EarStudio HUD100

General Information

HUD100 is the most compact and the first audio DAC to adopt ARM Cortex processor and MEMS oscillator to implement our proprietary algorithm and minimize jitter.

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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
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INTRODUCTION AND DISCLAIMER:
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 is currently available on Amazon for $200 shipped. I received the HUD100 directly from Radsone in exchange for a fair and objective review.

This review is also available on my blog.

TESTING CONDITIONS:
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.

DESIGN, BUILD QUALITY, AND ACCESSORIES:
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.

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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.

FUNCTIONALITY:

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.
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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.

POWER CONSUMPTION:

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.
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HUD100 high power output power usage with PC
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HUD100 high power output power usage with smartphone
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HUD100 standard output power usage with PC
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HUD100 standard output power usage with smartphone
Below are additional power consumption measurements from other USB-C audio devices:
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Meizu HiFi Pro
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xDuoo Link
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Apple Dongle
CONCLUSION:
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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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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.



Packaging:

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.

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Build:

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.

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Internals:

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.



Controls:

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.



Sound:

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.



Comparisons:

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.



Conclusions:

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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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
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.

Internals
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?

Sound
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.

Conclusion
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.

Specifications
  • 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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