Improving iOS audio with the Resonessence Labs Herus USB DAC


When comparing DSD and PCM versions of Steely Dan’s Gaucho some months ago it was the Resonessence Labs Herus DAC that made it happen. Back then, the Herus fronted a two-channel loudspeaker system and it sounded great. Its sonic personality could best be summarised as detailed, robust and punchy. The Herus’ abundance with acoustic mass is also what sets it apart from the likes of the m2Tech hiFace DAC and the Cambridge Audio DACMagic XS (which both sound comparatively delicate and ethereal).

That alone doesn’t automatically make the Herus better than the aforementioned competition, just different. However, its weightier aluminium body renders it more suitable to the rough and tumble of bag life.

The Herus’ higher profile accommodates two further points of difference: a Type B USB input and a quarter inch headphone output. Unlike the m2Tech unit the Herus is intended for use with headphones.

With Resonessence Labs having gone full size on input and output connectivity, not only am I able to lasso the Herus to my MacBook Air with the excellent LightHarmonic LightSpeed USB cable but, at the other end, headphones that ship with quarter inch jacks as standard – MrSpeakers Alpha Dogs, Audeze LCD-X and Sennheiser HD800 – can hook straight in.

I really dislike using 1/4”-1/8” adaptors. Even the short-cabled version that ships with Audeze headphones adds extraneous bulk that will likely inconvenience those looking to keep their portable rigs as streamlined as possible.


The LCD-X’s 20 Ohm impedance and 130db efficiency make them a suitable candidate for use with iOS and Android devices and whilst I’ve never really attained proper aural satisfaction from either a Google Nexus 5 or Samsung Galaxy S3, the iPhone 4/5 and 5th generation iPod Touch sound pretty damn good; not reference quality but perfectly acceptable.

With adaptor in place, the iPod Touch’s headphone output drives the LCD-X nicely but listening with the Herus connected via Lightning-to-USB adaptor and ‘bridge’ dongle ($10 from eBay), I got a much better handle on the Apple device’s sonic shortcomings. Post-Herus the iPod Touch matted the hair of music’s individual strands and its tonality inched closer toward monochrome. The Herus displayed better control with low frequency oomph to give music a better sense of foundation. Not only did I note more tonal colour with the Herus but its overall presentation sounded more relaxed and less tense than the iPod Touch running solo.

Why the disparity? The iPod Touch’s internal DAC and headphone driver are probably $0.50 parts (at most). The Herus features the ESS 9010-2M decoding chip and a stupendously low output impedance of 0.2 Ohms. As one might expect for a US$350 dedicated DAC, its designers have paid more attention to audiophile concerns than Apple – I’d wager that even non-audiophile listeners would eventually hear the improvement brought by the Herus appendage.


The downside is that the Herus running into Audeze LCD-X unveils the shortcomings of Spotify’s lossy encoded audio streams. I find it’s OK for short trips on public transport but lacks the engagement required for long-term nourishment. However, hit up FLAC equivalents via the Qobuz app and the benefits of lossless streaming become immediately apparent: better shimmer and decay up top, a thicker midrange. To sidestep buffering issues and unnecessarily eating into your mobile device data cap I recommend importing albums into the Qobuz app before heading out of the house.

There might be a small proportion of Audeze listeners who’d have no issue in wearing their favourite headphones out in the street. I’m not one of them; the LCD-X are heavy on the head and their open-backed design means sound leakage would surely irritate those in closer proximity.

For street life, my current favourites are the KEF M500. Their sleek aluminium headband hugs the head nicely and doesn’t connote the Cyberman look I try so desperately to avoid – precisely why I classify both sets of MrSpeakers’ Dogs alongside the Audezes as strictly indoor headphones.

Soundwise, the KEF’s scale beautifully, rewarding each uptick in amplification and D/A conversion. The Herus brings a substantial improvement to all-round solidity and dynamics.


To ensure pocketable portability the Resonessence Labs device was attached to the rear of the iPod Touch with an ‘extra thin’ strip of Velcro forming a duo that can (just about) slip into a front jeans pocket. The Herus detaches with a sharp tug when required.

And therein lies the minor compromise: this solution isn’t as physically slender as some might like (myself included). That’s the price one must pay for being able to benefit from all that Apple brings to the party – a high quality user interface and streaming service connectivity – whilst also being able to do justice to audiophile grade headphones. You can’t (yet) listen to Soundcloud, Pandora, Spotify, Deezer or rdio with DAPs from iBasso, Calyx, FiiO, Astell&Kern…or Pono!

I’d pegged the Cambridge DACMagic XS as suitably slender substitute but like the LH Labs GeekOut before it, iOS red-carded its power demands. Bugger.


However, I’ve saved the kicker for the kiss off: with a diet of lossless audio, the iPod Touch + Resonessence Labs Herus bests the sound quality of the first generation Astell&Kern AK120 – it’s meatier and better finessed. Kapow! It’s a difference that was more pronounced when listening with DITA Audio in-ears than KEF on-ears. DITA’s ‘The Truth’ IEMs are fussy bastards that demand the very best in amplification lest they sound a little too over-etched in the treble. It’s probably no coincidence that the DITA fellas used the INVICTA to voice their IEMs during the product development phase. Like its more luxurious counterpart, the baby Herus is an overachiever, particularly when it comes to noise floor – I heard no evidence of circuit hiss or hum.

This USB DAC/amplifier perhaps offers more juice than is absolutely necessary for most listeners building a portable rig around an iPod Touch or iPhone…but if your headphones demand a kick in the seat of the pants the Canadian dongle could be your first and only port of call.

One final thought: even though the iPhone and iPod Touch aren’t capable of hi-res PCM or DSD at the operating system level, the Onkyo HF player gets the Herus up and running with DSD playback on iOS.

Further information: Resonessence Labs | Addicted To Audio

[Part 1 of this investigation into adding USB DACs to iOS 7 devices can be read here.]

Written by John H. Darko

John lives in the NOW + HERE = NOWHERE. He derives an income from the ad revenues of DAR. John is also an occasional staff writer for Stereophile, 6moons and TONEAudio.

Twitter: DarkoAudio
Instagram: DarkoAudio
Facebook: DAR


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    • I take your point but this is a ‘hack’ that sounds better than the A&K AK120…..*and* it keeps Spotify and Qobuz in the picture which dedicated DAPs, like the AK120, do not.

  1. I’d consider this an excellent proof-of-concept and feel that it shows great vision – driven by a mobile device that can stream or play local files without the use of an extra battery or GUI, and that can make sweet, sweet music into headphones, an auto, powered speakers, or a full-fledged home stereo. I’ve made this case before and feel you 100% on topic Darko-san.

    • Thanks Junker. The question I asked myself with this investigation was: can we improve on what we already have? I believe this to be HIGHLY relevant for the man in the street who has already turned up his nose at Pono and just wants better sound from his *existing* device.

      I reckon this kind of iPhone/iPod hack is emerging as a wallet-friendly way to get great sound quality on the go without having to move audio playback to a separate DAP. That’s where users are often forced to make UI compromises. Let’s face it: the original A&K interface is more duckling than swan.

      The Herus’ relatively awkward size lends this hack less than a 100% approval rating but other DACs like the AQ Dragonfly and HRT microStreamer might bring a more acceptable balance between power and form. That’ll be the focus of Part 3.

      • I carry a Dragonfly & USB OTG cable daily for use with my Android phone & IEMs. For me, there was no going back once I experimented with it a bit.