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Old 4th May 2006, 07:51 PM   #1
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Default SPDIF Audio Cable

Running a length (20') of RG-6/U cable from PC to receiver. Added RCA adapters to both ends. Most "experts" say that RCA ends are not 75 ohm compliant. Why does everything use them then. What effects am I going to experience with my setup. Should I mod receiver input and motherboard output to something else (BNC).
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Old 4th May 2006, 08:37 PM   #2
wa2ise is offline wa2ise  United States
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I wouldn't worry about it. The impedance mismatch is too small, at the frequencies we are working at, to be of significance. Besides, there's also some impedance mismatches in the boxes' internal wiring around the receive and transmit SPDIF circuits. And as SPDIF is a 75 ohm impedance system, any decent video cable will work fine.

Anyway, with digital signals, if it works reasonably well it works quite well. Another way to say this is that a bad cable will fail quite obviously.
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Old 4th May 2006, 11:57 PM   #3
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Anyone who believes the above post is strongly encouraged to use the forum search feature, and look for my many posts on the subject.

Especially the $500 TDR challenge.

Jocko

P.S. Bring your money!
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Old 5th May 2006, 12:10 AM   #4
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Default Re: SPDIF Audio Cable

Quote:
Originally posted by trunkmonkey
Running a length (20') of RG-6/U cable from PC to receiver. Added RCA adapters to both ends. Most "experts" say that RCA ends are not 75 ohm compliant. Why does everything use them then. What effects am I going to experience with my setup. Should I mod receiver input and motherboard output to something else (BNC).
The difference will be similar to comparing original CD to its CDR copy: you may notice it, but not neccessarily.
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Old 5th May 2006, 12:55 AM   #5
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Jocko
Don't you think sophisticated reclocking makes DAC free from jitter induced by reflections or dispersion?
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Old 5th May 2006, 02:08 AM   #6
phn is offline phn  Sweden
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"If the use of an exotic cable makes a DAC sound better, then the DAC is not performing adequately and should be repaired or redesigned." --John Watkinson, Resolution magazine.

I do believe Jocko is right about the RCAs, though.
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Old 5th May 2006, 06:35 AM   #7
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You could extend that to any cable that makes your D/A box sound different indictes it needs fixin'. Or at least some serious tweaking.

When you get all the reflections down to almost zilch (and that means on both ends), you should not be able to detect a difference.

As for "sophisticated reclocking", I assume you are refering to an ASRC or a secondary PLL.

The less reflections, the less hard the PLL will have to work. (Mind you, an ASRC acts as a digitally implemented secondary PLL. Some like them, some hate them. Another story for another time.)

So, let us take the secondary PLL for the sake of discussion. Hard for an average DIYer to design. Easy to buy and install if you get one from one of our resisdent clockmongers. They just cost $$$$$$$$.

Compare the cost of it to BNCs, a linear input stage, and a decent driver. Not hard to design or build. And much less expensive. You are going to have to build those anyway, regardless if they are done properly or not.

Yep, some added expense if you mod your gear. This is DIY........kvetching about minor added costs is verbotten.

OK, but back to your question:

Yes, when you implement one of those, and one could make a strong case for doing so, the differences are hard to pick out.

In either case, there is little excuse for not doing it the right way. Phred will insist he can make an RCA connector scheme that compensates for those anomalies, but that is Phred. Without a TDR, your chances of doing so are damn near zero.

Again, I have written about this more times than I can remember. Not only here, but on 2 other forums. The search engine is your friend...........

Jocko
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Old 5th May 2006, 01:26 PM   #8
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Jocko
What would you suggest be built as per original post. I imagine there are a lot of people now storing AV on their PC and connecting to amps/receivers. PC's are probably nowhere close to the audio gear.

Quote:
Again, I have written about this more times than I can remember. Not only here, but on 2 other forums. The search engine is your friend...........
I have done a lot of searches - just looking for a plain jane answer

Also searched and found this Canare plug
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Old 5th May 2006, 01:48 PM   #9
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sorry - here is the canare link

http://www.canare.com/index.cfm?obje...A54F63C6A9870D
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Old 5th May 2006, 02:16 PM   #10
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Its unlikely the RCA socket or the PCB tracks are 75ohm.

The likes of the canare 75ohm RCA are just there to give people the warm fuzzy feeling that everything is perfect and to add cost to premade cables. (me? cynical? never!)

You will never see an RCA used for video or digital signals on pro or broadcast equipment, its pretty much all BNC. Certainly we use RCAs for audio and nothing else.
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