Head-Fi.org › Forums › Misc.-Category Forums › DIY (Do-It-Yourself) Discussions › DIY Digital coax question
New Posts  All Forums:Forum Nav:

DIY Digital coax question

post #1 of 11
3/3/10 at 9:00pm
Thread Starter 
I will be making a coaxial digital cable to use with my Gamma-2 (RCA to RCA).

I know that with analog interconnects made with coax, you want to ground the shield on the source end only, so the destination plugs have only the center conductor connected.

Does this hold true with digital cables as well? I assume it would, but I forget the rationale behind this and want to be sure.
Reply
post #2 of 11
3/3/10 at 9:09pm
In single-ended gear, the ground is the signal return as well, you need BOTH conductors connected with any kind of RCA cable, or it doesn't work. If you're using balanced cable (but RCA plugs), then the signal and ground/return are the two internal wires, and the shield is connected on one end only to the signal return.

With coax digital, the main thing is, you need 75 Ohm coaxial cable.
Reply
post #3 of 11
3/3/10 at 11:25pm
Thread Starter 
Ahh, yes, that was more to do with balanced cables. I remember now. So in my case, I connect the shield on both ends.

I am using 75 ohm cable, from DH Labs. I don't know how much cable quality, and things like solid/stranded, or SPC/copper, matter for coax digital (I'm sure there are strong opinions ). But this stuff was only a little more than the typical Belden cable, so I sprung for it.
Reply
post #4 of 11
3/3/10 at 11:31pm
There will be those that will tell you that you are fine and there are those that will state that your biggest issue is the RCA connector. 75 Ohm cable to 35 Ohm RCA connector. I've never compared the results.
Reply
post #5 of 11
3/3/10 at 11:47pm
you do need to connect shield at both ends. the gamma uses transformers (pulse) so ground loop is not an issue.

video cable works fine and is 'rated' at 75ohms. that's what spdif was designed around (existing video cabling; was done on purpose).
Reply
post #6 of 11
3/4/10 at 12:21am
Thread Starter 
That brings something else up for me...I will be using my Emu 1212m as the transport, for its coax output.

The 1212m will output either standard spdif, or AES3 through its digital outputs. First question is, is there a reason to use one over the other? I know gamma2 supports both. Second question is, does AES3 require a different kind of cable - maybe the 110ohm digital I have seen for sale?
Reply
post #7 of 11
3/4/10 at 12:23am
'consumer' spdif is a half volt over unbalanced '75 ohm' coax (or just video coax).

'pro' spdif (aes) is 5v (or more) over balanced xlr-connected '110 ohm' cable.

the gamma1,2 is 'wanting' the half volt unbalanced coax stuff, not the xlr 'high voltage' aes stuff.
Reply
post #8 of 11
3/4/10 at 3:25am
Quote:
The 1212m will output either standard spdif, or AES3 through its digital outputs. First question is, is there a reason to use one over the other?
A couple.


S/PDIF - Wikipedia, the free encyclopedia

Quote:
I know gamma2 supports both. Second question is, does AES3 require a different kind of cable - maybe the 110ohm digital I have seen for sale?
No, that is for balanced AES/EBU "cables".
(if you can plug an RCA jack into it use 75 ohm cable, if not use 110 ohm cable)
Reply
post #9 of 11
3/4/10 at 4:50am
Thread Starter 
OK...I looked at the Wiki article. I see some differences - greater output level for AES unbalanced, full support for 24-bit, among other things.

Forgive me, but I'm not sure how it all applies to this context, using the y2. Can you give me a simplistic answer as to which would be better for me?
Reply
post #10 of 11
3/4/10 at 6:14am
γ2 uses the CS8416 S/PDIF receiver chip, which supports "standard" S/PDIF with AES3 extensions (for the full set of standards supported, see the γ2 website "Specifications" section as well as the CS8416 datasheet). You'll see that CS8416 supports both the "standard" S/PDIF and the AES/EBU unbalanced formats, and automatically adapts. Thus, γ2 would work either way, and there is no inherent benefit one way or another (with the exception that AES/EBU unbalanced supports a much longer cable). 24 bits is fully supported in either format, of course.
Reply
post #11 of 11
3/4/10 at 6:36am
Thread Starter 
Thanks amb, that clears that up.
Reply
New Posts  All Forums:Forum Nav:
  Return Home
Head-Fi.org › Forums › Misc.-Category Forums › DIY (Do-It-Yourself) Discussions › DIY Digital coax question