"The said:
Crazy thing, I go to connect my SPDIF cable to the 5.1 system, and boom...
the card cuts out, and no audio is heard from anywhere. I eventually solve
this by randomly leaving the computer alone, and turning it back on later to
find everything is dandy, and drivers etc can be installed wirthout errors.
Before finding this simple soultion I tried many things, and even stuck in a
different hard disk. The audio worked fine on that, so I was confident that
I hadn't blown anything hardware wise... however... now using my normal HDD
again, I have EXTREME crackle coming from the speakers. It's definatly not
the speakers fault, because connecting headphones results in the same thing.
What on earth is going on?
I am using the same software, the latest, as I was when it was actually
working. Interestingly enough, the SPDIF port gives out perfect sound.
How am I to fix this, please help! Any sound that can be heard is quiet, and
mainly replaced by crackle etc. Even with no music playing, the speakers are
often hissing and popping.
Chris, help help help!
I would guess that the sound chip has been damaged by some
shortcoming of the computer SPDIF interface. It sounds like some
dangerous potential or current has flowed into the sound chip
and damaged it. This page is one of my sources of info on SPDIF.
http://www.epanorama.net/documents/audio/spdif.html
Some of the circuits on the spdif page are transformer isolated.
What this does, is avoid grounding problems, or DC problems with
the receiver at the other end of the line. Here is a sample
circuit, suitable for converting from a computer sound chip
output, to drive the cable and SPDIF receiver. No motherboard
I have looked at yet, has transformer isolation, and is an
accident waiting to happen.
|\
+-----| O----+
| |/ | S/PDIF output
| | 100nF (RCA or BNC)
| |\ | || T1
TTL level signal --+-----| O----+---||----+ +-------+--75R--- center pin
| |/ | || | | |
| | )|| | |
| |\ | 15 )||( 3 220R
+-----| O----+ turns )||( turns |
| |/ | )|| | |
| | | | |
| |\04 | | +-------+-------- ground
+-----| 0----+ |
|/ ---
74HCU04
I suspect something nasty happened when the SPDIF from your
computer was connected to the receiver. This is another
instance where the motherboard doesn't have a sufficiently
sophisticated interface. (Another example is Firewire, where
the computer doesn't have proper galvanic isolation, at least
compared to what chip maker Texas Instruments recommends.)
When connecting other electrical devices to a computer, a
conservative approach is to make sure the secondary device
is powered from the same power strip as the computer. Doing
so helps to keep the ground potential of all pieces of
equipment similar. I've drawn sparks and received a shock,
while bringing the ground of one computer, to the metal
on a second computer. I've actually measured the potential
difference between the two computers, and found 50V AC
between the machines. In that case, there was a problem with
the safety ground (cut in a distribution bar!).
If your receiver/decoder/stereo is 50 feet away, and powered
from another AC circuit, the best advice is to buy an optical
adapter, and use TOSlink for making the connection. Asus used to
make adapter brackets to do this, with TOSlink modules on them,
but I don't know if these are still available any more or not.
Using an optical link will prevent any kind of electrical calamity
that seems to have damaged your motherboard.
I would RMA the motherboard (as the damn thing should have
been designed better in the first place). Since the computer
design has no protection against either DC problems or grounding
problems, I would either convert the computer output via TOSlink
(adapter bracket or external copper to optical SPDIF box), keeping
the adapter powered from the same strip as the computer. If your
receiver doesn't have optical input, then you would need another
converter box at the receiver, to "armor" its interface. That
converter should be powered from the same AC power strip as the
receiver.
Computer ---SPDIF--Converter--Optical---Converter--SPDIF--Receiver
| | TOSlink | |
+---------+--------+ +--------+-------+
| |
Wall plug #1 Wall plug #2
These two devices, at $25 each, can sit at the two ends.
The optical fiber is potentially the most expensive part, at
$3 per meter of cable. The cable really shouldn't be that expensive,
as it is plastic fiber, and not glass like used in long distance
optical transmission. The TOSLink fiber can be purchased on this
site as well.
http://www.soundprofessionals.com/cgi-bin/gold/item/SP-COAX-OPTICAL
http://www.soundprofessionals.com/cgi-bin/gold/item/SP-OPTICAL-COAX
To repeat, this solution really shouldn't be necessary, but it will
prevent a similar occurrence in the future, expecially if you leave
the computer and receiver as they currently sit.
HTH,
Paul
