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Old 29th April 2012, 06:01 PM   #1
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Default Xonor STX Line-In Mods

I have read the thread Coris started with its excellent mods but unless I missed something they all appear to be for the analog output side of the STX card. I recently purchased an STX to replace a very old PCI sound card for the purpose of moving LP music to digital. The problem I am having (other than very poor Asus support) is that even with every slider I can find set at 100% and my RIAA preamp adjusted almost to the clipping point, the signal level in Audacity very low. Are there any known mods to improve the line-in signal level with this card? Thanks.
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Old 29th April 2012, 11:06 PM   #2
wwenze is offline wwenze  Singapore
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Just use effects -> amplify.
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Old 29th April 2012, 11:21 PM   #3
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The only Effect/Amplify I can find is in Audacity and as near as I can tell it can only be applied after the recording in a manner similar to Effect/Normalize. I was looking for a mod or solution that would provide normal signal levels direct from the STX . With my previous sound card I could adjust the levels to much less than 100% and didn't have to worry about over driving the preamp to just to have any signal.

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Old 30th April 2012, 12:58 AM   #4
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I had a large post typed out and I lost it all by mistake >.<

Either way the input to the Xonar follows the data sheet for its ADC fairly well. The first pair of opamps that you reach are a unity buffer followed by an inverter. This creates a balanced feed. This then goes into another pair of opamps that condition the signal prior to entering the ADC.

The first opamps aren't really suitable for modding. The second pair are but I would do so with caution. The Xonars PCB is quite fragile and the surface mount parts are quite small and tightly packed. Not to mention there are plastic SMD caps here too. These do not take kindly to an accidental poke from a soldering iron, often outright failing if you do so.

Either way I have attached an image that shows you what is what.

I strongly recommend you use a preamp before the xonar instead, or mod your phono stage to output more voltage perhaps.
Attached Images
File Type: jpg Xonar input.jpg (330.1 KB, 147 views)
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Old 1st May 2012, 02:21 AM   #5
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Originally Posted by 5th element View Post
I had a large post typed out and I lost it all by mistake >.<
I am sorry you had to do it twice. I know from personal experience how frustrating it can be. More than once I have taken so much time on a post for one reason or another that when I reached the point to submit the post I was asked to log in again which resulted in the post being dumped. In any case, I certainly appreciate the time you have put in on replying. Thank you.

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Originally Posted by 5th element View Post

Either way the input to the Xonar follows the data sheet for its ADC fairly well. The first pair of opamps that you reach are a unity buffer followed by an inverter. This creates a balanced feed. This then goes into another pair of opamps that condition the signal prior to entering the ADC.

The first opamps aren't really suitable for modding. The second pair are but I would do so with caution. The Xonars PCB is quite fragile and the surface mount parts are quite small and tightly packed. Not to mention there are plastic SMD caps here too. These do not take kindly to an accidental poke from a soldering iron, often outright failing if you do so.

Either way I have attached an image that shows you what is what.

I strongly recommend you use a preamp before the xonar instead, or mod your phono stage to output more voltage perhaps.
I have a Xytronic digital soldering station that I have had for years and I have used it many times on radios and other electronic equipment. The caveat however is that most of the equipment I have worked on had very little in the way of SMD components and I never had to try soldering or desoldering them. After looking your jpg, I think it is safe to say this is definitely not a good first time project to develop those skillsl. In addition although the hands are still steady, the eyes are not what they used to be. All in all, I think the smart move is to take a pass on the mod.

As for trying to increase the signal levels prior to them reaching the card, I seem to recall in another post either here or on the Asus forum that the STX is very unforgiving to strong input signal levels and that you can without too much effort over drive it to the point of failure. Based on this perhaps that prudent thing to do is not modify the preamp or add another stage of amplification.

I know you have already spent considerable time so I donít expect you to add anything further but perhaps someone else will. It would appear to me that if the volume is low in Audacity that might mean that the digital information that is being placed on the bus by the card is not using all the bits that could be used to reflect changes in volume and that in turn would mean less dynamic range? Is that really the case or is the Xonar Audio Center and/or driver software not performing correctly and actually reducing the original volume after the data leaves the ADC. If isnít in the software, would amplification after the fact in Audacity really help or would you only increase all volume levels an equal amount with dynamic range remaining the same?

I guess the smart thing is to find out the maximum safe signal level at the line-in input and then look at the output of the preamp with a scope to determine normal peak levels and see if there is any room for improvement..

The bottom line is that this has been a very disappointing purchase and experience. I would have thought that if you purchased a reasonably good sound card that you could just install it and have it work properly.
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Old 2nd May 2012, 03:41 PM   #6
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The inputs to the Xonar wont fry unless you feed them with a signal that is far past the clipping point. All that happens is that the first opamp in the input chain gets its inputs fried, replacing the opamp solves the problem. The opamps used cost very little but if you want to replace them you need to be careful while doing so.

The input to the Xonar is configured so that an analogue signal of ~2Vrms = the maximum amplitude on the digital scale (0dBfs) from the ADC. This is the normal standard voltage level that CD players, DVD players etc will output when reproducing a full scale digital signal. If you exceed this value the inputs clip but you have to overdrive them quite a lot for them to blow up.

Now the control centre is very basic, all it does is digitally attenuate the signal coming out of the ADC. This means that if the analogue signal level reaching the ADC is clipping the ADCs inputs, that turning the inputs down in the control centre wont do anything to stop the inputs clipping. All you do is turn down the clipped signal digitally.

All sound cards tend to work in this kind of way, if any change in levels is needed it is all done digitally, this is because we don't exactly have potentiometers wired up to our sound cards such that we can alter signal levels in the analogue domain. This means that if the Xonar did offer some gain on the inputs it would most likely mean that it would be done digitally anyway, after the signal had been digitised. The headphone output on the Xonar for example can be configured to work at different output levels depending on the sensitivity of your headphones, this is done in the digital domain. The PCM1792 DAC has a built in volume control and all the Xonar does is turn the output down via the DAC if you select 64ohm sensitive headphones.
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Last edited by 5th element; 2nd May 2012 at 03:43 PM.
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Old 2nd May 2012, 07:14 PM   #7
phofman is offline phofman  Czech Republic
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Originally Posted by 5th element View Post
Now the control centre is very basic, all it does is digitally attenuate the signal coming out of the ADC. This means that if the analogue signal level reaching the ADC is clipping the ADCs inputs, that turning the inputs down in the control centre wont do anything to stop the inputs clipping. All you do is turn down the clipped signal digitally.

All sound cards tend to work in this kind of way, if any change in levels is needed it is all done digitally, this is because we don't exactly have potentiometers wired up to our sound cards such that we can alter signal levels in the analogue domain. This means that if the Xonar did offer some gain on the inputs it would most likely mean that it would be done digitally anyway, after the signal had been digitised.
ADC chips in soundcards often feature analog input attenuator (IPGA), hooked by I2C/IntelHDA/some 3wire to the soundcard chip, controlled thus by the driver. I have never seen an attenuator before the input opamp, but the input attenuator in the actual ADC chip is analog. For details see e.g. http://www.akm.com/datasheets/ek4620a.pdf , DAC/ADC used in Infrasonic Quartet.
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Old 2nd May 2012, 07:29 PM   #8
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Originally Posted by phofman View Post
ADC chips in soundcards often feature analog input attenuator (IPGA), hooked by I2C/IntelHDA/some 3wire to the soundcard chip, controlled thus by the driver. I have never seen an attenuator before the input opamp, but the input attenuator in the actual ADC chip is analog. For details see e.g. http://www.akm.com/datasheets/ek4620a.pdf , DAC/ADC used in Infrasonic Quartet.
Interesting, it's the first chip I've seen with something like that. I can tell you that that isn't the case for the Xonar though ;/ What'd be perfect is if they used something like the CS3318 volume control chip. This isn't cheap but it has the performance and is flexible. If used correctly one chip could easily adjust the gain in the analogue domain for both the input and the output sections simultaneously.

I can't imagine any consumer grade sound card ever using something like that however, unless it'd fit right into the marketing of the card as being the reason to buy this card over something else.
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Old 2nd May 2012, 08:25 PM   #9
phofman is offline phofman  Czech Republic
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Interesting, it's the first chip I've seen with something like that.
IPGAs integrated into the ADC chip are not that uncommon. E.g. many cards use AKM ADCs, and only AK4528 used in Juli/Delta has no IPGA - git.alsa-project.org Git - alsa-kmirror.git/blob - i2c/other/ak4xxx-adda.c . Others (ak4524 - Terratec, Hoontech, WM8776 -
Maya44, Prodigy Hifi, WM8770 - Terratec Phase, STAC 9460 - Prodigy192, Waveterminal192, AK5365 - Revolution5.1 etc.) have either full IPGA or at least mic input volume control. For details check linux alsa source code git.alsa-project.org Git - alsa-kmirror.git/tree - pci/ .

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I can tell you that that isn't the case for the Xonar though

Are you sure? I do not have the card, but it appers to have CMI9780 before the CS5381 ADC Asus Xonar Xense Premium Gaming Audio Set Review Page 2 - Closer Look: Sound Card - Overclockers Club . git.alsa-project.org Git - alsa-kmirror.git/blob - pci/oxygen/xonar_pcm179x.c While the actual ADC has no input gain control, the AC97 mixer CMI9780 seems to provide mixing and input gain control capability git.alsa-project.org Git - alsa-kmirror.git/blob - pci/oxygen/cm9780.h git.alsa-project.org Git - alsa-kmirror.git/blob - pci/oxygen/oxygen_mixer.c
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Old 2nd May 2012, 09:22 PM   #10
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Originally Posted by phofman View Post
IPGAs integrated into the ADC chip are not that uncommon. E.g. many cards use AKM ADCs, and only AK4528 used in Juli/Delta has no IPGA - git.alsa-project.org Git - alsa-kmirror.git/blob - i2c/other/ak4xxx-adda.c . Others (ak4524 - Terratec, Hoontech, WM8776 -
Maya44, Prodigy Hifi, WM8770 - Terratec Phase, STAC 9460 - Prodigy192, Waveterminal192, AK5365 - Revolution5.1 etc.) have either full IPGA or at least mic input volume control. For details check linux alsa source code git.alsa-project.org Git - alsa-kmirror.git/tree - pci/ .
I guess I should rephrase what I said previously. I've only ever paid attention to the top line DAC/ADCs from semi manufactures and these don't tend to have that functionality. It isn't at all a surprise to find that some of the multi channel or 'all in one chips' have variable analogue gain. Now that I know some can do that it would make sense if all ADCs would come with some variable gain on the input but perhaps that would deteriorate the performance somehow. I do know that most digitally controlled pots tend to have rather lacklustre distortion performance. The CS3318 is one of the only products out that bucks the trend.

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Are you sure? I do not have the card, but it appers to have CMI9780 before the CS5381 ADC Asus Xonar Xense Premium Gaming Audio Set Review Page 2 - Closer Look: Sound Card - Overclockers Club . git.alsa-project.org Git - alsa-kmirror.git/blob - pci/oxygen/xonar_pcm179x.c While the actual ADC has no input gain control, the AC97 mixer CMI9780 seems to provide mixing and input gain control capability git.alsa-project.org Git - alsa-kmirror.git/blob - pci/oxygen/cm9780.h git.alsa-project.org Git - alsa-kmirror.git/blob - pci/oxygen/oxygen_mixer.c
Yeah the Asus switches the input between two different sets of circuitry with a relay. One set for the microphone, which goes through the 9780 and then the other set which simply comprises of a few opamps and then the CS5381 for the line in. I also tested this out before posting by feeding a signal that was slightly too hot into the Xonar so that I had clipping on the spectrum analyser, which I then turned down using the software and the spectrum remained clipped, only then attenuated by X dB.
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