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RocketScientist 4th August 2011 05:02 AM

The Objective2 (O2) Headphone Amp DIY Project
This has been in the works a while. At the request of friends (and a few critics) I've designed my own portable/desktop amp--The Objective2 (O2 for short). I just published the third and final main article to my blog.

It's a very objective approach (what would you expect from an electrical engineer?) at a low cost "one size fits all" headphone amp. The goal was to show how much performance is possible on a limited budget. It's designed to outperform even far more expensive desktop amps using solid engineering rather than audiophile designer parts or mythical topologies.

For now it's a DIY amp but it's a free open source design and a few commercial companies have already expressed an interest in offering it in various forms. Some have called it the spiritual successor to the Cmoy but the performance is in an entirely different league (sorry for not being more modest!). Some highlights:

* Enough output even for difficult headphones like the full size HiFiMan Planars and 600 ohm Beyers (7 V RMS and lots of current). It will drive nearly any headphone from 16 - 600 ohms to "live" levels.
* Completely silent even with the most sensitive BA IEMs (zero hiss with 131 dB S/N )
* Near zero ohm output impedance (0.5 ohms)
* Very low distortion of any kind--some tests push the lower limits of my dScope audio analyzer.
* ~8 hours battery life for the normal version & ~ 30 hours for the low power version
* Indistinguishable from Benchmark DAC1 in blind listening tests
* Switchable gain for use with different source/headphones
* Unique battery rundown protection
* DIY friendly, self contained on a single PC board, no surface mount parts
* Designed for a rugged inexpensive all aluminum case with a pre-made customizable front panel available.

And, perhaps the best part: You can build the fully functional self contained PC board for around $30 in parts with everything but the bare board available from Mouser.

The performance of this amp, as measured on professional instrumentation, genuinely rivals the well regarded headphone amp in the Benchmark DAC1 and is significantly quieter. It also beats every other amp, overall, I've ever had on my bench--especially its closest competitor the AMB Mini3.

I welcome feedback on the project and hope it develops into something worthwhile. I'm not looking to make any money from it in any way. Here's the link to the final article which has links to the earlier information as well:

I have put together a fault finding guide on the O2 (post #3775) that gives step by step testing and checking procedures. Click HERE

RocketScientist 4th August 2011 06:04 AM

Hmmm... there's no link! Let's try that again:

O2 Open Source Hardware DIY Headphone Amp Project

The above article is the best place to start but there are two more articles, a Wiki and some Google Docs files as well.

qusp 4th August 2011 05:40 PM

hang on, it beats everything youve had on your bench, yet its closest rival is the mini3 an amp that you publicly rubbished for its poor performance?

RocketScientist 4th August 2011 05:52 PM


Originally Posted by qusp (
hang on, it beats everything youve had on your bench, yet its closest rival is the mini3 an amp that you publicly rubbished for its poor performance?

I believe both statements are true and not in conflict. I can't help it if the Mini3 doesn't perform as promised but why isn't it otherwise close competition?

Do you know of another reasonably priced DIY portable headphone amp that's an overall closer rival to the O2?

qusp 4th August 2011 06:07 PM

ahh ok, the way your amble is worded and the use of the dac 1 headphone amp as a reference, did not really leave me thinking you had a limit on budget, or size for this comparison or position of superiority. in that case i dont know one off the top of my head, but i'm pretty out of touch in that sector

RocketScientist 4th August 2011 06:13 PM

No worries. I just happen to own a DAC1 making it a handy, um, "benchmark" to compare things against. It's also fairly well known and has been widely reviewed professionally so most people know what you're talking about. I agree it's otherwise kind of an apples-and-oranges comparison as it's a high-end desktop headphone DAC.

firechief 4th August 2011 06:16 PM

RS - do you accept complements? Clearly this is good work. I would use the term professional.

RocketScientist 4th August 2011 06:20 PM

Thanks firechief! I'll take any and all kudos! :) And while you might say "professional" others fall asleep reading some of my articles or their eyes glaze over. I'm still trying to improve my writing and presentation skills and have a ways to go.

qusp 4th August 2011 06:21 PM

there was a pretty impressive and very compact Japanese, or Korean language only lion powered and predominantly smd project posted on head-fi about 6 months ago that looked pretty spiffy. it was posted in the general portable amp forum and not diy area, with no schematic and they didnt export kits due to the fact lion cannot be shipped by air easily, if at all. i'll see if i can search it out, but it might not be terribly accessible for you to test or build for comparison.

I must say of its type the power supply in your amp is pretty cool. i dont always agree with your method or agenda, but the science is sound. i do also think that mostly you dont intend things to come off quite the way they do, or in the spirit that they seem to; perhaps linked to the writing i dont know and then things seem to get out of hand due to ego on both sides. just an observation, not a judgment.

RocketScientist 4th August 2011 06:30 PM

I'd be hesitant to publish a Li-Ion project as the dangers are substantial (search for "LiPo Fire" on YouTube for some entertaining, and often sad and very expensive, pyrotechnics). There are even documented cases of cheap eBay cell phone batteries burning cars to the ground because they caught fire on the passenger seat.

The power supply is a huge part of the O2's low cost performance. A real ground always beats a virtual ground. And the half-wave AC supply might seem "cheap and dirty" but properly engineered it works as well as any other AC power supply in this application. The proof is 131 dB of S/N and 0.0009% THD on battery or AC power.

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