DVD-ROM 2 Pin Digital Out w/ P5AD2 Onboard Audio

Discussion in 'Asus' started by David Swager, Dec 19, 2004.

  1. David Swager

    David Swager Guest

    How does one get digital audio out of a DVD or CD-ROM drive into the audio
    system on the P5AD2-E Premium motherboard?

    Is there a faq available somewhere dealing with auido issues?

    It's been awhile since I've built a PC and there has always been issues with
    limited input/output connectors on sound cards. Am I missing something at
    this point?
     
    David Swager, Dec 19, 2004
    #1
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  2. David Swager

    Paul Guest

    It is possible there are three ways to get audio from a CD:

    1) Connect analog four pin cable from drive to CD connector.
    (See lower left corner of motherboard for CD connector).
    2) Don't bother with the old four pin cable. Enable DAE (digital
    audio extraction), which allows the CPU to pull blocks of
    digital data across the IDE cable, for playback through the
    sound subsystem.
    3) Try the two pin digital output on the drive. It is some kind
    of PCM (pulse code modulation), but I find conflicting comments
    in Google on the topic. Some claim it is SPDIF, and at least
    one high end audio product hooks onto that output, and uses
    some high quality DACs to make audio from the stream.

    Comments in Google claim some drives have the 2 pins, but there
    are no electronics in the drive, to put signals on the pins.

    One person claims he connected the two pins to his SPDIF input
    and it worked. (Who knows, maybe he was using DAE and didn't
    know it.)

    In any case, be aware that the 2x3 SPDIF header on the Asus
    motherboard does not use standard SPDIF levels. SPDIF is usually
    transformer isolated and low amplitude, like <1 volt or so.
    The header on the Asus motherboard is intended for use with an
    Asus bracket first, and the bracket converts what presumably
    are logic level signals down to the low amplitude signal. One
    Asus bracket I looked at, has a resistor divider network on
    SPDIF_out, to convert the signal from the 2x3 header, to the
    proper level. On the input, that bracket had a buffer chip,
    to convert the <1 volt signal into a logic level.

    Note that, there are also some older versions of the Asus bracket
    that contained no buffer chip on SPDIF_in. It looks like someone
    at Asus thought that the AC97 chip would amplify the signal level
    or something, and a number of users were disappointed to find that
    their SPDIF_in (on the ALC650) wouldn't work, even though the
    chip rev number was sufficient for the purpose.

    This is the bracket I would try to find, if I were to try your
    experiment. Basically, you would run a coax cable from the two
    pins on the drive, to the SPDIF_in on this bracket. The 14 pin
    chip on the bracket converts the SPDIF_in signal to a
    level suitable for the 2x3 header on the motherboard.

    Since I never received any feedback from previous posters, I
    don't know whether anyone could find this, or got it to work.

    http://usa.asus.com/products/mb/images/accessories/SPDIF-IN-OUT-COA-Module.jpg

    And, this is the module I wouldn't want, as it has no buffer
    chip, and the design was presumably based on a wrong assumption
    about how the motherboard works:

    http://www.asus.com.tw/mb/mbimages/accessories/SPDIF_COA.gif

    AFAIK, this is the SPDIF spec for a real SPDIF device. The
    Asus only meets this on the RCA jacks on the SPDIF bracket
    (or any built-in jacks on the back of the motherboard).
    You'll need an RCA plug, length of 75 ohm cable, plus a
    couple of pins and contacts for the CDROM end of things.

    Cable: 75ohm +/-5% (l<10m) or 75ohm +/-35% (l>10m)
    * Line driver:
    * Zout: 75ohm +/-20% (100kHz .. 6Mhz)
    * Vout: 0.4Vpp .. 0.6Vpp, <0.05Vdc (75ohm terminated)
    * Line receiver:
    * Zin: 75ohm +/-5%
    * Vin: 0.2Vpp .. 0.6Vpp

    If you go to this site http://frontx.com/order_c.html you can
    find a 1x2 plug and some pins:

    http://frontx.com/cpx075_8.html "1x2 header plug"
    http://frontx.com/cpx076.html "female pins"

    If the pins on the drive are on 0.1" centers, the Frontx parts
    might work. But, there is a slightly smaller kind of connector
    sometimes used, and I don't know where to find a solution
    for that. I think the male pins in that case are smaller as
    well, and the frontx pins would be a sloppy fit.

    For all the hassle, I think investigating DAE is infinitely
    simpler.

    If you try this the hard way, please post back with your
    experiences, as there are still a few people who want a
    way to do SPDIF_in.

    Paul
     
    Paul, Dec 19, 2004
    #2
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  3. I wouldn't even bother messing with this, most CD player programs these
    days can do CD playback using DAE over the IDE bus which avoids issues
    with the separate connection to the CD drive.
     
    Robert Hancock, Dec 19, 2004
    #3
  4. David Swager

    David Swager Guest

    Thanks for the responses. I ended up letting the DVD-ROM and DVD Writer use
    the IDE Channel via the DAE options in the properties settings. This works
    fine.

    Connected a Leadtek PVR2000 TV/MPEG card to the only analog in port on the
    motherboard. Funny thing is that the Sound from this card is fine in
    Windows XP Media Center application, but I don't get any sound from the
    Leadtek PVR application.

    Thanks again!
     
    David Swager, Dec 27, 2004
    #4
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