A bit of audio tinkering

I’ve been quite busy the last two weekends, first on a weekend holiday trip to Tallinn, Estonia, and then playing in the Helsinki Casual go tournament which successfully took most of my time last weekend. This has somewhat delayed my continuation to the composite video decoder project.

However, I haven’t been resting on my laurels completely even electronics-wise. My trip to Tallinn had one good by-product, namely new Audiotechnica ATH-M50 headphones. They are a marked improvement over my previous HD-500 Sennheisers, and got me inspired to getting a headphone amp, a tube-based Little Dot mkIII to be more exact. The 32 ohm ATHs don’t necessarily need an amp, but now I’ll at least be prepared if I ever end up getting something like HD-650s.

While researching for a proper USB DAC I came across an amazing audio blog by NwAvGuy. Compared to a lot of “audiophile” coverage he seems to have a solid engineering perspective to audio issues, and he has put an amazing effort to long articles that deal with many issues that surround headphone amp gear.

In addition to great scientific info, NwAvGuy has also designed a USB DAC called ODAC, which I ordered from Head’n’Hifi (they conveniently ship inside EU so no customs). And while I was at it, I couldn’t resist getting a DIY version of NwAvGuy’s O2 headphone amplifier. Read on for my experiences on building it and pitting it against the Little Dot mkIII tube amp.

O2 headphone amplifier

The Head’n’Hifi as well as several other suppliers (see my links above) sell the O2 headphone amplifier in pre-assembled form for about 120 €, but the DIY kit can be had for half as much. This is what I found from the box (along with ODAC which uses surface mount components and only comes preassembled, with or without enclosure):

The assembly was quite an ordeal, with 187 pads to solder, and some rather small holes which didn’t always solder through very well. Also, the instruction post on NwAvGuys blog is probably about 30 pages long and in narrative form, so it took me probably two hours to just read the instructions scattered over that. I definitely wouldn’t recommend it unless you’re prepared to do some serious soldering!

Nevertheless, I beat the odds and managed to solder everything more or less into place. The fact that my parts were not exactly as described in the BOM (bill of materials) caused me to stumble for a while, until I reread relevant parts of the 30-page post again and noticed that alternative capacitors were suggested for regulators.

The O2 instructions also contained very good testing guide, and once everything seemed to check out I proceeded to try with headphones. The sound quality is amazing, as suggested by NwAvGuys measurements. Comparing to my 260 € Little Dot I’d say this opamp-powered little beauty gives a more detailed sound and even seems to pack slightly more punch. I may of course be biased due to my expectations, but it seemed like the O2’s sound was more accurate and neutral than the tube-based mkIII. Of course my ATH-M50s may also be slightly challenging to the tube amp (I don’t know its output impedance, whereas O2 has a very low 1 ohm), so a 300 ohm pair of HD-650s might be more comfortable for the Little Dot to drive.

If you’re looking for an excellent headphone amplifier that can also run on batteries (I chose not to install them in mine), O2 definitely is a worth looking into. And the ODAC as well – I’m quite sure that my wooden ears won’t detect much improvement beyond this combo.

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Joonas Pihlajamaa

Coding since 1990 in Basic, C/C++, Perl, Java, PHP, Ruby and Python, to name a few. Also interested in math, movies, anime, and the occasional slashdot now and then. Oh, and I also have a real life, but lets not talk about it!

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