HiFiMAN Express HM-101 Portable USB Sound Card (Playback 56)

Digital-to-analog converters,
USB interfaces, clocks, and soundcards
HiFiMAN HM-101 Portable USB Sound Card
HiFiMAN Express HM-101 Portable USB Sound Card (Playback 56)

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.

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