Asus Xonar Essence One
The Asus Xonar Essence One has replaceable op-amps and is aimed at hi-fi enthusiasts who like to tinker with their kit. Indeed, it looks more like a traditional hi-fi unit than your average USB audio device. Its black metal chassis is both well built and unusually large, with a footprint of 262x210mm. Its mains power connection and asynchronous USB data connection are designed to eliminate interference and jitter, and we encountered neither.
The Asus Xonar Essence One has three audio outputs, all of which work simultaneously. At the front, there’s a 6.3mm headphone jack capable of driving headphones of up to 600 ohms impedance. We were pleased to find that it’s also able to handle 16 ohm earphones without producing the high-pitched whine that affects some other high-impedance headphone outputs. On its back panel is a pair of balanced XLR outputs that are ideal for connecting to a pair of studio monitors and a stereo pair of RCA outputs.
The Xonar Essence One also has optical and coaxial S/PDIF inputs that you can use to connect high-quality CD players and other external audio devices. A button at the front lets you switch between input sources. LEDs display the frequency of your audio source, and the Xonar Essence One supports playback frequencies from standard CD-quality sample rate of 44.1kHz up to a sample rate of 192kHz, a rate commonly used in audio production. Another button triggers the Essence’s upsampling, which interpolates frequency data to create the impression of a recording made at a higher sample rate. We found that the effectiveness of this feature was dependent on the quality of the original source. Higher quality recordings benefitted the most, but the perceived improvements were typically subtle.
The Essence One comes with a pair of angle-ended electronics tweezers, needle-nosed pliers and a screwdriver, as well as a box of alternative op-amps containing four Texas Instruments Burr Brown OPA2132P and two National Semiconductor LM4562NA chips. Swapping op-amps might sound difficult, but the Xonar Essence One comes with detailed and illustrated guide to removing and installing them.
Separate banks of op-amps handle different elements of the sound, and a key requirement when switching op-amps is to ensure that you use matching sets at each stage. The main bank of four converts the current output by the DAC (digital-to-analogue converter) into voltage; a second pair acts as a low-pass filter to eliminate background noise while each output (headphone, XLR and RCA) has either one or two op-amps serving as a final stage amplifier.