spdif toslink to rca mod - diyAudio
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Old 7th November 2011, 12:14 AM   #1
hameay is offline hameay  United Kingdom
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Default spdif toslink to rca mod

Hi. I have a Jetway ITX motherboard which I'm using as a music server. The motherboard has an onboard Realtek ALC662 chip and a toslink S/PDIF output on the rear panel. I'd like to use an RCA S/PDIF output instead to connect to my external DAC. So I'd like to mod the motherboard and add one. This is similar to some Airport Express mods I've read about. I'm pretty new to all this so would appreciate any advice!

My plan is to (carefully!) solder a wire to pin 48 (SPDIFO) of the ALC662 and run it to the attached circuit, which is from the ALC662 datasheet (p.71).

(1) Does this sound reasonable?

(2) Where should I take ground from in the circuit below? Pin 4 (DVSS - digital ground for core) on the ALC662, or another pin (there are 4 grounds on the ALC662 given on p.8 of the datasheet)? Or can I avoid soldering another wire to the ALC662 and use something else (the ITX case is probably a bad idea right...)?

(3) Do i need to disconnect the existing toslink output on the motherboard?

Cheers.

ALC662 datasheet: http://aspire1.ru/_fr/56/ALC662_DataShee.pdf
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Old 7th November 2011, 07:27 AM   #2
UV101 is offline UV101  England
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I'd pick up both spdif and gnd from the pins on the tos tx. There should be 3 pins, +Ve, gnd & spdif.
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Old 7th November 2011, 08:14 AM   #3
hameay is offline hameay  United Kingdom
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Quote:
Originally Posted by UV101 View Post
I'd pick up both spdif and gnd from the pins on the tos tx. There should be 3 pins, +Ve, gnd & spdif.
Thanks. Taking the output from the tos tx sounds more sensible (no soldering to the ALC662 directly).

Will it matter if I leave the tos tx connected up?
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Old 10th November 2011, 09:24 AM   #4
UV101 is offline UV101  England
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I've done it that way myself with both connected and it worked. If it the "best" way is possibly another question! If you were looking for the "most correct" way for most accurate transmission, I'd remove the tos tx and I'd poss use some filtering and an isolation transformer. Look at any CD player service manual at the spdif and tos out, they are sourced from the same pin but there will be some additional components related to the spdif section ;-)
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Old 11th November 2011, 11:49 PM   #5
hameay is offline hameay  United Kingdom
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I've soldered wires onto the spdif and gnd pins of the tos tx. I managed to work out which pin was the 5V (D2 in diagram below), so by a process of elimination the other two must be the spdif and gnd Only question now is which wire is connected to the gnd and which to the spdif... The tos tx is part of a sealed unit so inspection isn't going to help, and no datasheet online, only this diagram:

http://www.ude-corp.com/uploads/cust...0611211803.pdf

Any advice here?

I think I'll leave the tos tx wired in at the moment and see how things sound (I'm waiting for the final bits for the dac at the moment). The dac (a gamma1/2) has both optical + coax spdif inputs so I'll compare the two. If I'm not happy with the sound I'll make things more, as you say, "correct"
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Old 14th November 2011, 09:24 AM   #6
hameay is offline hameay  United Kingdom
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Just to follow up, the manufacturers of the tos tx unit got back to me with the pinouts - diagram attached.
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