Last time, I discussed the overall objective of this project: to determine whether or not cost-effective upgrades to elementary computer-based audio playback hardware would deliver sufficient results to justify the prices paid for them. I also covered the services, genres, and other characteristics of the lossy-compressed music I'd be incorporating in the study, as well as the diversity of headphones I'd be leveraging as the playback end points of the audio reproduction process.

Now let's look at the A/D converter (ADC)-plus-headphone amplifier combo alternatives that I compared, at the midpoints of the playback chain. The baseline configuration was the one built into my early 2015 model 13" Retina MacBook Pro, currently running MacOS 10.12. Macs are generally regarded as having better-than-average audio subsystems, a reflection of their higher price tags (presumably correlated to, at least a degree, their higher bill-of-materials costs) coupled with their common usage in various multimedia creation and playback scenarios. That all said, keep in mind that the predominant application for integrated audio in computers is videoconferencing, for which pristine reproduction isn't necessary.

The cost-effective (IMHO, at least) upgrade alternative I compared it against was a two-piece configuration, tethered to the MacBook Pro over USB; the $79.99 Massdrop x Grace Design Standard DAC in combination with the $94.99 Massdrop Objective 2 Headphone Amp: Desktop Edition:









The headphone amplifier comes in two variants:

  • Medium Gain (1.0x Low, 3.3x High), intended primarily for use with in-ear monitors (IEMs) and other low-impedance headphones.
  • Standard Gain (2.5x Low, 6.5x High), particularly useful with low-voltage analog audio sources and/or high impedance headphones.

Even though the DAC delivered a 2.15V RMS output, I went with the Standard Gain variant of the headphone amplifier, to give me greater headphone impedance option flexibility. That said, I was unable to discern any noise floor or other hearing-perceptible difference between the two gain settings (selected using the front-panel toggle switch at far right on the front panel) on any of the headphones I used.

Not only does the laptop supply the DAC with a digital audio source (selection between the integrated and USB-fed external setups is accomplished via a straightforward audio output setting toggle), it also supplies power to the DAC. The headphone amplifier is powered by a separate 12V/220 mA output "wall wart" power supply. Analog audio options out of the DAC are a 3.5mm female tip-ring-side (TRS) connector and dual female RCA connectors (I went with the latter). The headphone amplifier exclusively leverages dual female RCA connectors as its input source. Here's a photo of them in action on my desk:



And in a nod to the aforementioned audiophiles, I even went with high-end thick-gauge interconnect cable, complete with gold-plated connectors:



Enough of the specs ... how do the various ADC-plus-amp-plus-headphones options sound? Before answering, I feel compelled to document some qualifiers. For one thing, this wasn't a true ABX setup, or even a reasonable approximation, quite frankly ... I knew what option I was listening to at any point in time, and switching from one option to another was a non-instantaneous process (which among other things, forced me to rely on oft-faulty memory to recollect what prior options sounded like in comparison). Also, I strove to overcome the flawed "louder is better" perception bias, fueled by the impedance differences between various headphones.

You also intentionally won't find any spectrum analyzer plots or such in the remainder of this piece. While they aren't value-less by any means, I trust my ears and brain at least as much, if not more (even though I suspect my high frequency discernment in particular has degraded somewhat over the past nearly-twenty years ... yikes!). After all, as electric guitar aficionados (for example) already know, some types of distortion are commonly judged to be beneficial to the output sound.

And that all said, what did my ears and brain tell me? Variances were more-or-less evident on different music genres, as well as across different tracks within a genre. But with that said, both of the Sennheiser-sourced headphones significantly outperformed their less expensive Koss-sourced counterpart, regardless of which DAC-plus-amp was feeding them. In contrast, I admittedly strained to discern any tangible difference between the Massdrop x Sennheiser HD 58X Jubilee and its somewhat more expensive Massdrop x Sennheiser HD 6XX sibling.

After factoring out the headphone-versus-headphone, genre-versus-genre, and track-versus-track variances, I was still able to discern a relatively consistent albeit often slight sonic improvement (along with never a sonic degradation, by the way) when the external DAC-plus-amp were in use versus with the MacBook Pro's integrated audio subsystem. The output of the external combo was more "open," for lack of a more scientific description, with the integrated audio more "thin," although I wasn't able to assuredly correlate this perception difference to a differential in detected frequency response across the audible range, for example, or a higher heard noise floor in the case of the integrated DAC-plus-amp option.

That all said, the difference wasn't dramatic, as long as I used a high quality set of headphones. If I was (for example) just listening to background music while working, or watching a movie on my laptop, I'd frankly be perfectly content to just plug a set of Sennheisers into the laptop's headphone jack. In my personal opinion, the external DAC-plus-amp combo would only be worth pulling out and hooking up for more concentrated music creation or audition sessions.

So is a nearly $200 hardware upgrade (not counting the headphones themselves) worth it? That's an individual decision, driven by both your pocketbook constraints and your desire for the ultimate sonic experience. At this point, I'll turn the microphone over to you, dear readers, for your thoughts on the question I've raised, either conceptually or (if you've also walked a similar audio upgrade road) based on your own experiences and results.

Brian Dipert is Editor-in-Chief of the Embedded Vision Alliance, and a Senior Analyst at BDTI and Editor-in-Chief of InsideDSP, the company's online newsletter.