NwAvGuy is/was an audio genius who posted for a couple of years on several audio forums, mainly at diyaudio.com. He created an audio equipment blog here and reviewed several pieces of commercial audio equipment in 2011. Late that year he introduced his do-it-yourself "O2" headphone amplifier project in this forum thread (he went by "RocketScientist" on the forum). The name "O2" came from being objectively measured for noise and THD+N performance. At the start of the next year 2012 he released a companion DAC that fit inside the O2 (if the batteries are removed) called the ODAC, also decribed in the forum thread and his blog. Then, 6 months later, he completely dissapeared as chronicled in this IEEE spectrum article (click "continue to article in the upper righthand corner).
Since NwAvGuy released his O2 headamp I've helped many folks get their DIY builds up and running in the diyaudio O2 thead. Here is a compilation of mistakes to avoid when you are building - or troubleshooting - an O2:
Electronics technology moves pretty fast and the O2 design and parts BOM is several years old now. Here is a list I've put together of modern part upgrades for the O2 headamp. With each one I explain why I consider it an an upgrade, where to get the part, and the price difference. In most cases the new part is slightly more than the original.
Finally here is a listing of actual modification to the O2, many from an O2 modification thread I started on diyaudio.com shortly after NwAvGuy released his O2 Headphone Amp. Unlike the O2 modern part upgrades, which apply universally, each of these modifications addresses a very specific issue. Most people wouldn't run into many or any of these issues. But you may want to scan the list and see if one or two applies to your specific situation!
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