I just got a new motherboard that has a SPDIF "riser". I think it was
3 or 4 pins.
Of course, the wires did not come with it to actually hook it up. I
think people call these "headers?"
Any ideas on getting digial audio out of this mobo? Is this something
I could buy at a radio shack?
If it is just going to a RCA connection, could I wire it myself? Would
that fry my low-end mobo?
Is it even woth playing with for a low-end mobo?
Mobo: ECS 661GX-M 1.0B Socket 478 SiS 661GX Micro ATX Intel Motherboard
Thanks-
First of all, consider what you get for your trouble. For most
sound applications, SPDIF delivers stereo (2 channels) only. It
is a 2 channel interface. When you use a movie player, and play
a DVD, the movie player application finds the Dolby AC3 stream on
the DVD and sends it to the SPDIF. At that point, the decoder
light on your receiver lights (means it is seeing AC3) and the
receiver gives you 5.1 (6 channel) sound. The way this works,
is the AC3 format is a compression standard. It squeezes 6 channels
of samples, into 2 channels. Very few things can create AC3 for
you, so the utility of SPDIF is not very good. Analog sound
has fewer restrictions. (If you make AC3 in real time with optional
software packages, the delay is about 0.5 seconds before the
sound comes out of the speakers.)
If you need an adapter bracket, primarily you should stick with
the motherboard manufacturer as the source. But some companies
don't seem to distribute their own brackets, leaving their customers
dangling in the breeze.
If you look in the manual, this is the pinout on your board.
Pin Signal_Name Function
1 SPDIF SPDIF digital output
2 +5VA 5V analog Power
3 Key No pin
4 GND Ground
Here is a picture of an Asus adapter. This one is output
only, and has an RCA coax output, and a TOSLINK optical module.
http://web.archive.org/web/20030406...w/mb/mbimages/accessories/SPDIF+out+v1_00.gif
And here is a web site (North America only), where you can buy one:
http://estore.asus.com/shop/item.asp?itemid=1013&catid=215
Now, while that adapter bracket has the right number of pins,
the right pattern (2 pins, a blank, 1 pin), the wiring is
actually opposite to the way your motherboard has it set up.
If you bought the above bracket, you'd need to take a hobby knife,
pry up the tiny plastic tabs on the connector on one end of the
cable, and move the pins to different holes. This is reasonably
easy to do.
If you look at a closeup of that adapter, there are three tiny
surface mount components near the RCA coax jack. Those components
AC couple and attenuate the logic level (high amplitude) signal
from the motherboard. You cannot take the motherboard signal
directly and connect it to the coax, as the voltage is too high.
A logic level signal is used, because of the second function on
that adapter - there is a TOSLINK module, which is an optical
connection for SPDIF. TOSLINK needs a logic level signal, in
order to send a nice 6MHz stream optically to a receiver. When
a motherboard uses the logic level signal, it makes it possible
to drive a coax (via attenuation network) and a TOSLINK (via
a cheap fiber optic module).
There are some motherboards that send low amplitude signals
directly. The header in that case only needs two pins, GND and SPDIF.
But that scheme is limited to coax output only (at least if
you don't want to pay a lot for the adapter). It looks to me
at least, like your motherboard header is a logic level type,
suitable for either or both of coax and TOSLINK.
So, loads of fun, but not worth the trouble.
Sending a digital signal, does have the advantage of using the
DACs in your receiver, rather than the DACs in the AC'97 codec (when
you use analog output). If you listened to classical music,
with high dynamic range (some quiet passages, then some loud
music), then digital from computer to receiver is worth it.
For games, the performance of the analog outputs is normally
good enough for the job. And there are more opportunities for
multi-channel speaker configurations, with analog.
Paul
