Resonessence Labs Herus USB Headphone Amp/DAC

Resonessence Labs Herus ($350)
There's been a recent trend towards ultra-compact, "portable" DACs. See the Audioquest Dragonfly, HRT MicroStreamer, Audioengine D3, Meridian Explorer, CEntrance DACport, and the list goes on. It seems everybody wants in on the action—the list grows on a regular basis and I'd be surprised if there weren't a dozen more entries in the field by year's end. Computer audio is hot right now, as is personal audio (obviously), and these little devices fit nicely in both categories. Traditional companies like Meridian likely see this as a way to attract customers they wouldn't normally reach due to pricing—build some brand loyalty, and before you know it that customer has graduated from college, landed a sweet job, and can now afford more expensive Meridian gear. Or so the theory goes.

These devices all have some common characteristics: USB is typically the sole input. Headphone outputs are common. And most are so small that they can't even fit RCA jacks, so the headphone jack doubles as a line out. Some look like a thumb drive and plug directly into a USB port while others use a cable to make that connection. Thus far they all tend to fit in the "affordable" category, although I'm sure one of these days someone will drop a "high-end" version with a four-figure price tag. For now everything seems to be south of $500 which again makes them attractive to a wide audience.

Resonessence Labs offers their Herus ($350) which sticks pretty closely to the script I've mentioned. It's roughly the size of a pack of gum—think old school Juicy Fruit in the rectangular package. Input is a full sized USB Type B on one side, while output on the opposing end is a 1/4" headphone/line-out jack. By not using micro-USB or a 1/8" headphone out, the Herus trades a bit of portable sleekness for some usability in more stationary situations. Fit and finish on this thing is typical Resonessence which translates to exceptional, being milled from a solid hunk of aluminum. Did I mention it was designed, manufactured, and assembled in Canada? Resonessence pays just as much attention to the little Herus as they do to their flagship $5,000 Invicta DAC, which I happen to use in my reference system.

With a bunch of these devices on the market, what makes the Herus stand out? A few things, actually. First, the Resonessence crew knows a little something about the ESS Sabre chips. Because they invented them. As I mentioned in my review of the Concero HP, Resonessence is made up of former ESS staff and therefore has an unmatched level of familiarity with these notoriously complex chips. The Herus is based around the new ES9010K2M 32-bit DAC chip from the Sabre Premier line. The 2M series uses the 28-QFN package which means an extremely small footprint with very low power consumption; just the thing for a tiny USB DAC such as the Herus. Due to the unique relationship between ESS and Resonessence Labs, I suspect Herus was the first device on the market to use this new Sabre chip, though I can't totally confirm it.

Aside from that, Herus has the distinction of being able to play just about anything you can throw at it. While some of these tiny DACs are limited to sample rates of 96kHz or below, and others top out at 192kHz, the Herus goes all the way to 352.8kHz which is used by the DXD format. It also handles DSD in both original and double-rate capacities (sometimes called DSD64 and DSD128). Is there a ton of material out there in these formats? Not really, but the catalog is growing at a steady clip now. If you like classical and jazz there's actually a rather large selection to be found. If you prefer other music then it's less useful to you but still fun as audiophile demo material—you can grab some free downloads here, here, and here. Plus, there's the matter of future proofing—DSD may not be super common at the moment but who knows what the future holds? It may take off incredibly in the next few years, so it makes sense to be prepared.

Like its siblings in the Concero series, Herus uses the internal 32-bit volume control of the Sabre chip. Digital volume control may raise audiophile red flags, but the Sabre volume control is actually quite capable. It's not like there's much room in the enclosure for a good analog pot anyway. A nice touch is that Herus takes over seamlessly, so when I adjust the volume in Foobar (Windows) or Audirvana Plus (Mac), I'm actually using the Sabre 32-bit volume solution rather than inferior software attenuation.

Detailed specs can be found here. Highlights include 126mW into 32 Ohm loads, maximum output of 2.4Vrms, 0.2 Ohm output impedance, and a signal to noise ratio exceeding 100dB. The USB implementation uses hardware from Cypress Semiconductor running custom Resonessence Labs code for asynchronous operation. That's similar to their Concero and Invicta families of products, and sets them apart from most others who use "off the shelf" solutions from the usual suspects like XMOS. In an interesting twist, the Herus can be used with iPhones, iPads, and some Android devices. You'll need the appropriate adapter—Lightning to USB for newer Apple devices, Camera Connection Kit for older Apple models, or an OTG cable for Android. I was able to confirm this with both types of iPad connection as well as with an older Samsung Galaxy S3. I had no luck with several newer Android devices including a Galaxy S4 and Note 3. Unfortunately, Android USB audio is still not standardized, so you never know what to expect from one device to the next. But that's no fault of the Herus.

After using the Herus extensively both at home and on the go, I've come to really enjoy it. Read on to find out why.

Resonessence Labs
863 Coronado Crescent
Kelowna, British Columbia V1W 2K3
(778) 477-5536

nnotis's picture

Thank you for pointing out this problem! Just about every one of these dongle DACs has it. You need only read through their respective threads on Head-Fi to understand why. People are obsessed with driving LCD-2s & HD800s with them. By doing so, manufacturers end up building amp components that sound poor with everything. From what I understand, even the Hugo is noisy with IEMs. But hey, I bet they sound kind of Ok with HD800s as a result. It's frustrating, since it should be possible to get reference quality sound from a mini DAC and top of the line IEMs. Lower the gain please!

John Grandberg's picture
I think "sound poor with everything" is taking it too far. The Herus, and (to a lesser extent imho) some of its competitors sound very good with the right headphones. As I said, I personally would prefer to have a silent amp section for use with IEMs. Obviously the masses demand otherwise. Makes sense, I suppose - on the high end, the full size market is probably far larger than the IEM market.
miceblue's picture

Have you had the opportunity to try Light Harmonic's Geek Out device? People in the LH forums seem to be talking about the Herus often and it would be really cool to see a highly regarded reviewer such as yourself do a comparison.

John Grandberg's picture
Tyll has a Geek though, and a bunch more, which is why I'm sending over the Herus for him to compare.
Broman's picture

"I also used a Lenovo Windows 8 tablet and had a good experience there as well. The app selection is not as strong (I used MediaMonkey)"
I don't understand this comment. If it is Windows 8 why can you not use Foobar, etc.?

John Grandberg's picture
To clarify - yes, you can use Windows 8 in "desktop" mode, and indeed you must do so initially to install the drivers. Foobar works fine but is not so fun on a tablet. I prefer MediaMonkey since the app is optimized for the touch screen and smaller display. Foobar is very flexible with customization so one could theoretically set that up to their liking, but I didn't feel like messing with it.
funambulistic's picture

MediaMonkey has a few quirks but the GUI is great on the Windows tablet.

NZtechfreak's picture

It'll work with a number of Droids via the app Ultimate USB Audio Player PRO (UAPP), I used it with my Note 3 and it worked fine. UAPP has its own USB drivers and bypasses Android audio handling allowing for greater than 16-bit audio (should the user want that) and much increased DAC compatibility. It's more or less local playback only, but then with the availability of 128gb microSD cards that isn't too bad (and in fact I'm using a 256gb full-sized SD card with my Note 3 via an adapter).

John Grandberg's picture
I consider USB Audio Player Pro a sort of work in progress. At first it was a mere novelty, and later it became somewhat usable. It's still got a long way to go compared to some of the top playback apps though. Still, I appreciate the project, and I check back in every few months to monitor their progress.
NZtechfreak's picture

Definitely a work in progress, but a serviceable enough player for those of us who care most about fidelity and using DACs that otherwise might not work with our phones. I use it on the go with my Dragonfly 1.2, whose form factor cannot be beat for this application being basically an inline DAC and amp - it requires UAPP however in order to use the amps volume control.

John Grandberg's picture
I can see it becoming a killer app in the next year or two. I just wish Android had this stuff built in from the get go.