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Old 16th November 2013, 05:09 PM   #431
Wungun is offline Wungun  Canada
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Found this old thread at Head-fi....
Really interesting solution to external power, with improved -12V rail...

http://www.head-fi.org/t/426049/maki...ar-essence/270


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Old 21st November 2013, 08:22 AM   #432
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Coris

excelent thread
you put much effort In modding ST/STX by Asus
because performance of audio card Is based on PS I like to know what are your recomendation about low noise computer PS - SeaSonic or Enermax or else
I can not find a shots from your setup
do you still think that Is worth dealing with ST/STX or there are better competitors
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Old 21st November 2013, 03:36 PM   #433
Coris is offline Coris  Norway
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Very sorry again about the missing pictures in thread. It were deleted by mistake of an moderator for a while ago...

I would like to repeat my opinion about a "silent" (low noise) computer.
A digital system, as the computer is, generate much electrical noises. There is the way a computer works, and is the way the digital systems behave. There is absolutely no reason to work to find low noise solutions, or expensive devices, which are stated as low noise ones, to power the entire computer, thinking it will help to get a better audio signal out of a sound card.
A low noise computer PSU is a great device, but will never replace a analogue PSU when about a analogue stage, as the sound card include. A low noise computer PSU is unusable for audio purposes anyway (to much noisy). Even more, one may know that on the mother board there are plenty of small switching PSUs to power the main processor as the other many chips on it. All those produce noises. These noises do not disturb the computer functionality, as there are filtered and rejected both hardware and software.
The computer noises disturb only the analogue stages of a sound card.
Another aspect is that a computer PSU have to deliver very high power. There is quite impossible to filter or find a so low noise power solution (to satisfy the analogue circuits) when heavy currents are involved.
The reasonable solutions are in this case two: heavy filtering of the power rails which goes only to the analogue stages, or replacing the build in PSUs for analogue circuits, with an external (analogue/low noise/audio suitable) PSU.

About Asus ST/STX cards I may say that basically are the only ones consumer cards which can 192Khz sampling (in/out), as I know. If somebody have another informations, please replay.
The weak part of these cards, are the power system for analogue stages, and the DAC circuit and post DAC processing of the audio signal. At least the most important parts of a sound card... Here is to be modded to get an exceptional quality sound card.

I work now to a more elegant/professional mod for an ST/STX card. There is about a completely new DAC design using the same PCM1792 chip, and also a new I/V and final stage. There will be also two solutions for powering the analogue stages: using the built in (moded) PSUs, or an external high end PSU. I will come out with some pictures in the near future.

Last edited by Coris; 21st November 2013 at 03:38 PM.
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Old 21st November 2013, 03:46 PM   #434
Coris is offline Coris  Norway
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Quote:
Originally Posted by Wungun View Post
Found this old thread at Head-fi....
Really interesting solution to external power, with improved -12V rail...

MAKING A DECENT HI-FI POWER SUPPLY FOR XONAR ESSENCE - Page 19


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Yes, indeed. This is a good solution, and I think to experiment more on it. I would like to have at least more than only +/-12v out of these PUSs. I think satisfactory will be to get +/-17v...
BTW, I have measured the +/-rails on the new edition of a STX card (ASM). Are surprisingly good. I will come back soon with some snap shots of these measurements.
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Old 21st November 2013, 11:32 PM   #435
Wungun is offline Wungun  Canada
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Trying to understand the changes to the -12V circuit for adding the 7912...and whether I'd have to do that if I were to supply regulated -12V to pin 3 on the board.
I'm guessing removing one of the resistors disconnects the -12V rail that's already there...?
And adding the 7912 restores the circuit.


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Old 22nd November 2013, 06:53 AM   #436
Coris is offline Coris  Norway
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Here is the last edition of STX board (ASM), rev 1.00, with some measurements points and some descriptions of circuits.

I took snap shots of the switching PSUs on board for the analogue stage. The signals looks similar for +/- 12v rails. A/-A is right on the output diode of the PSUs. B/-B is after first ferrite bead on the filtering cell. C/-C is after last ferrite bead, last filtering cap (quite difficult to be seen on this picture).

The positive PSU deliver a tension level of 15v, and then is regulated by 7812 regulator. The negative tension is -12v right out of the PSU. No regulation here. The designed 7912 regulator is not populated. Positive/negative rails are rigorous equal. I do not know if this is just by chance on this board, or it is like this for all the production... Anyway it is a improvement comparing with the old edition STX boards.
Attached Images
File Type: jpg NewSTX meaurements.jpg (852.8 KB, 115 views)
File Type: jpg A - diode.jpg (176.6 KB, 107 views)
File Type: jpg B - First filtering cap.jpg (199.8 KB, 102 views)
File Type: jpg C - After last ferrite bead.jpg (204.3 KB, 98 views)
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Old 22nd November 2013, 09:28 AM   #437
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thank you for detailed description
these measurments from left to right ar A-A B-B C-C and they are from not modded card?
out of box how card Is powered - from PSU conectors or from PCI
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Old 22nd November 2013, 10:02 AM   #438
Coris is offline Coris  Norway
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The measurements are made on untouched (original) PSUs on board. A/B/C are measurements points for positive rail, -A/-B/-C are for negative rail.
The card is powered through Molex connector for 5v/12v, and from PCIex for 3,3v.
I can not say for sure which of the Molex tensions are used for the +/- PSUs. This is not so important anyway. The 5v for DAC analogue stage is regulated from 12v Molex rail. The +/- 12v rails on board are also used for ADC stage of the card.
It looks to me that the 3,3v for ASM chip oscillator is taken from a own regulator (u21), and not directly from the 3,3v computer rail... In my opinion the oscillators on board it should be powered from a dedicated battery for better noise performances.

Last edited by Coris; 22nd November 2013 at 10:12 AM.
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Old 22nd November 2013, 10:06 AM   #439
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are these powered from computer PSU or other moded psu
can you show a shots from such PSU and also moded card
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Old 22nd November 2013, 11:28 AM   #440
Wungun is offline Wungun  Canada
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Default Xonar ST/STX mods...

Thanks Coris...
Looks as if my 1.02 also had a switching PSU on board as well.

If one was to inject -12V regulated at u34 (?), the unregulated -12V first has to be removed from the design...do you see a way of doing this?

I think if you remove the molex power and add external 12V to the 7812, then the -12V would also get power...?

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