compared stock Cayin usb-c cable vs DDHiFi, OE Audio, and even Lotoo and L&P cables. In every case I found about 130mA current draw and the same sound in comparison to Cayin stock cable. If you want a stiffer cable, go with OE Audio. If you need right angled connector cable, DDHiFi offers that. Otherwise, no need to upgrade since stock cable does its job.
External AMP pair up.
RU6 doesn’t have a dedicated Line Out. After all, this is a dongle intended for a portable use where you don’t expect to drag your smartphone and a dongle along with an external amplifier. But some people asked me how will it pair up with Cayin C9 portable dual NuTube amp, and if I hear any distortion as a result of double-amping. I assume these audiophiles are looking to use it in their desktop setup with RU6 connected to laptop. As I already mentioned, for the best audio quality it is recommended to keep the digital volume of the source connected to RU6 at the max level. Which brings me to the question of C9 setup, either Line Input or Pre-Amp input?
In my testing I was using Galaxy S9 with HibyMusic (USB Audio Performance mode enabled and USB Audio volume locked at max setting) and a few headphones, including ATH-R70x (open back, 470ohm). For Line Input mode, I set RU6 to its max volume (100) and was controlling the output volume from C9. For Pre-Amp Input mode, after enabling it on C9, I was using RU6 volume control.
The difference in sound between these two modes is literally night’n’day. In Pre-Amp mode the resolution was low, literally felt like bit resolution was reduced. The soundstage was narrower, and changing volume from RU6 was slower and you have to deal with short mutes every 10 steps. In Line Input, you are dealing with max digital volume (S9), max analog volume (RU6), and adjusting the output using smooth volume control of C9, yielding a dynamic, resolving, layered, fuller body sound without any hint of distortion. That is a setup I recommend, especially for demanding headphones.