ASUS Xonar Essence ST/STX soundcards
The first truly high-end soundcard of which I was awarethat is, one that would record and play back data with a 24-bit word length and sample rates of up to 96kHzwas the CardDeluxe from Digital Sound Labs, which I reviewed in September 2000. Since then, RME and Lynx have come to dominate the high-end soundcard market (footnote 2), even as, in recent years, the most activity has taken place at the low end of the soundcard market, fueled by the needs of video gamers. So I thought I would write about a new entrant in this arena, the Xonar Essence, from ASUS, a Taiwanese maker of motherboards and chips. It costs just $199.99, or even less from online stores such as Amazon.com.
There are many cards on offer in this sectorESI's Juli@ (yes, that's how it's spelled) and M-Audio's Audiophile 192 both seem popular with budget-conscious audiophilesbut I was particularly attracted to the Xonar Essence because it is advertised as having a signal/noise ratio of 124dB, which is true high-end territory. It even comes packed with a typical set of measurements, taken with the same Audio Precision SYS2722 measuring system that I use.
ASUS sent me both the Xonar Essence ST and Essence STX cards. They appear to be identical, other than the ST being configured to fit into a standard PCI slot on a legacy computer's motherboard, the STX conforming to the newer PCI Express standard. From here on, unless otherwise noted, my comments refer to both cards.
The Essence looks like any other soundcard, with one important difference: Its analog output circuitry is shielded by a grounded metal cover, this anodized black with a stylized image of a Chinese tiger printed in gold. The cover acts as a Faraday shield, preventing RF interference from contaminating the analog signals.
On the card's exterior is a vertical array of jacks. From top to bottom, on gold-plated RCAs, are the right and left analog line outputs, followed by the headphone output on a ¼" stereo phone jack. Below that, another ¼" stereo jack serves as both the line and microphone inputs, these selectable with the supplied Xonar Audio Center software. At the bottom is an RCA jack that provides a standard S/PDIF digital output capable of running at sample rates up to 192kHz. An optical S/PDIF driver is placed at the interior end of the jack, so that a TosLink cable can be used with an adapter, if that is preferred. There is no digital input.
The bottom section of the multilayer card carries the analog input circuitry, this based on a pair of R4580 low-noise dualop-amp chips, followed by a pair of 5532 dual op-amps. These feed a Cirrus Logic CS5381, a 24-bit A/D converter chip capable of operating at sample rates up to 192kHz and offering a S/N ratio of 110dB. At the bottom right of the card are two ASUS-branded LSI chips that do all the audio data processing, including Dolby Digital decoding, Dolby Headphone and Dolby Virtual Speaker processing, and Dolby Pro-Logic II, as well as volume and various reverberation and equalizer functions. Above the larger chip is the power-supply section, featuring multiple voltage-regulator chips, a large number of Nichicon Fine Gold electrolytic capacitors, and two purple Sanyo OsCon caps. As well as the attention paid to the power supply, ASUS makes much of what they call "Hyper-grounding," which minimizes noise that might degrade the analog output signal.
A high-performance, two-channel, 24-bit D/A convertera Burr-Brown PCM 1792, the same chip used in Musical Fidelity's V-DAC D/A processoris sited to the left of the supply section, adjacent to a vertical metal shielding strip. The analog output stages lie to the left of this strip and are covered by the removable cover mentioned earlier. Under the cover are two separate output stages, one for the line outs, the other for headphones. The headphone driver is a Texas Instruments TPA6120A2 chip, a current-feedback design capable of sourcing 80mWpc into 600 ohms with very low distortion. The line-level output stage is based on a pair of JRC 2114D dualop-amp chips (the 2114D is equivalent to the popular 5532 chip), followed by a pair of low-noise National LM 4562 dual op-amps. Although almost all the components used, other than the electrolytic caps, are surface-mount types, the four output-stage op-amp chips are socketed 8-pin types, to allow the owner to experiment with other pin-compatible chips.
I installed the Essence ST in an older PC running Windows XP with Service Pack 3, but for the STX, I bought a Shuttle PC (AMD Athlon 3.1GHz dual-core processor, 2GB RAM) running Vista Home Premium, which has a suitable PCI-Express slot. The advantage of the Shuttle PCs is that they are dead quiet acoustically, meaning that I could place the PC in my equipment rack and use short interconnects to the preamp. Installation of the Essence cards in both computers was straightforward; an important point about both cards is that they don't draw power from the PCI or PCI-E slot in the computer's motherboard. Instead, they have a hard-drivetype 4-pin socket that must be separately connected to the PC's power supply. That way, the analog circuitry benefits from being maximally isolated from the noisy ground on the PC's motherboard.
Footnote 1: For a primer on this subject, read my 2008 article.
Footnote 2: The original version of the Sooloos music server, reviewed by Jon Iverson in October 2008, used a high-quality RME Hammerfall HDSP 9632 PCI card for its analog output stage.