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Old 28th May 2010, 10:13 PM   #101
infinia is offline infinia  United States
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Quote:
Originally Posted by Speedskater View Post
Somehow I suspect that if we examine the input circuits of several units, they will diverge quit a bit from a true 75 Ohm circuit
nahh
see apps here

consumer (RCA jack ) uses 75 ohm instead of 110
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Last edited by infinia; 28th May 2010 at 10:15 PM.
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Old 28th May 2010, 10:31 PM   #102
dmills is offline dmills  United Kingdom
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Quote:
Originally Posted by Speedskater View Post
From an old Belden note:
If you go by the 1/4-wave numbers the critical distance (after which the impedance is important to match) is:
44.1 kHz = 5.6448 MHz= 44 ft.
Not quite, 5.6448Mhz is the symbol rate, but we need a reasonable eye pattern to be able to recover the data (much less lock the clock generator up cleanly), still it seems likely that the critical distance is longer then most HIFI wiring (and definitely longer then any reasonable connector).

In point of fact, if you source terminate the line then most of the reflected energy will just be absorbed by the source termination, and the only effect of the mismatch will be slightly slower edges at the receiver or slight ISI (Unlikely to be critical given the relatively low data rate).

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Old 29th May 2010, 03:49 AM   #103
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BNC combination at both ends (that is 4 X BNC) works much better than 4 X RCA. In fact, 4X RCA was completely unpredictable and was changing characteristics (sound) with the tiniest little change in cable length…. Internal wiring (within the transport and DAC) should also be executed with coax cable.

I obtained the best results with 2.5m length of RG6 quad shield cable terminated at both ends with BNC connectors. Much better than anything else I've tried.

Another interesting thing: I use almost exclusive properly annealed pure silver ribbons as power cables, speaker cables and interconnects (and internal hook-up wire!) Sounds detailed and very fast - great for valves.... however, nothing matched RG6, BNC terminated, when it comes to S/PDIF.

It is even more important to properly couple S/PDIF to receiver chip, using adequate PCB layout and adequate circuit / components, but this has been discussed at lengths here as well as "over there"....

Boky
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Old 29th May 2010, 04:41 AM   #104
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Quote:
Originally Posted by Extreme_Boky View Post
BNC combination at both ends (that is 4 X BNC) works much better than 4 X RCA. In fact, 4X RCA was completely unpredictable and was changing characteristics (sound) with the tiniest little change in cable length…. Internal wiring (within the transport and DAC) should also be executed with coax cable.

I obtained the best results with 2.5m length of RG6 quad shield cable terminated at both ends with BNC connectors. Much better than anything else I've tried.

Another interesting thing: I use almost exclusive properly annealed pure silver ribbons as power cables, speaker cables and interconnects (and internal hook-up wire!) Sounds detailed and very fast - great for valves.... however, nothing matched RG6, BNC terminated, when it comes to S/PDIF.

It is even more important to properly couple S/PDIF to receiver chip, using adequate PCB layout and adequate circuit / components, but this has been discussed at lengths here as well as "over there"....

Boky
And just to toss in a little more silliness, BNC connectors used to be 50 ohm devices. This became an issue when standard definition serial digital video became common in the early 90's and the impedance mismatch with the 75 ohm cable messed up data recovery. I don't know if the 50 ohm connectors are still manufactured but I haven't seen a new one in 20 years in the video industry.

FWIW I spent the last 2 days at work chasing down an impedance mismatch causing data errors in a video router control system It was a 6 foot cable with 50 ohm BNCs and insufficient spring force on the grounds. Ringing like you wouldn't believe but a simple cable replacement and everything is good again.

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Old 29th May 2010, 07:58 AM   #105
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Originally Posted by Speedskater View Post
OK, so enlighten me. How much (or little) can a good listener hear? I don't want to know about that one special guy, that when the planets align can hear all sorts of things. I know that the answer is complex with lots of conditions to deal with.

I remember that old 0.5555Hz jitter sounding pretty nasty!
We (Tentlabs, Grimmaudio) can hear everything around a ps, especially below 10Hz.
We have a new theory about the audibility. It has nothing to do with distortion, but with zero crossing modulation of the signal.

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Old 29th May 2010, 08:31 AM   #106
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Originally Posted by stratus46 View Post
And just to toss in a little more silliness, BNC connectors used to be 50 ohm devices. This became an issue when standard definition serial digital video became common in the early 90's and the impedance mismatch with the 75 ohm cable messed up data recovery. I don't know if the 50 ohm connectors are still manufactured but I haven't seen a new one in 20 years in the video industry.

FWIW I spent the last 2 days at work chasing down an impedance mismatch causing data errors in a video router control system It was a 6 foot cable with 50 ohm BNCs and insufficient spring force on the grounds. Ringing like you wouldn't believe but a simple cable replacement and everything is good again.

Yeah, I think it is shear unpredictability of RCA connectors (they are really "nothing" in terms of impedance...) that makes them unusable for this particular application (S/PDIF), so even if you get RCA terminated good-quality coax cable that sounds reasonable on one particular transport / DAC combo, it will sound completely unpredictable with another transport / DAC combo...
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Old 29th May 2010, 12:05 PM   #107
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Hello Speedskater
Quote:
Originally Posted by Speedskater View Post
OK, so enlighten me. How much (or little) can a good listener hear? I don't want to know about that one special guy, that when the planets align can hear all sorts of things. I know that the answer is complex with lots of conditions to deal with.

I remember that old 0.5555Hz jitter sounding pretty nasty!
Me and everyone coming at home are able to listen difference between RCA and BNC plug. If you want to reach high audio quality level, you must optimize all your setup: audio equipment, acoustic, main power, vibration, and other parameters...
It is not an easy problem, today 99.99% of audio system are not optimized. Optimization consist to cancel all source of audio degradations.
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Old 29th May 2010, 12:30 PM   #108
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Let me speak about some test that me and some friends made on various audio systems. We test many S/PDIF audio cables. The worst of all were hand-made NON 75 ohm cable. Whatever improvement you can do on these cable, results steels poor (hard-core silver, out of price connector...)
All standard 75 ohm cable sounds better than non 75 ohm hand-made audio cable. I agree with you, for a same cable, full BNC gives better results than RCA connector (with or without BNC/RCA adaptor...).

We test some overpriced audiophile cables. I must admit that all these cables gave better results than standard cables. All these cable were RCA plugged. It seems that since impedance cable is 75 ohm, internal and mechanical characteristics, or other parameters, are more important than connector's impedance. Many test were made with Tenlabs CD Drive and Jundac DAC .
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Old 29th May 2010, 01:32 PM   #109
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Eric, very nice projects
For Jundac DAC, change those 50R BNC's for 75R BNC's.
If you are using CS8416, please beware of Schmitt triggers on input. They will screw your input signal. Use driver circuit between your input and input of CS8416

Example with Schmitt triggers OFF
Click the image to open in full size.

...and with Schmitt triggers ON
Click the image to open in full size.
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Old 29th May 2010, 03:20 PM   #110
Pano is offline Pano  United States
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Interesting graph, where was it taken?
And will a decent receiver chip really have trouble with that little leading bump? It's pretty small.
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