NuForce Icon iDo Apple-Compatible DAC/Headphone Amp (Playback 56)

Headphone amps and amp/DACs
Nuforce Icon iDo
NuForce Icon iDo Apple-Compatible DAC/Headphone Amp (Playback 56)

I’ve been getting a number of inquiries of late from readers wanting to know if anyone makes a good, Apple-compatible DAC/headphone amp that sounds good, yet sells for a reasonable amount of money. The challenge, here, is that you can get individual products that meet some, or even most, of the requirements referenced, but that almost no one has been able to pull them all together in one accessibly-priced product—until now. Just recently, I received a sample of NuForce’s new Icon iDo ($249), which fits the bill to a “T”.


In simple terms, the iDo is an Apple-compatible, 24-bit, USB Host Mode DAC (maximum resolution, 48kHz/24-bit), coupled with a simple but very high-quality desktop headphone amplifier. Two unexpected but welcome detail touches are that A) the iDo is compatible with—yet does not require—Apple’s option remote control, and B) the iDo DAC section not only provides the expected stereo analog audio outputs but also provides a coaxial S/PDIF digital output. The upshot of this latter feature is that, while the iDo can of course serve as a perfectly satisfying DAC/amp in its own right, it can also be used as a “bridge product” that can pass jitter-reduced digital audio signals from an Apple device on through to a much higher-end DAC, if desired.

At the end of the day, though, the real reason to look into how much music from an Apple device can sound when you bypass Apple’s low-cost digital and analog audio circuits altogether, and let a much higher performance outboard DAC and amp handle the job. Readers will rightly ask if going to an outboard DAC/amp really makes all that big a difference (if, indeed, it makes any difference at all). The simple truth, as you’ll learn in this review, the iDo not only makes an audible difference; it makes a hugely audible difference that—once experienced—is pretty hard to resist.


Consider this DAC/headphone amp if:

•You want an affordable, sonically compelling USB Host Mode DAC that is geared specifically for use with a wide range of Apple devices.
•You’d like an Apple-compatible DAC that not only has analog outputs, but also provides an S/PDIF digital output.
•You also want an affordable headphone amp that works with a broad range of headphones and earphones.
•You want to see just how much better the audio data stored on your Apple device can sound when you bypass Apple’s low-cost electronics and let a high quality DAC/amp shoulder the workload (trust us on this one; the difference is pretty darned shocking).

Look elsewhere if:

•You were hoping for a highly versatile multi-input DAC; this one provides a USB input specifically for use with iPods/iPhones, and iPads (i.e., it’s not a general purpose USB input).
•You were hoping for a DAC with support for high-res 96/24 or 192/24 digital audio files; this one supports a maximum data rate of 48kHz at 24-bit resolution.

Ratings (compared to similarly-priced DAC/amps)

•Tonal Balance: 9.5
•Clarity: 10
•Dynamics: 10
•Output Flexibility: 9.5
•Value: 10



•The iDo is an Apple device-compatible DAC that supports the following Apple products:

oiPod touch (3rd and 4th generation)
oiPod classic
oiPod nano 6h generation)
oiPhone 4
oiPhone 3GS
oiPhone 3G
oiPad 2
oNuForce advises that, “only iOS3 and later version are supported.”

•DAC provides “bit-perfect, low jitter USB Host Mode operation.” The significance of this feature is that the iDo—not the Apple device—controls data transfers from the iDevice to the iDo and thus is able to bring the iDo’s superior low-jitter clocking capabilities to bear. Does it make an audible difference? Yes.
•The iDo uses a 24-bit DAC and supports digital audio files at up to 48kHz rates at 24-bit resolution. A footnote in the iDo manual explains that, “the maximum sample rate currently supported by Apple is 16-bit/44.1kHz or 24-bit/48kHz.”
•Unlike some Apple-compatible DACs, the iDo provides both analog and S/PDIF digital outputs, meaning that if the user would like to a higher-end DAC than the iDo (such as one from NuForce’s High-End product line), it is easy to do so.
•The iDo provides a high-quality onboard headphone amplifier that, says NuForce, “drives headphones up to 300-Ohm (12 mW@300-Ohm).” The amp provides a “digitally controlled analog volume control.” Note, too, that the volume control also sets output levels for the rear panel-mounted stereo analog audio outputs, meaning the iDo can also be used as a preamplifier.
•The iDo is housed in the familiar, attractive, slim-line (6” x 1” x 4 ½”) metal case used for most of NuForce’s desktop audio components.

oThe rear panel provides an on/off switch, a DC power input jack, a USB input jack, an RCA coax S/PDIF output jack, and a stereo pair of RCA analog audio outputs.
oThe front panel sports a volume control knob, and 3.5mm mini-jack headphone output, and clever, recessed LED volume control display.
oThe same display also contains a tiny receiver module that can respond to an Apple remote control (though NuForce emphasizes that the Apple remote is purely optional and to be used at the owner’s discretion; the remote is not required in any way to operate the iDo).
oThe iDo can be ordered in any of four satin-finished colors: black, silver, red, or blue.

•Accessories—The iDo comes with the following items:

oA wall-wart type power supply.
oAn Apple-compatible digital audio cable (fitted with an Apple 30-pin connector on one end and a USB plug on the other).
oA non-skid, non-marring translucent white rubber tabletop-stand for the iDo.
oA simple yet reasonably detailed manual, complete with a well thought out document entitled “A Beginners Guide to Good Audio”.



The iDo brings a number of sonic benefits to the party, the most important of which I’ll try to describe here.

First, I noted that the iDo brought about an increase in perceived detail and resolution, with a concomitant reduction in noise. I use the word “concomitant,” here, because two related things are happening at once. On one level, the iDo is simply decoding and relaying more sonic information, including in particular very low-level information, than Apple’s iDevices could ever hope to capture. But at the same time, the iDo lets you more fully appreciate the newfound information on offer by eliminating subtle but nevertheless distracting layers of background noise and digital hash. Indeed, a not uncommon reaction among first-time listeners would be comments to the effect that, “I didn’t know an iPod could ever sound so clear.”

Next, I found that the iDo ushered in a newfound sense of precision and control, as if the NuForce was holding headphones and earphones with a firm and secure grip, and bidding them to behave precisely as they should. The benefits of this heightened control or “grip” were clearly audible at both frequency extremes, though I felt the iDo’s impact was perhaps most significant in the mid-to-low bass region. I tried the iDo with headphones and earphones that normally sound quite good with iDevices, but with the iDo in play their low-end performance rose up to a whole new level, taking on greater depth, improved transient clarity, and better overall impact and definition. It was almost as if the iDo enabled already fundamentally good ‘phones to become even better, so that they could finally get on precisely the same page with the music.

Finally, and I think we may have the iDo’s ability to serve as a USB Host Mode DAC to thank here, the iDo significantly improved the overall stability—and especially the timing characteristics of the sound (an improvement some listeners interpreted as a greater sense of “focus.” My Playback colleague Garrett Whitten made a very astute comment after his first listening experiences with the iDo. He listened with his eyes closed for a long stretch, head bobbing in time to the music, and then looked up and said, “Wow! I really didn’t expect the iDo would or even could have so much impact on the way the timing aspects of the music seem to unfold. Music can sound pretty good straight through an iPod, but with the iDo in play music just flows naturally, with timing that’s super-crisp and just sounds right.” I would concur.

How big a difference does the iDo make? Let me answer by simply saying that, once you hear the iDo in action, you probably won’t be happy going back to listening straight through your iDevice. The difference is much like the difference you might hear if playing a piece of music through your headphones hooked up to an iPod, and turning around to play the same piece of music with your ‘phones connected to a good amp being fed by a high-end disc player. Is it dramatic and worthwhile? It most certainly is (and not outlandishly costly, either).

Note, during Playback’s listening tests we used several good sets of headphones and earphones including: V-MODA Crossfade M-80 headphones, Audeo/Phonak PFE 232 universal-fit earphones, ACS Custom T2 Live custom-fit in-ear monitors, and Ultimate Ears In-Ear Reference Monitors. In each case, I was wowed by the extent to which the $249 iDo was able to hold its own with more costly amps and DACs that I’ve heard in the past.



Jen Chapin’s rendition of Stevie Wonder’s “You Haven’t Done Nothing” from Chapin’s ReVisions [Chesky] is a track that’s powered partly by Wonder’s infectious grooves, hooks, and wickedly funny and politically supercharged lyrics; partly by the sheer chops displayed by Chapin’s band; and partly by the sweet, soulful, sassiness of Chapin’s voice. It’s the sort of track that can sound pretty good through many different types (and grades) of audio equipment, but that really comes alive with equipment that can power, control, subtlety, and nuance, all at the same time. Perhaps for this very reason, I’ve always felt iDevice-driven systems failed to capture the full measure of magic of which I know this track is capable.

The iDo, however, changed all that. I plugged my iPhone and a good set of headphones (the V-MODA Crossfade M-80’s referenced above) and then listened in wonder (pardon the pun) as the iDo unleashed a jaw-droppingly good performance. The acoustic bass sounded wonderfully taut, punchy, and expressive, displaying tons of “snap” on more vigorously plucked notes, while the saxophone sounded appropriately jaunty, with a just-right quantity of delicate reed sounds and breathiness. But the real treat involved Chapin’s voice, where the iDo let me here the crafty way in which she triggered Wonder’s most ironically humorous lyric lines with a profound yet not histrionic touch of “Question Authority”-grade fierceness. Suddenly, thanks to the iDo, my iPhone no longer seemed like a second-class source component, while my V-MODA ‘phones were sounding better than ever.

A recording I’ve long admired for its sumptuous textures, eerily believable soundstaging, and haunting, otherworldly feel is “Timeless” from Larry Coryell, Badi Assad, John Abercrombie’s Three Guitars [Chesky]. What goes on in this track is that first one of the master acoustic guitarists, and then the other two, join forces so that the overlapping and yet perfectly distinct voices of the three acoustic instruments merge and meld in delightful, often unexpected combinations. Midway through the track, Assad (at center stage) switches to a hand-held thumb-harp to add complimentary percussion accents as Coryell (on the left) and Abercrombie (on the right) continue to trade intertwining lines. Because all of the instruments involved play in nearly identical ranges, the track only works to the extent your audio system is capable of resolving subtle textural and transient details that distinguish one instrument (or performer) from the others.

I’ve gotten good but never truly superb results when listening through iPod-driven systems in the past, but again NuForce’s iDo helped turn the situation around in a significant way. For this track, I listened with my ACS Custom T2 in-ear monitors and my trusty iPhone connected to the iDo, and immediately noticed that the iDo unlocked a deeper, subtler performance than the iPhone, alone, could ever have produced. Through iDo, the top-end of the T2 monitors opened up and almost immediately sounded more delicate, refined, and extended, so that I could hear how the harmonic “signatures” of the guitars were each different, as were their attack and decay characteristics in the hands of their respective players. Where the iPhone on its own tended to allow the sound to collapse a bit (so that the difference between the guitars became less distinct), the iDo seemed to free the performance from invisible constraints, allowing it to breathe and flow freely. I also noticed that iDo helped tighten up and refine the already very good lower midrange/upper bass characteristics of the T2 monitors, enabling them to do a terrific job with the lower registers of the guitars and—especially—the lower notes from the thumb harp. The net effect wrought by the iDo was to make the whole performance sound more refined and engaging, again in much the same way that a top-shelf high-end disc player might have improved the sound. What’s very cool, though, is that the iDo brings these benefits without costing an arm and leg.


Up to this point, HRT’s excellent iStreamer DAC ($199) has set the standard for value among Apple-compatible DACs and with good reason; it’s a simple and very good-sounding DAC that’s very reasonably priced.

Now, however, I would say that for just $50 more, the $249 iDo raises the bar in several important ways. Both products are USB Host Mode DACs and offer excellent though by no means identical sound quality (the iStreamer has a somewhat warmer and perhaps more “organic” sound, while the iDo is cleaner, clearer, quieter, and more precisely controlled). However, the iDo ups the ante with arguably superior fit, finish, styling, and ergonomics; with a headphone amplifier that is actually good—not just thrown in as an afterthought; and with a DAC section that offers a coaxial S/PDIF digital output (allowing users to pass Apple-derived digital audio signals to even higher-end DACs, should they wish to do so). Put all these factors together, and the iDo becomes our new Apple DAC value champ.


We’re very enthusiastic about NuForce’s versatile and well-made iDo, largely because it so consistently helps Apple iDevice/headphone-based systems step up to the next level of performance (or even beyond that). We also like the fact that the iDo helps unlock extra layers of performance in what are already very fine headphones, earphones, and in-ear monitors. As one Playback staffer put it, “The iDo makes a much bigger difference than you’d ever think possible,” so that at $249 it represents a legitimate bargain.

One small word of caution: Good though it is, the iDo is probably not the right amp to use with ‘phones known to be ravenously power-hungry. But with most ‘phones, it should afford a substantial step forward in sound quality.


NuForce iDo Apple-compatible DAC/Headphone Amplifier
Resolution/Sample Rate: Supports maxim rates of 16-bit/44.1kHz or 24-bit/48kHz files (from Apple iPod, iPhone, and iPad).
Input: USB (from Apple iPod, iPhone, and iPad). For specific compatibilities, see the “FEATURES” section, above.
Outputs: 1 x coaxial S/PDIF, 1 x stereo analog audio output (variable level, 2 Vrms, via RCA jacks), 1 x variable level stereo headphone output (via 3.5mm mini-jack).
Headphone Outputs: 3.5mm output jack drives headphones up to 300-Ohm (12 mW@300 Ohm)
Frequency Response: Not specified
Dynamic Range: 95 dB
THD + Noise: .01%
Output Power: 1.5W
Weight: 1 lb.
Dimensions (H x W x D): 6” x 1” x 4.5”
Warranty: 1 year, parts and labor
Price: $249

NuForce Inc.
(408) 890-6840

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