Asus' Xonar Essence STX
Another arrow in the quiver
As a company that makes just about everything you can plug into a PC, Asus was bound to tackle the sound card market eventually. I'm not sure anyone expected the Xonar series to be so good so fast, though. The first Xonar D2X was a revelation, offering superb sound quality, reasonable 3D audio acceleration, and most importantly, the fresh perspective one would expect from a new entrant in the market. We loved the card, and were happy to see Asus follow up with an even cheaper model in the Xonar DX, a sound card that has been a staple of our system guide recommendations ever since.
Asus has since expanded its Xonar lineup to include a prodigious eight different add-in cards based on the Oxygen HD audio processor. Among the new family members are several HDMI-specific cards targeted at home theater PCs, and most recently, the headphone-oriented Essence STX.
The first thing you should know about the Essence is that it's a PCI Express card. Although the Oxygen HD, er, AV100 is a native PCI chip, Asus uses a PEX8112 PCI-to-PCIe bridge to squeeze the Essence into an x1 slot. Asus also makes an Essence ST with a PCI interface, but it's not listed on the company's North American website, and it doesn't appear to be available for sale online.
Astute readers will no doubt notice the thin metal skin covering roughly half of the Essence. In addition to providing Asus room to display its logo and what appears to be a cryptic drawing of some sort of elephant/lion hybrid, this bit of metal sheeting also serves to shield the card's sensitive components from electromagnetic and radio-frequency interference.
Removing the shroud gives us a look at the Essence's DAC and ADC, among other goodies. Asus handles digital-to-analog conversions with a Texas Instruments "Burr Brown" PCM1792A DAC that has a claimed signal-to-noise ratio of 127 decibels. A Cirrus Logic CS5381 ADC takes care of conversions going in the other direction, albeit with a less impressive 120-dB SNR rating.
Burr Brown DACs and Cirrus Logic ADCs have appeared on all the Xonar models we've seen thus far. However, the Essence's Texas Instruments TPA6120A2 "high fidelity headphone amplifier" is a new addition. The Texas Instruments chip has a 120-dB SNR and supports headphones with up to 600 ohms of impedance.
A trio of OPAMPs provides the Essence with additional amplification. All three are socketed and user replaceable should you wish to swap out the National Semiconductor LME4972 or either of the JRC 2114Ds. Interestingly, the Auzentech card uses the same National Semi OPAMP for its front-channel output.
Another interesting element of the Essence is the presence of a four-pin Molex power connector on the card's rear edge. This plug isn't used to provide the card with additional power beyond what's available through the PCI Express slot; rather, it's used to feed the card with cleaner power than can be pulled from the motherboard.
Beside the power plug are internal pins for an alternate S/PDIF output. You'll also find a front-panel output and auxiliary input headers located along the top edge of the card.
Asus combines these internal inputs and outputs with an unconventional mix of external ports. The coaxial S/PDIF port is the only multi-channel output option on the board, and you'll need a compatible receiver or a set of digital speakers to make it work. Otherwise, you have your choice of two-channel stereo outputs: a set of front-channel RCA plugs or a meaty 6.5-mm headphone jack. The larger 6.5-mm jack size is standard for high-end headphones, and a similar port feeds the Essence's analog mic input.
Since many folks are no doubt running headphones with smaller 3.5-mm plugs, Asus throws an adapter in with the Essence. The card also comes with a dongle that transforms the RCA outputs into a standard 3.5-mm jack and an adapter that allows you to use a TOS-Link cable with the coaxial S/PDIF output.