Using SPDIF header on motherboard directly to RCA digital out for receiver input OK? - AVS Forum
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post #1 of 12 Old 01-28-2013, 12:24 PM - Thread Starter
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I just bought a Gigabyte B75M-DH3 motherboard and built a new HTPC for TV viewing and to replace Verizon STBs using HDHomerun Prime. The audio has been somewhat challenging for me. Currently just watching via the TV speakers (HDMI to TV) - when I tried the Samsung TV's digital optical out from whatever source is selected to receiver I noted I can only get stereo (Dolby pro logic) even on channels which are broadcast in Dolby Digital 5.1 (my receiver does not do HDMI)

The computer motherboard has a Realtek full HD two pin SPDIF header which is noted to be enabled and working in the audio part of control panel. Seaching on the web I saw a lot of information about connecting such a header to a video card or sound card to enable mutl-channel out on either peripherals optical or RCA digital audio outs. Also saw discussions about internal SPDIF headers being 5 volt; with tosllink still using 5 volt even though optical and RCA being reduced to 0.5 volts.

I found this direct connector on the web that seems to indicate that you can use it to directly connect an RCA digital audio output from motherboard SPDIF header (ground and signal - which is what I have available), allowing me to get full digital output to my receiver

Any feedback on whether this will work and hopefully not result in frying my receiver or motherboard.

Thanks

link to connector I have sent for:

http://www.frontx.com/cpx106_2.html

This cable can be used to transfer RCA Composite Video or RCA Coaxial SPDIF to the front panel. It connects to the Composite Video or SPDIF header/pinouts on the motherboard, sound-card or video-card.

Please take notes of the "IN-OUT" icons as shown in the pictures on the right.

This cable can be used for dual purposes, i.e. for "IN" or "OUT" usage. The port holder can be turned 180 degrees to mark the port either as "IN" or "OUT" function.

RCA VIDEO / SPDIF INTERNAL

SPECIFICATIONS
PRODUCT NAME
FRONTX RCA Video / SPDIF Internal

PRODUCT CODE
CPX106-2

BAY USAGE
Half of small bay

CONNECTORS
RCA (nickel plated) female
1x3 header connector female

CABLE
28awg X 1c (UL 1533)
Length - 2.5 feet (762 mm)


WIRE ASSIGNMENTS



Black: Ground / GND
White: Composite Video Signal / SPDIF


HEADER CONNECTION GUIDES


Diagram 1: On most motherboards, the composite video header/pin-out consists of 3 pins in one straight row.

Diagram 2: Simply plug the connector onto the header, in such that; the white wire is connected to the video signal pin (IN or OUT depending on your usage) and the black wire to the ground pin. No connection to the NC pin (empty) is required.

To connect to SPDIF header, simply connect the white wire to SPDIF pin (IN or OUT depending on your usage) and the black wire to the ground (GND) pin.

You might have to rearrange the wires to match with the pin assignments, or change the header connector if necessary, depending on the layout of the video / SPDIF header.
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post #2 of 12 Old 01-28-2013, 01:52 PM
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You're right about your Samsung optical passthrough. This link is a little old, but some discussion took place around their HDMI passthrough limitation. While there are several things I'm not 100% pleased with regarding my sony led, I'm surprised to see that it's one of the few sets that will passthrough dd/dts from hdmi. http://forums.cnet.com/7723-13973_102-328443/dolby-5-1-pass-through-from-hdmi-input-to-optical-output/


On to your question. . .

The optical out should work fine from the spdif header to send dd/dts and this would not fry your motherboard

I really don't know anything about "frying" the receiver with this, so I can't comment there
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post #3 of 12 Old 01-28-2013, 03:02 PM
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I think any discussion about 5 volts is as a voltage source to drive an optical output card USING a "powered" SPDIF header (and by powered I mean it includes not only SPDIF and GND but Vcc and GND (again)). It's my understanding connecting just the SPDIF and GND to the RCA will work for a hardwired, coaxial SPDIF connection to your AVR.
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post #4 of 12 Old 01-28-2013, 05:12 PM
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I connected my SPDIF header to an RCA jack which then sends digital audio to my AVR. I saw several articles about doing this & it works for me. Here's a discussion about the subject & some people say it's not correct to do that way. Just to clarify, some mobos have 3 pins for SPDIF. One is a +5V pin which would be needed in case you had to power the circuitry for an optical output. But no such circuit is needed for coax output. This particular thread is about the actual signal level on the SPDIF output pin.
http://www.avsforum.com/t/1422202/extract-audio-from-hdmi

Since that thread I have contacted my mobo manufacturer (ECS) & asked if the output signal was 0.5V or 5V TTL which would need to be converted to the proper 0.5V SPDIF voltage. They replied "The SPDIF pin carries the proper voltage. It does not need to be converted."

As mentioned in the link above, the only thing I ever came across about a 5V TTL signal was converting a 2-pin CD-ROM drive audio to SPDIF.

Your mobo may be different. But again there are several articles explaining how to simply attach an RCA jack to the header so I think the odds are on your side that the item you are getting will work.
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post #5 of 12 Old 01-28-2013, 05:33 PM - Thread Starter
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Thanks Darkslayer for confirmation on the limitations of the Sampsung TV line. One nice feature of the limitation to stereo out is that whatever channel I am watching can have the volume controlled out of the receiver by changing the HDMI source volume (in this case HDPrime tuner and using windows volume with WMC remote control.

But its not multi-channel

So thanks to Andrew for clarifying that my proposed approach to get a coax RCA out to receiver from spdif and ground pins on motherboard should work for multi-channel
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post #6 of 12 Old 01-28-2013, 06:11 PM - Thread Starter
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Quote:
Originally Posted by Mike99 View Post

I connected my SPDIF header to an RCA jack which then sends digital audio to my AVR. I saw several articles about doing this & it works for me. Here's a discussion about the subject & some people say it's not correct to do that way. Just to clarify, some mobos have 3 pins for SPDIF. One is a +5V pin which would be needed in case you had to power the circuitry for an optical output. But no such circuit is needed for coax output. This particular thread is about the actual signal level on the SPDIF output pin.
http://www.avsforum.com/t/1422202/extract-audio-from-hdmi

Since that thread I have contacted my mobo manufacturer (ECS) & asked if the output signal was 0.5V or 5V TTL which would need to be converted to the proper 0.5V SPDIF voltage. They replied "The SPDIF pin carries the proper voltage. It does not need to be converted."

As mentioned in the link above, the only thing I ever came across about a 5V TTL signal was converting a 2-pin CD-ROM drive audio to SPDIF.

Your mobo may be different. But again there are several articles explaining how to simply attach an RCA jack to the header so I think the odds are on your side that the item you are getting will work.

Mike -

I didn't see your reply before composing my previous reply. But looking into the links and discussion it is very clear that there may be a problem if I try to do this and the internal pins are normal TTL voltage. I will have to find out from Gigabyte whether the voltage is for internal TTL at 5 v or external SPDIF at .5 v

My connector will take some time to get here. In the meantime I may just open the packaging on a $25 usb external sound card I bought and use that digital output to receiver instead. Hopefully there is no problem running the motherboard sound circuits to HDMI output and external sound card output to receiver simultaneously
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post #7 of 12 Old 01-28-2013, 07:06 PM
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From manual:
Quote:
SPDIF_O (S/PDIF Out Header)

This header supports digital S/PDIF Out and connects a S/PDIF digital audio cable (provided by expansion cards) for digital audio output from your motherboard to certain expansion cards like graphics cards and sound cards. For example, some graphics cards may require you to use a S/PDIF digital audio cable for digital audio output from your motherboard to your graphics card if you wish to connect an HDMI display to the graphics card and have digital audio output from the HDMI display at the same time. For information about connecting the S/PDIF digital audio cable, carefully read the manual for your expansion card.

Such graphics cards are only older GeForce 8xxx/9xxx cards (that lack HD audio controller of their own) and the above statement clearly says SPDIFO is 0.5V (no GeForce 8xxx/9xxx card accepts 5V).
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post #8 of 12 Old 01-28-2013, 07:37 PM - Thread Starter
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Quote:
Originally Posted by renethx View Post

From manual:
Such graphics cards are only older GeForce 8xxx/9xxx cards (that lack HD audio controller of their own) and the above statement clearly says SPDIFO is 0.5V (no GeForce 8xxx/9xxx card accepts 5V).

Thanks for that info which seems to confirm it is safe to use the direct connection considering that graphics cards do not accept TTL voltage level signals
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post #9 of 12 Old 01-28-2013, 07:55 PM
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Quote:
Originally Posted by RalphArch View Post


My connector will take some time to get here. In the meantime I may just open the packaging on a $25 usb external sound card I bought and use that digital output to receiver instead. Hopefully there is no problem running the motherboard sound circuits to HDMI output and external sound card output to receiver simultaneously

Your not going to be able to play the same source simultaneously with Windows 7

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post #10 of 12 Old 01-28-2013, 08:50 PM - Thread Starter
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Quote:
Originally Posted by Andy_Steb View Post

Your not going to be able to play the same source simultaneously with Windows 7

Bummer - maybe I'll just wait on the RCA jack and return the USB card unopened. No way I want to switch onboard audio on and off in bios or plug in usb sound card on occasions when I want to get DD or DTS (windows 8 btw but I can't imagine this part is different)
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post #11 of 12 Old 01-29-2013, 03:19 PM - Thread Starter
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Got the reply from Gigabyte:

Answer : Dear Customer,

I'm sorry, but you can not. The voltage is different and may damage your receiver.

Thank you for choosing Gigabyte products

________________________________
I guess I am SOL. I may first just try the usb sound card and see what limitations that brings. I dpn't want to fry the receiver

Perhaps a longer term solution involves replacing my onboard video and sound with a graphics card which will output sound over HDMI as well as provide a separate digital out to my receiver. Or instead upgrade my receiver to an HDMI model. On second thought maybe frying the receiver is not such a terrible idea

EDIT

On third thought I think I will just leave the computer as-is. The stereo out to receiver or TV speakers works for most viewing. If I really care about multi-channel for a show I will just join the beta DLNA program at SiliconDust and use my PS3 for playing these shows with the HDPrime. That has multichannel out to receiver already
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post #12 of 12 Old 01-30-2013, 08:18 PM - Thread Starter
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Got multichannel working on HD channels so I won't need to send SPDIF from motherboard to receiver and tempt fate which Gigabyte indicated could damage reciever.

The HDHomerun Prime beta firmware now allows me to stream subscribed HD channels directly to my tv via its DLNA server - and the Sampsung TV does return muti-channel to the receiver via its optical digital when this is received ethernet and it does play the HD stream fine via its DLNA client.

Another solution I was thinking about but didn't pursue was to get an HDMI switch which incorporated optical digital out of the selected source. These were a bit pricey and I didn't really need a switch with 4 inputs on the TV but it should have worked as well
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