Are there any dac/headphone amps that are in the quality/price range of the nuforce udac-2, maybe a bit cheaper? All it needs is USB input, and a headphone output with a headphone amplifier and decent quality dac.
With a lod. It will bypass the internal DAC. Fiio sells them also on Amazon.
I'm not an iPhone owner, so I'm not positive about this. But I'm pretty sure the LOD bypasses the headphone amplifier in the iPhone, not the DAC. LOD=LINE OUT DIRECT. So it would be an analog signal that has already been processed by the DAC in the iPhone.
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Do any of these units connect directly to iphone? I mean do they bypass the Iphone's built in DAC?
Unfortunately, no. Even a Line-Out Dock connector wouldn't do much. Only iDevice approved DACs can bypass the internal DAC inside an iDevice (iPod, iPhone, iPad). The only other way to bypass the internal DAC is to use the Pure i-20 dock and set it up with an external DAC. However, this eliminates any possible chance of portability.
If portability is what you want, check out ALO Audio as their DACs are iDevice approved. However, if you are on a tight budget, these may not appeal to you.