ASUS Xonar Essence STU DAC/Amp

Introduction

ASUS is expanding its Essence line with a brand-new DAC/amp design which, like the Essence One, focuses on headphone and DAC performance. As with the recently reviewed ASUS U7, the Essence STU has a wealth of connectivity options, but only two channel analogue outs. The STU slots in between the STX and the Essence One, a very interesting DAC/amp combo.

The STU is priced at €250, which is €200 less than the Essence One, or approximately €100 above that of a normal PCI-E STX sound card. We put it through its paces to see if it is a worthy upgrade over the Xonar STX card which has for some time now held the top position in our bang-for-the-buck category.

Specifications

• Excellent audio quality as inherited from acclaimed Xonar Essence ST/STX
• Precision clock-tuning technology and asynchronous USB transfer ensure jitter-free fidelity
• Integrated 600 Ohm headphone amplifier optimizes sound detail with two gain settings
• 120 dB signal-to-noise ratio (SNR) delivers high definition audio clarity
• Dedicated jumper switch allows direct audio delivery to your power amplifier, bypassing DAC volume controls
• Three swappable Op-Amps enable tonal character tuning based on personal taste

Asynchronous USB is a nice feature, but jitter-wise, you can create something that performs just as well without it. The DAC in the STU sounds very natural and life-like, so jitter is definitely not an audible issue. The "Integrated 600 Ohm" amplifier is of course a marketing gimmick, and the integrated headphone amplifier is the same as on the STX and Zx-series sound cards from Creative. It is supplied by TI. The headphone amplifier chip is a TPA6120A2 capable of driving loads of up to 600 Ohm impedance, which does not mean anything when it comes to wattage delivered, making it a piece of useless information.