If I put my notes here, I might be able to find them again later!
ASUS Xonar Essence STX soundcard
https://www.asus.com/Essence-Hi-Fi-A...r_Essence_STX/
I admit I did not give ASUS the benefit of the doubt and seriously consider their Essence STX soundcard as a replacement for my Onkyo SE200-PCI. ASUS make nice motherboards, but unlike Onkyo have no previous expertise in high end audio.
I am happy to report - a bit late in the game, the card came out in 2009 - that they've done a really good job with it and the drivers for Windows 10, technically still in beta, work just fine.
*****
Asus updated the design recently to the STX II. The PCB has been redone, but the only visible change is the PCM1792A DAC has been moved towards the top of the card closer to the IV conversion op amps. An second LDO regulator IC, U34, empty on the STX, is now populated. A "TXCO" clock source is added next to the ASUS audio controller IC. The four film caps next to the output IC are replaced with WIMA brand. It's basically identical, so it is curious that ASUS bothered with a new PCB layout. It suggests to me that there was something in the original layout that needed to be fixed.
*****
Cool things about the ASUS STX:
TPA6120A2 headphone amplifier, with software programmable 0/+12/+18dB gain.
Relays (physical, I mean "click") to switch the output between line and headphone, rear and front panel.
DAC IV and filter stage op amps are socketed.
Power is connected through a 4 pin molex rather than the PCIe x1 bus.
PCM1792A DAC is definitely top class.
I haven't used it yet, but the ADC stage appears to be very high quality, so this card should be useful for recording my LPs.
Card comes with a full set of test measurements for line in and line out. Data for the headphone stage is curiously absent.
Driver control software utility looks like a Winamp skin from 1998 (sigh...) but it works fine.
*****
Sound quality. 1) Line output. Disappointing only in that it hints at greatness while falling short. It is musical and lively and pleasant, but its not the last word in either authority or refinement. Soundstage is frustratingly fuzzy and indistinct. 2) Headphone output. People have reported problems with low impedance headphones. My 300 ohm Sennheisers, at any rate, were driven well enough. Just a bit less in every respect than what is available from the line out into my Sapphire3.
That may sound like faint praise, but you have to take into account that I find many digital components straight-up unlistenable. To get where the STX is, which is a consistent 70-80% of where I would ideally want to be, with no outstanding flaws, is actually a pretty solid achievement.
And I do think you have to factor the convenience of an internal card with no additional boxes / clutter and the option to route the line and headphone output to the chassis front panel audio jack... as well as the relatively modest cost. All in all a solid value.
*****
There is a button "HF" (hi fi) that you are supposed to press on the control panel to bypass any DSP. With HF mode enabled, and 24/192, I have to say the STX has risen a notch or two in my estimation. There is pretty amazing ambient retrieval, but the soundstage is still indistinct. It is pretty, but lacks presence.
There is a very long thread on people's impressions of the STX over at head-fi, here. I figure I might as well try a few different op amps to see if it makes any difference.
I also plan to upgrade the four 2.7 nF film caps that are used for the LP filter around the buffer op amp to Wima FKP.
*****
2.7 nF caps replaced with WIMA FKP (FKP2D012701D00HA00). All op amps replaced with TI NE5532AP. This is my baseline reference, with trusty, work-well-in-anything 5532. Heck, even the PCM1792A datasheet specifically recommends the 5534 for the IV stage for optimal performance.
*****
Funny what familiarity brings. I know the NE5532/4 already quite well, and putting those op amps into the STX immediately made it feel more comfortable. The 5532 has a distinct "burr", a warm throatiness that I basically enjoy. In comparison the LM4562/JRC2114D set were way too lean.
*****
Comparing the headphone output and line output allows an indirect way to check the effect of the substitutions in the IV stage (both outputs) and LP filter stage (line out only). It suggests that most of the improvement actually came from substituting the JRC2114D for NE5532 for in the IV stage. The difference between the LM4562 and NE5532 in the filter stage is more subtle.
*****
The card, or the new op amps, or the caps I added, seems to be breaking in over time. Getting better and better.
I admit I did not give ASUS the benefit of the doubt and seriously consider their Essence STX soundcard as a replacement for my Onkyo SE200-PCI. ASUS make nice motherboards, but unlike Onkyo have no previous expertise in high end audio.
I am happy to report - a bit late in the game, the card came out in 2009 - that they've done a really good job with it and the drivers for Windows 10, technically still in beta, work just fine.
*****
Asus updated the design recently to the STX II. The PCB has been redone, but the only visible change is the PCM1792A DAC has been moved towards the top of the card closer to the IV conversion op amps. An second LDO regulator IC, U34, empty on the STX, is now populated. A "TXCO" clock source is added next to the ASUS audio controller IC. The four film caps next to the output IC are replaced with WIMA brand. It's basically identical, so it is curious that ASUS bothered with a new PCB layout. It suggests to me that there was something in the original layout that needed to be fixed.
*****
Cool things about the ASUS STX:
TPA6120A2 headphone amplifier, with software programmable 0/+12/+18dB gain.
Relays (physical, I mean "click") to switch the output between line and headphone, rear and front panel.
DAC IV and filter stage op amps are socketed.
Power is connected through a 4 pin molex rather than the PCIe x1 bus.
PCM1792A DAC is definitely top class.
I haven't used it yet, but the ADC stage appears to be very high quality, so this card should be useful for recording my LPs.
Card comes with a full set of test measurements for line in and line out. Data for the headphone stage is curiously absent.
Driver control software utility looks like a Winamp skin from 1998 (sigh...) but it works fine.
*****
Sound quality. 1) Line output. Disappointing only in that it hints at greatness while falling short. It is musical and lively and pleasant, but its not the last word in either authority or refinement. Soundstage is frustratingly fuzzy and indistinct. 2) Headphone output. People have reported problems with low impedance headphones. My 300 ohm Sennheisers, at any rate, were driven well enough. Just a bit less in every respect than what is available from the line out into my Sapphire3.
That may sound like faint praise, but you have to take into account that I find many digital components straight-up unlistenable. To get where the STX is, which is a consistent 70-80% of where I would ideally want to be, with no outstanding flaws, is actually a pretty solid achievement.
And I do think you have to factor the convenience of an internal card with no additional boxes / clutter and the option to route the line and headphone output to the chassis front panel audio jack... as well as the relatively modest cost. All in all a solid value.
*****
There is a button "HF" (hi fi) that you are supposed to press on the control panel to bypass any DSP. With HF mode enabled, and 24/192, I have to say the STX has risen a notch or two in my estimation. There is pretty amazing ambient retrieval, but the soundstage is still indistinct. It is pretty, but lacks presence.
There is a very long thread on people's impressions of the STX over at head-fi, here. I figure I might as well try a few different op amps to see if it makes any difference.
I also plan to upgrade the four 2.7 nF film caps that are used for the LP filter around the buffer op amp to Wima FKP.
*****
2.7 nF caps replaced with WIMA FKP (FKP2D012701D00HA00). All op amps replaced with TI NE5532AP. This is my baseline reference, with trusty, work-well-in-anything 5532. Heck, even the PCM1792A datasheet specifically recommends the 5534 for the IV stage for optimal performance.
*****
Funny what familiarity brings. I know the NE5532/4 already quite well, and putting those op amps into the STX immediately made it feel more comfortable. The 5532 has a distinct "burr", a warm throatiness that I basically enjoy. In comparison the LM4562/JRC2114D set were way too lean.
*****
Comparing the headphone output and line output allows an indirect way to check the effect of the substitutions in the IV stage (both outputs) and LP filter stage (line out only). It suggests that most of the improvement actually came from substituting the JRC2114D for NE5532 for in the IV stage. The difference between the LM4562 and NE5532 in the filter stage is more subtle.
*****
The card, or the new op amps, or the caps I added, seems to be breaking in over time. Getting better and better.
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