review

EarStudio HUD100 Review 32-bit DAC headphone amplifier

Monday, February 17, 2020

Anything from fan noise, spinning hard disks to, simply moving the computer mouse can undermine the audio conversion of even the best of sound-cards. If you hear strange whining noises coming the audio playback, the easiest way to solve this problem is with a dedicated, external USB DAC.
Depending on your multimedia applications needs, you may want to go with a small or larger USB DAC. The most important factor though, is the accuracy of the USB DAC master clock to prevent jitter (sound distortion).
The EarStudio HUD100 is one of the smallest USB DACs on the market that comes with a reliable master clock. On top of that, the HUD100 has a high dynamic range (118dB) and low Total Harmonic Distortion (0.000%), which means noise-free playback when listening to audio in low volume.
Most external USB DACs either use a temperature-compensated crystal oscillator (TCXO) or oven-controlled crystal oscillator (OCXO), both of which are made of quartz. The EarStudio HUD100 uses a silicone-based miniature microelectromechanical-systems (MEMS) oscillator that is a fraction of the size, yet it's able to provide a stable master time clock, which is crucial to maintaining the timing between samples
EarStudio HUD100 internal circuitry is enclosed inside a robust aluminium metal chassis, just like larger external USB DACs, which helps dissipate temperature, lower noise and maintain the timing and synchronization of the master clock.
EarStudio HUD100 integrates three sound modes, including an audio bypass (tone defeat) mode, which disables the signal processing circuits inside the HUD100 and sets the tone control (bass/treble/mids) to 0. In audio bypass mode, the sound is unaltered, allowing you to route raw audio signal from the audio source, through the HUD100 DAC without any added signal processing (i.e. sound effects).
The other two modes are "DCT processing" and "Dynamic processing", both of which let you alter the balance and "color" of the sound coming from the audio source the HUD100 is connected to.
The EarStudio HUD100 is mainly designed to be plugged directly into the USB port of a Windows computer (Win 7/32/64 or later) or Mac computer (MACOS 10.10 or later). That said, you can also use it with an iOS or Android device via an adapter, which is not included. You will need a  lightning to USB camera adapter for iOS devices (iOS 10.3.3 or later) and an OTG adapter for Android devices (android 6.0).
The EarStudio HUD100 supports high rate PCM (32bit/384KHz) and integrates a AK4377 DAC chip, which means the HUD100 supports native DSD. The HUD100 is capable of playing back high rate DSD files up to DSD128 via DoP, which is DSD over PCM. To play 32bit/384KHz PCM via Windows, you must download a driver. 
Sound-wise, there is virtually no difference between so-called native DSD and DSD via DoP because the DSD data isn't altered or changed during the DoP conversion. The DoP audio conversion doesn't cause any extra processing but, DoP audio can sometimes carry audio distortions such as tick, pop noises. While the EarStudio HUD100 currently supports DoP, it may well support native DSD (non-DoP) through future updates since the HUD100 firmware is being constantly updated.
The EarStudio HUD100 measures 45mm long, 32mm wide and 8mm thick so, it's smaller, more slimline and lighter (22 grams) than the ES100 USB DAC, which features a 2.5mm balanced output and EQ/app support. While the EarStudio HUD100 doesn't have a 2.5mm balanced output or EQ/app support, the HUD100 does have a high power 3.5mm output.
To give you an idea of audio power. The voltage that comes out of a standard phone 3.5mm headphone jack is 0.77 volts RMS, while the EarStudio HUD100 USB DAC can output four times more audio power.
The 3.5mm headphone on the front left of the HUD100 outputs 0.91 volts RMS (vRMS), while the 3.5mm headphone on the right outputs 2.26 volts RMS (vRMS), which is enough power to drive 250 Ohm high impedance headphones.
It's worth mentioning that when you plug in headphones on both headphone outputs at the same time, the output with the lowest output (0.91 VRMS) takes over. In order words, you cannot listen to audio from both audio channels at the same time.
Being so small, the EarStudio HUD100 doesn't have a screen display to view audio information. That said, there is a small status led built-in on top of the unit that is designed to feedback the sample rate via different light colors.
The EarStudio HUD100 is powered by the audio that the HUD100 is connected to. In this case, a computer or USB-C device (i.e. Nexus 6P or Chromebook), which can supply enough power to power the HUD100.
USB-C phones are able to supply over 1A back to a connected device so, the HUD100 is able to get even more power than  via the standard USB 2.0 (0.5A) or USB 3.0 (0.9) port of a computer.
Depending on your computer soundcard, you may see "Realtek Digital Output"listed as one of your connected playback devices. This means, you have a Realtek soundcard to output digital audio via external speakers or headphones at a maximum of 16-bit audio via various sample rates (44100Hz to 192000Hz). With the EarStudio HUD100, the audio bit depth is increased to 32-bit.
USB power port and firmware update mode switch
The Radsone EarStudio HUD100 gives more expensive USB DACs a run for their money and at a fraction of the size. Build quality and performance-wise, the EarStudio HUD100 does a superb job of bringing high quality audio to life.
As far as low quality audio such as 128kbps mp3 files, don't expect miracles from the EarStudio HUD100 or any other similar solution because external USB DACs cannot fix audio quality that is already compressed (low quality). To take advantage of the EarStudio HUD100, the audio needs to be at least CD quality (44.1kHz, 16-bit)
In terms of accessories, you get two cables of different lengths (10cm and 1 meter) included with the EarStudio HUD100 to allow you to extend the distance of the EarStudio HUD100 to the audio source. Both cables feature a USB-A connector on one end and a USB type C connector at the other end.
A leather pouch is also included to carry the EarStudio HUD100, which is nice and, while it has an open design the fit is very snug so, the EarStudio HUD100 does not fall out of the pouch. Buy it on Amazon.

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