Review – i-dSp and dSp Portable DAC/Headphone Amplifiers from HRT

A few years ago, we witnessed the first truly portable and affordable USB-powered DAC (digital-to-analog converter) headphone amplifiers. The idea was that with a simple plug-and-play unit, not much larger than a flash drive, you could bypass your computer’s low-cost and often inferior audio-quality DAC and headphone amplifiers. The price ranged from $200 to $300, but most consumers thought the step up in audio quality was a bargain. The Audioquest Dragonfly was one of the first to the market and was so small it was almost unnoticeable, with great audio quality. Within a few years a slew of similar products hit the shelves, from DIY solutions to specialized models able to decode DSD natively such as the Korg DS-DAC-100M Mobile 1Bit USB DAC unit we reviewed last year.

HRT has long offered superior external DAC solutions, which we have reviewed in the past. With the introduction of the i-dSp and dSp, at a price under $70, they have rewritten the rulebook for external DACs. Not much larger than a cigarette, both units are identical in terms of their specs, but with different interfaces. The i-dSp is designed to connect to an Apple OS device, whereas the dSp is a traditional USB powered unit, able to connect to a computer, or an Android phone.

Both units come in a small box; the dSp has all you need to get started – a Micro USB cable makes it instantly plug and play. The i-dSp requires an Apple Camera Connection kit to connect to a Lightning-equipped iPad or iPhone, adding another $30 to the total cost. Of course many consumers already have the connection kit, so might not need to purchase the small cable adapter.

Once attached, both units showed up immediately on whatever system we plugged them into, from a MacPro, MacBook Pro, Samsung Virgin Galaxy S5, or iPad, and for the i-dSp, using a Lighting-equipped current generation iPad. In all cases, the HRT units showed up immediately, and were instantly usable. We find the improvements in DAC chips and circuitry a parallel to the improvements in digital cameras, in which the quality improvements aren’t due solely to increased sensor pixel counts, but instead go hand in hand with better DSP and DAC image processor capability. 

Several years back, we reviewed the HRT MicroStreamer and found it eminently musical, with a warm, open sound. Its sleek aluminum case was not much larger then a lipstick container, and its sharp rectangular block projected a solid build quality. It also included a row of tiny LEDs to indicate sampling rate, a welcome confirmation that sampling duties were being handled properly.

The i-dSp and DSP units take a different design direction. One tiny LED indicates power is on, but that’s it – no sampling indicators. The units are also much lighter and smaller, made of high-quality plastic. They are so slim, once you plug in earphones or headphones it’s easy to forget about them; they just blend into the cable and we found ourselves just leaving them attached. One of the best things about the new design is ease of use, plus they are light enough it’s easy to simply forget you have them on. The dSp unit is small and bright red, while the i-dSp is longer, with the USB port inside the longer tube, so the Apple Camera Connection kit can connect inside and make sure no strain can damage the unit, and in keeping with the Apple aesthetic it is a clean white design.

They have their limitations compared to other HRT units. They can’t decode DSD natively, and the top end for their sampling rate is 96k, so if you live and die by 192k files, or DSD, then you might have to settle for a lower sampling rate. But to keep it in perspective – these are designed for portable on-the-go use. And sitting in a plane or bus, with the level of ambient noise, it’s doubtful one could actually hear a difference between 96k or 194k files, so that’s a moot point in our eyes. One thing that surprised us was that they were capable of driving our test headphones and earphones to louder levels than the Microstreamer, and the audio quality was not only a match for MicroStreamer, we actually found it a bit more enjoyable with more “air” in the soundstage, remarkable performance for $70.

We would have liked to see some sampling rate indicators on the unit, but when I talked with the company, they explained that adding the LEDs would have not only raised the price, but most likely forced a physical change resulting in a larger unit. So, given that the primary design point was the best possible sound, in the smallest and lightest package they made to date, coupled with an extraordinary price-point, I guess we can live without a few LEDs. They also lose the line level output of the MicroStreamer, but remember – these are one-third the cost, lighter, slimmer, and smaller, so we think it's a reasonable compromise.

We tested the units using Sonic Studio Amarra, Decibel, and iTunes (Yosemite on the Mac), and found that all the apps instantly recognized the HRT hardware, and worked without any problems. Amarra and Decibel sounded better than iTunes, and the native soundboard in my MacBook Pro. HD Tracks was kind enough to provide some recent high-resolution releases from Led Zeppelin, so we had ample bass to judge how they HRT units handled such demanding low-end source material, and they didn’t disappoint, from John Paul Jones’ bass lines to John Bonham’s drumming, the punch of the music, as well as the gentle nuances (yes, Led Zeppelin always included tracks that celebrated a stripped-down acoustic sound) they came to embrace once they moved past the sonic bombast of their first two titles.

James Taylor’s lovely new release Before This World, available in high-resolution from HD Tracks, was also a great test for the two DACs, revealing a warm, open sound, that made you feel like Taylor was sitting in your kitchen with your guitar. Before This World is a superbly produced and recorded album, and we deserving of the plaudits it received. As a new 2015 release, recorded, mixed, and mastered in high-bit, it is tracks like this that really reveal the capabilities of new hardware. Taylor’s voice is clear and concise, believable and sincere.

Dr. Chesky’s new release, “You’re Surrounded,” is a demanding test for hardware and software alike and part of the Chesky Binaural + Series, all recorded with a single microphone. The Chesky Records binaural series is a must for any serious headphone or earphone enthusiast. The series reveals extraordinary sound, recorded with only two small microphones, and requiring careful attention to the placement of instruments and musicians, as well as the environment chosen for recording. The 14 tracks include The All-star Drummers of Guinea, The New Appalachians, POWERHOUSE, Javon Jackson and Billy Drummond, The Manhattan Brass Quintet, The Cerddorion Vocal Ensemble, and Wycliffe Gordon, a superb compilation. Once again, the HRT units didn't disappoint and the rich percussion of the All-star Drummers of Guinea revealed the unit’s ability to power even bass heavy content. As we went to press the new Keith Richard’s solo title, Crosseyed Heart was released, and HD Tracks provided a high-resolution version, whose bass lines are consistently demanding. On the opening track, the HRT units provided a sense of air in the room, along with a sharp attack of the guitar strings, and bass riffs. Richard's Twelve-String guitar on Good Night Irene sounds great with the dSp, driving Oppo PM-3 headphones.

We applaud HRTs approach to the portable DAC/Headphone Amplifier market. They proved that the holy grail of audio, that of low-cost, affordable gear that provides killer sound, is here. With great sound, at an unbeatable price, both the HRT i-dSp and dSp come highly recommended.

Harris Fogel, posted 9/25/2015

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