The HUD-MX1 comes with a high-gain setting. Something that’s not obvious unless you read the manual (something we all rarely do). Accessing the high gain mode requires you to open the casing. Not the most convenient method, but hey, it’s not terribly hard to do either. Inside, you’ll find two jumpers that will raise the gain of the headphone to work with 300-600 Ohms cans. Although the default jumper setting supports 16-300 Ohms cans and I certainly have no problem driving the 300 Ohms HD800 with the jumper set on default. When the jumper is moved to high gain, the built in amplifier drove my HD800 fairly comfortably at around 11 O’clock.
The HUD-MX1 does have some extra features that I think are very handy for an external DAC to pair with a computer. Using an SMD OPA2134, it sends an analog line out through a pair of RCAs through the back panel. It seems that the analog line out was designed to be used with powered speakers, as active speakers seem to be the norm for computer hi-fi. Output level on the line out is controllable through the volume knob on the front panel, although you have to switch the toggle to turn on the line out signal (meaning you can’t have signal on the line out and headphone out both on at the same time). The HUD-MX1 also comes with a digital optical that I use for daisy chaining DACs.
The auto-on feature is quite neat. It doesn’t come with a power switch, and when it detects audio signal from the USB cable, the HUD-MX1 will automatically turns on. Audinst supplied a 15Volts wallwart to be used with the HUD-MX1, but it really is not mandatory, as the USB connection can supply enough power for the MX1. Of course, it has to be a high power USB socket. This is very welcome, as it reduces clutter on your desk, and for laptop users working outdoors or in coffee shops, that simplifies your set up to just the Laptop, HUD-MX1, and say a multi-driver custom IEM, and you’re instantly in audio-bliss.
You do have to know that the circuit runs more optimally at 24 volts with the wallwart plugged in, as opposed to 16 volts from the USB. Hence, when using high impedance cans, it’s recommended to have the wallwart plugged in.
The HUD-MX1 also supports 24/96 playback, and playing 24 bit files from the MacPro, I find 24 bit playback through the MX1 to be very good. Oh, and it’s plug-and-play on the Mac, no separate drivers needed. On Windows, basic USB Audio driver installation should be automatic, although I don’t have a Windows machine to test it on.
To be frank, I’m not crazy about the front faceplate. Functionality wise, it’s great. But aesthetically, it’s not the prettiest design, and I’m sure that the Korean designers at Audinst could’ve come up with something that looks better. Of course, I’m just nitpicking here, and other people would’ve been very happy with the overall look of the HUD-MX1.
At the end of the day, I think the HUD-MX1 is an excellent product. It’s not an excellent product in the sense that it can compete with $1000 DACs for the price, but more that it’s a well thought, well designed stand alone DAC at a very competitive price. The free from any coloration sound makes it an easy pair with a separate headphone amplifier. The dual 1/4″ and 1/8″ headphone outs, power through the USB, analog line out with volume control, rollable op-amp, high gain selector, and 24/96 playback support all makes the HUD-MX1 a very nice companion for the computer. I would’ve welcomed having an external gain switch, but on some circuits having external gain switch requires you to compromise on the PCB layout, and so I can understand having to access the jumpers.
You can buy the HUD-MX1 directly from Audinst’s eBay store for $179, and right now they’re having a free shipping promotion.
System used for review:
Headphones: AIAIAI Tracks, Sennheiser HD800, Audio Technica AD700
Source: MacPro, Itunes, Audinst HUD-MX1
Amplifier: HUD-MX1, Doobooloo’s TPA 6120 Balanced Amp