[ClieOS]

Headphone-out is driven by the powerful TPA6120A2, so it should do well with full size. My concern is the 10ohm output impedance of the chip though. Will be nice if everyone can take a hint on how iFi implements TPA6120A2 on iCAN and still get less than 1 ohm of output impedance.

 

[project86]

Quote:

Headphone-out is driven by the powerful TPA6120A2, so it should do well with full size. My concern is the 10ohm output impedance of the chip though. Will be nice if everyone can take a hint on how iFi implements TPA6120A2 on iCAN and still get less than 1 ohm of output impedance.

 
Agreed. The Audinst HUD-mx2 also has the TPA6120A2 and achieves 2 ohm output impedance. If they can do it, and iFi can do it, I'd like to see Asus do it as well. 
 
I also used the STU as a DAC and I think it works quite well in that mode. Probably better as a DAC than an amp. But that tends to be the case with almost all of these integrated DAC/amp units. 

 

[mikeaj]

The 10 ohms is not an inherent part of the chip.  It's a recommendation for a resistor value to be placed on the output for stability.  
 
A lot of designs, DIY too, use TPA6120.  I think there are some discussions and info there about possible workarounds.  In fact, I think some "Guy", maybe involved in audio and perhaps with something to do with the northwest, took a look at Per-Anders' QRV09 DIY amp and played around with some ferrites to reduce the output impedance seen in the audio range.  There might be some info on a blog somewhere, if you can search for the "output impedance modification" section.
 
 
But anyway... rather than us guessing, at least for the STU, could one of you please just take a couple of quick voltage measurements with a multimeter, each with a different load (constant tone with consistent volume control and setting), so the output impedance can be calculated?  That said, for most headphones it's really not a big deal.

 

[ClieOS]

The 10 ohm OI has been listed on STU spec, and I already did a measurement to confirm it.
 
Regardless, 10 ohm is still the chip maker's recommendation to the user and I don't think many designer will venture very far out from the chip maker recommendation. It is just a shame really, cause TPA6120 is a rather good sounding chip on its own right. NwAvGuy is not the only person who comes up with an way to solve the issue. As mentioned, iFi does a great job on designing their iCAN with an air coil output to lower the output impedance down to 1 ohm as well. I wish more manufacturer will pay attention on how to employ TPA6120 so it doesn't always have to fall back to a 10ohm resistor for stability.

 

[project86]

Further impressions after having listened to the STU a bit more:
 
*I love having separate controls for headphone out and line out. I'm using it at my desktop with some active speakers (Serene Audio Talisman) and it's great to have full control over them.
 
*The headphone gain switch on the back is kind of weird. At first I thought it was a toggle switch, and maybe it was broken, because it will only stay in one position. But then I figured out it isn't supposed to actually have two different positions - just push it to cycle to the next setting, but the physical switch goes back where it started. Ok, so that makes sense, but then it stopped working. Later I figured out it won't work with a headphone plugged in. Maybe this is all caused by me not reading the manual first though.... I can see why they made it this way.
 
*Sound - as a DAC, the unit sounds quite nice. Detailed and clean, mostly grain free, very spacious. It's a bit light in terms of bass extension, but maybe that's just me being used to more expensive DACs. Now that I think about it, the STU sounds like a junior version of the $1100 Firestone Audio Tobby DAC which I recenty reviewed. 
 
*As an amp, the "cleanness" might be a little much for my tastes. It's not an issue with my LCD-2 but with HD800, the result was pretty lean. Seems like this would be a good pair for the Denon Dx000 models though, and maybe even the HD650 would sound nice. I'll keep trying other models to see what works. IEMs are not the best though, just due to the 10 ohm output impedance. Too bad, since the background is nice and quiet on the low gain setting. 

 

[lithium1085]

Quote:

Further impressions after having listened to the STU a bit more:
 
*I love having separate controls for headphone out and line out. I'm using it at my desktop with some active speakers (Serene Audio Talisman) and it's great to have full control over them.
 
*The headphone gain switch on the back is kind of weird. At first I thought it was a toggle switch, and maybe it was broken, because it will only stay in one position. But then I figured out it isn't supposed to actually have two different positions - just push it to cycle to the next setting, but the physical switch goes back where it started. Ok, so that makes sense, but then it stopped working. Later I figured out it won't work with a headphone plugged in. Maybe this is all caused by me not reading the manual first though.... I can see why they made it this way.
 
*Sound - as a DAC, the unit sounds quite nice. Detailed and clean, mostly grain free, very spacious. It's a bit light in terms of bass extension, but maybe that's just me being used to more expensive DACs. Now that I think about it, the STU sounds like a junior version of the $1100 Firestone Audio Tobby DAC which I recenty reviewed. 
 
*As an amp, the "cleanness" might be a little much for my tastes. It's not an issue with my LCD-2 but with HD800, the result was pretty lean. Seems like this would be a good pair for the Denon Dx000 models though, and maybe even the HD650 would sound nice. I'll keep trying other models to see what works. IEMs are not the best though, just due to the 10 ohm output impedance. Too bad, since the background is nice and quiet on the low gain setting. 

Hi John,
 
This sounds really interesting. Do you have a Xonar essence one base model for comparison? Thanks 

 

[project86]

Hi John,

This sounds really interesting. Do you have a Xonar essence one base model for comparison? Thanks 

No, I don't, sorry. I'm wondering the same thing though - will this STU, maybe will an upgraded opamp like the MUSES, surpass the base model Essence One with the stock opamps? I'll try to get my hands on one if I can.

 

[lithium1085]

Quote:

No, I don't, sorry. I'm wondering the same thing though - will this STU, maybe will an upgraded opamp like the MUSES, surpass the base model Essence One with the stock opamps? I'll try to get my hands on one if I can.

The price of the base model essence one often drops below 550$ and that makes it very close to this one at 400$. It does have the advantage of being balanced but is that really an advantage? I like the look of the STU....It looks very much like a miniature version of  vintage integrated amplifiers from the 1970s (at least to me)....

 

[project86]

Quote:

The price of the base model essence one often drops below 550$ and that makes it very close to this one at 400$. It does have the advantage of being balanced but is that really an advantage? I like the look of the STU....It looks very much like a miniature version of  vintage integrated amplifiers from the 1970s (at least to me)....

 
 
Good news - I managed to find a friend who can loan me an Essence One for a comparison. His is stock, not Muses or other rolled opamps, so it's perfect. 
 
Asus actually calls the STU layout a "fully balanced stereo representation" based on the mirrored PCB layout. It's not quite true balanced operation as we might define it, due to the single DAC chip instead of dual DACs. But other DACs have earned the title "true balanced" with a similar configuration. The STU takes each channel of output from the PCM1792, runs it through a separate I/V conversion and LPF, but merely omits XLR outputs. The One is similar but has more opamps involved in the process handling the same jobs.

 

[Limniscate]

I'm curious to read about your comparison to the Essence One.  I have my bro's right now and have been comparing to the O2/ODAC on the HE500, AudioTechnica W1000X, and the AKG K702 65th Annies.  So far, I can't really tell a difference.

 

[lithium1085]

Quote:

 
 
Good news - I managed to find a friend who can loan me an Essence One for a comparison. His is stock, not Muses or other rolled opamps, so it's perfect. 
 
Asus actually calls the STU layout a "fully balanced stereo representation" based on the mirrored PCB layout. It's not quite true balanced operation as we might define it, due to the single DAC chip instead of dual DACs. But other DACs have earned the title "true balanced" with a similar configuration. The STU takes each channel of output from the PCM1792, runs it through a separate I/V conversion and LPF, but merely omits XLR outputs. The One is similar but has more opamps involved in the process handling the same jobs.

Thanks for the explanation John.....

 

[cheuh]

How would the new STU compare to the older STX sound card? Would it be an upgrade at all?

 

[xeizo]

Quote:

How would the new STU compare to the older STX sound card? Would it be an upgrade at all?

 
Not much, it's essentially the same but as a break out thingy, could be worse as it is USB which is jitter-prone. On the other hand so does the original teoretically suffer from a harsher electromagnetical environment inside a PC.
 
For myself, as I'm a cheapskate, I feel like I've found my ultimate fidelity source for the buck in the form of Xonar ST with the LME49990:s on the RCA. I prefer my Linux box for handling my music files, so in my case the DAC can as well be inside ...

 

[zetafunction]

Does anyone know if Dolby Headphone will work over line out for the Essence STU? I'm interested in this for both gaming and music, and from what I've read, previous Essence ST/STX cards only did Dolby Headphone processing when outputting through the headphone jack. With the 10 ohm impedance on the STU's headphone out, I'd prefer to use an external amp.

 

[project86]

Quote:

How would the new STU compare to the older STX sound card? Would it be an upgrade at all?

 
Good question. Theoretically, an Asynchronous USB connection would have lower jitter due to the way timing is controlled.
 
There's also the issue of EMI/RFI from the various signals bouncing around inside the PC, which of course don't apply to the external STU.
 
Another thing is the power supply - the STU has an external power brick kind of like a laptop would have. It probably falls somewhere between a basic wall-wart and a dedicated linear power supply. Is it better than the PSU in your computer? Depends. Some people have really nice PSUs in their machines, others don't.
 
Lastly, and this might be the biggest deal - volume control. When using the ST/STX, all volume control is handled in the digital domain. That results in a loss of resolution. Is it audible? Probably not, if you only reduce it to 90% or something. But who listens at nearly full blast? Most listening is likely to be done in the 20-50% range, which is almost certain to cause audible degradation. The STU doesn't have this issue, instead relying on a pretty good quality analog potentiometer to adjust volume. Note that when using an external headphone amp, this difference no longer applies, since the ST/STX could then be used at 100% volume, and the external amp would be used for volume control. 
 
Quote:

Does anyone know if Dolby Headphone will work over line out for the Essence STU? I'm interested in this for both gaming and music, and from what I've read, previous Essence ST/STX cards only did Dolby Headphone processing when outputting through the headphone jack. With the 10 ohm impedance on the STU's headphone out, I'd prefer to use an external amp.

 
Depends on how Asus did the drivers. Some DACs still allow software volume control, or EQ, to be performed in the digital domain prior to spitting out a digital stream for the DAC to decode. If that's the case on the STU, then any sort of plugins or extra processing should work. Others, due to their drivers, specifically block any sort of data manipulation, leaving all controls such as volume to be handled by the DAC only. I have yet to connect my PC to the STU so I don't know how it works yet. I'll get to it though. But I think the STX had hardware Dolby Headphone on board? The STU definitely doesn't have that.