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THE COOLER & INSTALLATION
Popping the EMI cover off reveals an immensely complicated circuit board —
a testament to the wide variety of features on the card. It also reveals a couple
of additional connectors on the top edge of the card that we missed in our initial
inspection: An AC97 / HD Audio header to connect the card to the front audio
ports that most cases have, and a 4-pin digital AUX in port designed to receive
a signal from an optical drive (or any other audio device).
At the heart of the card is Asus' AV200 Audio Processing Unit, which gets its
heritage from C-Media's Oxygen processor (a.k.a. CMI8788).
Other important chips include Asus' Splendid HD video processor, two unidentified
"CAT"-branded chips that appear to be HDMI / HDCP controllers, and
a PCI to PCI Express bridge.
Naked. Note the front panel audio and AUX in ports along the top edge.
A top-down view of the card's analogue topology.
The most interesting part of the card from a circuitry point of view is the
analogue stage, pictured above. All of the electronics come from highly reputable
sources and can be expected to do a good job. The output stage starts with PCM1796
DACs from Burr-Brown (TI) and then passes through two stages of op-amps:
a 2114D
op-amp from New Japan Radio (JRC), and then the touted LM4562
op-amp from National Semiconductor. Both chips use a DIP8 package and can
be replaced by those who like to tinker. The two stage design appears to be
intended to allow a second possible analogue source, with a separate first stage
for each. The secondary source is an Asus-branded DJ100 chip, which is apparently
a modified C-Media CMI9780 AC '97 codec that contains an 8 channel DAC of its
own. It should be noted that the DJ100 chip is not duplicated on the surround
daughterboard, but the first stage op-amp is (as are three additional PCM1796
DACs), which suggests a fairly long analogue signal path for surround channels
decoded by the DJ100.
It's not clear why this second (inferior) analogue source is included, so allow
us to speculate. While the Burr-Brown DACs do an excellent job with standard
PCM audio, they are incapable of decoding non-PCM sources such as Dolby Digital
or DTS Ordinarily, this is not a problem since they are decoded in software
before they enter the hardware stream. But, what if these formats are output
directly, either because the software is instructed to pass through the signal
via S/PDIF or because an encoder such as Dolby Digital Live or DTS Interactive
is used? Our guess (and it is a guess) is that the DJ100 chip is used as a decoder
in situations like these, allowing simultaneous S/PDIF and analogue output of
Dolby Digital or DTS streams.
The input path contains two pairs of op-amps (a
Texas Instruments RC4580 followed by a
New Japan Radio NJM5532) and before the signal finally reaches the CS5381
ADC from Cirrus Logic. It seems safe to assume that two signal paths are
used to differentiate between mic-in and line-in (which share the same input
jack), but it's not clear why a two stage design is used here. All of the op-amps
in the input path use a DMP8 package which is not user-replaceable.
Op-amps op-amps everywhere! A view of the daughterboard with a PCM1796
DAC at the far right, followed by a JRC 2114D op-amp and another LM4562
op-amp. Each of these chips carries two audio channels each. Note there
are two JRC chips in each two channel pair; the second is presumably used
to output audio from the DJ100 DAC on the main board. |
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