[stv014]

Apparently, there are only minor differences other than the card now supporting the Xonar H6 for 7.1 channel analog outputs (previously, this was limited to the ST, and the PCI bus is now becoming obsolete). It probably still has the same problems as the STX, like the output impedance of the headphone amplifier, and noise with very sensitive headphones/IEMs (due to the lack of analog volume and gain control), maybe even the increased noise floor at 44.1/88.2/176.4 kHz sample rate is still there.

 

[Blackbird09]

Edit: Removed for redundant information.

 

[Gradius]

So far what I see on STX II:
 
- Better Power Supply (new caps) and regulator on MOLEX section;
- Better cap on SPDIF section;
- Realocated position for AV100;
- New IC "asmedia" ASM1083;
- Better Clock/Cristal;
- Double clock;
- Changed OPamps to Muses.
 
Asmedia infos:
http://www.asmedia.com.tw/eng/e_show_products.php?item=114&cate_index=112
 
In other words... ASM1083 is just the interface between AV100 and PCIe.
 
On original STX PLX PEX8112 was used.
 
Original STX photo for comparison:

 
I might perform the upgrade, waiting for prices and reviews.  Of course, I would never use IC OPamps, and stock clock.

 

[Gradius]

  It probably still has the same problems as the STX, like the output impedance of the headphone amplifier, and noise with very sensitive headphones/IEMs (due to the lack of analog volume and gain control), maybe even the increased noise floor at 44.1/88.2/176.4 kHz sample rate is still there.

 
My modded STX is dead silent, using HD650.   I'm planning to get HD800 soon.

 

[MrTechAgent]

   
My modded STX is dead silent, using HD650.   I'm planning to get HD800 soon.

Modded ?  .....I don't hear anything at all with my system and that's stock , could be because of my Seasonic PSU 

 

[Ra97oR]

Those MUSE are the budget version, not the MUSE 01 and MUSE 02.

 

[Gradius]

  Those MUSE are the budget version, not the MUSE 01 and MUSE 02.

Correct, but I wouldn't use them either.  Unless I had no choice (no space or something like that).
 
MUSES01: $29~$37
MUSES02: $44~$59

 

[Blackbird09]

I wonder if this version will be just as moddable as the original. I have 2 AMB σ11's (1@12v and 1@5v) that I put together awhile back for the purpose of a dedicated PSU for my STX. I just haven't gotten around to soldering the MOSFETS and purchasing the transformers.
 
The different crystal oscillator remains to be seen as an improvement. Maybe a bit overkill to add an audio-gd or burson audio clock upgrade.
 
I remember people replacing the Nichicon Fine Gold capacitors with the Elna Silmic II.
 
Finally, was it ever deemed a waste to upgrade the opamps to the audio-gd or burson audio discreet opamps?

 

[cimbolic]

 Output impedance - 10ohm (headphone out)

 
Why is it 10 ohms? Why do manufacturers still build DACs/sound cards with headphone output impedance that are more than 1 ohm when there are many articles/people (perhaps even Asus employees themselves) that are against it?
 
Are the articles professing the benefits of < 1 ohm headphone output impedance just rubbish? And it doesn't really matter if its 1 or 10 or 12 ohms?
 
Or is it terribly difficult or cost prohibitive to make them as low as possible?

 

[James neutron]

Xonar ST's output impedance is largely identical to that of the TPA6120A2 op--amp (which is the actual headphone amplifier of the soundcard).
As I understand it, lowering the output impedance is a fairly tricky process and cannot be done without some design changes.
The typical ways by are employing negative feedback in the circuit, or putting resistive networks before the output (but that will automatically lower the power output), using inductors or filters (but those affect signal purity), etc
 
All solutions come with compromises, some more drastic than others, and I think Asus preferred a slightly higher output impedance (which is more than fine for all +5-60 ohm headphones) and offer more power.
Lots of tube amplifiers have much higher out impedances and that didn't stop anybody from enjoying their sound.
 
*And although I am an advocate of low output impedance myself, I also think people get caught up in it too much.
There's more to an amp than just that number. I'd take a better quality design over lower impedance any day.

 

[Manel]

I'm about to buy a Sound Blaster ZxR. Should I make that move or wait to see how this one turns up on reviews? I wonder if STX II is more moddable than ZxR. 
As you are talking about the output impedance on the headphone jack, I read here on the forum that ZxR's is even higher (~40 ohm) despite sharing the same headphone amplifier with STX. 

 

[Gradius]

  I wonder if this version will be just as moddable as the original. I have 2 AMB σ11's (1@12v and 1@5v) that I put together awhile back for the purpose of a dedicated PSU for my STX. I just haven't gotten around to soldering the MOSFETS and purchasing the transformers.
 
The different crystal oscillator remains to be seen as an improvement. Maybe a bit overkill to add an audio-gd or burson audio clock upgrade.
 
I remember people replacing the Nichicon Fine Gold capacitors with the Elna Silmic II.
 
Finally, was it ever deemed a waste to upgrade the opamps to the audio-gd or burson audio discreet opamps?

From photo (ain't help that much since is low quality), I can see just one single 7805 (5V) regulator.
 
On STX, I used a better clock, it does improves the quality around 20~25%.   The rest (of quality) was done with Bursons OPamps.
 
I was planning to mod the PSU with AMB σ11's too, but now with STX II, I don't think I'll do it on original STX as I'm planning to upgrade (STX 2) and then mod it (of course!).

 

[Blackbird09]

 
From photo (ain't help that much since is low quality), I can see just one single 7805 (5V) regulator.

 
Weird. On the old STX there are two regulators (silkscreen component labels: U20, U24) plus empty outline on the silkscreen where another regulator could go (U34). On the STX II the U20 regulator (I assume this is still a 7805) is still there. Both the U24 and U34 spots are populated with two identical ICs. Could these be some weird SMD regulators? 
 
Here is the area I'm talking about on the STX II:

 

[stv014]

  My modded STX is dead silent, using HD650.   I'm planning to get HD800 soon.

 
The HD650 is not exactly very sensitive, or even typical at all, compared to most new headphone models that are low impedance and are optimized for portable devices. On the other hand, the Shure SE535 IEMs for example would have a noise floor of ~31 dBA at 44.1 kHz sample rate, which is not quite dead silent, not to mention the frequency response problems because of the output impedance. Nevertheless, these cards are indeed fine for high impedance full size headphones.

 

[stv014]

  As I understand it, lowering the output impedance is a fairly tricky process and cannot be done without some design changes.
The typical ways by are employing negative feedback in the circuit, or putting resistive networks before the output (but that will automatically lower the power output), using inductors or filters (but those affect signal purity), etc

 
The use of a parallel inductor and resistor serially connected to the output is a fairly standard practice in speaker amplifiers, to isolate capacitive loads in the RF range for stability, but allow for low output impedance in the audio band. Of course, the problem could also be avoided by not using the TPA6120 in the first place. For example, the two parallel NJM4556's in the O2 are stable with much lower output impedance, and are even cheaper than the TPA6120.