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Hi, Fotios.
It isn't possible in any case, because an -12V voltage regulator is installs in place of L1. -15.6V will be present on input of the voltage regulator, but -12V on output and on negative rail.

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Yes, you are right. I was confused from the description. Thanks for the reply.

Fotios

Hello Fotios ! I remember you from the Asus forum. It's great to have you here esp as you are a very nice guy and very knowledgeable too.

Can I use this linear PSU (60 euro) with the Xonar ST/STX?

Using a molex cable from an old power supply, connecting the cable-ends to the lab-psu and the other cable-end (with the molex connector) to the STX. Then set the lab-psu to 12v and max current (3A).

Is this possible or will i blow the card? And how much sound improvement should i expect comparing to a modern ATX PSU? The ripple on the lab-psu is only 1mv.

Hi,

Yes, it'll work but you'll need one to supply 12V and then another power supply for the 5v line. Lots of $$$ for not much improvement.

Tbh, the onboard regs are going to limit the quality of juice that gets to the chips, especially because there is a buck/boost/invert circuit which is noisy. So pro supplies like this are overkill. You won't blow the card and you won't hear any major transformation - the xo and op amps are the best things to change to hear a very obvious improvement.

You should really look at something simpler using two LM317A or a very good pair of 7812 and 7805 regulators. Here's an example of an excellent 7812 with very good specs - better than the ones that are used on the soundcard itself :

STMICROELECTRONICS|L7812ABV|V REG +12V, 7812, TO-220-3 | Farnell Hong Kong

You could very easily make your own using this :

The σ25 Regulated Power Supply

And many electronics suppliers have pre-built kits. There are lots here in Hong Kong.

GT*Mini Voltage Regulator (5V, 5A) - WECL Online

It was posted above that it is worth modifying the card with a 7912 regulator to improve the noise on the -12V on board rail. So bear in mind that however good the power you feed this card, that -12v line with no regulator after the boost/invert is gonna stay noisy - far noisier than any decent atx supply - dc-dc converters typically have 30mV noise.

I didn't dare saying it, but indeed an external PSU won't cure digitis....look into some better opamps first, make baby steps

I am trying to put together a custom PSU for this purpose. I've done some DIY work before, but never messed around with power supplies. I have read a lot on the subject (here, here and here). I can design PCB boards so once this is done I'll release the eaglecad files to whoever wants it.

Question:
If I used one transformer that outputs 14v 1.8A in series (x2 outputs), could I take one output and put a regulator to run that down to 12v and take the other output with another regulator to run it down to 5v without messing up anything?

Thanks for the reply. So this lab-psu is useless because the STX boardcircuit adds alot noise anyway. Sadly, I don't have any experience with modifying electronic stuff.

What about this Antec Earthwatts? It has 3.0mv on the 12v and 5v line. Do you think there will be any noteable difference in sound quality (with the Stock ST/STX) if you compare it to that lab-psu?

I'm looking for an ATX PC powersupply that is ubersilent but also has ripple values like that Earthwatts. It's very hard to find this combination. Corsair CX400 has nice values but it's fan is way too loud for me. I'm searching for something that is as silent like a Nexus Value 430 with the Efficiency of a PicoPSU at low loads and the Ripple of a Lab-PSU. I would pay the price of a Seasonic X-750 if some manufacturer can get me such a high quality PC power supply.

I am trying to put together a custom PSU for this purpose. I've done some DIY work before, but never messed around with power supplies. I have read a lot on the subject (here, here and here). I can design PCB boards so once this is done I'll release the eaglecad files to whoever wants it.

Question:
If I used one transformer that outputs 14v 1.8A in series (x2 outputs), could I take one output and put a regulator to run that down to 12v and take the other output with another regulator to run it down to 5v without messing up anything?

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A linear supply will have less high frequency noise than an smps ATX psu. Regulators are pretty good for noise control up to about 100Khz so a linear supply will outperform an smps one because the regualtors will do very well at killing the linear supply's noise.

An smps ATX supply has more noise and much more noise at high frequencies, which regulators can't kill.

So, if you can, use a simple linear psu - it will be better than atx. If you can't, then I'd personally choose a Corsair.

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Hmm, that explains why I always feel the treble sounded muffled on all soundcards with my Corsair HX620W. The HX620W has 9mv ripple @ 150watt according to SPCR, but I need to use an equalizer to get a detailed airy treble sound with every card (X-Fi, Xonar, Realtek). I also noticed this on PC's with other brand power supplies like Enermax. The high end always lacked detail, openness and air. I guess I really need a linear PS or use SPDIF with an external DAC/AMP.

I don't think it'd make the trebles muffled...that's what crappy opamps do. It'd make them spikey, edgy and agressive.

I have to say that the ST's design, although very very good, has problems and the main one is the horribly jittery xo. Far and away the best way to remove the mush and muffle is to get that replaced. But that requires 'surgery'. Cleaner power can improve things (read the cs8416 datasheet) but not hugely.

That nasty xo is the main weakness of the ST/STX imo. Next up is the 7912 regulator mod. After that are the caps in the I/V feedback circuit - nasty high distortion ceramics - which need to be replaced with metallised polypropylene or similar. After that, upgrading or removing the output coupling caps on the line out.

When these have been done, or not, then I think it's best to turn to the power. Finally, start rolling op amps to colour the sound to your preference. I'd start with LM4562 (most neutral imo), AD8620 (most dynamic) and LME49720HA (biggest soundstage).

I hope this helps you see that the last two steps won't significantly 'improve' the sound but should help you get a sound you like.

Just imo.....enjoy the music !

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I found that changing the caps in the I/V feedback removed a lot of that edginess. I don't think it's the op amps fault really - I think they are being crippled by the poor choice of caps they work with. Asus put plastic caps in the buffer, so why not in the I/V ? It makes no sense to me. Cost cutting ? Board layout redesign ? It's a damn shame for sure.

The 7912 cost less than US$1, the caps were US$4, the xo could be replaced with something like this, which, according to the datsheet, has less than 1ps noise :

http://www.euroquartz.co.uk/oscillat...ProductID=2821

With bulk discounts, this would have cost Asus less than US$10 and added less than US$20 to the retail price, and it would have sounded so much better and might even have earned its 'audiophile' tag for real.

Hey Glingrem,

I finally got around to doing this mod. The R2 on my board was 88K. I replaced it with 120K and I'm getting -15.65V before regulation which is more than enough.



However, a good 7912 is hard to find. Most seem to have 70uV of noise and only 60dB of ripple rejection. The case size is a dpak-3 I think and I think 500mA will be enough. So far, the only one I have found is this :

ON Semiconductor | Semiconductors | Power Supply and Control | Linear Regulators | Negative Voltage Regulators, On Semiconductor |MC79M12BDTG

Do you or anyone else know a better component ?

Thanks anyway for posting this mod - even with an average 7912, it reduces noise on the -12V line by a factor of over 10 and vastly improves line and load regulation. Awesome !

Tom

EDIT : Given up looking - decided to use the d2pak I already have. It works fine - I get a total of 23.90V across pins 4 and 8 of the op amp sockets. I cut the legs a little so the top sits at the same height as the caps around it so it won't catch/touch on anything when I put the card into the pci slot. I made the rear leg from a resistor lead.