EarStudio HUD100

Disclaimer:

I would like to thank Radsone for providing a review unit of the HUD100 MK2. Rest assured that my impressions written in this review are my own personal thoughts and opinions and in no way influenced by outside parties.

I am not an expert in this hobby nor claim to be an audiophile. I just love listening to music and am fond of writing articles.


Introduction:

Korean-Fi. It’s a rarer term here on head-fi from what I noticed. Not a lot of talks regarding this wonderful segment. Radsone, short for Radical Sound, is a South Korea-based company that is “a full stack audio company with a vision to make everyone enjoy high-quality sound easier than before. Music that deeply moves one’s heart should be delivered with high quality.” For this review, we have the Radsone Earstudio HUD100 MK2, a portable DAC/Amp that currently sells for 119 USD with free DHL shipping in most countries at the time of this writing.


These were plugged to my Oppo Reno 4 and Asus X409 for the review.


Technology:

• Compact, yet high-performance / Plays up to PCM 32bit/384kHz and DSD128 / 45 x 32 x 8mm / 21.5g / USB Type C
• Jitter-Resilient / The first audio DAC to adopt ARM Cortex processor and MEMS oscillator to implement Radsone's proprietary algorithm and minimize jitter
• 2 Power x 3 Sound Processing Modes / 1.29Vp Standard, 3.20Vp High Power Output
• Bypass processing mode for pure sound enthusiasts / DCT processing mode for users searching for well-dithered analog-like sound / Radsone-tuned Dynamic processing mode for more powerful sound with balance
• Elaborate 8-layer circuit design to bring the best performance out from such a small size

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Package: HUD100 MK2. Protective case and Adhesive (2x). USB-C to USB-C, 10 cm. USB-C to USB-A, 12 cm. Paperwork. User Manual.

Design and build: It’s mind-boggling how impossibly small Radsone was able to create the HUD100 MK2. This is research & development in all it’s glory. The HUD100 MK2 is a highly portable DAC/Amp and I’d be surprised if there’s a dongle/stack more portable and practical to use than this one (I can think of only one – ddHifi. But, personally speaking, the design itself is a big point of failure concerning durability). Design choice is quite the curiosity – it’s a DAC/Amp that looks like a rectangularly shaped dongle but stacks on a smartphone. I attached a pic for you guys to get an idea of how small it is and the look when used with a phone using the included case. Build is metal and feels sturdy on hand. There’s a light indicator that changes color depending on what sampling rate is utilized. Jack (3.5mm, low power & high power) inserts don’t feel loose and are secure. DSP/Bypass switch satisfyingly clicks in place.

Connectivity: Plug and play. Everything you need is provided in the box, unless you have an iPhone with its determination and rock-solid stand to not adapt USB-C. I, however, had to turn on USB OTG manually for my Reno 4 so that the HUD100 MK2 can be detected in the overly buggy Hiby Music Player. With Poweramp, no further action is necessary to listen to music other than plugging in the HUD100 MK2. When used with my laptop, with first connection, it was automatically detected and finished setting up within seconds. Using MusicBee, there’s no jitter or problem with playing music and the listening experience is flawless.

I, however, wasn’t able to test it with an iPhone due to not having the necessary adapter (Lightning) but it should work based on advertised compatibility.


Now, onto sound:
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The Earstudio HUD100 MK2 is an analytical, neutral DAC/Amp. Bass is linear, tight and isn’t emphasized, providing an articulate reproduction of the region. Midrange is natural, textured and defined, though it might come off as cold for some individuals as there’s zero, zit, null, nada coloring of the sound happening. Treble is very clean and detailed, like I said before, is of the colder, analytical side. Note weight isn’t thin and the DAC/Amp won’t change the overall profile of the transducer used. Technicalities will depend on the drivability of the transducer, but generally - soundstage, imaging and separation improvements are minimal. If you want a pure, clean, clear, and transparent listening experience, then the Earstudio HUD100 MK2 is the DAC/Amp to get.

Regarding the sound modes of Bypass, DCT, and Dynamic, in most cases sonic change isn’t drastic. However, I have noticed that the degree of said change depends on the transducer used. Generally speaking - Bypass is bypass, DCT is more “analogue-ish,” while Dynamic sounds more fun, increasing sub-bass with a slight decrease in mid-bass. For what it’s worth, I prefer to use Bypass for like ~85% of my listening. I do have to note that it only works in 44.1 kHZ sampling rate.

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Low Power vs. High Power: The Earstudio utilizes an unconventional output set-up. When people would most of the time expect one balanced and one unbalanced port, the HUD100 MK2 uses two 3.5mm. The difference comes in power output. Low Power (LP) dishes out ~0.9 Vrms based on tests by other reviews while the High Power (HP) has a beastly ~2.2 Vrms in this bonkers tiny body. Impedance is less than <1 ohm in LP so it shouldn’t be a problem for sensitive transducers, particularly IEMs.

Hiss Amount:

KZ DQ6 (24 ohms, 112 dB) – no hiss on LP but noticeable hiss on HP. Preferred setup is DCT in low power.

Moondrop SSP (16 ohms, 94 dB) – no hiss on LP but that lacks power to drive the SSP. Switching to HP and the HUD100 MK2 doesn’t break a sweat driving the hard-to-drive SSP. No hiss at all. Preferred setup is bypass in high power.

Blon BL-Mini (16 ohms, 115 dB) – no hiss on LP but very slight hiss on HP. Preferred setup is bypass in high power.

Audiosense DT200 (14 ohms, 99 db) – no hiss on LP but very slight to none on HP. Dynamic works wonderfully with this pair in low power.

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Battery Drain: I wasn’t able to do a timed test with my laptop or phone on-the-go due to the COVID-19 situation here in my country. However, with the Oppo Reno 4 that has a 4015 mAh battery, drain isn’t noticeable at all and the HUD100 itself is very efficient while in LP using the KZ DQ6 (low-medium volume; Hiby Music bit-perfect mode). Using HP and noticeably faster drain is observable but what I would still consider negligible decrease in battery life. I don’t know about you guys, but for me, that’s more than enough to last me the whole day


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Conclusion:

The Earstudio HUD100 MK2 is a DAC/Amp made for the modern human living in the modern world of portability, minimalism, and practicality. If you can’t survive the “dongle” and find it as “detrimental for the development of mankind,” then having a more usual “audiophile” stack should be a workaround for you. If you want a clean and neutral DAC/Amp, with two Power Modes and three Sound Modes, coupled with the insane size for portability, then for the sale price 119.99 USD and free DHL shipping (for most countries) on Radsone’s online store, go ahead and grab the HUD100 MK2.

It looks like a face! | O < o > O |

The usb-c arena is getting crowded, but if you have the money to spend, and you want a dedicated portable usb-c unit that can drive moderately inefficient phones, hud100 will please those looking for a neutral-to-lean sound signature(Ety-head here). It delivers a clean and articulate tone in a small, somewhat over-engineered package covering pretty much all protocols and frequencies, ranging up to PCM 32bit/384kHz and DSD128. It also supports MQA(MQA debate aside for the scope of this review).

Built around a AK4377 chip on a 8 layer PCB, it contains discrete MEMS oscillators and an ARM cortex that can apply "propriety algorithms" to the signal. Rather than a hi/lo switch, they have designed separate signal paths for the high and low power outputs, giving the device its wide yet slim rectangular body. All that separation ensures a dead quiet noise floor, and I haven't run into any cellphone interference either. It also has a filtering switch that allows choosing bypass/dct/dynamic modes with subtle effects on the sound.

Filtering
I mostly tested it on DCT and transparent modes. The effect is subtle, and only works for 44.1khz sources. I asked Radsone exactly what the filtering does but haven't got an answer yet. I don't know if it's a DSP separation rather than a straightforward eq. Regardless, the effect of DCT mode is a subtle emphasis of sub-bass, and perhaps some noise shaping (welcome to the psychosomatic zone), I don't know about pre-ringing and so forth. The dynamic mode is a much clearer bump in lower regions, rolling into the lows, which I find to be a bit much for my preferences.
Although it makes visual sense to put the recommended default (DCT) in the middle, from a user experience point it is actually hard to set a tiny three way switch to the middle without looking. It might be better to swap it with the dynamic mode (they could do this in firmware).

Build and accessories
Considering the price of the package approaching bluetooth cabable usb-c dacs, I will do some nitpicking in this section.
My biggest issue is with the 3.5mm jacks. They are rather loose, which worries me for a dongle type device. I was trying to figure out if I was having sampling sync issues when I realized that my earphones had come unplugged by a hair. For this type of device, where the cables are inevitably going to bend and pull, I much prefer the snap-in-place, secure connection of the apple dac dongle.

The body is an unibody aluminum rectangular prism with a thin bottom cap. A bottom with a matching finish would feel more solid and offer some extra (perhaps unneccessary) shielding.

Included in the package is a clear plastic sleeve and two adhesive mounting points that stick to the back of your host device for a tidy portable stack. I do like the design as the permanent mounting point is rather unobstrusive once you remove the dac. It is a bit of a puzzle as to how you could have your earphones come out the top side and fit a usb-c cable loop in your pocket. For the most part, I find myself preferring the dac dangle out of my pocket rather than risk my usb-c ports.

There is one usb-c–c cable and one usb-c–a(Full size) in the box. The c-c cable is better built with an extruded usb-c connector sleeve rather than the loose fitting crimped one present on the a–c. The c-a cable itself is also stiffer and cheaper feeling with roughly molded strain reliefs. The color and line quality of their branding and logo don't match the c-c cable either. I think at this price, they should really include a better a-c cable. Also, it was 4"/10cm longer, you could use one of the extra sleeve attachment points on the lid of your laptop that kept your stuff off of the table.

Impressions
Ka Baird - Vivification Exercises I (44.1khz/24bit)
The hud100 maintains superb channel separation, and its articulation capacity in the low end renders a clear sonic topography, with other dacs at hand feeling blunt in comparison

Laura Marling - The Lockdown Sessions (44.1khz/16bit)
This album has a tendency to sound a bit nasal on the other dacs, the hud100 being an exception. Here, Marling's voice burns through with tactile graininess. The lean response tames the resonance of the guitar body a bit so that it doesn't bleed into the mids. The recording is not particularly expansive, so there isn't much difference in terms of the stage, but it feels a row or two farther thanks to the recessed lows.

Son Lux - Tomorrows II - Live Another Life (44.1khz/16bit)
The beginning of this track has a very distinct, rectangular soundstage set by a percussion that I can best describe as a rimshot hit with a thick plastic bottle, recorded from the inside with the lid on. My sonic ramblings aside, the hud100 really flaunts its colors here. The beginning section is rendered in exquisite detail, drawing a laser sharp wide rectangle with such detail that I find myself rambling as noted above. The channel separation and the leaner signature really helps distinguish the cacaphony of later sections, especially after the bass kicks in at 4:10.

Bjork - Hunter (48khz Spotify - Coreaudio)
As with other synthesized percussion above, the lean signature backed by its capacity for articulate sub-bass renders really rich percussions that are alive and detailed. This example is a bit interesting for me as I can group all other devices as different articulations of the same recording where the hud100 somehow stands apart almost as a remaster. The expansive soundstage really benefits from the channel separation and the rock bottom noise floor as the drums roll around and through your head.

Takuya Kuroda - Rising Son (44.1khz/16bit)
Apparently the theme is percussions today. This is one of those songs that builds itself out from its components, starting with a muted rim-shot. Hud100 lays it all out in great detail, you hear the stick hit the rim, the ever so separate bounce, and the resonance of the springs as Nate Smith keeps throwing in more elements. I really can't fault much with its rendition of this song, perhaps the trumpet comes through a little short on breath, but that's more likely my Etymotic ER2XRs.

In Sum
Compared to other dacs and devices that I currently have around (Dragonfly v1, Apple and Google Adapters, the pixel 3a, ipad pro), the Radsone has a significant edge in separation and detail, and it does so without sounding overly analytical. I'm very happy with the sound.
Even with the ER2XRs, the difference with the Apple adapter is significant enough for me to carry the hud100 around on the go. Perhaps if you are looking for a warm/tube-like tone, you might want to look elsewhere, especially if you are going to combine it with diffuse field earphones, but other than that, the hud100 is solid.
The one question I have is about the price –though still well under desktop dacs that it can rival– that it is high enough to make an upgrade to the ES100 or equivalent hybrid wireless dac tempting. If they were to upgrade a few small details (longer and better usb-a cable, up build quality and plugs, allow filtering in other frequencies, perhaps add an eq/app option?) I would be less likely to ask this question.

Note for others: On my macbook air, only one usb port would work for frequencies above 192khz including DSD. The other only worked above 192 when MQA was active.

HALF DONE, HALF WON - EARSTUDIO HUD100 DAC/AMP REVIEW
by George Dobrescu - November 03, 2020
Half Done, Half Won - Earstudio HUD100 DAC/AMP Review


When you need something tiny, something that's practical, you know that there will be some sacrifices. The HUD100 is smaller than BTR5, it has a nimble body, and it is priced at 140 USD, and for that price, it has two headphone outputs, one in low gain and one in high gain, three filters, and a Type-C input, but not a lot of power. It will be compared to the Earmen TR-AMP, Lotto Paw S1, and Pro-Ject Pre-Box Digital S2 DAC/AMP. As far as pairings go, I selected Periodic Audio Carbon, iBasso AM05, and Fischer AMPs FA-4E-XB.




Introduction

The tiny thing that HUD100 is, really really tiny. It looks like a small pack of mints, and even then, it is tiny. The company behind though, is not so small, and they're known as a Korean producer of high-quality audio products, and are also known to be fairly reliable.

It should be noted that I have absolutely no affiliation with Earstudio. I'd like to thank Earstudio for providing the sample for this review. This review reflects my personal experience with Earstudio HUD100. Every opinion expressed is mine and I stand by it, the purpose of this review is to help those interested in Ear Studio HUD100 find their next music companion.




About me

https://www.audiophile-heaven.com/p/about.html




Packaging

First things first, let's get the packaging out of the way:









The package is minimalistic. As I presented in my video review, it doesn't quite compare to the likes of FiiO Q5S, but it is fairly good. The price is high, so I have to mention that the carrying leather case is only for carrying it, you can't use the HUD100 while inside the case. Furthermore, the cables selection is not great, and you can't use any cable with it, so the package gets a passing grade, but is only minimalistic.




What to look in when purchasing a high-quality entry-level DAC

https://www.audiophile-heaven.com/p/what-to-lookl.html




Technical Specifications








Build Quality/Aesthetics/Functionality

The unit itself has two headphone outputs, one in low gain, and one in high gain. I would recommend always using the high gain, as it tends to have better dynamics and punch, although it also has marginally higher noise output, which I could hear with IEMs like Campfire Atlas and FiiO FH7.



They named the outputs standard and high power, but the truth is that neither doesn't have enough power for more than IEMs anyways, even if you listen at moderate levels. The weight of the unit is really low though, and although in my photos, and every other reviewer's photos it looks kinda big, the unit is really tiny. Portability is the key word here, but for that portability, some things had to be sacrificed.

There's a filter selector, which you can use to select between three filter modes, and the filter is at the front, in between the headphone outputs. Although the most processed variant of the filter, the Dynamic, sounds the best. There's an off variant, a DCT variant, which is Radsone's own algorithm and dithering, and a DCT with tuning too.



The input is in the Type-C format, which works great, but you will need an OTG adapter for some smartphones, which makes using it a bit odd. There is no short Type-C to Type-C cable, so although the unit is tiny, the portability is not that great as you will need an OTG adapter to use, besides the Type-C 10 cm cable. A short USB cable, if you can find one on Aliexpress, would be great, but in my experience, the cables that came with FiiO Q5s or other portable DAC/AMPs did not work.




Video Review

https://www.youtube.com/watch?v=sH7fzVW1bC8




Sound Quality

There are three versions of the sound quality, depending on how much you engage the filtering. With that filtering turned off, the sound is kind of deaf and boring, a bit flat in every way. It works great for a reference sound, but not so great if you're looking for a fun sound. Well, if you want to listen to the best that the HUD100 has, I totally recommend engaging the dithering and even their own flavor, after all you paid for the entire DAC, you should use the entire DAC.



The bass is pretty deep and well rounded, it is not particularly quick, but it gives the impression of good impact and a nice amount of volume / body. The overall bass leans on a natural speed to achieve a full-bodied impact. There's very little times that I wanted more, but more bass would have been welcome with IEMs and Headphones that are naturally bright, like the SoundMagic HP1000, or the iBasso AM05.

On the other hand, with the dithering and Earstudio's own flavor engaged, the midrange is quite natural, flows freely, has a uniquely effortless presentation, and has great dynamics. The tonality is ever so slightly thick and not the most edgy or textured out there, but the amount of clarity it has, makes HUD100 a great pair for IEMs that are made for monitoring like the FA-4EXB, and even something the Audiosense AQ3 sounds quite nice with the HUD100 when it comes to the midrange.

The treble is on the slightly smoother side, without much edge, which makes it seem a bit compressed dynamically too. The very top edge works well for brighter IEMs, because it doesn't reveal brightness, and it tends to hide mastering mistakes, making listening to music quite easy and fun, even if you have slightly less expensive headphones, or if you listen to older music with poor mastering. Makes me wonder why we keep calling it poor mastering, when those older songs had way more dynamic range, and even with their brighter presentations, sounded really good, while some more recent remaster variants, while toning down the treble, also removed some of that dynamic and punch that made those songs fun in the first place.

At the end of the day, you have about two signatures, one that is flat, a bit boring, but great for reference, and one that's smoother, more liquid, with a well rounded bass, to enjoy with the HUD100.




Comparisons

The comparison list includes pretty pricey competitors, but this is because the HUD100 is quite pricey by itself. With a price tag of 140 USD, it needs to stand up against products that are at least similar to its price, if not products that cost more, because it is not coming from a brand that's as known, like Lotoo, Earmen or Pro-Ject.



The Pre-Box Digital S2 is indeed quite a bit more pricey, but here's a fun thing, the HUD100 may actually be a bit better than it when it comes to driving certain IEMs, although the HUD100 cannot work as a standalone DAC, not having a true Line Out, which may actually have been a nice feature.

Earstudio HUD100 vs Earmen TR-AMP (140 USD vs 250 USD) - Earmen TR-AMP is a much more interesting DAC/AMP if you need something to drive headphones too, or if you need a DAC that you can use with your desktop setup too. Furthermore, it has a more dynamic sound in general, with more punch and more impact, but it doesn't have the same smooth midrange that HUD100 has, and it is much much larger. It also has a battery that you need to charge and you need to make sure it has enough juice to be able to enjoy it. By comparison, HUD100 only eats a bit of battery from your laptop or Smartphone, and it doesn't need two cables, one for power and one for data, it uses just one. If you don't need the extra portability, the TR-AMP is more versatile, but for something small and magically smooth, the HUD100 makes a lot of sense.

Earstudio HUD100 vs Lotoo Paw S1 (140 USD vs 170 USD) - Lotoo PAW S1 is very similar to HUD100 in terms of overall usage and design. The main differences are that Paw S1 has a traditional EQ, and it has a balanced headphone output too, so it can do much more than HUD100 at pretty much the same price. Not only that, but Paw S1 has much more driving power, with more punch and impact. The HUD100 has a bit more hiss, but actually manages to have a smoother midrange, and with all the settings engaged, it somehow manages to be more musical, while being similarly detailed, and have a smoother treble, being easier to pair with a wider variety of IEMs. For headphones, you'll need S1, the HUD100 may not be enough unless you're using something really easy to drive, like Verum One.

Earstudio HUD100 vs Pro-Ject Pre-Box Digital S2 (140 USD vs 400 USD) - The Pre Box S2 is also pretty pricey compared to the actual performance, and compared to its competition, so I thought it would make an interesting comparison to see how it compares to HUD100. Most people will be purchasing the S2 Digital to use with a speaker system, where it is undoubtedly great, but if you have just a pair of headphones or IEMs, you'll probably like to know that HUD100 sounds quite a bit more natural with a smoother midrange, with more bass body, and with a deeper impact. The treble is also smoother, with less edge and comes through as sounding more natural in general.




Pairing

The pairing list will include iBasso AM05, Fischer AMPs FA-4E-XB, and Periodic Audio Carbon. All of those are pretty close to perfect when paired with HUD100, and all of them show how versatile it is.



It ain't perfect, but it is pretty darn close.

Earstudio HUD100 + iBasso AM05 (140 USD + 300 USD) - AM05 is an interesting pairing because it was hard to pair, it is a bit too lean, the bass doesn't have enough body and mass to be substantial, but HUD100 somehow manages to make the AM05 truly sing, it gives them both a smoother treble, a smoother midrange, but also a fuller bass, that in the end sounds quite natural and open. There's also a great sense of dynamics, and the detail is top notch, so all in all, this is a favorite pairing of mine.

Earstudio HUD100 + Fischer AMPs FA-4E-XB (140 USD + 450 USD) - The Fishcer AMPs FA-4E-XB is a different thing, very linear and precise, quick, and lacking a sense of fun and enjoyment, being there for the artists, and letting you experience music as an artist is, while performing live. It is an irony, but I always imagined that a singer would listen to the most beautiful melodies, but instead they need the ultimate precision and clarity, without much enjoyment and fun. Here's where HUD100 can come in handy. On one hand, it can give you a transparent window, revealing how that type of sound is like, but if you want to tune in the FA-4E-XB to sound more fun, you can also do that through the HUD100, by engaging the effects, and listening to a much more fun presentation, with a smoother bass, smoother midrange and smoother treble, with ,more body and impact, and ultimately, to a presentation that is more fun.

Earstudio HUD100 + Periodic Audio Carbon (140 USD + 400 USD) - The Carbon is a very heavy IEM, with a smooth midrange and a strong enough treble to counter that really heavy bass, but on a scale from one to ten, it is in top three the most bassy IEMs I heard to date, in the same line as the IMR Acoustic R2 Aten and IMR Acoustics R1 Zenith. This is where the "flat" preset of the HUD100 comes in handy, it makes the Carbon slightly more settled, it makes them reveal just how detailed and musical they are, and it flattens some of those bumps in the bass and the treble, making the entire IEM shine.




Value and Conclusion

The price of HUD100 is really high for what it is, if you don't plan on driving particularly fun-sounding IEMs, and if you don't need the shape and design, as there are alternatives in this price range that fare better, like the PAW S1, which has a balanced output, and much more driving power. This being said, nothing doesn't have quite the same signature with the rounded bass, liquid and smooth midrange, and the smoother treble that pairs well with both brighter and darker IEMs, and nothing doesn't have quite the same small rectangular shape of the HUD100.



The package is once again not exactly right for the price range, as the carrying leather case cannot be used while using the device, and the cables need an OTG adapter which is not included in the package.

The sound though, is fairly smooth, fairly detailed, and has a good amount of impact. The bass is well-rounded, the treble is somewhat smooth, and there's a good amount of dynamic, if you engage the dithering and all the effects possible, but you also have access to a flat signature, if you need one.



At the end of the day, the HUD100 may be a bit controversial, but especially for those who need a light, small DAC for driving mainly IEMs, and if you want to experience a rather dynamic sound, if you don't have a very hiss-sensitive IEM, and if you want to have access to two headphone outputs, the HUD100 is an interesting product, right out of Korea.



Full Playlist used for this review

While we listened to considerably more songs than those named in this playlist, those are excellent for identifying certain aspects of the sound, like PRaT, Texturization, Detail, Resolution, Dynamics, Impact, and overall tonality. We recommend trying most of the songs from this playlist, especially if you're searching for new most, most of them being rather catchy.


Youtube Playlist



Tidal Playlist

https://listen.tidal.com/playlist/64555551-ec3c-4279-ae44-248fdfcf6c4b


I hope my review is helpful to you!

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