Check out the CNET - STEVE GUTTENBERG review of the NuForce iDo:
http://news.cnet.com/8301-13645_3-57340313-47/improve-the-sound-of-your-iphone-ipod-with-the-nuforce-ido/?tag=cnetRiver
NuForce is a high-end company that makes an unusually wide range of products, from the tiny uDAC-2 portable headphone amp ($129) all the way up to the Reference 18 power amplifiers ($6,600 for a stereo pair). NuForce is based in Milpitas, Calif.
Today we'll be looking at the Icon iDo, a dedicated USB digital-to-analog converter/headphone amplifier designed to work with iPods, iPhones, and iPads, which cannot be used as a USB/DAC with computers. The iDo is awfully little, it's just 6 by 4.5 by 1 inches, and it shares its all-metal chassis with NuForce's other Icon desktop amplifiers and DACs. Setup is supereasy; connect any Apple mobile device to the Icon iDo with the included 30-pin sync/charging cable, plug the wall-wart power supply into the iDo, and that's it. The iDo is available in black, white, blue, or red. It's $249.
The iDo is the first USB DAC I've come across that can't be connected to a computer, it only works with iPods, iPhones, or iPads, and the iDo must be plugged into an AC power outlet. The iDo was designed for people who bring their Apple devices to work and want the best possible sound, but don't have access to music on their computers. NuForce says the DAC used in the iDo is capable of 24bit/96kHz sampling rate, but it's limited to 24bit/48kHz due to Apple's format support. If you want a USB DAC for your computer NuForce's Icon HD ($349) is the way to go. Want a portable USB powered headphone DAC/amp? Check out the Icon Mobile ($79).
The Icon iDo bypasses the iPod, iPhone, or iPad's built-in digital-to-analog converters and extracts the audio data stored on the device and converts the files to analog signals, and then drives your headphones.
The connectivity quotient is decent; there's a USB input, and coax digital and RCA analog outputs. Upfront you'll find a volume control, and a blue LED that moves along a long slot to indicate volume level. There's a 3.5 mm headphone jack on the front panel, but I wish NuForce had also included a 6.3 mm jack, so you could plug-in full-size headphones terminated with 6.3 mm plugs. Sure, you can snap on an adaptor, but they can be pretty bulky.
My Audio Technica ATH-M50 headphones (review to come) seemed to like the iDo, with my old Bob Marley albums. The clarity and detail were exceptional, the bass wasn't boomy or thick, and every note was clear. I quickly compared the sound of the iDo with the iPod directly driving the headphones. Big difference, the iPod squashed the music dynamics, and the iDo restored them. The difference must be attributed to the iDo's superior digital-to-analog converter and more powerful headphone amplifier.
Bass seemed more potent, but it was the iDo's improved transparency that really made the difference. I also tried the iDo with my Monster Turbine Pro Gold in-ear headphones with Jakob Dylan's "Women and Country" album. This recording has a ton of bass, vocals sounded more natural, and the treble detailing improved with the iDo. I suppose part of the difference can be attributed to comparing the iPod's battery powered amp to an AC-powered iDo. In any case, the iDo's bass punch was excellent, and the Turbine Gold sounded like an even better headphone than I thought it was.
I also used the iDo as an iPod "dock," with its coax digital output feeding my PS Audio Perfect Wave DAC in my high-end system. The iDo's coax digital output bypasses the NuForce's internal DAC, so it's a straight connection between the iPod Classic and the PS Audio DAC. My iPod never sounded better. The iDo can also be used as a preamp and its RCA outputs can feed a power amp or powered speakers, like my little Audioengine A2s.
The retail price of the NuForce iDo is P11,700.
