If you're a dyed-in-the-wool Apple fan and want a little more convenience, an emerging class of products — call 'em dockless docks or whatever you like — interfaces directly with your iDevice via Apple's 30-pin connector. The upside is that you can use some of these with your other iOS devices as well (for some reason, the iPhone 4/4s and iPod Touch don't work with the current Camera Connection Kit, so you're out of luck using those with your with USB DACs.)
On the other hand, by conforming to the "Made for iPad/iPhone/iPod" spec (and using Apple's 30-pin connector), these devices limit your playback to the iDevices' specified limits on bit depth and sample rate — i.e., you'll max out at 24 bit, 48 kHz playback.
The battery-powered Cypher Labs Algorhythm Solo DAC ($579, cypherlabs.com) and Fostex HP-P1 ($649, fostex.com); and the desktop HRT iStreamer ($199, highresolutiontechnologies.com); and the NuForce iDo ($249, nuforce.com) all aim to play by Apple's rules while providing a big step up from your iDevice's onboard DAC and headphone amp.
While we look forward to exploring this product category further in the future, we got to spend some time with the NuForce iDo ($249, nuforce.com), which is perhaps the most complete of these officially endorsed iOS DACs, although it's the least portable. This is a desktop unit, not a portable (it comes with a chunky rubber foot, so you can stand it on end to minimize its, er. . .footprint), and as such it requires an external power supply. Unboxing the iDo is a bit of a shock. If you're familiar with NuForce's popular uDAC-2 series of DAC/amp combos, you might expect that the iDo would resemble those tiny units — but no. Rather, it shares a form factor with the larger units in NuForce's Icon line. That means it can — like the HRT iStreamer and unlike the luggable Fostex and Cypher Labs units — charge your iPad as it plays. It's basically a minmalist dock meant for headphone listening.
NuForce's Jason Lim told us that he imagined the device would be popular among those who wanted high-quality audio at work, but were unable or unwilling to keep content on their work machines. Reasonable enough, and a likely application, certainly in the case of iPad use.
the iDo is a fine-sounding headphone amp; output impedance is given as a very reasonable 5 Ohms, and it supplied plenty of power to drive whatever headphones we had on hand, including our reference HiFiMan HE-500s ($699, hifiman.us). The iDo also provides stereo analog and S/PDIF output for interfacing with the bigger system of your choice. Given its desktop orientation, it'd make a good pairing with any of the new generation of small powered monitors, but it'd sit nicely (or unobstrusively) alongside your high-end gear as well.
Being able to use the 30-pin connector directly actually makes it a lot more convenient than any Camera Connector Kit solution, and if you're the sort of person who forgets to charge your devices at night, you'll appreciate the fact that the iDo does the work for you while your're listening. And the sound quality is noticeably better than the iPad's onboard output jack. The only real downsides are the lack of portability, the fact that you can't use it with non-iDevices, and the unavoidable Made-for-iOS downsampling of your precious FLACs — but, of course, there's no law specifying you can't own another DAC or headphone amp for other listening situations.
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