The O2+ODAC that JDS Labs (among others) manufactures, based on an open source design, is the most innovative concept in our round-up.
In 2011, a mysterious blogger who used the handle "NorthWest Audio/Video Guy" (NwAvGuy) began ranting about the snake oil he believed was being sold to the audiophile community. He set out on a personal crusade to design and build a low-cost headphone amplifier that, through blind tests, could not be distinguished from the Benchmark DAC1.
That design eventually became what's known as the "O2" (from Objective2) headphone amplifier. NwAvGuy went on to create an implementation of ESS' ES9023 chip to function as a DAC feeding the O2, using similarly objective criteria. That latter device came to be known as the "ODAC" (from ObjectiveDAC). Both devices can easily be connected and integrated into a single enclosure.
The O2+ODAC is an uncommon design by most standards. The headphone amplifier, in particular, was originally designed with battery-powered operation in mind (for portability). While the JDS Labs implementation does away with the batteries, it retains many of the portability-related design choices. It employs an external AC transformer, not the internal one you'd find on most comparable DAC/amps. There are no RCA stereo outputs at all. And the O2 does not use an amplifier chip (like the TPA6120A2), but rather a custom design on the output stage.
Feature-wise, the O2+ODAC is really barebones. It has a 3.5 mm line-in connection up front, a mini-USB port in the back, and a 3.5 mm headphone-out jack. That's it as far as I/O goes. Controls are limited to a gain switch and an analog (high-quality) volume control.
Based on NwAvGuy's open-source license (which, paraphrasing, states: anyone and everyone can manufacture one of these without paying me a dime, as long as they don't change the design), a variety of manufacturers are now selling O2+ODAC devices.
In 2012, after being banned from the headfi.org forum for, according to his version of the story, criticizing one of that forum's sponsor's products, NwAvGuy started building a desktop-oriented version of the O2+ODAC, called the Objective Desktop Amplifier. The twist is that NwAvGuy mysteriously disappeared without a trace in mid-2012 before completing the ODA's design. Nobody seems to know why he stopped blogging or what happened to him. So we're left with the O2+ODAC to test, and a lingering dream of what the ODA could have been.
The manifestation we're testing today is provided by JDS Labs. It is sold fully assembled for roughly $290, including the required AC transformer. If you're nimble enough with a soldering iron, you can pick up the O2 do-it-yourself kit for $69, add the ODAC board for $99, and buy the transformer for $11. That'd get you going for about $180, not including the enclosure.
Aside from the performance commentary you'll find through the following pages, I encountered one specific problem with the O2+ODAC. After receiving and unpacking it, I clicked into high-gain mode, plugged in my Sennheiser HD 800s (300 Ω impedance), turned up the volume, and noticed that the sound was terrible, affected by massive distortion. It turns out that the supplied transformer isn't powerful enough to drive high-impedance phones using the high gain setting. Unfortunately, JDS Labs doesn't stock higher-power transformers, so a replacement wasn't an option. The only solution was to use the low-gain setting at much higher volume. That did successfully solve the distortion issue. But JDS Labs should consider, in my opinion, stocking AC transformers that better-support the high gain setting. Going one step further, transformers should really be included with the assembled product.
So, did NwAvGuy end up winning his crusade? Can the O2+ODAC be distinguished from the 7x-more expensive and 5x-larger Benchmark DAC2? Read on...
Update: We received the following response from JDS Labs:
"AC adapters for O2 are packaged separately because JDS Labs ships worldwide. There's little incentive to bundle AC adapters since each customer requires a unique plug. Thus, the items are presented separately for customer's selection. Our shopping cart reminds customers to choose an appropriate model. As of late December, we now stock a higher-power model for U.S. customers who need additional current; this represents less than 2% of customers, though. All European, Australian, and British AC adapters stocked by JDS Labs are high-power models."
- Turning The PC Into A True Hi-Fi Audio Platform
- Four Devices Tested: From $2000 Down To $2
- Benchmark DAC2 HGC
- JDS Labs O2+ODAC Combo
- Asus Xonar Essence STX
- Realtek ALC889
- Test Setup: Sennheiser HD 800 And AKG K 550 Headphones
- Test Setup: Volume Matching And Testing The Listener
- Test Setup: Cables, Software, And Tracks
- Test Setup: The Blind Testing Process
- Results: Dragonborn / Jeremy Soule
- Results: Soothe My Soul / Depeche Mode
- Results: Through The Fire And Flames / DragonForce
- Results: Get Lucky / Daft Punk
- Results: Symphonic Dances / Andante Con Moto / Rachmaninoff
- Bonus Test: DSD Versus PCM; Billie Jean / Michael Jackson's Thriller
- Why We Need To Test Low-Impedance Headphones Soon
- Why Audio Formats Above 16-Bit/44.1 kHz Don't Matter
- Anything Above $2 Buys More Features, Not Better Quality