EarStudio HUD100


Previously known as sub30
Pros: Miniscule footprint
Portability and “stackability” with included “jetpack” case
Relatively low noise floor even in High Power mode
Driving Power in relation to its size
Efficient battery consumption on phone
Premium build
Minimalist yet practical design
Everything you need is in the box
Sampling rate reaches way past dolphin levels
Currently sells for 119 USD with free DHL shipping*
Cons: Degree of Sound Mode change depends on what transducer is used
Neutrality might not match with certain transducers

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.


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.


  • 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

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:

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.


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.

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 :)



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.

****If you have other questions/concerns with the DAC/Amp mentioned, feel free to message me****​


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1000+ Head-Fier
What a dedicated little dac! Great sound, minor nitpicks.
Pros: + Clean and Articulate
+ Well Built
+ Discrete High Power Output
+ Hybrid analog/digital volume
+ Dead quiet noise floor
~ MQA support if you wish
Cons: - Price close to hybrid wireless units
- Loose fitting jacks
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.

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.

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.

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Nice review :) Liking the new accessories too. Good update @radsone !
Thank you for your review!

Dobrescu George

Reviewer: AudiophileHeaven
Pros: + Tiny Form Factor
+ Smooth Midrange with IEMs
+ EQ Filters that go from really flat to musical
+ Doesn't eat a lot of power
+ Good build quality
Cons: - Doesn't work without an OTG Adapter
- Cannot drive full sized headphones
- Not the most beautiful thing out there
- From the two headphone outputs, only the high power one sounds good
- Price is a bit high compared to what the competition offers for the same money or lower
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.


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



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


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


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.


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.


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


I hope my review is helpful to you!


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Luigi Milazzo
Luigi Milazzo
The paw s1 more power? No. Even in balaced mode.
Dobrescu George
Dobrescu George
@Luigi Milazzo - Do you have both? I am asking because HUD100 is really quiet, at least MK I. I am also reviewing the MK II which should have more power, but at least HUD100 MK I vs Paw S1, S1 has much much more power. To give you some idea, Paw S1 can drive HIFIMAN Sundara and Deva well, while HUD100 can barely drive most IEMs well if you listen really loud. Either of us may had had a unit that was underperforming if things about driving power and volume don't match or don't add up lol :)

Otto Motor

Headphoneus Supremus
Pros: Versatility (connects to all possible devices and has three filters for adjusting sound); runs high-impedance headphones better than the dongle competition; contains no battery as bottleneck for longevity; super portable.
Cons: Some basic adapters should have been in the box; battery consumption is relatively high on phones.


The Earstudio HUD100 is a jack-of-all-trades dac/amp: although extremely small, it has two power modes and even handles high-impedance headphones well; it connects to PC, Mac, and phones (iPhone/Android); and it offers three different processing modes (filters) for individual sound adjustments.


Earstudio are a company out of Korea that appeared on the map with their popular ES100 Bluetooth amp and their HE-100 single DD earphones. While I don’t care much about Bluetooth owing to the planned obsolescence (non-serviceable consumable battery limits lifetime), I became interested in the Earstudio HUD100 by its small size and wide applicability. I was wondering how it compared to my Audioquest Dragonfly Black v1.5, which I had acquired more than 5 years ago. After all, there must have been some progress since.

Radsone is currently running a promotion of the Earstudio HUD100 for our blog users and Facebook Group members. You find all info/link in the specs below.


DAC chip: AK4377
Inputs: USB-C
Outputs (3.5 mm): Standard (0.914 Vrms), High Power (2.26 Vrms)
Output Impedance: < 1 Ω
THD + N (Standard): -105 dB (0.00056%)
THD + N (High Power): -102 dB (0.00079%)
Dynamic range (Standard): 118 dB
Dynamic range (High Power): 118 dB
Sample rates: Up to PCM 32-bit 384 kHz, DSD128 (DoP)
Desktop compatibility: Mac OS 10.10 or later, Windows 7 (32/64-bit) or later
Mobile compatibility: iOS 10.3.3, iPhone 6 or later, Android 6.0 or later
Dimensions: 1.8 x 1.3 x 0.3 in (4.5 x 3.2 x 0.8 cm)
Weight: 0.8 oz (21.5 g)
Tested at $139

Product page: https://earstudio.store/products/hud100

Download manual: https://drive.google.com/file/d/11v189-R_pifC78USahTk1xDPFuDDJKCt/view

Get it on sale from the new Earstudio Store


In the box are also:
C to A USB Cable (1M)
C to A USB Cable (10cm)
Leatherette Travel Pouch

Earstudio HUD100

With either cable, you can connect the Earstudio HUD100 from its USB-C port to a PC/Macwith a standard USB-A port. But the HUD100 also works with Android phones and iPhones. In order to connect to the iPhone, you need the $29 Apple USB camera adapter, and to connect to a current MacBook or an Android device, you need a USB-C to USB-C cable or a USB-A female/USB-C male adapter (costs <$1 on aliexpress). One of the two should have been included in the box.

The actual dac/amp has rounded corners – ergonomically very good – and is built of metal. Looks and feels solid – and it has the dimensions of an eraser, just a bit flatter.


Operation is very easy. The HUD100 connects to devices through a cable from USB-C port. It works with your phone natively. If connected to your computer, the operating system’s sound preferences have to be set accordingly (details are in the clearly laid-out manual). You find two headphone jacks on the front panel: plug “normal” impedance earphones into the left one and your full-sized cans into the right one labelled “HP” (yes, you got it, it means “”High Power”). The filter switch is located between the two jacks. On top of the the housing is a LED that is illuminated during operation, the colour depends on the sample rate. There is no volume dial – volume is adjusted on the source.

Earstudio HUD100

From the manual.

Earstudio HUD100

Back of the Earstudio HUD100.

Earstudio HUD100

Front of the Earstudio HUD100.


Since the Earstudio HUD100 does not have an internal battery but draws power from the source, this only matters when connected to a phone – but not really when operated from a computer.

I let the fully charged iPhone SE (2016 model) (screen off, only “Music” app running…identical conditions for each dongle) play a song in a three hour loop at the same audio volume (calibrated with white noise at 85 dB through a Dayton microphone) also with the Hilidac Atom Pro, Apple audio adapter, Tempotec Sonata Pro HD, and the Audioquest Dragonfly Black v1.5, attached to the Blon BL-03 earphone at its standard 32 Ω. I ran some of the tests twice. The remaining charge in the iPhone after three hours was:

  • Apple Audio Adapter: 93%
  • Audioquest Dragonfly Black v1.5: 82% and 82%
  • Tempotec Sonata HD PRO: 75%
  • Earstudio HUD100: 64% and 61%
  • Hilidac Atom Pro: 62% and 61%
This indicates that the Earstudio HUD100 is a bit of a battery hog (and even more so when using the “High Power” jack with a high-impedance headphone) – you better get a phone with a large battery. Be aware that the absolute numbers listed above are meaningless, what alone counts is the differences between the dongles. After all, the iPhone SE has a relatively small battery (1500-1600 mAh).


My tonal preference and testing practice

My test tracks explained

The Earstudio HUD100 measures well, as established by Audio Science Review, the question is: does it sound as good as it measures? Since the the HUD100 offers sonic versatility through its 3 filters by the flick of a switch, the listeners has choices of these three algorithms – which currently only work at 44.1 kHz sample rate:

Bypass: the leanest most neutral presentation. For the purist.

DCT: the most analog presentation of the three: adds warmth and thickens the image at the expense of transparency. For people who miss their tube amp Andorra their vinyl.

Dynamic: adds punch and kick. Not the most realistic, but sometimes one is the mood for that extra bit of sonic edge.

I listened with the iPhone SE (2016) and my MacBook Air. The differences between the filters are not earth shattering but they are distinct. I preferred the DCT algorithm for most music, as it comes closest to “analog” sound. First is to note that the HP output provides plenty of punch and power for the 300 Ω Sennheiser HD600.

As to the sound, the HUD100 does not offer the headroom of a full-size headphone amp but it does a pretty decent job. It is fast, has very good clarity but it boosts the upper midrange a bit to achieve this – and things can get a bit sharp at high volumes. But it does not unwantedly bloat the bass like the Audioquest Dragonfly. Bigger headphone amps play a bit more relaxed – and cost more. While this may not sound encouraging – it actually is. The sonic performance of this tiny rascal is astonishing.


The Earstudio HUD100 has fixed sample rates for iPhone phones and PC/Mac: which means, in iTunes the HUD100 does not automatically play the sample rate of the music file but rather the one chosen in the Mac’s Audio MIDI setup/Windows preferences. This can be circumvented by using advanced players such as Foobar or Audirvana. In the iPhone’s music player, the HUD100 ignores the file’s native sample rate completely and plays every file as PCM 44.1 kHz, unless you use a special player for dacs such as the Onkyo HF Player. On Android phones, the sample rate is also fixed to the device’s default sample rate (which is usually 192 kHz on a Galaxy phone).

The manual states that DCT and Dynamic modes currently work on only PCM 44.1kHz (on any device). In comparison, the Audioquest Dragonfly does automatically utilize each music file’s sample rate on both, iPhone’s music player and Mac (but plays only up to 96 kHz/24 bit, the Earstudio HUD100 up to 384 kHz/32 bit).

Shape-wise, HUD100 is a bit of an oddball. Yes, it connects to basically everything but, although small, its rectangular dimensions (dictated by the two headphone jacks) make it an unusually shaped phone dongle — and it can be quite a power drain on the phone. On the other hand, when used with a computer, it occupies very little space on a desk. And since the small size sacrifices performance, it could have been bigger for the desktop purpose. Its shape is therefore a compromise to satisfy all possible functions, be it connectivity, mobility, and varying headphone impedance loads.

Earstudio HUD100 COMPARED

In low-impedance “normal” mode, there is not much difference in sound quality between an Apple Audio Adapter and the Earstudio HUD100 (in “Bypass”) while ignoring the other two processing modes. The latter two make Radsone a bit more flexible in the sound signatures. AND: the HUD100 has way more power and drives high-impedance headphones – the Apple Audio Adapter does not. The $115 very neutral Cozoy Takt-C is much less versatile with its fixed cable (USB-C and lightning versions) and it has a bit less power, but still drives a 300 Ω headphone. The $45 Tempotec Sonata HD PRO surprises with accessories the HUD100 would like to have (USB-A female to USB-C male adapter for connecting to the current MacBooks, lightning cable for connecting to iPhones), it sounds a bit warmer, lacks a tad of refinement and transparency, is just powerful enough for a 300 Ω headphone, but it holds up impressively against the much pricier competition.

Earstudio HUD100

Size study: Earstudio HUD100 with ifi nano iDSD Black Label and Apple USB-C audio adapter.


Please take the following comparison with a grain of salt. I compared three different setups using the 300 Ω Sennheiser HD600 headphone. First, I listened to the 1987 Colourfield album “Deception” on vinyl (Thorens TD 147 record player with Elac pickup) through a Luxman L-410 amp and a Schiit Magni 2U headphone amp. Absolutely godly…super headroom and depth. I then listened to the same music on my MacBook Air, iTunes (AAC audio file, 256 kbps at 44.1 kHz; rip from remastered CD; NOTE: the CD mastering may sound different from vinyl). First I used the $199 ifi nano iDSD Black Label amp. To my surprise, the vinyl setup had more depth, tallness of stage, and transparency. I then connected the infinitely smaller Earstudio HUD100 using the DCT “analog” filter. The HUD100 had plenty of power to drive the HD600. They were a bit sharper around the edges compared to the more relaxed playing ifi nano iDSD Black Label but they also had the better kick and transparency, fueled by a slightly elevated upper midrange. Pretty impressive for their small size. Let’s put it like that: whenever I look at the tiny box while listening with my HD600, I can’t believe what I hear.


I would have included a USB-C male to USB-A female adapter for connecting to a current Macbook or Android phone, i.e. added versatility, considering it costs <$1.


The Earstudio HUD100 is a unique beast without real competition: it is powerful, versatile both sonically and functionally while being super small and therefore very handy. Great for travel with a notebook or when connected to a desktop with little desk space. While it does not offer quite the headroom of a full-sized headphone amp, it does a pretty decent job even with high-impedance headphones. And because it does not rely on a built-in (but non-serviceable) battery, the Earstudio HUD100 will provide many years of good service – just like my Dragonfly Black v1.5 it will replace. In the end, it is relatively easy to decide whether this one is for you or not.

Until next time…keep on listening!

Jürgen Kraus signature

You find an INDEX of all our dac/amp reviews HERE.


The Earstudio HUD100 was provided from Radsone upon my request. Thank you very much. I do not receive any remuneration for posting the promotional link.

You can get the Earstudio HUD100 from the new Earstudio store.

Our generic standard disclaimer.

About my measurements.

You find an INDEX of our most relevant technical articles HERE.
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How does it compared with say tempotec sonata hd Pro as par sound quality only?
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Otto Motor
Otto Motor
Much much better!


Reviewer at Headphonesty
Pros: Incredibly small and convenient form factor
- Solid build quality
- Easy setup, just plug and play
- No charging required
- High sample rate support
- Versatile: 2 power modes and 3 sound profiles
- Powerful headphone amplifier
- Clean and highly detailed sound
- Transparent and fast transients
- Superb separation and imaging
Cons: Essential packaging and accessories
- Adapter needed for iOS and Android devices
- Thin notes
- Upper mids rise is too intense
- Unforgiving to poorly-mastered recordings
- Not too suitable for bright phones
If you’ve ever wanted to get serious audiophile gear without letting your significant other know, do take a look at the Radsone EarStudio HUD100, a tiny, easy-to-hide but powerful USB DAC for your laptop and portable devices.

A long time ago in a neighborhood far far away, my best friend and I sat under the stars and contemplated life. We were teenage idealists, and attempted to describe what made the world a better place, in one word. “Stability”, I said at once, feeling proud. My pal replied, “compactness”, and I’ve never looked more confused. “So everything is smaller and easier to carry, you know? Get more things done.”

Today, the world is nowhere near stable, heck it’s going the other way! But my friend is closer than ever to seeing his version of utopia come to fruition. Damn near everything is consolidated and shrunk to tiny, multifunctional devices that fit into the pocket. The laptop is now his office, the smartphone his virtual assistant. He’s gloating now, the visionary living the dream… of compactness!

The people of Radsone probably think the same way. Founded by Mr. Jay Yoo in 2011, Radsone (short for Radical Sound) dreams about providing high quality audio to the masses by providing hardware and software solutions in Bluetooth and USB audio, DSP (Digital Signal Processing), circuit design as well as a host of their own innovations. EarStudio is the sub-brand of Radsone that releases finished hardware.


Tiny assistant will help reduce your paperwork.

Side note: all their products are tiny, with portability firmly in mind. Their first claim to fame was the ES100, a Bluetooth amplifier/receiver that was released to plaudits and acclaim for delivering wonderful sound in a convenient form factor.

Today we look at EarStudio’s newly-released USB DAC (Digital-to-Analog Converter) and amplifier, the HUD100. Designed for use with laptops, iOS and Android devices, HUD100 supports sampling rates up to PCM 32bit/384kHz and DSD128, and comes with a powerful amplifier, three sound profiles and two output modes, all in a tiny (there’s that word again) package that weighs only 21 grams.

I’m still trying to wrap my head around the HUD100’s impossibly miniscule size. You really have to see it to believe it, photos only make it look larger! The HUD100 is available via its official website. I’d like to thank Kyle Choi of Radsone for reaching out and providing the review sample.

This review was first featured in Headphonesty.

Equipment Used:
  1. Radsone EarStudio HUD100
  2. Asus N55SF
  3. Samsung Galaxy S9
  4. Moondrop A8
  5. Acoustune HS1650CU
  6. Sennheiser HD660S
  7. Massdrop x Focal Elex

Albums Listened:
  1. Adele – 25
  2. Amber Rubarth – Sessions from the 17th Ward
  3. Fleetwood Mac – Rumours
  4. Fleetwood Mac – Tango in the Night
  5. Macklemore & Ryan Lewis – The Heist
  6. Miles Davis – Kind of Blue
  7. Patricia Barber – Verse
  8. Rebecca Pidgeon – The Raven
  9. Various Artists – Jazz at the Pawnshop

Technical Specifications:
  • Inputs: USB Type C
  • Outputs (3.5mm): Standard 0.914Vrms (1.29Vp), High Power 2.26Vrms (3.20Vp)
  • THD+N: Standard -105dB (0.00056%), High Power -102dB (0.00079%)
  • Dynamic Range: Standard 118dB, High Power 118dB
  • Sample Rates: Up to PCM 32bit 384kHz, DSD128 (DoP)
  • DAC Chip: AK4377
  • Desktop Compatibility: macOS 10.10 or later, Windows 7 (32/64bit) or later
  • Mobile Compatibility: iOS 10.3.3/iPhone 6 or later, Android 6.0 or later
  • Dimensions: 45 x 32 x 8mm
  • Weight: 21.5g


Not exactly a successful shakedown.

Packaging and Accessories

This is a succinct and straightforward packaging. The HUD100 is kept in a matte gray box, which displays a glossy image of the DAC and documents its main features. The image on the box is bigger than the actual HUD100, I might add. The accessories bundled are as follows.
  • Leatherette travel pouch
  • 1m USB Type C to Type A cable
  • 10cm USB Type C to Type A cable
  • Quickstart manual
This is an “essentials” package to get you started immediately. The HUD100 does not need to be charged (it draws power straight from your device), nor do you need to install any drivers or apps for it to work. It’s plug-and-play heaven. The accessories are sparse, and the leatherette pouch is a tight and frustrating fit, but you’ll get over it soon.

Design and Build Quality

Let the tips of your thumb and pointer finger meet. The HUD100 is just about as large as the opening your fingers created. Wrap your mind around it. It’s smaller than a matchbox or a Tic Tac packet, but has an ARM Cortex processor inside and is able to play DSD128. I’m still getting mind-blown, but have to keep writing to keep you entertained.


Mugshots from the first day of lockdown.

The topside of the HUD100 has a color-coded LED that shows you the audio sampling rate, while the bottom is the EarStudio logo. At the front is a switch to change sound profiles, and two 3.5mm jacks, one for standard output, the other labeled “HP” for high-powered output. At the back is the USB Type C port, and a slider switch used to update firmware.

The HUD100 has a compact, no-nonsense design, with an emphasis on function and action. Changing between sound profiles is just a flick of the switch away, and it is well-built with a satisfying click. The aluminium body is rock-solid but not immune to scratches, so while not ideal, it’s good to have the leatherette pouch giving some protection when out and about.


The provided cables are all you need to connect the HUD100 to a laptop. I like to use the short cable because it makes for a tidy setup. Just plug the USB Type C cable to your laptop’s USB port, and Windows should be able to recognize it. Select HUD100 as the playback device by left-clicking on the speakers icon in the notification area (bottom right of the screen).


Time for some shameless plugging amirite?

For iOS and Android devices though, you’ll need an additional adapter to get the HUD100 working. Namely, the Lightning to USB Camera adapter for the former, and an OTG adapter for the latter. It adds additional bulk and hassle to the process, reinforcing the fact that HUD100 is best used with laptops I guess.

The saving grace is, unlike laptops you don’t need to activate anything once the HUD100 is connected to your smartphone or tablet. From there, just plug in your favorite in-ear monitors (IEMs) or headphones, select your music app, and play away.

The Laptop Setup

Windows/macOS laptop
> USB Type C to Type A Cable > EarStudio HUD100 > cable > transducer (IEMs/headphones)


Not the blue light of death.

The Portable Setup

Android device
> OTG Adapter > USB Type C to Type A Cable > EarStudio HUD100 > cable > transducer (IEMs/headphones)


Very much still portable!

I’m allergic to fruit, so I don’t have any photographs with Apple devices. But I’m sure they are just a Google search away.

Features and Functions

Power-packed Technology
Under the hood of the blisteringly compact HUD100, is a trove of hardware and engineering ingenuity showcasing EarStudio’s devotion to the highest quality audio possible.

AK4377 DAC Chip
Developed by Asahi Kasei Microdevices (AKM) of South Korea, this DAC chip with a built-in headphone amplifier supports sampling bit-rates up to PCM 32-bit 384kHz and DSD128. I’m not a DSD believer, but go right ahead if you have tons of storage space.

ARM Cortex Processor
Honestly, I’ve never heard of a processor inside a DAC, and Radsone claims they are the first to do so. This particular one was deployed to implement Radsone’s proprietary algorithms in two of the HUD100’s sound profiles.

MEMS Oscillator
Another industry first, this is used as a master clock to minimize jitter, or irregularities in the audio signal, resulting in a clean background.

DCT (Distinctive Clear Technology)
This is a dithering algorithm implemented in Radsone’s sound processing to eliminate digital noise in the sound signal, which in turn produces a more precise and natural sound.

Elaborate Circuit Design
The HUD100’s tiny size is the result of an intricate and meticulous 8-layered circuitry design to maximize performance from a small form factor.


Beauties in a row, bathed in purple glow.

Color-coded Sampling Rates
The AK4377 DAC is a multi-tasker capable of audio output in a varied spectrum of quality, and in the HUD100, the sampling rates are color-coded for your convenience.
  • Green: 44.1kHz
  • Blue: 48kHz
  • Cyan: 88.2kHz / 96kHz
  • Red: 176.4kHz / 192kHz
  • Yellow: 352.8kHz / 384kHz
  • White: DSD64 / DSD128

Sound Profiles
The HUD100 is home to no less than three distinct sound signatures for the user to fine-tune their preferences. It’s like Neapolitan ice cream where if you can’t choose, you get three favorites. These sound profiles are easily switchable at the front of the HUD100.
  • Bypass mode: For the purists, this mode does not undergo sound processing via Radsone’s proprietary algorithms.
  • DCT mode: As mentioned, a dithering algorithm is applied for a smooth, analog sound
  • Dynamic mode: Another Radsone-applied tuning for a powerful and lively signature.

The Beast Unleashed
The HUD100 has two power output modes:
  1. Standard
  2. High Power (HP)
Standard output produces 0.914Vrms of power and is well-suited for use with IEMs and low-impedance headphones. In HP mode, the HUD100 pumps out 2.26Vrms for high-impedance, power-hungry headphones rated at an impedance of 250Ω and above.

I like that the abbreviation HP implies HeadPhone use, instantly reminding you that this is the output with higher power. It can be a tad confusing if you work for Hewlett Packard or Hush Puppies though.


Aww shucks, Michael Scott was nowhere to be found.

Power Output

The HUD100 ran the gauntlet with my ragtag collection of transducers.
  • Moondrop A8, an 8 balanced armature (BA) IEM
  • Acoustune HS1650CU, a single dynamic driver (DD) IEM
  • Sennheiser HD660S, a DD headphone rated at 150Ω impedance
  • Massdrop x Focal Elex, a DD headphone rated at 80Ω impedance
Standard output drove both IEMs flawlessly, with good volume, spaciousness and dynamics, set against a black background. They remain hiss-free at higher volumes. High Power output did the same for my moderately demanding cans. The HUD100 drove them effortlessly with lots of volume to spare, and even better, the sound did not distort or mush together at higher volumes.

I am not left wanting in loudness levels and dynamics at all. The HUD100 is evidently a pocket beast.

Sound Quality

At this point in time, I think it’s safe to say most of the planet is under lockdown due to an infectious, crown-shaped organism that just activated Hulk mode. With that in mind, it’s as good a time as any to read up on diffuse-field (DF) neutral to understand what I mean next.

Overall Sound Signature

For a transducer, a neutral tuning is hit-or-miss since not everyone enjoys a flat, sterile sound. It is highly detailed but emotionally uninvolving. But for audio sources such as the HUD100, I believe that a neutral tuning is functionally ideal, so the sound is as uncolored and unaltered as possible, providing a blank slate for the transducer to show off its signature.

Think of the HUD100 like raw chicken fillets with no seasoning. Allow the transducer (and maybe the cable) to provide the salt, pepper, soy sauce and what have you. The chicken just has to be as clean and fresh as possible. Ergo, the HUD100 focuses on providing a clean, pure audio signal. Get it now?


Loving the company of famous people, especially that swift tailor.

The Three Amigos

From that standpoint, the HUD in Bypass mode is unmistakably neutral. The bass all the way up the mids are devoid of elevations or boosts, delivering an honest, if unappealing sound. The upper mids and lower treble are elevated, but comes back down gradually to a flat mid-to-upper treble. Notes are thin, quick, precise, and crispy. Scientific listening, I’d call it, but this is easily my favorite sound profile.

In DCT mode, with Radsone’s dithering technology applied, the note edges are smoothened, and music is rendered more liquid and flowing. This contributes to the immeasurable characteristic known as “musicality”. For a relaxed and effortless listening experience, DCT is the sound profile to go for.

The Dynamic mode reminds me of Bypass mode, but with a twist. The signature rendered is more V-shaped for an intense and invigorating listen. The sub-bass is more physical and thumpy, while the treble is sharper and airier. I might as well call this the “fun” switch, and this is my second-favourite setting after Bypass.

I should note however, that due to limitations of sound processing, the maximum bitrate allowed for both DCT and Dynamic modes is currently limited to PCM 44.1kHz only. Higher bitrate files will be down-regulated to 44.1kHz. It’s just as well that I mostly use the HUD100 in Bypass mode.

The following sound impressions are based on the Bypass mode.


Like getting to know a close friend in times of crisis, this is a side of the bass not often seen. Completely free of bloat and extra baggage, the bass becomes a lean body of fine texture and intricate detail, uncovering loads of yummy musical information normally masked or obscured by full bass notes or an over-long decay.

Downward extension is very good, and transparency levels are among the best for the price. Notes are tight, punchy and disciplined, with just enough body in attack, sustaining minimally before decaying quickly into the background. Speed and timing is of the essence, as the HUD100 bass maintains a steady, irresistible rhythm and maxes out on dynamics. A Fleet-foot Mac that unveils layers of bass, if you will.

The bass might be neutral to a fault, but do not despair. If your headphone is bass-enhanced, the HUD100 will play it. It is after all, your canvas. The Elex’s bloomy, punchy bass is displayed in full glory, along with a healthy dollop of detail. Ditto the HS1650CU, where bassy passages like the intro to Macklemore’s “Thrift Shop” are meaty and handled with confident swagger.


Not exactly a friendly atmosphere at the boys’ toys convention.


A wise man once said one good taco deserves another, so the mids carry over the speed and eye for detail from the bass. That is no big surprise. The lower-to-middle mids are precise, even in tone and, here’s a slight deviation, smooth. This is the most liquid and euphonic region in the spectrum, sounding realistic and true-to-life.

The accurate timbre is balanced with good clarity, and together are a delight to listen to. Male vocals and guitars have authority and bite, although overall the notes remain thin. The upper mids, however, are significantly elevated. Note speed is enhanced, becoming airy, crispy and wafer-thin. Your attention is diverted here because they sound so prominent.

This is a slight mis-step, especially when paired with brighter transducers, because the upper mids tend to become shrill, reedy and too bright for its own good. Using the Moondrop A8, which already has raised upper mids, cymbals and brass instruments sound hollowed-out and screechy, even with well-recorded material like in Fleetwood Mac’s “The Chain” and Miles Davis’ “So What”.


The HUD100 serves up a congruent and solid signature, like a chain link. I’m trying not to think of lockdowns lol. The lower treble resumes the handiwork of the upper mids, sounding bright and intense, though at a lesser degree, thankfully. You don’t have to worry about brass and percussion instruments having not enough bite, there’s plenty of crunch to be had.


Bribery and bling-bling will get you nowhere.

However, in poorly mastered recordings, expect the treble region to be laid bare and massacred by the HUD100. It’s revealing nature won’t shy away from imperfections and artifacts. Adele’s 25 was a victim of this at the higher registers. When paired with Moondrop A8, the album was an unbearable listen because of the harsh and distorted treble.

By mid-treble, the signature slowly rolls off and leaves behind a trail of air. This region still boasts a lot of clarity and speed, but is no longer peaky and sibilant. I would never doubt HUD100’s technical ability. It serves up a wondrous (perhaps a bit overbearing) amount of detail and air, laying down a clean, astute foundation for the transducer. HUD100 won’t be caught out as a bottleneck in the audio chain, it refuses to.

Soundstage and Imaging

The soundstage is a treat, like ice cream on a warm summer day. In lockdown. Though boasting average dimensions, the HUD100 staging is cube-like and similar in width, depth and height. Music envelopes your head-space, coming from slightly in front and to the sides. It is a natural, non-exaggerated stage that puts you in the front row of a performance. It won’t enhance what your phones are already capable of, but it won’t hamper them either.

Where the HUD100 emerges triumphant is in separation and imaging. The proprietary technologies implemented by Radsone, work their magic here. The background is clean as a whistle and gloriously dark. Notes are precise, well-defined and well-spaced without any smearing. In turn, layering and positioning are pinpoint-accurate across the three axes, with a clear, comfortable distance between instruments. Let me make one more quarantine joke, ok? The HUD100 imaging is like social distancing at its best.


Holy doughnuts! There you are.

Final Words

The world is shrinking. Not in a literal, comedic sense unfortunately, because I’d love to see shrink-rays in real life. But because advancements in communication mean that people are brought closer than ever before. Not only that, years back we had to choose between form or function, when in many cases today, it’s feasible to have both. The Walkman and iPod jump-started the revolution for portable audio, which is snowballing until today.

Radsone is firmly on-board the shrinking planet. With the ES100, and now the HUD100, they are making a brilliant case for capturing high quality audio in small packages. Looking at ancient, blocky portable amplifiers, 10 years ago I would not have dreamt that such a stellar product is possible, but here we are. A clean-sounding DAC and powerful amplifier rolled into a device smaller than your car keys.

It would be a stretch to say the HUD100 is capable of replacing full desktop systems, but for the casual listener, an audible improvement in sound quality from normal laptops, tablets and smartphones will be enough. The HUD100 made my Galaxy S9 sound cheap and tinny in comparison. The best part is, the small and quite affordable HUD100 won’t dent your pocket physically, and figuratively. The chic shall inherit the earth, surely.
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Headphoneus Supremus
Pros: Flat-neutral-uncoloured sound, good transparency, good single-ended power output, sturdy metal construction, low battery consumption, can play up to 32bit/384khz and DSD128
Cons: Slightly cold sound, average imaging and soundstage, some distortion with bass at high volume, not the cleanness sound, not very textured or detailed, no volume control, no USB-C to USB-C cable included, not competitively priced


SOUND: 8/10
VALUE: 7.5/10
RADSONE (aka Radical Sound) is a Korean audio company specializing in portable audio solutions like audio IP for smartphones, digital audio decoding and audio hardware implementation. They are as well the creator of EARSTUDIO company which got good recognition worldwide for their excellent portable Bluetooth DAC-AMP, the legendary Earstudio ES100.

As a big fan of the ES100 myself, which I still use very often due to its excellent sound and powerful balanced output, I’ve been waiting for a higher-end successor that would deliver an even more powerful and beautiful sound. After a year of waiting, Radsone do launch the ES100 MK2, but it was the very same DAC-AMP with a minimal upgrade in construction material.

The waiting still continues, and Radsone surprise us by launching their first earphones, the HE100, while it was good and quite maturely tuned, this isn’t what we were asking to Radsone. The fans dream about a flagship Bluetooth DAC-AMP from you guys, are you working on it, are you?

And then, the EARSTUDIO HU100 comes in the game. A super powerful and super small portable DAC-AMP, especially thought for laptop and tablet….great….but why too? Is it what we were waiting for? Hum, not really, not me at least. Well, apart that if the sound is fabulously clean and powerful and the device is very versatile and do not drown phone battery life and and…even then, I’m not sure I do really need this. Because well, it’s 160$ and I just review a lot of excellent DAC-AMP dongle at way cheaper price like the Tempotec HD PRO.

But wait, it’s now priced 135.99$ and it has an unbalanced power output of 3.2V and it’s so small so so tiny small and the device look invincible. It might be interesting for some audiophiles that aim for minimalist DAC-AMP solution, isn’t it?

Let’s see in this review if the HUD100 can have a valuable purpose in your audiophile setup.

You can buy the Earstudio HUD100 directly from the official Earstudio website HERE.


Check Out The EarStudio HUD100 USB DAC - Samma3a Tech


The HUD100 might be small, but the intern is a complex micro-environment of 8 layers circuit design that uses the latest technologies to take full advantage of DAC implementation. At the core, we have an AKM AK4377 DAC that supports PCM stream up to 32bit/768khz and DSD256, but the HUD100 is limited to 32bit/384khz and DSD128. This DAC is the first to adopt an ARM cortex processor, which permits to implement Radsone proprietary digital audio algorithm for fast and precise sound decoding. As well, the HUD100 uses a MEMS oscillator as the master audio clock, this oscillator is more advanced than the crystal oscillator used with most DAC and delivers extremely low jitter so the signal conversion from digital to analog is free of any distortion.





I was very underwhelmed by both the product presentation and accessories of the EARSTUDIO ES100 and I most admit it did improve a lot with the HUD100. It comes in a solid box and when you open it you see the HUD100 inside a cute little leather carrying case. In terms of accessories, you have 2 USB to USB-C cable of great quality, but no USB-C to USB-C cable to hook the HUD100 to your phone, neither a USB to USB-C converter. I can see this as a problem for those who haven’t already proper cable to connect the HUD100 to their phone.





The HUD100 is as big as a matchbox, it’s really small at only 4.5cmx3.2cm of size. Construction is all metal and the finish looks quite scratch resistant. In hands, this feels very solid, with no loose part. The switch is made of metal too, but the 3 steps lack a bit of proper click. On the front, we have everything: two 3.5mm output with the sound filter switch in the middle. Audio jacks are made of plastic but feel sturdy and of good quality. For its miniature size, the device has a good reassuring weight.

DESIGN is simple, you have the USB-C connection in back side and connection in front. Unlike other DAC-AMP that need high gain to be selected either by a switch or option, the HUD100 permit you to directly connect your headphones into low or high gain output. Depending of your need, you will then choose Bypass mode or a sound filter that will suit you. Their no volume control, no possibilities to change tracks or play-pause, which is quite a bummer and make you fully dependant of your laptop or phone for music control. I guess the small size obsession does not permit for such control, but I find this cumbersome.

EarStudio DAC/AMP HUD100

In terms of interface, you have only the filter switch to play with. An interesting feature is a little led light that changes color with the music sample rate. It does work properly and I discover I have a lot of 48khz album as must of the time it’s a dark blue light that comes up.



After having installed the window driver, the HUD100 gets automatically recognize from my SurfacePro and works perfectly without any clicking, jitter or sound cutting. Using a good USB-C to USB-C cable, it gets recognize automatically by my phone and I was surprised to see it do not drown phone battery a lot, as after one hour of use my LG G6 battery lower by 10%. I don’t know if it’s me, but I feel the sound is slightly less loud with my phone comparing to my laptop. Unlike ES100, you do not have a dedicated app so you can use and custom every feature of HUD100, to me this is a serious drawback because ES100 app is a game-changer in whole users’ experience.



We have 2 types of power output with the HUD100, the low gain deliver a max of 1.29 volt per channel while the High Power mode (HP) deliver up to 3.2 volts per channel. This is what Radsone stated. Audioscience measurement show 23mW @ 33ohm for low gain and 138mW @ 33ohm for high gain. This is about the same power output than ES100 when used balanced. Though this is impressive amping power for unbalanced output, it’s still not enough to drive anything above 300ohm or capricious low sensitivity headphones. For earphones, it will drive mostly anything properly. The low gain mode is very useful for sensitive earphones prompt to hiss, and the low output impedance of 0.31ohm promises good clarity free of any hiss. Still, this impedance isn’t top of the line as I tend to be more confident with an impedance 0.1ohm or lower. To my ears, the amping stability is just above average for its price range, but not particularly stable in low frequencies which demand a lot of currents, this means that the HUD100 can act weakly with too hard to drive headphones or earphones. This does happen too with its ES100 predecessor but to a less extent.



The overall sound of the HUD100 is flatter than flat, with lean bass, slightly dry timbre, good transparency and not the cleanest black background. It has an intimate feel to it with good wideness but average tallness and deepness. Imaging is rather average too, and to my ears overall tonality has a ”digital” feel to it, slightly cold especially when used in BYPASS mode. It’s not what I would call an analytical sounding DAC-AMP, because they’re a hint of warmth in resolution, which perhaps is there to mimic naturalness. So, why do I find it cold sounding? Perhaps because timbre tends to be dry and thin as well as dynamic impact slightly tamed. It’s hard to explain and the IEM or Headphones your using will react differently to this. Simply put, it tends to ”discolor” the overall sound rendering of your pairing, as well as sometimes improving (taming?) bass and treble control. As said, Flatter than flat.

CLARITY does not blow my mind, it isn’t very sharp and does not ”add silence” that will improve instrument separation. With sensitive IEM, higher is the volume lower would be the clarity and at high gain, if you try to drive demanding headphones it will perhaps create distortion in the lower bass region as it struggles to deliver stable current. Macro-resolution is quite good, but micro-resolution isn’t very crisp and revealing.

BASS is slightly recessed in sub-region, it has a slightly brightish-dryish timbre and extra texture that help delimitating bass notes. Midbass has a good impact with extra control to it, this tends to improve the presence of mid-range by keeping it clean. Lean is the bass and smooth is the impact, it’s not the kind of DAC-AMP that adds extra energy to bass, and in fact, it will render your basshead IEM more docile and polite.

MID-RANGE is impressively clear, smooth and transparent. It’s not very thick, timbre isn’t very textured, giving extra softness to vocal resolution and perhaps lacking a little bit of grain for extra nuance. Presentation is rather intimate and centered, it’s not very open and holographic. Again macro-resolution is better than micro-resolution, as the music is decoded in a flat way, not in a vivid super-articulated way. The impact of the piano notes does not gain extra weight and the violin strike sound more organic than abrasive. The highlight of mid-range it’s his transparency and cohesive fluidity, it sound tonally right tough not injected with extra life or energy.

TREBLE is quite natural, perhaps the less ”digital sounding” frequencies range of HUD100. Highs are crisp with good brilliance, decay is fast and you do have extra bite in upper highs so some micro-details became more sparkly. Anyway, it’s not highly rich, textured or detailed treble and even has laid back feel to it apart from extra upper highs that tend to add a little bit of air. Highs are on the thin side, and lower treble isn’t extracting a lot of sound info that will add nuance and texture to the instruments.

DCT Filter SOUND is slightly warmer and thicker, but it’s extremely subtle. Bass became a little loose and give some extra meat to mids and vocal. Treble is less sharp and sparkly. Soundstage feels wider but less deep.

DYNAMIC Filter SOUND a little more vivid and punchy, especially in the mid-bass and mid-range. It tends to offer a more rounded up sound with a weightier attack for piano and drums. The overall dynamic is more lively, but this is extremely subtle and it take some time for your brain to discover this change. All in all, Bypass mode is the cleanness and more digital-sounding mode and as it’s not the most revealing already, I don’t see why I would make it warmer by using other filters. In fact, I would have preferred a bass boost switch instead of these 2 very minimal sound coloring.



WITH HIFIMAN SUNDARA (hard to drive Planar)

The HUD100 can drive the SUNDARA, but I need to use High Power mode at full volume. I’m quite impressed by the clean sound it delivers because it does not make any distortion with bass this time and the whole sound is very well balanced. The soundstage is impressively open for such minimal amping, it’s very deep and imaging is extremely precise. Mid-range tend to jump even more at you while the bass keeps its punch and lose somebody and thickness. Timbre is smooth and transparent, even more, polished and liquid than amped with more powerful (but less clean?) DAC-AMP. TREBLE keep it’s revealing micro-details and feel rightly balanced. The SUNDARA is driven at about 90% of there full potential, which is a little miracle in its own right. Nice pairing!

WITH AUDIOSENSE T800 (sensitive iem)

These are very capricious IEM that need a VERY low impedance output of at least 0.1ohm, the HUD100 being 0.32ohm it, unfortunately, makes the T800 act strangely. What happens is that sound became unbalance and more V shape and bass create distortion even at rather a low volume. The mids became more recessed and dry. Treble is more forward and grainy. Not a good pairing even using Low Gain.

WITH FINAL AUDIO E5000 (low sensitivity)

The HUD100 barely drive them at full potential, the bass did dig very low and sound is full with good dynamic but not completely open even using High Power mode. If I push at full volume, the sound will become less clean and bass can distort. Overall imaging isn’t improved, and mids feel slightly more recessed. Bass isn’t particularly well controlled and struggle to offer a natural extension. Treble feels a little more forward but affect tonal balance too. This is a decent pairing, nothing more.

WITH DUNU DK2001 (easy to drive and versatile)

This is a good pairing wich is fully driven at Low gain. The background isn’t the blackest one. Soundstage gain in deepness and imaging is very precise and even improved because of higher bass. DK2001 lows tend to warmth overall mid-range with a lot of sources but not so much with the HUD100 wich tame its sub-bass boost and make overall bass more controlled and balanced. MID RANGE is clean, detailed and improved in layering. TREBLE gains some extra snap and brilliance. This pairing is excellent.




Priced 100$, the ES100 can be used as Bluetooth DAC-AMP and USB DAC but is limited to 24bit/48khz, so no DSD or hi res codec. The APP that comes with it permits to select 4 sound filters, use a great EQ, select dual gain mode which delivers double of power output than HUD100 when using balanced output (6.4vpp vs 3.2vpp). The construction is a little rubbish as its all plastic apart from the shirt clip. It does have button control for everything, unlike the HUD100.

In terms of sound, as it’s more powerful it can drive the SUNDARA at a higher volume in balanced mode, the overall sound is more textured and detailed but not as deep as HUD100. SOUNDSTAGE feels wider with ES100 and the bass is slightly more present due to better texture and dynamic. IMAGING is sharper, more analytical and holographic with ES100. CLARITY is higher with the ES100, tonality sound a little brighter too with more grain in timbre. The whole sound is more vivid and lively with the ES100, making the HUD100 sound flat and laid back with some extra highs presence. Timbre is a little thicker but transparency is better with HUD100.

All in all, while the HUD100 can play higher bitrate music, I still prefer how sound 16bit/44khz flac files fromES100 than 24bit/96khz files from HUD100. ES100 is more aggressive and energic, while HUD100 is more liquid and transparent.

VS FIIO BTR5 (140$)

Again, this is a Bluetooth DAC-AMP, this time it use dual ES9218P DAC and delivers 240mW @ 32ohm which is more powerful than HUD100. Construction is excellent, but about 2 times bigger than the HUD100. The unbalanced output of BTR5 is near 2 times less powerful than the High Power mode of HUD100 (80mW vs 140mW).

In term of sound, the HUD100 is more flat and transparent with deeper soundstage, the BTR5 has a wider and taller sound with a more holographic around your head spatiality. BASS is notably more present in sub-region with the BTR5, it’s thicker and has more punch and rumble and texture. This makes the tonality slightly warmer too even if the overall resolution is on par with HUD100. Mid-range sound fuller and more forward with the BTR5, attack have extra weight and timbre extra thickness the HUD100 cruelly lack. TREBLE sound more balanced with BTR5 and dig more sound info in lower-mid treble region which permit to offer a more natural and nuanced sound. The HUD100 is a little airier and has more air between instruments, the upper highs are more sparkly too.

All in all, BTR5 sound more natural and neutral to W shape while the HUD100 sound colder and more neutral to V shape. I think HUD100 has a blacker background noise floor too, but only when with headphones or earphones it can drive properly.



The EARSTUDIO HUD100 is a very capable DAC-AMP for its size and delivers a very neutral sound with impressive unbalanced power output which can be useful for those searching a small DAC-AMP that will drive properly most of their headphones and IEM. It’s ultra-small size makes it extremely portable and can be great for transforming your phone into a good audio source, still, the amping isn’t the most stable one and can create distortion in the bass region, as well, output impedance isn’t the lowest too.

I would be lying saying that I prefer the HUD100 over ES100, which is still a way better value even if it cannot play DSD. The HUD100 feel a little anachronical in today ultra-affordable DAC-AMP dongle world and the sound does not stand apart either in term of details retrieval, low THD or cleanness.

If you really need to play high res music and do not want to use balanced IEM or Headphones, the HUD100 is a decent audio solution, but it’s not an audio revolution like the ES100.


500+ Head-Fier
Pros: Powerful for its size, USB-C, standard 3.5mm outputs, heat management, sound modes add utility
Cons: pricy, limited value versus a desktop setup assuming space available, limited volume on Android
The Radsone Earstudio HUD100 is a USB-C DAC/AMP with two 3.5mm outputs (a standard output intended for IEMs and a high power output for high impedance headphones). The HUD100 has three sound modes: Bypass, which does not apply any effects, DCT, which applies Radsone’s proprietary advanced dithering, and Dynamic, which applies an EQ filter in addition to Radsone’s dithering solution. The HUD100 currently retails for $139.99. I received the HUD100 directly from Radsone in exchange for a fair and objective review.

This review is also available on my blog.

I used the Radsone Earstudio HUD100 with two different PCs running Windows 10. My listening impressions were taken with the Tanchjim Oxygen and the Moondrop Starfield using Spotify Premium and local music files of varying sample rates and bit depth. Visit my last.fm page to get an idea of what I listen to.

The Radsone Earstudio HUD100 is diminutive, as long and wide as two SD cards laid next to one another. I measured its dimensions as 46 mm x 31 mm x 8 mm. It is just tall enough to accommodate its 3.5mm jacks.

The top of the HUD100 is unmarked apart from a small LED which changes color depending on the sample rate currently used by the device. The bottom is marked with the Earstudio logo and the tagline “HUD100 | Hi-Fi USB DAC | Designed by RADSONE.”

The standard output is on the left front face and the high power output is on the right front face. “H-P” is marked to the left of the the high power output. Between the two outputs is a three-position switch which controls the sound mode. On the rear of the HUD100 is a single USB Type-C port and a firmware upgrade switch. The HUD100 does not have physical controls.

The HUD100 has a good heft to it, with all-metal construction and an advertised weight of 21.5 g (my postage scale is not precise enough to verify this beyond a general weight of around 20 g). The HUD100’s finish did chip on one corner during the few weeks I spent using it, revealing the aluminium underneath the anodized blue-gray steel finish. It remained impressively cool after sustained use.

Included with the Radsone Earstudio HUD100 are a 1 m USB-C to A cable, a 10 cm USB-C to A cable, a small synthetic leather carry pouch, and an owner’s manual.


The objective performance of the Radsone Earstudio HUD100 dongle has been extensively evaluated at Audio Science Review. As far as subjective impressions are concerned, I found the HUD100 to have great resolution, dynamics, and instrument separation. I could not distinguish between the HUD100 in bypass mode and my JDS Labs The Element in level-matched testing using the Tanchjim Oxygen. With IEMs, the noise floor was inaudible using the standard output.

I used the HUD100 primarily in bypass mode. DCT mode seems to make high notes like cymbal crashes a tad less distinct. I did find some use for the Dynamic mode, which appears to only affect frequencies below 800 Hz. The Dynamic mode boosts sub-bass and cuts mid-bass, which generally increases the heft of a given headphones’s presentation while cutting away bloat.
HUD100 Comparison.jpg
Comparisons of the Radsone Earstudio HUD100 DAC/AMP’s different sound modes using the Tanchjim Oyxgen
With the Oxygen (110dB sensitivity and 32 ohm impedance), I typically set my system volume to 18–24/100 using the standard output. With my Sony MDR-ZX100 headphones (using Hifiman HE-series velour pads), I set my system volume to 40–50/100 using the high power output. Sony’s advertised specifications for the MDR-ZX100 show a significantly lower sensitivity than independently measured, but using the MDR-ZX100 in an over-ear configuration as opposed to on-ear does raise the amount of power necessary for a good perceived listening volume.

The HUD100 does work with a USB Type C-to-C connection. Unfortunately, the Radsone Earstudio HUD100 is limited by stock Android to 43% of its actual volume output. Because the HUD100 lacks hardware volume controls, USB Audio Player PRO (UAPP) is necessary to use the HUD100 to its full potential with Android devices.


The Radsone Earstudio HUD100 dongle draws power from the transport device. It does consume a fair amount of power, and I do not recommend its use with smartphones.
HUD100 Headphone PC.png
HUD100 high power output power usage with PC
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HUD100 high power output power usage with smartphone
HUD100 IEM PC.png
HUD100 standard output power usage with PC
HUD100 IEM Smartphone.png
HUD100 standard output power usage with smartphone
Below are additional power consumption measurements from other USB-C audio devices:
Meizu Pro.png
Meizu HiFi Pro
xDuoo Link.png
xDuoo Link
Apple Dongle.png
Apple Dongle
The Radsone Earstudio HUD100 is a nifty little device and will find a place on my office desk. However, it is quite expensive and difficult to recommend to people who are primarily using full-size headphones and have the space for a full sized stack. If you mostly use IEMs and have limited desk space it is worth a look.
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Thank you so much for your review. FYI, HUD100 Firmware 1.02 which fixed the low volume issue on Android smartphones is available on the homepage :) The default volume is changed from -20dB to -3.5dB.


Headphoneus Supremus
Pros: Good build, small form factor, tuning options, output power options
Cons: USB Only, uses device power as it has no battery, needs OTG cable (not included) for android use.
disclaimer: The HUD100 was sent by Radsone for the purpose of this review. I have no financial interest in Radsone, nor have I received any remuneration for this review. If you have an interest in purchasing the HUD100 or other Radsone products, check out their website.


The packaging of the HUD100 is deceptive as the picture on the front of the box belies the size of the device. The lift-top style box has the photo on the front and data on the sides of the box. Lifting the cover reveals the instruction booklet on top and then the DAC in a foam surround. Under that, we have a small leather case a 1 meter usb cable and a 10 cm usb cable. The only thing that is missing is an OTG adapter for use with android phones. With IOS the CCK is required so the standard cable works fine, but with android an OTG is required so it would be nice to have in the package rather than having to find one elsewhere.



This thing is small, like smaller than you probably think even looking at the pictures, thus the quarter in the photos. The unit is about the same height and about two quarters wide and 1/3 of a quarter thick. In inches, that is 1.75 wide, 1.25 tall, and 1/3 of an inch thick. Construction is all metal with controls on top and bottom and sides slick save for an LED hidden in one side. The Top has two 3.5mm jacks for different impedances and a 3 position switch between while the bottom has a USB-C input and a switch used for firmware. The unit has little heft, but feels very solid with no play in the connectors and very positive clicks to the switches.



The HUD100 packs a lot of tech into its tiny package with an AK4377 DAC, and arm cortex cpu, mems oscillators to reduce jitter compared to standard crystal oscillators. The usb-c input port supports up to 32/384kHz for PCM and DSD128 depending on the source and driver in use. Radsone officially supports IOS (10.3.3 and above), Android (6 and above), Mac Os (10.10 and above), and windows (7 or newer). The HUD100 was discovered on all my device types without need of a driver, but the driver provided on the Radsone website does allow Windows to use the full capability of the device while it is limited to 24/96 without it on my system. The two output jacks on the HUD100 offer .914 V rms for the standard port and 2.26 V rms for the High-power port. I found my HD6xx ran fine off the standard power port while my HD800s needed the High power port to have enough headroom when using the little dongle.


The HUD100 is fairly straight forward and realistically you could simply plug it in via USB and plug a headphone into it and go. There are two buttons, one between the two headphone jacks, and the other on the back side next to the USB port. The switch nearest the USB port is used only for firmware updates and at the time of review no such release existed so I can't speak to ease of use on that one. The other switch (the one on the top between ports) is a 3 position switch that controls the tuning. With the switch in its left most position (nearest the standard output), the system is in bypass mode and no tuning is applied. In the center position, the device is in DCT mode which Radsone lists as processing the signal for a well-dithered analog like sound. In its right most position (nearest the HP output), the device is in Dynamic mode which provides a more powerful sound while retaining balance according to Radsone documentation.

A single LED in the center of the blank side of the box indicates sample rate with green representing 44.1kHz, blue 48kHz, aqua 88.2 -96kHz, Red 176.4-192kHz, Yellow 352.8-384kHz and white for DSD. I had no trouble distinguishing white, and the lighter blue that can be an issue with some of the cooler leds on the market.


First off, the modes do make a difference with the bypass being nearly linear with just a slight bump in the upper-mids/lower-treble to my ear. The DCT mode does produce a warmer tone with a slight emphasis to the mids and a bit more sparkle than the bypass comparatively. The Dynamic mode is a more V shaped tuning with emphasis on the sub-bass and lower mid bass and again on the treble region. I found detail to be good in all three modes and found that depending on the source material in use I could find myself preferring different settings. For pop/rock, the dynamic is fun, while for string quartet the bypass or DCT are preferable, and for full orchestral works, I'd choose the bypass every time. There is also a notable difference in the two outputs. For me it was easier to discern the differences in output power by looking at the noise floor of the two options. For sensitive in-ears, the standard output has a jet black noise floor while the High power output has a bit of hiss when paired with the same. On full size cans, the High power output provides more headroom although many low impedance cans may work just fine using the standard. It is also worth noting that the HUD100 does have its limits, things like the He-560 or T50rp that are famed for their power handling are both a bit too much for the HUD100, but things like the HD700 and even HD800 are within the High-power outputs wheelhouse.


Ikko Zerda - Probably the biggest difference here is that the Zerda forces you to pick either usb or lightning up front and you cant have both unless you buy two. Both have good sound, but the HUD100 is a bit more versatile with its dual outputs and tuning modes. Output power is a bit higher on the high power output while the low power side is a bit lower than the Zerda's output and may make the HUD100 a bit more useful with high sensitivity models to avoid hiss.

Hidizs Sonata S3 - I found the HU100 to be considerably more potent when compared to the S3. This one is a no brainer as build, power, sound, and versatility all favor the HUD100. The S3 is a good bit cheaper of course and has a smaller form factor which may also play into the argument for some.

Audirect Beam - Here we have a similar form factor to the HUD100 with a removable cable, DSD support (including 256 which the HUD does not support). The Beam also offers device controls on board while the HUD100 relies on the parent device to provide the same. Output power favors the HUD100, and tuning options do as well. During testing the beam was easier to knock the cable lose on in pocket and lose signal during playback. Also while my personal Beam has been solid, reports of build issues are common enough that I have some concern about long term durability. This is a much closer fight, but between durability concerns, price, and tuning make me lean toward the HUD100 as the more solid option.

Dragonfly Cobalt - So does spending this much more get you much more as a result? Short answer, nope it doesnt. The Dragonfly is limited to 24/192, build quality is much better on the HUD100 as the plastic shell has considerable slop to it on the dragonfly. Sound is where the dragonfly does well with good linearity and a very crisp sound. I do think the detail is slightly better, but lacking the tuning options of the HUD100 which give the HUD the ability to adapt a bit more than the dragonfly. Unless you just have to have MQA support, you can save a couple hundred dollars by looking into the HUD100 first.


there is an odd dichotomy in the market today, we have phone vs DAP, TWS vs dongle DACs, and streaming vs local files all going on in the portable, daily commute kind of space. The HUD100 is Radsone's take on the dongle for those who want a small DAC/amp that packs a lot of function into the package. It is tiny, but still provides more output power than typical for dongles and more versatility with its dual outputs and tunable signature. While the HUD100 was never meant to be a desktop DAC/Amp, it works well enough with most full sized cans to be a good option for something that goes in an office drawer when not in use. The HUD100 gives the purchaser a lot for their dollar, tunable sound, both high power and low noise floor options, a tiny form factor that stashes easily when not in use, and construction that should stand the rigors of the daily commute with no ill effects. While the market is certainly crowded for dongles, the HUD100 does a lot to stand apart from the crowd and deserves your attention. I guess it shouldn't surprise me that the company that developed probably the best 1st gen bluetooth adapter in the ES100 has now worked the same magic on the dongle. It might just be these Radsone boys know a bit about what they are doing.


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Headphoneus Supremus
Pros: Easy to setup
3 different sound modes
Standard and high-power outputs
Dynamic, detailed but liquid sound
Tiny footprint
Cons: Has a lot of competition at this price point
No dedicated volume or playback controls
Of all the products I’ve reviewed over the last few years, the Earstudio ES100 Bluetooth receiver has been one of the most popular by far. However, when it comes to desktop use, a compact dedicated USB DAC often makes more sense. Enter the Earstudio HUD100, a DAC that has a tiny footprint but plenty of output power and Hi-Res audio quality.

So why do you need an external DAC, instead of just using your laptop or phone’s headphone jack? Well, laptops generally have low-power and low-cost built-in audio solutions. So the default audio quality is not that great and there is a lot of internal electrical interference or noise that can degrade the audio signal. In addition, the Earstudio HUD100 supports higher bitrates (PCM up to 32bit/384kHz) and has native DSD support for up to DSD128.

Radsone Official website: https://www.radsone.com/earstudio

Disclaimer: This sample was provided for the purpose of an honest review. All observations and opinions here are my own based on my experience with the product.

Package and Accessories
  • earstudio-hud100_1-1024x683.jpg
  • earstudio-hud100_2-1024x683.jpg
The Earstudio HUD100 comes in a simple compact box. Inside the box, you’ll find:
  • Earstudio HUD100
  • 1m USB Type C to A cable
  • 10cm USB Type C to A cable
  • Leatherette travel pouch
  • Owner’s manual
Build and Functionality
Starting with the physical build, the first thing I noticed is how tiny this device is. It’s smaller than a matchbox and in fact, is only 43% volume size compared to the already diminutive ES100MK2. The chassis is aluminium and feels robust despite its mere 21.5g weight.


On the front face of the device are 2 headphone jacks: the first is a standard 3.5mm low-powered (0.914 Vrms) jack which is perfect for sensitive earphones. On the right is a high-power output (2.26 Vrms) that can drive more demanding headphones up to and above 250 Ohm.

Also on the front face is a switch for choosing one of the 3 available sound options. Option 1 is Bypass mode which bypasses any internal sound processing, giving you an unaltered, uncoloured and transparent audio signal. 2 and 3 are DCT and Dynamic modes respectively. DCT produces an analogue-like sound while Dynamic is Radsone’s own processing mode that offers a powerful and balanced sound.

HUD100’s rear face has a USB Type C port plus a firmware update switch. On top of the device is a single small LED that lights up in different colours depending on the current sample rate. For example, when playing a 44.1kHz file, the light glows green and when playing back a DSD128 file, it’s white.

How Does It Work?

All you need to do to start using the HUD100 is plug it into your source device (laptop, smartphone etc.) It’s worth noting that Windows users will need to install the driver to unlock the full functionality. The Windows driver can be downloaded from Radsone’s website. For those who want to use the DAC with their Apple or Android smartphone, you will need a separate adapter which isn’t included in the box.

I’ve seen some people on Head-Fi asking if there is any app or EQ for the HUD100 and the answer to that is no. But, you can simply use the EQ settings on your music software, whether you use Foobar2000, MusicBee, or JRiver etc. On top of that, there are the 3 sound modes which I will cover more in the sound section below.

One thing I dislike about the Earstudio HUD100 is the lack of any physical volume or playback controls. While in general, all laptops have multimedia control functionality via the keyboard, desktop PCs do not. That means unless you have a keyboard with multimedia controls, you have to pick up the mouse to adjust the volume which is hardly convenient.

According to Radsone, the Earstudio HUD100 has an “elaborate circuit and layout design for best performance in small size”. Furthermore, they claim that this is the first DAC to adopt an ARM Cortex processor to implement their own proprietary algorithms.

The device is built around an AK4377 DAC chip and has a dynamic range of 118dB. Another first for the HUD100 is the MEMS oscillator used as a master audio clock which provides clearer clocks and further reduces jitter. While all that seems rather impressive, it doesn’t mean much unless it actually sounds good. So does it?

Let’s start with the Bypass mode. True to its namesake, the Bypass mode sounds transparent and uncoloured. What impressed me right away here was the space and air that the music was delivered with.

Firing up Joy Wants Eternity’s “Abide, Moment“, HUD100 sounds wide, deep and has impressive levels of separation. I loved the openness and tonality the song was presented with. Of course, good headphones will make a difference too and for this test, I was using the Beyerdynamic DT990 Pro 250 Ohm with the high-power output. As an aside, the HUD100 has more than enough juice to drive the DT990 Pro’s: I was hovering at around 30-40/100 volume on my Windows PC.

Next up was the DCT mode, playing Outkast’s “In Your Dreams“. The HUD100 delivered the track with good energy and body but didn’t quite match the clean presentation pitched by the Yulong Canary II or its own Bypass mode. Here I matched the HUD100 with the Hifiman Sundara. From the standard output, there was ample volume but to my ears, the bass came across with more depth from the high-power output. Volume levels on my Windows PC were around 24-30/100 (High-Power mode).


Moving onto the Dynamic mode, the bass and midrange are slightly lifted and the sound is filled out with more body. The Earstudio HUD100 in this mode was a great match for Baden Powell’s “Reza“. It’s a track that changes pace and dynamics regularly and the HUD100 flows along with it masterfully. Moreover, it establishes a large, well-defined stage that the various instruments are clearly spread throughout with lots of empty space in between.

For testing the Dynamic mode, I used the DUNU DK-3001 Pro. Plugged into the standard output, the DK-3001 Pro sounds dynamic, full-bodied yet clean and airy and at with Windows volume at around 8-14/100, there was obviously no need to move to the high-power output.

A Note On Source Pairing
While testing the Earstudio HUD100 with my smartphone, I noticed that with my personal setup the power levels were quite limited. This is possibly specific to my older phone (Samsung Galaxy Note 5) and its Micro USB port but I don’t have a compatible OTG cable to test my other phone with its USB Type C port.

Even with fairly sensitive IEMs, I was maxing out the volume when using the standard output and going up to or over 60% from the high-power output. Needless to say, there was nowhere near enough power to drive the DT990 Pro. Even the much less demanding Sundara was too much for this setup. They sounded good but the phone’s volume was maxed out so there was absolutely zero headroom.

Radsone’s Earstudio HUD100 is a unique device that has some unique capabilities. In terms of audio quality, it really sounds fantastic and the 3 various sound modes give some welcome extra versatility.

When plugged into a laptop or PC, the HUD100 can easily drive full-size dynamic and planar headphones with confidence. However, as I found out (at least with my phone) – pairing it with a smartphone may limit you to using easy-to-drive earphones due to power limitations.

So who is the Earstudio HUD100 for? That is the question I kept asking myself during testing. It would obviously be a good choice for people who need portability: someone who spends hours sitting in Starbucks working with a laptop comes to mind.

But for use on a desktop, there are compact DACs like the FiiO K3 which adds a dedicated volume pot, balanced output, bass boost plus line, coax and optical outputs and it costs less. Then there are the dongle DACs like the DragonFlys and the Cozoy TAKT C which has its own onboard volume and playback controls. Furthermore, there are several good DAPs for the same price or less that have the same functionality and Bluetooth.

As I said, the Earstudio HUD100 sounds good – really darn good. It’s compact, well-built and uncomplicated. But it just seems like a weird implementation that will appeal to a small niche audience. If you are one of those people, however, you will be delighted by what you hear.

  • Inputs: USB Type C
  • Outputs (3.5mm): Standard 0.914 Vrms / High Power 2.26 Vrms
  • THD+N: Standard -105dB (0.00056%) / High Power -102dB (0.00079%)
  • Dynamic Range: Standard 118dB / High Power 118dB
  • Sample Rates: Up to PCM 32bit 384kHz, DSD128 (DoP)
  • DAC Chip: AK4377
  • Desktop Compatability: Mac OS 10.10 or later / Windows 7 (32/64bit) or later
  • Mobile Compatability: iOS 10.2.2/iPhone 6 or later / Android 6.0 or later
  • Dimensions: 45 x 32 x 8mm
  • Weight: 21.5g
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