Review: Aune S9c Pro Reference DAC Headphone Amplifier

Review: Aune S9c Pro Reference DAC Headphone Amplifier - The S9c Pro has headphone outputs of single-ended 6.35mm, balanced XLR and 4.4mm, compatible with all kinds of headphones and IEMs.
5/5 - (1 vote)

Even if “Aune” could be the title of a sci-fi series from a streaming service, The Aune S9c Pro (price: 749 euros) is a very earthly DAC and headphone amplifier. This test report should highlight whether there are galactic features, spacey data, and stellar sound experiences.

For the test I had the Aune S9c Pro in the black version; depending on your preference you can also opt for silver. The case (28.8 x 21.1 x 6.3 mm, WxDxH) of the S9c Pro, made in China, has side walls that are slightly slanted inwards and completes a gallant swing with its cover plate. A screen is housed centrally “under the dome, ” providing information about the status and settings. On the left are the connections for headphones and the IR sensor for the small remote control supplied; on the right, a large rotary encoder with a push function.

The Aune S9c Pro offers a richly laid table for headphone connection formats. Of course, there is a classic 6.35 mm jack socket, which, as is well known, also accepts 3.5 mm headphone plugs using the ubiquitous adapter. This format is unbalanced. A four-pin XLR socket and a Pentaconn TRRRS (“Tip, Ring, Ring, Ring, Sleeve”) are available for balanced connections. If you don’t know this, It is a connection format developed for mobile balanced headphone connections, primarily aimed at the Japanese market.

The actual headphone amplifier in the Aune S9c Pro is fully discrete and delivers up to 5780 milliwatts (32 ohms, balanced connection) depending on the impedance of the headphones and the signal output. A distortion (THD+N) of 0.00085% is a decent value, and the noise is also very presentable at 7.71 µV. Two JFETs are used in the analog input stage per channel.

Of course, the signals go not only to headphones but also to devices with a line-level input. This can be done unbalanced with a pair of RCA sockets ( cinch ) or with the two balanced, three-pin XLR sockets. On the input side, the Aune S9c Pro receives its signals exclusively in digital format. That’s a shame since the device could be used as a headphone amplifier in an analog environment. The DAC accepts AES3 (AES/EBU), S/PDIF electrical/coaxial or optical via Toslink fiber optics, USB connections via a USB-B socket, and Bluetooth, for which a small stub antenna can be screwed.

AES3 and S/PDIF enable resolutions of up to 24 bits and sample rates of up to 192 kHz, while quantization of up to 32 bits and sample rates of up to 768 kHz are possible via USB. In addition to PCM, bitstream reception is possible via USB up to DSD512. In the case of an MQA feed, the Aune S9c Pro recognizes this and notes it with the corresponding abbreviation on the display. In addition to SBC, AAC, and aptX, Bluetooth can decode aptX HD and Sony’s LDAC; the maximum resolution is 24 bits/96 kHz.

The conversion is done with a pair of ES9068 DAC chips from ESS. The chips used are one thing – whether they can play to their strengths in the devices is another. The latter is mainly due to the respective integration, starting with a stable power supply. The Aune contains a 50 VA power pack with a toroidal transformer and filter capacitors with a total capacity of 23900 µF.

Aune seems to be particularly proud of the in-house development of the PLL algorithm. The 2nd generation of the phase-look-loop circuit guarantees low jitter values ​​and a clean sound image. External clocking with a 10 MHz master clock is also possible, but even without one, the jitter is only 594 femtoseconds (between 10 kHz and 30 MHz). The PLL circuit and the filtering can be operated in two different modes, one of which has been optimized for low latencies, and the other for particularly precise clocking.

Setting up and operating the Aune S9c Pro is pretty simple. On the device, the encoder controls the output level, a click switches between headphone and line output, a double click selects the input and a long click switches between the two PLL modes. Active inputs and outputs, output level, tuning mode, MQA status, external clocking, and current sample rate are shown on the display. The metal remote control is elegant and feels good in the hand, which makes it different from the plastic things that are sometimes included.

Aune S9c Pro: Listening test and comparisons

The first round of listening with the Aune S9c Pro on the closed, dynamic Focal Celestee headphones does not produce a “wow effect” – and that is a very good sign because it is the greatest strength of the Aune to play thoughtfully and at the same time very high quality. The first important term that describes the character is “balanced” on the tip of my tongue – the S9c Pro plays without peaks and without real coloratura. It is striking here that the device is very broadband and covers the limits of infra- and ultrasound as effortlessly as it does in the medium frequency range.

Bass range

I like to check bass and deep bass with organ recordings and electronic music, or I use a synthesizer directly. If you want to see what’s happening in the bass and sub-bass, I recommend “Spybreak!” by big-beat great Propellerheads. The Aune’s octaved synth bass has a lot of volume but still doesn’t seem “too loud.” This is because a fast rewind happens in the bass. Instead of being washed out or banging, the lows are controlled down to the sub-bass. If the level were lower or deliberately lowered to a 100% neutral level, you could accuse the S9c Pro of keeping the lower frequencies on a too-short leash and allowing them too little agility. However, the slight emphasis and beautifully dry detailing fit perfectly; the depths never seemed to slow down. A Stax SR 2170 electrostatic device, which plays with the Aune in the bass in a more controlled and detailed way than, for example, my Lavry DA11, which is twice as expensive and, of course, also getting on in years, benefits particularly from this.

Middle position

One could fear that the mids would appear depressed or lifeless due to the strong but dry bass range. This is by no means the case, on the contrary. The Aune is open, dynamic, and alert from the upper bass. In addition, the presences are perfectly balanced; in my opinion, they don’t tilt in the direction of squeaking or vice versa in an indirect sound.

I cheekily cheated my production into this test report, the sound of which I am, of course, very familiar with: Getaway is the latest album by my garage psychedelic progressive rock band Mouth. The somewhat vintage-sounding drums, deliberately represented with only three microphones in the mix, thrive on systems that present the mids in a balanced way and allow them to run dynamically freely. This is exactly what happens with the Aune S9c Pro. The snare drum is particularly sensitive to mid-range inconsistencies, but the Aune is where I wanted it to be. The fact that the focus range of the Aune is slightly reserved is good for (not only) this production. Here it’s the crest of the ride basin, which can be heard on “Once”, for example, which shouldn’t come across as too biting, otherwise, it’ll prick your ears. The slightly milder tuning of the S9c Pro in the presence range contributes to the long-term audibility.

Up in the spectrum

Even further up the spectrum, in the highs, the tonal quality of the Aune is evident. Some devices aim to display the resolution particularly clearly. This is impressive at first but can also become a bit exhausting in the long run. As great as the Waversa Mini-HPA (1,950 euros) was, the highs could be a bit too much of a good thing due to a slightly crystalline note. A comparison of the Aune with the Merging Technologies HAPI mkI/Premium (eight-channel AD/DA around 7,500 euros) naturally reveals that greater clarity in the upper octaves is also possible without scratchiness – but the price level and field of application of the two are also very different.

Productions like Diversions vol. 4: Songs and Poems of Molly Drake by The Unthanks (interestingly, the surname of two siblings) play it into the cards when the high-frequency range is transparent and high-resolution but works with a little gentleness. The highs of the Aune appear neutral in terms of level and, about the price range, very well resolved – but not “worked out to the limit.” Allow me to make a small comment: In addition to an exceptionally high-quality production, which one can at most attribute a little bit of kitsch to, this is Unthanks-Album also musically a true gem that every friend of Nick Drake should heartily recommend. Molly Drake was his mother. While listening you can not only feast on the great piano and the magical sounding and exemplary produced voices but also recognize from whom the tragic person Nick Drake must have inherited her incredibly good songwriting.

Resolution, micro, and macro dynamics

It was already evident in the previous sections that the Aune S9c Pro has a high resolution. A decent converter chip, which almost every manufacturer buys, is the basis for the work of a D/A converter. Still, it is the concrete integration into the data, audio, and power supply environment, especially regarding fine dynamics and detailed representation of actual properties defined. Aune has done a great job. “Cover Me” in Björk’s post gains in depth when the structure of the noisy parts is revealed to the listener in great detail. Based on this alone, I would bet on a higher price in the blind test than the one with which the S9c Pro is shown.

The Aune also masters the language of high-quality reproduction macrodynamically but ranks behind more expensive DACs. The Lavry mentioned, for example, shows advantages in the coarse dynamics, which are simply reproduced with larger differences. The quiet and loud passage levels seem closer to the Aune than the Lavry and the Waversa. The question is, however, whether this affects every music listener negatively.

In any case, it’s great that the extremely low-noise headphone amp delivers enormous power reserves. The 35-ohm Focal Celestee headphones are driven as effortlessly as the AKG K-240DF studio headphones (still made in Austria), which come with 600 ohms per side. The S9c Pro also produces high levels without batting an eyelid. By the way: The Aune is advertised explicitly for its suitability with in-ear headphones. A check with the Sennheiser IE 40 Pro confirmed this, especially in terms of spectrum and dynamics.

A comparison of the headphone amplifier built into the Aune with the external SPL HPm (399 euros, but without the necessary rack with power supply and audio connections) reveals that both are on a similarly high level in terms of sound, even though the Aune when using closed headphones and in- Ears’ quite advantageous setting options for the SPL (crossfeed, level of the stereo center, width of the stereo image) are not available.

Spatial representation

In the stage presentation – with headphones and loudspeakers (specifically: Harbeth Super HL5plus XD + Abacus 60-120D Dolifet) – depth, breadth, and localization sharpness are convincing. However, it will not immediately rain Nobel prizes for it. The drum kit on “Getaway,” for example, is exactly where it was positioned during the mix (namely, quite narrow, i.e. not completely fanned out between the left and right channels), the pad sounds of the Mellotron and other keyboard instruments span between the two Harbeths, but don’t go beyond that, the stereo center is kept on the baseline and minimally more compact, the depth of the stage is decent, but not breathtaking. Considering the price tag, what I’ve heard sounds fine to me. However, the plasticity can stand out positively: Signals appear nice and tangible.

Input question

As is so often the case, the various entrances do not differ noticeably from one another, which is also obvious. Unless you force connection errors, such as excessive cable lengths or interference from copper connections, which means that subsequent error correction gets more work, S/PDIF and AES3 connections are very similar. Things look a little different with Bluetooth.

Regarding the USB connection, it is noticeable that the Aune has a clear advantage over a Lavry DA-11, which is lagging behind due to its age. This is noticeable with the Lavry in a lower sharpness of the stereo image and somewhat duller highs. With AES3 connections, there were no differences in this regard.


“The tuning is based on the sound of real instruments and pieces of music, which leads to a natural and musical signature,” is written in the Aune shop for the S9c Pro. I don’t think that’s a very catchy statement, but what counts is “on the pitch”. And once there, it becomes clear that one can understand what could be meant …

The Aune S9c Pro is characterized by a powerful but firm bass, a balanced, finely resolved midrange, and a slight mildness in the presence. The highs are clear and neutral but never glassy or even hard. Overall, the audio quality is above what is usual in this price category, except for the rough dynamics and the stage design – expectations are not disappointing here, but they are not exceeded either.

The connectivity of the Aune is another plus. However, the headphone amplifier is so powerful and of such high quality that one would like an analog input. He would have deserved it!

Profile of Aune S9c Pro:

  • This D/A converter with a headphone amplifier is a wonderfully balanced device that effortlessly covers the entire spectrum from the low bass to the top treble band.
  • The bass is slightly stronger in level, but this is not perceived negatively due to its precision and speed. Rather, the opposite.
  • In the middle, the S9c Pro is extremely clear and lively. The presences are perfectly balanced – the sharpness range has been minimally reduced, contributing to long-term suitability.
  • Clear highs in high, but not the highest resolution, kept neutral in terms of level.
  • Detailed presentation and fine dynamics are not what you would call self-evident in this quality in the price range under 1,000 euros.
  • Decent, price-class adequate coarse dynamics.
  • Good stage presentation that is neither strikingly expansive nor compact. Pleasantly plastic illustration.
  • All types of headphones are really suitable, whether open and high-impedance, closed, IEM, symmetrical or asymmetrical.


  • Model: Aune S9c Pro
  • Category: DAC and headphone amplifier
  • Price: 749 euros
  • Dimensions & Weight: 288 x 211 x 63 mm (WxDxH); 5kg
  • Inputs: USB (audio up to PCM 768kHz/32bit, DSD512), S/PDIF coaxial, Toslink, AES/EBU (AES3), Bluetooth (codecs: SBC, AAC, aptX, aptX HD, LDAC), 10MHz word clock
  • Outputs: 2 x line out (XLR, RCA); Headphone outputs: 1/4″ stereo jack, Pentaconn TRRRS, 4-pin XLR
  • Other: MQA capable, remote control
  • Guarantee: 2 years