Pros –

Slender and lightweight design, Strong output power, Spacious stage, Great dynamics, Superbly linear bass and midrange

Cons –

Slightly brighter leaning treble won’t suit all, Rubbish included Type-C cable and no Lightning cable in the box, Could do with more fine volume control

Verdict –

The S9 Pro is versatile, nicely resolving and a strong overall package that I can highly recommend.

Introduction –

Hidizs are admittedly a company I have a rocky relationship with though do take note that most of my experience with them was regarding their first product launches, the AP60 and AP200. Their designs are attractive and underpinned by strong specification and reasonable pricing. However, I felt these devices faltered in day-to-day usability and real-world performance. With that said, it has been some time and the company has gone through many product cycles since I last tested their products. The dongle DAC/AMP movement has been strong lately and Hidizs were quick to join the race. In a short time, they are already on their 6th release, each being more highly specced and more refined than the last. The S9 Pro is their latest model and their highest end design to date. It has uncharacteristically high power output for such a compact source and a high-end ESS DAC chip. Moreover, it supports both single-ended and balanced output. At $119 USD, it represents very strong value on paper. Let the testing ensue.

You can read all about the S9 Pro and treat yourself to a unit on HiFiGO and Amazon.

Contents –

Specifications –

  • DAC: ES9038Q2M
  • DSD/PCM: Native DSD64/128/256/512, PCM up to 768kHz/32bit
  • Output Power: 100mW per channel (32 Ohms), 200mW (32 Ohms Balanced)
  • SNR: 120 dB (single-ended), 119 dB (balanced)
  • Channel Separation: 80 dB (single-ended), 118dB (balanced)
  • Dimensions: 18 x 59 x 8 mm
  • Weight: 11g

Behind the Design –

ESS9038Q2M + Discrete AMP

This is ESS’ former flagship 2-channel DAC chip that has now been succeeded by the ES9068AS which represents a very minor spec bump but most notably supports MQA rendering. At present, the ESS9038Q2M remains a very high performing 2-channel DAC with wide codec support including Native DSD64/128/256/512 and PCM 768kHz/32Bit. Usually, this would then be paired with the Sabre9602 amplifier. However, taking a loot at the datasheet, the numbers don’t align so it’s entirely possible that Hidizs are using a discrete setup here. You get excellent power delivery alongside both balanced and single-ended connectivity which is a good bump over most dongle-style DAC/AMPs.

Unboxing –

The S9 Pro provides a good unboxing experience and a passable accessory set. It comes in a small hard box that slides open to reveal the device in plastic nestled within a foam inlet. Fabric pull tabs ease the process. Beneath are the accessories, a type-C to type-C interconnect cable, acrylic case with shirt clip and a type-C to USB-A adaptor for use with older PCs. The adaptor is of great quality with a nice aluminium shell, but the interconnect cable could be nicer, this one has a basic construction and is not especially flexible either. I would have liked one of Hidiz’s braided cables at this price point, in addition, no lightning cable is provided so iPhone users will want to factor in the cost of this too.

Design –

I quite enjoy the overall design of the S9 Pro, it has slender proportions that are minimise the footprint in the pocket and it’s super lightweight as well. It’s medium sized and on the slimmer side for a dongle, especially one with both single-ended and balanced outputs. While it has the usual glass/aluminium sandwich design one might see on competitors, the protruding jack mounts do give its design some visual flare. Despite this, the feel isn’t quite as premium as many competitors, the finish isn’t as consistent, the glass isn’t curved, and the aluminium frame is boxy. However, all of these are “nice to haves” and don’t irk during daily use; this definitely comes across as a more function over form device.

Besides this, the finish and construction leave little to complain about, there are no obvious points of weakness nor issues that affect its function. The Type-C port is snug and offers a reliable connection, similarly, I experienced no issues with the headphone jacks. Some earlier dongles did have issues here with certain plugs failing to activate the power switch where here, the S9 Pro simply powers on when connected to the source for more reliable operation. The faceplate is adorned with the Hidizs logo and it is backlit by an RBG LED that illuminates to denote power and the resolution of the current audio playing. On the opposite end are both 3.5mm and 2.5mm balanced ports. Note as well a lack of any physical controls, this device is entirely operated by the source device.

Usability –


The S9 Pro is a simple plug & play device, drivers auto installed on my Windows 10 PC and laptop in a matter of seconds and my Android smartphone connected instantaneously. Once connected, audio playback was fluent with no issues without the installation of a third-party driver.

Lacks Volume Granularity

Once connected, the daily usability is where I have the most complaints. Unlike some competitors, the S9 Pro has no internal volume control, scaling according to the source. With sensitive IEMs, it lacks granularity. This is fine if using a PC where most apps have digital volume control, similarly, listening to music stored on your phone as you have a wealth of apps that offer similar control. However, when streaming such as Spotify, I was left wanting.

Power Consumption

Some reviews have mentioned the S9 Pro has a high power draw, and this is something I can also confirm if not to the extent experienced by some others. You can observe that the Hiby FC3 has a relatively minimal impact on power draw as per Accubattery and most competitors occupy a similar ballpark. The S9 Pro is drawing about twice the power on the other hand. For my Xperia 5 II with its 4000mah cell, this was not so much of an issue, however, I can imagine that a phone with a smaller battery could run into difficulties here. Still, to me, this is not bad given it has triple the output power of the FC3.

Next Page: Sound Breakdown

Sound –

I believe my stance on sources and dongle especially are quite apparent by now if you’ve read my other reviews. Many sound nigh identical due to the adoption of SOCs which encompass the entire audio path. Indeed, implementation may vary, but as the all-in-one unit contains so much of the system, you really are looking at very incremental changes amongst different models. The S9 Pro evidently shakes things up a bit with its discrete amplifier chip, or at least, it’s unique implementation of ESS’ chipset. I am happy to confirm real world benefits in listening, this one is a clear step above the norm.

Frequency Response –

Testing Methodology: RMAA via Startech External Sound Card

The S9 Pro has a linear frequency response suggesting that it represents audio with great fidelity. Due to the quality of my sound card, I am unable to reliably test other measures such as distortion and crosstalk so they will be used as a personal reference only. Qualities here can also impact the sound as I will detail via subjective listening.

Output Impedance & Hiss –

Testing Methodology: SPL volume matched comparison through an inline splitter to THX789 + SMSL SU9 to Campfire Audio Andromeda and Ara

Hidizs don’t state these specifications on their website, but they really should because it is would be a selling point of the S9 Pro. Empirically tested, I would estimate the S9 Pro to have a sub 1-ohm output impedance. I tested using the Campfire Audio Ara which has an ultra-low 8.5-ohm impedance and a mechanical crossover that can discern even between 1-ohm and sub 1-ohm sources.

Compared to my THX 789 (1-ohm), the S9 Pro gave it a slightly smoother sound suggested a sub 1-ohm output impedance. It showcased a similar character as my low output impedance sources with other sensitive IEMs, an excellent result. Noise handling is equally impressive, being dead silent on both the Andromeda, which is renowned for its sensitivity to source noise. The S9 Pro had a black noise floor with all of the gear I tested it with no matter how sensitive, another excellent result.

Subjective –

Testing Methodology: SPL volume matched comparison through an inline splitter to THX789 + SMSL SU9 to Soft Ears RS10 (flat impedance). Powered by Xperia 5 II with Poweramp Pro via high-resolution output.

As was my experience with other ESS9038-based dongles, the S9 Pro has a very linear and balanced foundation to its sound. This is carried through to the final output with aplomb, offering an almost perfectly even-handed rendition with minimal tonal colouration. I am hearing a slightly revealing top-end but nothing that would hugely affect synergy or polarise for most personal preferences. Rather, it imbues just a little vibrance and zing into its overall image that some may enjoy as it draws greater focus to fine details. Compared to a high-end source based on similar componentry such as A&K’s SE180, transients aren’t quite as defined, and its imaging isn’t so immersive. But the S9 Pro is definitely one of the best hyper-portable sources/dongles I’ve tested when taken as a whole. Surely, the power output is coming into play as well as the S9 Pro does have quite a robust low-end and is able to keep up with even my least efficient IEMs and many headphones too.

Balanced vs Single-Ended Out

It should be noted that balanced isn’t a feature you should feel is necessary, as it doesn’t necessarily bring benefits, but rather solutions to issues that are not present here. That being said, if you do have a balanced earphone or the cables to take advantage of a balanced output, then benefits are to be found. With double the output power and a huge jump in channel separation, this is more true here than on many other sources. I still found the single-ended output to provide a highly impressive sound, in fact, my very favourable comments below were using this output. However, balanced does improve the listening experience further. Staging was the biggest difference to me, you get a noticeably wider and airier stage with greater separation. The background was more resolved and stretched further, creating a more multi-dimensional sound. I would recommend using the balanced output on this dongle if possible, if not, you are still receiving a very accomplished source.

Bass –

Desktop sources will always be the best foundation of judgement for bass performance as dynamics are tied directly to the power supply, and a larger one invariably has a higher capacitance ceiling. Compared to my THX789, I do notice a drop off in the sub-bass on most portable sources, but the S9 Pro gets impressively close considering the form factor. You won’t get huge physical slam at the very bottom nor the utmost affirmative note attack relative to a larger source; bass drums aren’t as authoritarian nor rumble as powerful.

However, this remains a tight and snappy low-end with no shortage of audible sub-bass kick. Bass is linear with no apparent emphasis working towards a well-separated and defined response. Control is well above average for a dongle, note definition impresses as does its ability to discern texture in the mid-bass. As note attack isn’t too aggressive, this does provide the impression of a smoother bass texture. In turn, its assets are more its dynamics in-class combined with its texturing as you will find sharper timing elsewhere.

Mids –

Like the bass, the listener is instantly able to appreciate a superbly linear midrange rendition that contributes to versatile synergy and overall separation. The S9 Pro has no huge tonal deviations as you’d expect from any decent modern source, though small qualities in its note presentation do imbue certain qualities. For instance, I am hearing a tinge of dryness in its voicing, lacking the liquidity and delicacy of higher-end sources. Similarly, resolution of fine details operates at a high level but won’t replace your desktop stack. Specifically, the S9 Pro prefers a slightly denser voicing relinquishing articulacy and separation whilst prioritising coherent and well-structured notes.

In turn, it discerns textures well and instruments are portrayed with a realistic timbre. This is a nicely layered source too, with great contrast between its background and foreground crafting an impressively wide image. However, it doesn’t discern between individual layers such as vocal harmonisations especially well. My main criticism here is regarding organisation on complex tracks where the characteristics of its note presentation can make it sound busier than some. This isn’t to the extent that the source sounds coloured nor remotely congested, and the S9 Pro remains altogether, a clean, clear and well put together source.

Highs –

As aforementioned, I am hearing a lick of forwardness in the highs, imbuing just a hint more zing than a dead neutral source – such that I would consider Topping’s high-end gear. To preface, this isn’t to the extent of the infamous sabre glare you may have heard of coming from their previous generation DACs; I do think the 9038-based sources I’ve tried have all been mostly well-behaved, so this is more a repercussion of individual implementation. The lower treble is impressively even and linear, portraying a well-bodied, textured foreground. There’s a hint of middle-treble emphasis above that slightly lifts instrument clarity and draws greater focus to shimmer, air and decay.

The presentation is characterised then by its slightly energetic nature but remains free of glare or grit in so doing. That said, this does detract slightly from the initial transient, I do perceive the S9 Pro to have a slightly softer note attack. This means that though it is a well-detailed and honest representation of music, micro-details can get smoothed over more than some. I would suggest this is responsible for robbing the midrange of some articulation as well. Above, headroom is top level for such a compact source, clearly better than the majority which contributes to a strong imaging performance. It won’t give you huge micro-detail and sparkle nor the highest resolution, but a slightly vibrant expression realised through nigh class-leading extension.    

Soundstage –

It’s here that the S9 Pro’s sound makes a lot of sense, it images far better than you’d expect for such a compact source. Many sources are able to effectively provide a linear sound and detailed lower-treble but fall short when it comes to soundstage and layering, providing a superficial experience. The S9 Pro is no such creation, delivering out of the head width on the right IEMs and a good amount of depth too, forming a multi-dimensional image. It remains width biased, but I was impressed by its dimensions combined with its neutral note size.

Specifically, there’s a palpable air surrounding each element often absent on competitors. Again, layers are well defined, and the background isn’t super detailed, but does showcase impressive width. Separation is likely its weakest link, with note definition lagging slightly in the treble (somewhat counterbalanced by its tonality) and the bass and midrange being more structured over ultra-concise. It’s not a poorly separated sound, aided by the larger stage, but not the best I’ve heard. 

Driving Power –

Fir M4 (6.4 Ohms): The M4 is a very low-impedance hybrid monitor and is highly discerning, showcasing source quality clearly. This was a terrific pairing and a great showcase of the S9 Pro’s ideal environment. Even compared to my desktop stack, I was getting near identical extension and power. Notes weren’t quite as controlled and defined, but very close. The top-end was detailed and well-extended. The soundstage showcased impressive dimensions and proportions, similar between depth and width but both scaled down slightly compared to my larger sources.

Soft Ears RS10 (25 Ohms, 100 dB): The RS10 is deceptively difficult to drive and highly resolving, scaling with sources. The S9 Pro did admirably here, I was only using 7% volume output, bass was almost as extended as my desktop stack but lacking that last ounce of pressure and control. Mids were slightly less revealing and articulate but equally well-structured and layered, but layers were less delineated. The top-end was slightly brighter with more shimmer and air but less transient attack. The soundstage presentation impressed; it was similar but scaled down.

Final D8000 Pro (60 Ohms, 98 dB): The D8000 Pro is a highly resolving planar with special emphasis on bass extension. This pairing does demonstrate where such a small design shows its limits, though was an admirable performance on the S9 Pro’s behalf. Bass was full and robust but not especially well-controlled, being a little fuzzy around the edges. My desktop stack had noticeably more power and weight. The soundstage was the next biggest change, being just as deep on the S9 Pro but quite a bit narrower. I felt the sound was superficially balanced, certainly enjoyable and a far cry from the stock output on my phone and laptop. But for full-size headphones, you won’t get the full experience.

Suggested Pair Ups

The higher driving power and generally neutral note size and tone means the S9 Pro rarely polarises and achieves wide synergy. Though I’m sure there are rare outliers, it drove all of my IEMs with aplomb, delivering outstanding dynamics and soundstage expansion for a hyper-portable source. I didn’t find it too bright on already brighter earphones either, especially as its transient response isn’t to sharp so brightness is compounded upon. Headphones are driven well too, full-size headphones at a stretch but the vast majority of portable headphones with relative ease both from a volume and current point of view. This is especially so from the more powerful balanced output. Where with many portable sources you do feel like you’re missing out on dynamics and power. While it still isn’t ideal here, you don’t miss out tonally but more with regards to note presentation which is less impactful on the overall listening experience.

Next Page: Comparisons & Verdict

Comparisons –

Hiby FC3 ($69): The FC3 is a slightly smaller device but has similar usability overall. It does have internal volume control which gives it a slight edge with sensitive IEMs, but the S9 Pro has a slightly cleaner noise floor and a lot more power for less sensitive gear making it the more versatile source altogether. In terms of the tonality, the S9 Pro is slightly brighter and more revealing around the treble especially, while the FC3 represents a more linear sound overall. That said, under scrutiny, the S9 Pro is a substantially more impressive source as you’d expect given the large price gap – but the difference in performance grows small with more efficient IEMs. Immediately, its bass is deeper extending and more dynamics, delivering greater rumble and power.

The FC3 is just a touch warmer here but less nuanced and robust altogether. Its midrange is slightly more even, that said, and it does have a slightly more neutral and defined note presentation. The S9 Pro stretches wider, its layers being far more delineated, but its foreground is not quite as textured due to its denser voicing. The S9 Pro has a more energetic treble, and it has a little more bite to its transients, giving it the advantage on detail retrieval. The S9 Pro especially has a much larger soundstage which cements it as the superior source although the FC3 nails tonality at a much lower price.

Astell & Kern Dual DAC ($149): The Dual DAC is a smoother and more refined sounding source with a greater focus on tonality and staging. It too is dead silent but also with lower output power and a slightly higher 2-ohm output impedance, plus a lack of balanced output. It makes up for this with class-leading build quality and some unique sonic characteristics. Bass is more dynamics and powerful on the S9 Pro as one may expect. The Dual DAC has less authority but does have a slightly more articulate and controlled mid-bass in return. The midrange is slightly more even-handed on the Dual DAC, both are smooth and dense. I did find the Dual DAC to discern textural nuances slightly better here than the S9 Pro but the two are very similar overall.

This same trend continues to the treble, the Dual DAC has a little more bite to its lower-treble and more texture here, it also has a cleaner background and matches the S9 Pro for extension. The S9 Pro has more energy, its presentation is more vibrant and airy. Staging wise, the two also trade blows, the Dual DAC has a more rounded stage with noticeably more depth, making it slightly more immersive. The S9 Pro has a wider stage with slightly better layering and a more focused foreground. Still, as much as I want to love the Dual DAC, you do pay for the refinement in the form of a higher output impedance, fixed cable and lack of balanced IO.

Earmen Sparrow ($199): A closer competitor with balanced output and focus on high output power (current unspecified). The Sparrow is a slightly higher contrast source, still showcasing strong balance but is more coloured than the S9 Pro. Despite its size, it matches the S9 impressively well on output power but at the cost of being less shielded from EMI drying my testing. The S9 Pro has slight edge on bass weight and extension, rumble is slightly more defined and powerful. The Sparrow gets close and it has a lick of deep-bass emphasis which gives it a slighty bolder note presentation. The Sparrow has a higher contrast midrange with a leaner note weight.

It resolves slightly better, its notes being slightly more defined and separation being slightly better. The S9 Pro meanwhile has better layering and a slightly more accurate timbre. The Sparrow has a little more bite in its lower-treble, giving it an edge on fine detail retrieval. Meanwhile, the S9 Pro has more air and headroom, and it’s background is more stable and defined. This plays most into its soundstage performance, though the Sparrow is actually wider, this comes at the cost of a diffuse centre image, the S9 Pro being noticeably more organised and stable. The Sparrow will appeal to those wanting a more engaging tonality and the widest soundstage.

Verdict –

The biggest accolade I can award the S9 Pro is mostly contextual but still speaks well for Hidizs creation. Mostly, many dongles do little that calls for complaint but similarly, little to differentiate themselves. The S9 Pro does, however, and in numerous categories. It manages to sound much bigger than you’d expect from a portable source, both with regards to dynamics and soundstage expansion. While some match it, few are as well-rounded. The S9 Pro nails the fundamentals being convenient to use whilst boasting a black noise floor, linear FR and sub 1-ohm output impedance. Balanced connectivity and well above average driving power are nice to haves that do enhance versatility and better justify its more premium pricing. This is not suited for those wanting a smooth or warm sound and is lacking volume control granularity for sensitive IEMs. Overall, the S9 Pro is versatile, nicely resolving and a strong overall package that I can highly recommend.

The S9 Pro is available from HiFiGO and Amazon (International) for $119 USD at the time of writing. I am not affiliated with Hidizs, Amazon or HiFiGO and receive no earnings from purchases through this link.