tb said:
My old PC does not have front audio ports, so I would like to purchase
the part described in this web page:
http://www.frontx.com/cpx110.html
The internal front panel header (male) on my sound card (ASUS Xonar DS)
has two rows of pins: One row has five pins and the other one four +
one blank. I have no idea what the pinout is...
The female connector used for the part that I want to purchase seems to
have: One row with three wired holes + two blanks; one row with four
wired holes + one blank.
Since I am not much of an expert, I am wondering if the female connector
is wired correctly for the male header. I can readily tell that the
male header will plug into the female connector but will I have audio
in/out from the ports?
The Xonar claims to have an HDAudio header. That uses the same
kind of 2x5 (with one pin missing) as the older AC'97 front panel
audio header. The missing pin is for keying, to help guide you
to the correct orientation of the cable assembly.
Back in AC'97 days, there weren't enough ports on the CODEC chip,
to drive all possible audio connections. They decided the "LineOut"
from the chip, would be used to drive both the rear (Lime colored)
jack, and the front panel headphone jack.
By putting an insertion detection switch inside the headphone
jack, they had a way of deciding whether the user was using
headphones or not. If a headphone jack was connected to the front
panel header, it would cause the rear (Lime colored) jack to be muted.
The signal was electrically disconnected by the switch, to cause the
rear output to mute.
When the headphone plug wasn't inserted in the jack, the switch would
close, and forward the audio signal from the AC'978 CODEC chip, back
to the Lime colored jack. That would cause the speaker connection
on the back of the computer, to work again.
If you look at the FrontX diagram, their wiring is "classical AC'97".
L_OUT_R and L_OUT_L are line_out signals from the CODEC chip.
BL_OUT_R and BL_OUT_L are returned signals from the front panel assembly.
When the headphones aren't plugged in, audio signals come down these wires.
On the motherboard, these two pins would be wired back to the Lime colored
lineout connector.
On an HDAudio sound device, this scheme isn't used any more. That means,
the BL_OUT_R and BL_OUT_L pins on the sound card, can be used for other
purposes. In the HDAudio standards, they're used for jack sensing.
If I was using that FrontX assembly on my computer (HDAudio type) here,
I would lift the two tabs on BL_OUT_R and BL_OUT_L, tape up the pins and
leave them sitting in mid-air. That would leave a total of five wires
still installed in the nylon shell of the 2x5. You don't have to pull them
if you don't want to, but for my peace of mind, I prefer not to have
audio connections wired back to the jack sensing resistor tree. You never
know whether some silly driver software, will be using that function
or not. As far as I know, the alternate sensing scheme is used, and
the jack sense using those two pins, isn't enabled/working. And if it
was enabled, an AC'97 wiring harness (like the FrontX), wouldn't do
the right thing with respect to the resistor tree.
To connect two stereo jacks, you have tip, ring, and sleeve on the jack.
For headphones, those go to
left, right, ground.
For microphone, those go to
input, bias, ground (if mono-microphone input) or
input_L (pre-biased), input_R ([pre-biased), ground (if a stereo microphone input)
Since the ground is a signal common to both jacks, that means there will be
a total of five wires that are "essential". Disconnecting BL_OUT_R and BL_OUT_L
would leave you with the five essential wires to run headphones and
a microphone.
So, no reason to panic. If you can't be bothered worrying
about it, just plug in the FrontX cable and enjoy it. Or, if
you wish, retract and remove BL_OUT_R and BL_OUT_L and tape
them up, as returned audio signals are not used by an
HDaudio motherboard or HDaudio sound card.
*******
How to lift the tab on the side of the nylon shell of the
FrontX, so you can retract a pin, is shown here.
http://frontx.com/head_conp3.gif
http://frontx.com/head_con.html
If you want diagrams of the HDAudio header standard, versus AC'97, they're here.
I've added a few notes below.
http://www.silverstonetek.com/downloads/pindefine.jpg
AC'97 HDAUDIO
MIC_IN X X GROUND PORT1_LEFT X X GROUND
MIC_POWER X X (+5VA) PORT1_RIGHT X X PRESENSE# (ground if HDaudio wiring)
R_OUT X X R_RETURN PORT2_RIGHT X X SENSE1_RETURN
(HP_ON) X (key) SENSE_SEND X (key)
L_OUT X X L_RETURN PORT2_LEFT X X SENSE2_RETURN
Notes:
(+5VA) - not wired on the FrontX, motherboard powers this for the purposes
of running a power amp (like 2W speaker amplifier) on older computers
(HP_ON) - not wired on the FrontX, logic control signal to enable or
disable optional power amp. Computers don't have power amps
on the front panel connector PCB any more.
MIC_POWER - this is a weak power source. Anywhere from 3V to 5V
or so, in series with a 2K ohm resistor, for powering
electret microphones. Easily overpowered, by other
signal sources when required. Functions as the right
channel input on a stereo microphone, if the CODEC is stereo
(key) - the missing pin, to help orient the connector during insertion
PORT1 = Microphone (re-taskable)
PORT2 = Headphones (re-taskable)
PRESENSE# = Cable assembly grounds this pin if HDaudio wiring,
Cable assembly leaves this open circuit if AC'97 wiring
"Classical" cabling won't ground this pin, because of the
danger that +5VA is on there! That's another good reason for
the FrontX to not connect a wire there.
SENSE_SEND, SENSE1_RETURN, SENSE2_RETURN = wired to resistor tree for jack sense
HTH,
Paul
