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February 2014
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Pro-Ject Head Box DS
A headphone amp with 24-bit/192kHz DAC that can be the centerpiece of your high-end desktop system.
Review By Tom Lyle


Pro-Ject Head Box DS


  I was in search of an affordable headphone amplifier to follow my review of the $799 Musical Fidelity M1HPAP. It was then that I became aware of Pro-Ject's newest iteration of their popular Head Box, the Head Box DS, which is to some extent an upgrade of their Head Box SE II. The most significant difference between the two is that the Head Box DS contains a 24-bit/192kHz digital-to-analog converter with three digital inputs – S/PDIF via RCA, optical, and most importantly to many, an asynchronous USB 2.0 input. Of course there is still an analog input via a pair of gold-plated RCAs which is accessible on the back panel along with the digital inputs and the connector for its wall-wart power supply. Along with these changes, the Head Box DS has four small push-buttons on its front panel instead of the control knobs that graced the SE II, placing a pair on each side of an LED screen. This headphone amp's rather diminutive cabinet is available in either a black or silver finish.

The Head Box DS is made with what Pro-Ject deems ultra-low-noise semi-conductors, and utilizes the modern practice of surface-mount-technology, which ensures a short signal path, at least compared to the older method of filling circuit board which would entail running short wires through the holes of the circuit board. The power supply of the Head Box DS has also been upgraded from the earlier model, and it also includes an analog output via a pair of RCAs enabling the unit to be used as a stand-alone DAC or as a pass-through for the record-out if the Head Box DS is connected to one's system in this manner.

I auditioned the Head Box DS with essentially the same systems and the same headphones as my last headphone amp review. Again, most of the time I used the outstanding Grado PS-1000, occasionally a set of older Sennheiser HD 600s that was a short time ago reconditioned by Sennheiser USA, and the very-deserving less than $100 Grado SR-80. When really getting down to serious listening with the Pro-Ject Head Box DS I connected it to the record-output of the preamplifier in my main system that has a digital front end that uses a Dell Studio XPS 3.20 GHz PC as a music server with 8G of RAM with over 4 terabytes of external hard-drive storage. It runs FOOBAR 2000 to play FLAC files stored on the drives. Kernel Streaming (KS) is set up to bypass the PC's internal mixer, and the audio signal is sent out of the USB ports via Furutech GT2 USB cable, connected to the DAC de jour, currently a Wadia 121 Decoding Computer. I also play the occasional SACD and DVD-Audio through an Oppo BDP-83 Special Edition universal disc player. The analog front end of the system has a Basis Debut V turntable with Lyra Kleos phono cartridge mounted on a Tri-Planar 6 tonearm. The phono preamplifier is a Pass Labs XP-15. The interconnects running from the cartridge to the phono preamp consists of Discovery cable terminated with Cardas RCAs hardwired throughout the tonearm, and a balanced pair of MIT cables that runs between the phono preamp and the BAT.


Pro-Ject Head Box DS


To some it might seem a bit silly using a $399 headphone amp/DAC with my main system. Some are likely to protest that is just not how this component is going to be used in the real world. True, but using it this way certainly brought out all the sonic strengths and weakness of the Head Box DS, but still, I did not neglect to use it in a desktop system routing the USB cable directly into its internal DAC, and I also used an iPod connected to the headphone amp's analog inputs. No one has come forth to complain that I used an iPod filled with uncompressed AIFF files in my preview headphone amp review, but even if they did, I would still have used it to perform most of my listening because that is the way I do much of my headphone listening on a day-to-day basis, let alone how I listen when auditioning a pair of headphones or a headphone amp. I'll repeat what I said in the previous review: I did not make a habit of listening to mp3's or any other compressed audio through the Head Box DS. Still, occasionally a 320 kbps mp3 file might slip by (usually a live bootleg or other rare recording), but 99.99% of my digital files are 16-bit/44.1kHz or better, and on the iPod these are lossless compressed AIFF files that sound identical (at least to me) to native WAV or FLAC files from which they were converted. Furthermore, when listening through the iPod I bypass the unit's internal audio stage by using a SendStation Pocket Dock Line-out adaptor that snaps into to the iPod's dock connector, with a 1.5 meter Kimber interconnect with a mini-plug on one end to connect to the SendStation adaptor, and a pair of gold-plated RCAs on the other end to connect to the Head Box DS's analog input.


Using the combination of listening methods; directly from my large main system, desktop, or from a mobile device, I was able to paint a fairly good sonic picture of the sound quality of the Head Box DS. However, during my first few sessions with this Head Box I thought it sounded so dreadful I considered returning it to its distributor – I didn't think it was worthy of a review in a high-end publication. During this time I read and re-read the manual to make sure I had connected and/or configured the unit correctly, and I even perused a few reviews of previous models to see if they also thought that the sound quality of the Head Box was below par. In none of these reviews did they state that they thought that the Pro-Ject was a poor headphone amplifier, but in some they either seemed to be politely sidestepping the fact or claimed flat-out that its bass response was attenuated, and insisted that this led to this Pro-Ject headphone amp having a thin sound.

What I discovered, though, was that these reviewers were most likely not as patient as the unit demanded – it needs a very long break-in period. These reviewers had obviously not listened to or otherwise run signal through their Head Box long enough for it to reach its full potential. I am not trying to disparage these reviewers; I could see how this type of thing could happen, especially to those reviewing more than one headphone amp or component at a time. The Head Box DS that was given to me to review took an awfully long time to break in; so if the previous versions of this headphone amp were anything like the Head Box DS, I could see how they could become inpatient and move on to the next sample under review. I consider myself lucky that at the eleventh hour the Head Box DS started to sound more like the high-end component that it was purported to be. The change in its sound quality from out-of-the-box to fully broken in was one of the most dramatic I've experienced, and without doubt the most dramatic for such an affordable component.

I agree that even when fully broken in the Head Box DS sounds a tad lean. At the same time, though, it is the one of the most detailed headphone amp I've ever heard anywhere near its price. I like this type of sound in a headphone amp. Headphone listening allows me to dig into the nuances of a recording that might not be possible with regular hi-fi. When listening to headphones I like to be able to take advantage of the fact that they are eliminating not only the room sound from the sonic equation, but all outside interference that would distract one from the music. The quest is then to find not only a headphone/headphone amp combo that can deliver qualities that replicate the musical experience as much as possible, be that live or recorded, acoustic or electric, real or man-made as much as possible, but also comes within the constraints of our budgets. The Head Box DS seems to have found how to manufacture a component that delivers this detail without too many downsides such as colored sound, lack of frequency response, etc. at a price nearly all audiophiles can afford. I've heard some very nice (in other words, expensive) headphone amps that can come as close to headphone-listening "perfection" as I've ever experienced. I'm not going to pretend that the Pro-Ject Head Box DS delivers all the sonic qualities of these expensive designs, but through the Head Box DS I hear at least a taste of what these designs offer for much less money. Some audiophile-type traits might be missing from this headphone amp, but the amount of detail it delivers is not one of them.

What is also surprising is the level of transparency the Head Box DS is able to achieve, at least through its analog input. I'll agree with the other reviewers that the Head Box DS is a bit lacking in the amount bass it provides, but it is not lacking in the depth of the bass frequencies it can reach. The extension of the bass seemed to reach as low as the recording demanded, and though the quality of that bass was not as good as some of the bigger players in the field of headphone amplification, it was certainly better than its low price would indicate.  I've been comparing two versions of Genesis' The Lamb Lies Down On Broadway, one an original stereo mix ripped from a CD released in the 1990s, the other a 5.1 mix combined to stereo ripped from the CD that is in the CD/DVD box set of complete Gabriel era albums, 1970 - 1975. In it Mike Rutherford's bass-pedals enter during the fifth track, "In The Cage". I'm not going to pretend I know the exact frequency of these tones (or if Rutherford was still using the Dewton pedals or had moved onto the Moog Taurus bass synthesizer pedals), but when using the combination of the Grado PS-1000 'phones and the Head Box DS I had the sense that I wasn't missing one iota of the pedals contribution to the song. The jury is still out, so I haven't totally made up my mind whether I prefer the remixes of the earlier Genesis albums or this 5.1 version of The Lamb, which sometimes sounds peculiar when mixed down to "only" two channels. Nevertheless, the rest of the album makes it clear that the Head Box DS has no trouble reproducing the deep bass present along with any other sound that is on the original master tape, either acoustic, electric, or "Enossification" (via Brian Eno's studio tape manipulation and effects). The Lamb… along with the other Genesis albums recorded around this period are nearly perfect headphone albums, as there are so many instrumental layers to their complex compositions. Quality-wise, they might not be the best recordings ever made, but they've certainly aged well, and through the Head Box DS they prove that they've been designated progressive rock benchmarks for good reason.

Again, my listening sessions using the various ways of getting the signal to the Head Box DS revealed that the analog input was the best method. The internal DAC of the Pro-Ject was fine for desktop listening through small self-powered monitors using its analog output, as it was for using inexpensive headphones such as the Grado SR-80s. When using the USB input with the Grado PS-1000s it revealed the limits of the DAC section. When feeding the Head Box DS through its analog input via the record out of the preamp via the computer's USB decoded by the Wadia Decoding Computer, the differences between the two were considerable. But I don't think that has much relevance when using the Head Box DS in a system for which it was designed. When using it with either the desktop speakers or through less revealing headphones, this headphone amp/DAC made itself right at home. Even through its analog input the Head Box DS couldn't bring out the best in the Grado PS-1000, which are often able to perform a level of suspension of disbelief that is beyond compare when connected to a top-flight headphone amp, yet it was still able to reproduce a full orchestra with fair amount of realism because of its relatively high level of transparency. But still, it couldn't project a simulated soundstage outside one's skull like it could when connected to, for example, the $1200 Audio Electronics Nighthawk.

In spite of this, it speaks well of the Pro-Ject Head Box DS/Grado PS-1000 combination that I could listen to a classical SACD through my main system with and not only enjoy it to its fullest, but forget that I was listening to a "budget" headphone amp. I played Bruckner's Fifth Symphony with the Vienna Philharmonic conducted by Nikolaus Harnoncourt on RCA. On it the pizzicato strings in the beginning of the first movement (Adagio) I was able to detect the delicate initial strike of the strings in the violin section as distinct events, leading to the changing tempos that distinguish the score's sections from one another. The themes remain similar, as three of the four movements also begin with these pizzicato melodies, and yet it is pure Bruckner throughout. Even though it couldn't convey the weight of the full orchestra, the Head Box DS allowed me to get lost in the score, as I usually do with this composer, as I find the repeating themes meditative.


Pro-Ject Head Box DS


When I switched to a file of the CD layer of the same symphony as played through the USB output of my PC through the Head Box DS's USB input and DAC, there wasn't just the loss of fidelity that comes from comparing an SACD to a 16-bit/44.1kHz file, but also a reduction in everything that audiophile's value in high-end reproduction. But lest you think I'm an audiophile snob, I was still able to enjoy the work through the Head Box DS's USB input when fed this signal. The high level of quality that came from this sub $400 unit is quite astounding, really. It was still able to draw me into the composition because of its ability to make space between instruments and groups of instruments, and preserve the timbre of all the instruments in the large orchestra. Its detail was used to great effect, such as making the venue in which the concert was recorded quite audible, which added to a sense of immersion to the recording. And it was able to offer me the important aural cues that I was listening to a recording of real instruments recorded in a real space as I could hear bodies shifting in their seats, occasional grunts from the podium, and even a whisper or stifled cough from the very attentive Viennese audience.

Thankfully, with headphones and headphone amps, the laws of diminishing returns do not set in until one reaches the uppermost tiers of these categories. Imagine if $2000 could buy the "best" speakers on the market? When shopping for headphones or headphone amps, the different between $500 and $1000 are marked. Although the price of the Head Box DS isn't going to buy one the best headphone amp out there, it is still much, much better than anyone could have expected even a short time ago. That it also includes an internal DAC for this price is also quite astounding.


Kudos to Pro-Ject for making such a high quality high-end headphone amp/DAC that cost so little. As time marches on, so do advances in not only digital technology, but all realms of audio technology. And with those advances, comes lower prices. For under $400 one can purchase a headphone amplifier that not only sounds good, but sounds better than any inexpensive headphone amplifier that has come before. Throw in an internal DAC with not only a USB input, but an S/PDIF and optical inputs, and one can have a headphone amp that can be the centerpiece of an impressive high-end desktop system. I used the Pro-Ject Head Box DS not only as a review sample, but for listening to music for my own enjoyment in a number of ways, and in every way it transformed my listening experience into a captivating high-end listening experience. At this price, I predict Pro-Ject is going to sell a ton of Head Box DS units.


Ratings: I tend to rate very conservatively as a 5 note rating is equivalent to the best I've ever heard.


Sub-bass (10Hz - 60Hz)

Mid-bass (80Hz - 200Hz)

Midrange (200Hz - 3,000Hz)

High Frequencies (3,000Hz On Up)



Inner Resolution


Fit And Finish

Self Noise

Value For The Money



Type: Stereo headphone amplifier with preamplifier
Line-Level Input/Output: One pair RCA/phono sockets each
D/A-Converter: Cirrus Logic CS4344, 24 Bit/192kHz Delta Sigma
Supported Audio Formats: PCM (LPCM)
Sample Rates: USB 2.0 (MiniB) input: 44.1, 48, 88.2, 96, 176.4 and 192 kHz
Coaxial Input: 44.1, 48k, 88.2, 96, 176.4 and 192 kHz
Optical Input: 44.1, 48, 88.2 and 96 kHz
Power Output: 350mW/30 Ohms, 60mW/300 Ohms
Headphone Connection: < 30 Ohms
SNR: 112 dB (A weighted) at full output
Frequency Response: 20Hz to 20kHz (0.5dB)
THD: 0.0014%
Gain: 9dB
Headphone Jack: Standard 1/4"
Power Supply: 18V @ 1000mA DC suitable for country's mains supply
Dimensions: 4" x 2.75" x 5.75" (WxHxD)
Price: $399


Company Information
Sumiko Audio 
2431 Fifth St. 
Berkeley, CA 94710
Phone: (510) 843-4500

Email: mail@sumikoaudio.net
Website: www.SumikoAudio.net













































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