[th0m]

I'm planning on soldering a separate RCA socket to my sound card (ESI Juli@). It's a quite common mod, because you no longer need to use the horrible breakout cable. Three good examples can be seen here:
 
http://s.lowyat.net/uploads//attach-14/post-24914-1252965665.jpg
http://www.phasure.com/index.php?action=dlattach;topic=1191.0;attach=1649;image
http://usr.audioasylum.com/images/0/2901/IMG_2367_28Large29.JPG
 
What I don't exactly understand is the polarity. In the first photo, the signal conductor is soldered to what's supposed to be the negative spdif output, with the shield soldered to +. In the two other examples, it's done the opposite way. So, apparently it doesn't matter? Why then solder the shield at all, since in this case no ground is involved? I'm confused...

 

[MisterX]

Polarity doesn't matter but it does have to be grounded.  
 
See the wikipedia article about biphase mark code modulation for details.
http://en.wikipedia.org/wiki/Biphase_mark_code

 

[th0m]

Well, I didn't understand much of the wiki article, but I guess I can solder either way then, and it will still work?

 
Going by this thread, neither + nor - connects to the ground anyway, so I still don't understand why the shield would need to be soldered at all, but as long as it works out, then I'm not really that bothered...

 

[th0m]

Ehm ok, so... I did this mod a couple of weeks ago, but it didn't quite work out the way I'd hoped.

It worked alright at first, but I noticed there was a crackling noise whenever I just tugged or jiggled the attached cable a bit, and when I tried to play files at higher sample rates, everything turned silent. Then after a while, there was no sound at all, even when going back to the break-out cable. I assume the card was fried somehow.
 
I managed to get a new card faily cheap, so I'm not that mad about it, but I'd really like to know why that happened, in case I make a new attempt.
 
What I'm wondering is this; was I supposed to have isolated the RCA socket from the case? The way I did it, I placed the grounding-ring-thingy of the socket (to which I then soldered the negative signal) against the backpanel of the sound card, which I'm thinking might have been wrong? In the pics I've seen, they have always used connectors which have been completely isolated, like in this example.

 

[civilmonkey]

Quote:

.... I noticed there was a crackling noise whenever I just tugged or jiggled the attached cable a bit, and when I tried to play files at higher sample rates, everything turned silent. Then after a while, there was no sound at all, even when going back to the break-out cable. I assume the card was fried somehow.
 

 
Crackling can be a loose connection.  So, just a guess, but if it crackled and made noise when the cable was moved the solder joints may not have been up to snuff.  When you say after a while it just stop working maybe the wire came loose at the solderered connection and shorted something on the card.  Maybe not, maybe pictures would help.  One thing for sure, you don't want moving the cable to move the wires soldered to the PCB.  After a while, the wires are guaranteed to break at the joint.  In that picture you linked, you can see how the jack is secured to the metal of the PCI card, so moving the jack doesn't really move the wires at the soldered connection.

 

[th0m]

Didn't take any pics and I've thrown the card away, but the joints were rock solid as far as I could see.
 
Like I said, since there isn't any ground connection in this case, only + and -, I'm thinking I was supposed to have isolated the socket from the case? I used this socket and assembled it in the same order, with the PCI backpanel and loop between the isolators, and as a result connecting the loop to the computer chassis, which I now think was wrong since in this case the loop will be used as a a signal conductor, not as a ground connector.

 

[qusp]

yes it was meant to be isolated, you defeated the transformer isolation by shorting the - output directly back to shield/chassis ground and probably indirectly every other ground and although this would not have been directly connected back to the card, it would have reflected the impedance and any ground currents back, hard to say exactly how this would effect the situation, but clearly not well. 
 
just a note, the whole reason that spdif transformer is there (the device you connected to) is to isolate the output ground and match impedance of the transmission line. transformers do not have a ground winding as such (sometimes shield, or center tap but we wont go there) as they have an AC output, thats why you didnt see any ground marking, just a negative pole marking. but as far as the device you were connecrting to was concerned you were connecting ground. is that ok? as you also shorted it to chassis ground

 

[th0m]

Thank you, very helpful answer and pretty much what I thought myself. My DAC is fine (thank god).
 
I'll probably try again, and do it correctly this time.

 

[qusp]

no problem glad to help, always best to use isolated jacks, they dont cost more, well at least not significantly more. good luck and dont forget to post the successful mod if you do it, always good to see these sort of threads with a working solution also posted. plus the juli isnt all that well covered here except as an i2s transport, which is actually what i would recommend you do if you can find the i2s input on your dac. afaik the juli@ actually has i2s output on one of the headers?. make sure thats correct though as its a direct connection, no transformers to isolate there.

 

[th0m]

Yes, apparently the 20-pin header provides i2s output, but having to mod my DAC for i2s input goes way over my DIY skills, so I probably won't go that way just yet.
 
btw, is there any advantages to using a BNC socket instead of an RCA on the card? I mean, I would still need to use a BNC-to-RCA-cable, so I'm guessing it shouldn't matter?