Jude has kindly agreed to lift the ban on discussion of the works of banned members to allow discussion of the O2 headphone amp. However, please pay attention to the following before posting, otherwise this thread is likely to get locked:
1.This thread is about the amplifier, not NwAvGuy.
2. No links to NwAvGuy's website, or resources maintained directly by him.
3. No links to sites where NwAvGuy is in direct and regular communication with people on such a site.
4. No discussion of the above rules or indeed moderation, as usual.
(The schematics and bill of materials I am mirroring (in compliance with CC license) in order that they may be linked to)
So, down to business. The O2 is a headphone amp designed purely around objective measurements and released under a non-commercial license (Creative Commons). It is cheap to build (PCB+parts run to 30 dollars) and also generally goes against much of what can be considered audiophile design philosophies; there are capacitors in the signal path, plenty of 50-cent ICs and it uses an AC wall transformer as part of the power supply.
It also has an incredibly low noise floor and vanishingly low distortion, as well as easily enough power to drive popular dynamic headphones (K701, HD650, DT880) - even enough for high-end orthos if you don't listen excessively loud. Other notable features include current limiting and the ability to run off two 9V (8.4 volt in reality) batteries (power management kicking in to shut down the amp when the batteries are getting too low). Finally, it also fits perfectly into a cheap ($10) enclosure and has no SMD parts.
Amp schematics and BoM (mirrored on my Google Docs): https://docs.google.com/viewer?a=v&pid=explorer&chrome=true&srcid=1WGBCwFbHXt-q82Ujih8IVu2vXsgMtlNpe6oHLLg_Klrf2LFxv5e9F1zloEZK&hl=en_US (WARNING: OUTDATED. See designer's site for latest)
So, are you planning to build one? Any other thoughts?
EDIT: Added Measurements Summary
Edited by Willakan - 10/31/11 at 10:15am