A good entry-level portable DAC or sound card should have five primary characteristics: it should be inexpensive, compact, lightweight, glitch-free, and sound good. The $39 HiFiMAN HM-101 is the size of eight credit cards stacked together, weighs about the same as a pair of small earbuds, and works reliably, so it’s got four of the five covered. But how does it sound?
Built around the Burr-Brown PCM2702 E chip, the HM-101 supports 32, 44.1, and 48 kHz 16-bit music files. The DAC chip used in the HM-101 is a low-current draw design developed specifically for small portable devices. It includes the newly developed SpAct™ (Sampling Period Adaptive Controlled Tracking) system, which recovers a stable, low-jitter clock for internal PLL and DAC from the USB interface audio data. The PCM2702 is based upon Texas Instrument’s enhanced multi-level Delta-Sigma modulator, and includes an 8x oversampling digital interpolation filter and an analog output low-pass filter. Digital attenuation, balance adjustment, and soft-mute features are controlled via USB audio class requests.
The HM-101 offers two output options. Both are available via mini-stereo connections on the bottom edge of the DAC. One output is for headphone use while the other is for connecting to an audio system. The headphone output has more drive capability with maximum output of 96 dB, while the other only goes to 76 dB. With some headphones the lower-level output will be a better match. The determining factor will be whether you can get adequate volume. It’s usually better to use the least amount of digital volume attenuation possible, but if you can’t get enough volume from the low-level output, the HM-101 gives you the welcome option of another 20 dB of gain through the headphone output. HiFiMAN’s HE-300 headphones (93 dB sensitivity) mated well with the lower output connection—most of the time I listened with the volume slider at full level with no attenuation.
• Integrated USB interface: Full-speed transceiver supports 12Mbps data transfer, fully compliant with the USB 1.0 Specification, adaptive mode for isochronous transfer
• Self-powered (USB) device
• SNR: 96dB
• THD+N: 0.07%
• Sampling Rates: 32kHz, 44.1kHz, 48kHz
• On-chip clock generator with single 12MHz clock source.
The HM-101 was designed to be a plug-and-play device. On all the Macs (MacPro, MacPro portable, Mac Mini) and a Dell D-620 portable PC that I tried in my listening tests, the HM-101 proved to be plug-and-play as promised. Checking my Mac’s Midi Control panel showed the HM-101 supporting 32, 44.1, and 48 kHz files at 16-bits. Operation with iTunes, Amarra, Pure Music, and Audirvana Plus was glitch-free and without any operational issues. The only operational quirk I noticed was a very occasional issue with USB mouse movement causing low-level noise: a reboot immediately fixed the problem.
Since the HM-101 doesn’t have buttons, switches, or controls of any kind, volume must be controlled by software. If you’re in the habit of leaving your iTunes volume slider all the way up when you first begin playing music, you’ll want to rethink that unless you enjoy getting blasted by maximum volume at start-up.
The HM-101 comes with a short but serviceable 1-foot long USB cable. Naturally, some users will want to experiment with a better USB cable, but they should be aware that the HM-101 uses a mini-USB rather than a full-size USB connection, so standard USB cables won’t fit. For the review I used the supplied USB cable, as I suspect most HM-101 users will also do at first.
The only physical sign that the HM-101 is connected and working (other than playing music) is a bright blue LED light. The LED is brilliant, and so penetrating that in a pinch you could use it to illuminate your way home on a dark, moonless night.
Most of my listening time with the HM-101 was spent tethered to a pair of headphones. My reasoning was simple: Most HM-101 users are going to be using it with headphones. The overall sonic signature of the HM-101 is clean, clear, and very direct. With some headphones, such as the AKG K701, the HM-101 sounds slightly thin and lacking in midbass warmth. But when coupled to the HiFiMAN HE-300 headphones, which can sound bass-heavy, especially in the mid-bass, the HM-101 proved to be a synergistic match-up.
Regardless of what headphone or earbud you use with the HM-101, the trick to getting the best performance is to choose an output level that lets you run the slider on your computer’s volume control as close to maximum as possible. I recommend trying the lower level output option first. If you can’t get enough volume, go to the headphone output with 20 dB more gain.
If most of your prior music listening has been through your computer’s built-in sound processing and delivery system the added clarity of the HM-101 will be the first thing you’ll notice. Compared to the HM-101 the sonics from both my PC and Mac portable computers were murky, slow sounding, and lacking in anything approaching dynamic spark. The term “grayish” accurately describes the overall impression of built-in audio compared with the more vibrant, articulate, and involving sound of the HM-101 soundcard.