EarStudio HUD100 DAC/AMP


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 renumeration for this review. If you have an interest in purchasing the HUD100 or other Radsone products, check out their website. To purchase an HUD100, visit RadSone’s new store directly. Also worth noting, the price has dropped since we originally received the review sample with the HUD100 now selling for $139.99.


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 impedance 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.


Headphoneus Supremus
Pros: Standard and high output options - Compact size and build quality - Sample rate support
Cons: Limited mobile device connectivity ootb - DCT and Dynamic modes limited to 44.1kHz for now

Today we're checking out Radsone's newest DAC/amp, the HUD100.

2018 saw the release of the ES100 which was an outstanding Bluetooth receiver that took portable audio forums by storm. It offered up a mind boggling feature list along with sound quality and wireless performance at a price the competition simply couldn't match. From what I've been seeing, they're only now beginning to catch up.

The HUD100 isn't a replacement for the ES100, instead taking on the growing USB dongle DAC/amp segment. With strong specs, outstanding file format support and some handy features like a 2.26 Vrms high power output for demanding headphones, along with three available sound profiles and a very compact footprint, the HUD100 is an intriguing prospect for anyone in the market for a new portable DAC/amp.

Let's take a closer look, shall we?


Packaging and Accessories The HUD100 arrives in a small, grey, lift top box that is all business. On the front is a glossy image of the HUD100 along with the usual branding and model information. Down the left side you find some basic specifications and a list of package contents. On the right you find an explanation of the three in-built sound modes and two power modes, as well as a compatibility list (Android, PC, Mac, iOS). Lifting off the lid you find the unexpectedly tiny HUD100 protected by a flat foam insert. Lift that out and the leatherette travel pouch rests within a cardboard insert. Remove that layer to find two more compact cardboard boxes holding the included Type-C cables. Last of all is a Quick Start Guide. In all you get:
  • HUD100
  • 1m USD Type-C cable
  • 10cm USB Type-C cable
  • Leatherette travel pouch
  • Quick Start Guide
Overall a very simple and straightforward unboxing experience. The travel pouch is a nice inclusion though I wish it were a bit larger. Part of the HUD100 sticks out the top and will still be subject to scratches if you're not careful. The included cables are 1m and 10cm in length and are welcome additions. It's annoying to be given one or the other, as is usually the case. That said, it would have been even better if Radsone included a Type-C to Type-C cable too. As with the Earmen TR-Amp I recently reviewed, leaving out this cable on a device intended for portable use is a bit of an oversight since you'll need an adapter to connect to most DAPs, Android, or iOS phones. This observation is especially applicable given that the HUD100's diminutive footprint makes it perfect for on the go use.

Build Quality Given the size and price of the HUD100, Radsone would be forgiven for crafting it from plastic. But they didn't. The shell of this tiny (45mm x 32mm x 8mm) device is made from two pieces of aluminum giving it some weight and a feeling of solidity you might not expect from something so compact. On the front you find two 3.5mm jacks placed on either side of a three way toggle switch. The left jack is the standard power output (0.914Vrms) while the right houses the high power output (2.26 Vrms), as denoted by H-P printed next to it. Out back is the Type-C port and a DFU slider switch used exclusively for firmware updates (visit www.radsone.com/hud100). The bottom of the device contains Earstudio branding as well as HUD100 / Hi-Fi USB DAC / Designed by Radsone. The top of the device is completely bare, except for a single teensy LED light that tells you when the device is on and the sample rate being played.
  • Green – 44.1kHz
  • Navy Blue – 48kHz
  • Blue – 88.2kHz/96kHz
  • Red – 176.4kHz/192kHz
  • Yellow – 352.8kHz/384kHz
  • White – DSD64/DSD128
Fit and finish is quite good with all the ports and switches fitting neatly within their applicable cutouts. The base aluminum plate protrudes a fraction of a millimetre and as such isn't completely flush, but the visible seam is tight so you won't have to worry about anything working it's way inside. The toggle switch on the front that enables you to select from one of three sound processing modes moves cleanly into each position. A bit more resistance would have been welcome as it's easy to overshoot the centre notch, but this definitely is not an issue and isn't worth more than a passing mention. The spring-loaded DFU slider in the back feels good and snaps back into the default position smoothly.

Overall a very simple and well-build device, and a notable step up from their previous offering, the ES100. Great job Radsone.


Sound, Power, Select Comparisons The HUD100 provides users with three different sound processing modes, selectable via a small switch on the front of the device. Moving the switch to the left bypasses any processing for an unedited sound. In the middle you find the DCT processing mode intended to provide a more analogue-like sound. To the right is Radsone's own Dynamic processing intended to provide a more powerful yet balanced sound. This is what I think of each.

It is important to note that DCT and Dynamic modes currently work on only PCM 44.1kHz. I'm sure this will be expanded on in the future since Radsone is always updating and improving their gear through firmware updates.

I've found the bypass to, unsurprisingly, be the least coloured and most neutral signature of the three available options. Through this filter, the HUD100 sounds the most critical and analytic. Detail is most prominent in this mode and notes slightly leaner and cleaner. This option is the one to choose if you like a neutral source, or if you enjoy applying your own EQ settings. I like to use this setting with analytic earphones like the EarNiNE EN2J and Hifiman HE350, and darker or overly warm products that benefit from being toned down a bit, such as the Massdrop x Mee Audio Planamic and Meze 99 Neo. If comparing to other devices in my inventory, I'd say the iFi hip-dac best matches the bypass setting. I find that device quite neutral and clean with a near clinical level of detail on tap. It is a bit leaner sounding than the Bypass setting on the HUD100, but overall they seem alike to my ears.

DCT: The DCT filter is my personal favorite and is used whenever available (i.e. I just leave the switch in the middle). It brings some warmth back to the presentation and smooths things out. This does negatively affect detail retrieval ever so slightly, but to my ears it's worth it. Compared to the Bypass option, the midrange and low end feel like they been pushed up and filled out. This extra weight helps out the midrange in particular giving vocals more weight and density. Radsone says it evokes the presentation of an analogue system, and to a point I agree. Tube lovers will probably find themselves leaving the HUD100 here. I don't really have a preferred headphone or earphone to use with this setting since I feel it is an excellent all rounder. It is just as nice with the Shozy & Neo CP and it is with the Campfire Audio Solaris. Compared to other devices in my inventory, I'd say it best matches the Earmen TR-Amp which shares a slightly warm, analogue sound signature. That device is quite a bit more powerful though. The power and the inclusion of plenty of additional features come as the expense of size, as the TR-Amp is magnitudes larger and less portable than the HUD100.

Dynamic: This filter makes the most difference to my ears, but not necessarily in a way that matches my personal preferences. This one feels like it's for the Beats crowd, bumping midbass thereby making the presentation more dense overall. It's the most coloured of the three options, losing some of the airiness and clarity found in the Bypass and DCT modes. This one is great for countering overly bright headphones and earphones or propping up those with a particularly weak low end. The TinHifi T2 and P1 come to mind. I don't have any DACs or amps that fully mirror this setting, though the Hifiman Megamini DAP and XDuoo Link come the closest. Both are warmer sounding products with a more reserved detail and clarity presentation, best matched with neutral to bright headphones and earphones.

When it comes to power output, the HUD100 is pretty impressive for such a compact device. The regular output provides more than enough clean power for the vast majority of products, such as the AKG K553 Pro, Moondrop Starfield, Campfire Audio Andromeda, Hifiman Sundara, etc. While the output impedance is not provided, I suspect it is low. The Campfire Audio Solaris is the earphone most subjective to source I've got, even more so than historically picky Andromeda. Through the HUD100 the background is clean and volume across the entire frequency range seems to raise evenly without anything spiking, a problem I occasionally come across with various hybrid earphones. Moving over to the high-power output, I can verify it too provides a clean sound experience, though not quite as clean. There is some hiss to be found if you're pairing it with something that has a high enough sensitivity (most products around or above 100dB I've noticed). It does an amazing job of getting my stubborn old Havi B3 Pro I up to comfortable volumes without pushing the source device handling the volume. It also works well to run various planar headphones, like the Hifiman Sundara, Advanced Alpha v1, and even the Hifiman Susvara (!). It doesn't push the latter with quite the same authority as the TR-Amp. I've found that through either output, there is a ton of headroom for volume increases with anything I tossed at it. This is great because I can keep the output on my device low, thereby draining less battery. Other low volume listeners will likely appreciate this. I can't speak to high volume listeners because I'm not one, and what is uncomfortably high to me may be normal or even a little low for you (as I commonly experience with my wife who likes to blast her tunes).

Value Since cost seems to be a bit of a hot topic with this device, I figured I'd weigh in on the subject. My thought is that the HUD100 isn't a great value, nor is it overpriced. Instead, it's priced appropriately. Why do I say this? Let us look at two generally well-received products that fit into price brackets below and above; the Cozoy Takt-C (115 USD) and Periodic Audio Nickel (299 USD).

The Takt-C has the benefit of being half the size and a DAC/amp with volume and basic media controls. Both are very well-built with durable aluminum shells, but the removable cables that come with the HUD100 feel like they were made to a higher standard than the fixed cable of the Takt-C. The fact that they are removable also enables greater versatility and longevity for the HUD100. The Takt-C provides nowhere near the driving power of the HUD100, unable to push the same high impedance, low sensitivity products as well. As such it is best suited to earphones and portable headphones. While the Takt-C has an impressively black background that matches the HUD100's standard output (besting the high-output port in noise), the sound quality is a noticeable step up on the HUD100. The Takt-C keeps up with the HUD100 in terms of clarity and detail with near equal as impressive end-to-end extension, but it sounds somewhat cold, sterile, and artificial after a/b'ing them. The Takt-C also lacks the high-output mode and sound profiles/filters of the HUD100. In terms of extras the Takt-C includes nothing while the HUD100 gives you multiple cables and a protective case. In my opinion, the 54 USD premium the HUD100 demands (going off the MSRP for each) goes a long way, giving you a slew of useful features and handy accessories. It feels even better knowing that to get a removable cable option with the Takt lineup you need to step up to the also well-reviewed Takt Pro. It is virtually identical to the Takt-C minus the removable cable and a 174 USD price jump to 289 USD. Yeah, the HUD100 is looking real good right now.

I had issues with the Nickel's price when I reviewed it a year ago (almost to the day actually), and that qualm is even more applicable now. While it is plenty powerful and has some cool features, auto power on/off and an insane 30 minute charge time for 8 hours of use being standouts, it felt more like a prototype than a retail ready product. Plus, it failed to provide a good experience with high sensitivity, low impedance products, among other nitpicks. Its faults really stand out when pitting it against the HUD100. The Nickel is twice the size. It has only one output option. It uses a less durable micro-USB port. The Polycarbonate body is tough as nails but fit and finish is subpar and visually, well, it looks like a DIY project. In fairness, the review unit I was sent was b-stock with blemishes you would not find on a standard retail unit, but I've seen plenty of images of ideal units and they are not much nicer. That includes the devices pictured on Periodic Audio's product page. I know it sounds like I'm bashing the Nickel which is not the intent of this section. I really do like it a lot and commonly pair it with my Shanling M0. They are about the same size and strapped together make for a powerful, compact, mobile setup. However, The HUD100 can do pretty much everything the Nickel does, but in a smaller, more attractive, more feature rich package that costs almost half as much. I really see no reason to pick up the perfectly capable Nickel when something like the HUD100 exists.

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Final Thoughts The HUD100 is set to shake up the USB dongle segment. It is absurdly small for the feature set, offers flexible power outputs, measures very well for a dongle, supports a wide variety of high quality file formats, and is stuffed with impressive tech. I also love that the cable isn't fixed, and that there are three sound profiles available at the flick of a switch.

While there are some features that would have been nice to see carried over from the ES100, like volume controls and a 2.5mm balanced out, their absence is easily dismissed. Many devices have external volume controls that are easy to access from a pocket, and the high-power output here is just as strong as the balanced out from the ES100. I'd rather use a thicker, more durable 3.5mm jack to get the same power if the option exists, and with the HUD100 it does.

The only real qualm I have, and it is minor, comes down to accessory omissions. You get everything you need to connect direct to a MAC or Windows PC. Connection with an Android device will require buying an OTG adapter, and to iOS devices a USB Camera adapter. Since Type C equipped devices are vastly more common than Apple's proprietary option, tossing in a short Type C to Type C cable to allow pairing with phones and Type C equipped DAPs out of the box would be nice.

Overall though, I really enjoy the HUD100. Setting it up requires no effort, there are no hurdles to jump to start enjoying your music, and pricing is appropriate when comparing to similar products across a variety of price brackets. Radsone is once again entering a popular, ever growing segment and seems to be providing one of the better performance for your dollar options.

Thanks for reading!

- B9

Disclaimer A big thanks to Kyle with Radsone for reaching out to see if I would be interested in reviewing the HUD100, and for arranging a sample for testing. The thoughts within this review are my own subjective opinions and do not represent Radsone or any other entity. At the time of writing the HUD100 retailed for 169.99 USD, but was on sale for 135.99 USD. You can check it out here: https://earstudio.store/products/hud100

Edit: They've opened their own store and with it came a price drop for the HUD100! 139 USD instead of 169 USD. Woohoo!! https://earstudio.store


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@Shlaghett0 Glad you enjoyed it. ES100 is a beast of a device :)
Well I ordered it, hope it plays nice with Ety’s!
Got it! And the DD USB C to USB C cable before they disappeared. Lovely little combo, not quite as good as the output from my LG V20. But for a newer phone without a headphone jack it’s great!