ASUS Essence STU USB DAC and Headphone Amp Review

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I have many times (not so) jokingly referred to the rise of the mp3 as “the Day the World Went Deaf”. I say jokingly only because it actually began with the CD more so than the mp3, but the mp3 definitely solidified it. Why do I say this? Simply because that was the point that convenience absolutely won out over quality. Being able to take the music with you, or have it take up less room, or go instantly from track to track was deemed more important than how good the music actually sounded. Now, just a short time later, the majority of people have never even actually heard an audiophile quality playback, or even seen equipment or mediums capable of producing it, because, unfortunately, the truest reproduction comes from analog sources. And, no, that is not a misprint.



While digital sources add very limited background noise, have frequency ranges more easily extended, and are considered “cleaner”, they also have the obstacle of dealing with square wave forms rather than the smooth, fluid sine wave form that occurs in natural sounds (an illustrative example can be seen here). This is a huge obstacle to overcome. Playback is generated right from the source in lossy fashion compared to natural or analog sound. This results in what is often described as “brittle” or “harsh” audio, and is by nature inaccurate and causes listener fatigue far more quickly than natural or analog sources. The other huge obstacle digital sound reproduction faces is synchronization. Musical playback with poor digital synchronization creates dissonant passages which may not be noticeable, but are subliminally irritating. The device responsible for turning the zeros and ones into a wave form for listening, as well as synchronizing the sound, is the digital-to-analog converter, or DAC for short, and since day one, the goal of audiophile DAC designers has been the same; to make digital sound like analog….just without the background noise.



The ASUS Essence STU adds incredible versatility for the audiophile looking to incorporate digital platforms into their world. With great flexibility and functionality, the ASUS Essence STU is a perfect fit as the DAC for all of the digital equipment in your entertainment center or as a standalone audiophile quality headphone amp. The Essence STU offers 3.5mm analog, Toslink, Coax and USB inputs to go along with line out and a 600 ohm headphone amp. Front controls make for easy source selection and sit alongside independent line and headphone volume controls. In terms of output, the Essence STU lives up to the high standards set by its predecessors with >120dB S/N, THD less than 0.0004%, and astounding 10Hz-48KHz frequency response. At its heart, we find the TI PCM1792A DAC delivering exceptionally clean and smooth conversion. On the output end, the Essence STU couples NS-LME49720 and NS-LM4562NA Op-Amps for exceptionally warm, smooth and natural sound with great detail. All Op-Amps are easily changeable to tailor the sound to your particular preferences and existing components. ASUS has posted a listing of recommended swaps along with variations that can be expected. For those looking to go even further into the audiophile tweak, ASUS has you covered. An onboard DC Servo can be enabled through jumpers to negate any turn-on pops. The volume control circuit can be bypassed entirely for fixed output and no added noise or coloration from the circuit. Outputs can be individually tuned right at the resistor for perfect balance. The headphone amp has selectable gain switching for use with any headphones from 16-600 ohms, complete with protection circuit to prevent accidental switching while the headset is plugged in. On the output side of the headphone amp is the highly regarded TPA6120A2 headphone amplifier for an exceptional experience. Included with the Essence STU is the required power supply, USB cable and vertical stand.