Inverting O2

An inverting version of NwAvGuy's O2 Headphone Amplifier. B5-080 case with 1/4" and RCA jacks. +/-15.3Vdc power rails, input select switch for ODAC. Many upgrades and improvements over the orginal O2 headphone amplifier.

No new version of NwAvGuy's famous O2 Headphone Amplifier has been introduced since he disapeared in the fall of 2012. agdr Audio has created a brand new version of NwAvGuy's O2 Headamp that contains several significant new designs. The new "O2" fits in the B5-080 case, which is slightly taller and an inch wider than the O2's B2-080 case. The new amplifier is nearly all easy-to-solder through hole parts, similar to the O2, except for a half dozen bypass capacitors under the PC board.

The original NwAvGuy O2 Headphone Amplifier used non-inverting op-amp stages for the gain and output sections. See a writeup here, with the non-inverting writeup below it. Inverting amplifiers lower common mode distortion and harmonics by keeping the voltage levels at the two inputs at zero volts with respect to ground. The voltage level at the input of a non-inverting stage varies with the incoming signal. See a good discusion of the inverting op-amp configuration vs. sound quality here.

The original NwAvGuy O2 Headphone Amplifier also used conventional (not low dropout) fixed (12V) voltage regulators that were not heat sinked. Low dropout (LDO) voltage regulators are used here to prevent going into dropout under heavy loads, a known design problem with the original O2 headamp on 12Vac. They are heat sinked to the case rear panel prevent the overheating the original O2 experiences with transformers over 12Vac. The new regulators (LT3015 and LT3080) are lower noise than the O2's 7812 and 7912 regulators.

Part of the reason no new versions of NwAvGuy's O2 Headphone Amplifier have been designed is (confusion over) the "no derivatives" license that NwAvGuy invoked with his O2, which essentially says derivatives of the design have to be approved by him. But... he has disappeared and is non-contactable for license releases. I would love to be able to contact NwAvGuy for his measurements and design approval. In several countries that issue alone of a license holder (or their representative) being non-contactable for over a year will cause a license to revert to the public domain.

For a design to pass the test as a "derivative" it has to be extremely similar to the original. Nearly the same parts, same (or nearly the same) layout, etc. The amplifier presented here is significantly different to the point where we believe it is not considered a derivative, but a new design. The part that is similar is the overall format of gain stage, followed by volume pot in the middle, followed by output stage. This design uses the slightly wider B5-080 case, with two "9V" NiMH batteriues

The new agdr Audio version of an Inverting O2 Headphone Amplifier has several benefits over the original NwAvGuy O2 including:

So how does this new version of NwAvGuy's "O2" headphone amp differ from my version of the O2 Desktop Amp and my O2 Booster Board? :) This new amp also makes a fine desktop unit and is positioned halfway between the orginal O2 and the ODA. The ODA has several premium design features which raise the price quite a bit:

The agdr version of the Inverting O2 Headphone Amplifier is a do-it -yourself proect posted on the headphone forum at All the project materials are posted there: schematic, layout, part ID diagram, build instructions, Bill of Materials, panel CAD drawings for Front Panel Express, Gerber files to a make a PC board, photos, etc.

For information on buying a PC board and parts, please see here.

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