Introduction
The purpose of this "engineering review" is to provide a side-by-side comparison of the Xonar STX and the Xonar ONE, to help consumers evaluate if it is worth to them to upgrade, and/or which one to go for in the first place.
The main focus of this review is oriented towards the use of these hardware devices as high-end headphone DAC/AMP combinations. The logic here is that this is likely to be the most common use scenario (although other uses are certainly possibly). I do touch on other characteristics but I will not focus on those. If you plan to use the STX and/or ONE as anything other than a headphone DAC/AMP combination, then this review is likely not the most helpful for you.
Also the purpose of this article is not to debate if integrated-circuit amplification is better, worse, or equal to discrete-circuit amplification and/or to tube-based amplification. We're comparing IC devices in this case - I'll let the latter comparison to other posters with more knowledge than me on that subject.
Stage-by-stage review
Stage 0: Input signal processing
I'll skip reviewing the USB/SPDIF/PCIe circuitry as I believe they do not affect sound quality in any meaningful way.
One important note, however, is that the Xonar One, being driven by USB or SPDIF signals, have to deal with jitter - whereas the STX does not. Whether this introduces any audible difference can be debatable, but it without a doubt contributes to making the ONE more expensive.
The digital section of the STX, especially when used in low-latency ASIO or Kernel Streaming modes, is just as Hi-Fi as anything will get this decade.
Stage 1: DSP
Xonar STX:
C-Media CMI8788 OxygenHD (a.k.a. AV100)
BoM: ?
Xonar ONE:
Analog Devices ADSP-21261
BoM: $6.64 (@ 1k units)
According to AD, "The ADSP-21261 is the lowest cost member of the third-generation of SHARC® programmable digital signal processors".
I believe, for the basic EQ needs that a typically headphone user will have, that either chips turn out to be equivalent (and, AFAIK, are mostly bypassed in Hi-Fi mode so not such a big deal).
DSP Verdict: DRAW
Stage 2: DAC
Xonar STX:
1x Burr-Brown PCM1792A (stereo mode) - 127dB Dynamic Range - THD+N: 0.0004%
Supports 16-20-24bit up to 192kHz
SSOP-28 package
BoM: $10.65 (@ 1k units)
Xonar ONE:
2x Burr-Brown PCM1795 (mono mode) - 123dB* Dynamic Range - THD+N: 0.0005%
Supports 16-24-32bit up to 192kHz
SSOP-28 package
BoM: 2x $3.95 = $7.90 (@ 2k units)
* The datasheet for the PCM1795, unlike the one for the PCM1792A, does not differentiate Dynamic Range values between mono and stereo mode
Here we have two slightly different solutions with otherwise world-class DAC chips. The ONE sacrifices some Dynamic Range (it could have achieved 132dB with 2xPCM1792A in mono mode), saves some cost, but provides a dual-mono solution - which, in theory, should have better channel separation and allows for the Asus-marketing-statements of "8x symmetrical upsampling" and 32bit operation.
In real-world applications, I doubt any human being can tell the difference between 123dB and 132dB of dynamic range - hey, it is still controversial if there is any perceptible difference between 24bit and 16bit audio, and a 16bit signal "only" has 65536 levels! I know for one, I certainly wouldn't be able to.
As for 32bit... given that no audio commercially available is encoded at this bit-depth, I see no use to give a DAC/Amp credit for supporting it.
DAC Verdict: DRAW
Stage 3: Differential Input Current to Voltage (I/V) OpAmps
Xonar ONE:
2x National Semiconductor LME49720NA (stereo mode) - THD+N: 0.00003%
20V/uS Slew Rate - 55MHz Bandwidth
DIP-8 package (USER REPLACEABLE)
BoM: 2x $1.15 = $2.30 (@ 1k units)
Xonar STX:
2x JRC2114D AKA NJM2114D (stereo mode)
15V/uS Slew Rate - 15MHz Bandwidth
DIP-8 package (USER REPLACEABLE)
BoM: 2x $0.619 = $1.24 (@ 2k units)
I am not a believer in replaceable opamps, especially when very cheap parts can do the I/V conversion process perfectly. Hence, I won't delve into further details.
If you disagree, just spend $4 and change them anyway.
I/V Verdict: DRAW
Stage 4: Headphone Amplifier
Xonar ONE:
2x National Semiconductor LME49600TS (mono mode) - THD+N: 0.00003%
2000 V/µs Slew Rate
TO–263 package
BoM: 2x $4.05 = $8.10 (@ 1k units)
Xonar STX:
1x National Semiconductor TPA6120A2 (stereo mode) - THD+N: 0.00014%
1300 V/µs Slew Rate
DWP-20 package
BoM: $2.05 (@ 1k units)
This is the one area where the ONE definitely steps up as compared to the STX. The LME49600TS are, without a doubt, better headphone amps than the TPA6120A2 (which was pretty good to begin with), and the ONE uses two of them in mono mode!
HP AMP Verdict: ONE leads
Price
Xonar ONE: $600
Xonar STX: $180
Price Verdict: STX >3X cheaper
Other stuff
Xonar ONE:
- XLR Balanced output (imho you must be really hardcore to want to use these with a short 1-2m headphone cable, but, eh... why not, if you're willing to spend ~$400 on cables alone or to re-terminate your stock HD-800 cable).
- Handy volume control on your desk
- One additional PCIe slot free in your case
Xonar STX:
- Does not suffer from jitter
- Less clutter on your desk
- One additional USB slot (or SPDIF out) free in your case
Other Stuff vedict: Comes down to personal preference
Conclusions
The Xonar ONE improves marginally on the STX by using DAC and Amp chips in mono mode, but at the chosen price point (>3X the price of the STX) it is hard to recommend from a value standpoint over the already very good STX.
Ultimately the purchasing question will then come down to cost and form factor. If you don't have and/or want to use a PCIe slot for the STX and have no object to spending $600 for a headphone DAC/AMP, then the ONE is for you. If you're fine with a PCIe card, the STX will likely sound almost as good as the ONE, at a third of the price, and would thus be recommended.
Final verdict: Get an STX if you have a free PCIe slot and want far better value; get the ONE if you don't have a PCIe slot and/or don't mind spending $400 extra for slightly higher quality DAC/Amp.
Edited by mechan - 12/27/11 at 5:13pm
