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Old 15th December 2003, 10:24 AM   #1
dkxdn is offline dkxdn  Denmark
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Default Cable termination

Hi

I have a CD player - Teac VRDS 10 with a digital coax output - impedance = 75 ohm.
Then I want to connected it to a pro gear Behringer DCX2496 that has an input impedance = 110 ohm
Could that be a problem - I use a 75 ohm cable ?
Should it be terminated and how ?
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Old 15th December 2003, 10:56 AM   #2
UrSv is offline UrSv  Sweden
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Seems you have consumer S/PDIF 75 Ohm and the Behringer input you refer to is AES/EBU 110 Ohm. They do not mix AFAIK. The unit also has S/PDIF in but optical. Maybe that's an option from your TEAC?
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Old 15th December 2003, 11:01 AM   #3
UrSv is offline UrSv  Sweden
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...but if I'm not completely lost you may be able to get help from Guido Tent here on the forum...
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Old 15th December 2003, 11:06 AM   #4
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The consumer signal is much weaker, that's that big problem and if you have short cables the impedance difference isn't a major problem (reflexions).

Why don't you test? If it works, it works, very "digital".
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Old 15th December 2003, 11:39 AM   #5
dkxdn is offline dkxdn  Denmark
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I have try it and it works but the DCX2496 has a level indicator that very offen goes up in the red so I thougth there could be something wrong - Termination ???
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Old 15th December 2003, 02:40 PM   #6
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Quote:
Originally posted by dkxdn
I have try it and it works but the DCX2496 has a level indicator that very offen goes up in the red so I thougth there could be something wrong - Termination ???

Hi,

Termination will attenuate the signal even further. You'll need to actually convert from SPDIF to AES. This may help:

http://www.epanorama.net/links/audiodigital.html#spdif

regards
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Old 15th December 2003, 02:43 PM   #7
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Default Oh, brother.......

Quote:
......and if you have short cables the impedance difference isn't a major problem (reflexions).
You don't want to get me started on this, P-A.

Will it work?

Yes.

Will it sound good?

Depends on your expectations.

Jocko
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Old 15th December 2003, 03:22 PM   #8
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Quote:
Originally posted by dkxdn
I have try it and it works but the DCX2496 has a level indicator that very offen goes up in the red so I thougth there could be something wrong - Termination ???
The normal signal level from a consumer signal is much lower than a professional.
1 Vpp vs several volts.

As Jocko says, if you are satisfied, don't do anything. It sounds like crap => get a converter (transformer).
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Old 15th December 2003, 04:33 PM   #9
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Quote:
Originally posted by peranders
The consumer signal is much weaker, that's that big problem and if you have short cables the impedance difference isn't a major problem (reflexions).

Why don't you test? If it works, it works, very "digital".
Sorry Per-Anders,
But I get the giggles from your post. The cable termination issue is explained in Horowitz page 879 a.f. in my edition: Transmission Lines, Chapter 13.09, stating that a transmission line should be properly terminated at both ends.
Looking forward to your 3000th post. I really envy you.
This forum should have a box obligatory to have checked before posting "Have you searched Horowitz?" instead of "have you searched?" for technical issues.
Postscript: I am a bloody chemist but you are an EE. To my ears your post sounds like pouring water into concentrated sulfuric acid or trying to extinguish a petrol fire with water. Warning don't try to repeat these silly experiments!!!
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Old 15th December 2003, 05:59 PM   #10
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I say that digital signal are the same as for instance analog video signals. If you have reflexions which don't are near the logic threshold, the problems aren't huge. Some ringing or extra steps (due to reflexions) won't be a big problem.

I think we should ask dkxdn what he thinks about the sound coming out of his box. Does it sound horrible or does it sound nice? If he thinks it sounds not too bad I'll guess the problem isn't so big after all. But it gets more important the longer the cable is. In this case we have only missmatch in one end of the cable.
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