Toney said:
This motherboard has an nVidia nForce3 250GB chipset with audio
provided by a Realtek ALC850. Some boards with these chips provide
S/PDIF In as well as Out. My board has a Coaxial as well as an
Optical S/PDIF Out, but no S/PDIF In.
Does anyone know of a way to get S/PDIF In happening on this board?
Any help appreciated.
Toney
The reason this project isn't going to be easy, is there is no
SPDIF 2x3 header on your motherboard. At least I don't see one
in the manual. To add SPDIF in, would require soldering to
the ALC850, and that will violate the warranty. (It is also
tough as hell to do - I know how to solder, and the risk is
great, that you'll bridge pins together, short something, and
damage audio entirely. Part of modding, is figuring out a
safe way to get connections to the board, and it is not
clear to me, how you can do that in this case.)
In terms of the components needed, you need a SPDIF bracket
that has a line receiver chip. Asus made several SPDIF brackets,
and some of those are duds (can never work). This one, shown
on Newegg, but currently unavailable, contains the line receiver
chip needed to convert 0.5Vpp SPDIF signals, into a logic level
signal needed to drive the ALC850 (or a ALC650 for that matter).
While RealTek may have intended the SPDIF-in pin on the chip
to convert directly (0.4V hysteresis Schmitt trigger, 1.65V
bias point), it never seemed to work properly.
S/PDIF IN-OUT/COA Module (14 pin chip, right hand corner)
http://usa.asus.com/products/mb/mb_accessories.htm
http://usa.asus.com/products/mb/images/accessories/SPDIF-IN-OUT-COA-Module.jpg
Basically, to use this module, you would need to connect three
wires from the bracket to the motherboard. You would need
+5V and GND (to run what I think is the differential line
receiver chip), and the third wire would be SPDIF-in. You
would need to connect the SPDIF-in wire to pin 47 on the
ALC850 chip. The SPDIF-in wire must be kept short, as there
is a 6MHZ signal on the wire. You could, for example, use some
110 ohm ribbon cable, run that down to the motherboard, and
make a partial termination scheme using a thevenin equivalent
of 110 ohms. That would allow a slightly longer cable to be used,
as a partial termination scheme would suppress reflections on
the wire, without overloading the line receiver output too
much.
My only reason for mentioning all this, is to indicate that
this is not a viable alternative. As Måns suggested, buying a
solution is going to be a lot easier.
This is an expensive way to do it:
Edirol UA-1D USB Digital Audio Capture $118
http://www.studica.com/products/product_detail.cfm?productid=12139
A bit cheaper M-AUDIO Delta 410 PCI Sound Card w/ SPDIF $78
http://www.newegg.com/app/ViewProductDesc.asp?description=29-121-105&depa=0
One thing you should research, is how copy protection works
on SPDIF. Now, I don't know how the bits are used in practice,
but you can get a feel for the SPDIF format, in this text
document plus three GIFs.
ftp://members.aol.com/mihartkopf/interfc1.zip
This page mentions "SCMS copy protection info", but I'm
having trouble understanding what sources use it, or don't
use it. If you are picking up SPDIF from some other recording
device, this likely isn't an issue.
http://www.bnoack.com/data/SPDIF.html
HTH,
Paul
