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RCA versus Coax , explain me that ....

Yasser 06

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While i was looking for a cheap way to switch between 2 coax someone suggested that i could use a RCA swith (my cables are super short).
Since i had a pair of "quality" rca cables (both are independant) i replaced the coax from my Pi hat to my DAC with a one this RCA.

It probably degraded the sound but i took no notice (i had no way to compare) , but then i fired the monumental "rider of the storm" which is in 192khz (not my deed this is what the Russian distribute) and it was mostly noise (you could still somewhat recognize the song) .

So it seems that rca can more or less carry low bandwidth digital signals (Genesis a trick of the tail in 96 was getting through) but totally failt at 192.

So digital cables do matter, now since a faulty digital signal is unusable cables for digital transmission may have a binary quality instead of a constinuous one. Either the signal goes thought and error correction reconstruct the initial signal or not. So situation is very different from the case of an analogue signal.

Since Coax was designed for Video which require way more bandwidth than audio, it is probably the case than any low grade coax can carry any reasonnable high definition audio (<= 192 khz, i have nothing beyond and don t plan to get any 784 // why not 778 // or 384 khz pcm).

Anyway more information would be welcome, rca work fine with 44khz and seems ok with 96khz but totally fail at 192khz.
 

Taddpole

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It is unclear whether you passed the audio through the switch box or just the cable
 
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Yasser 06

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It is unclear whether you passed the audio through the switch box or just the cable
I have no switch box yet, but i may/must get one since it s hard to find a DAC with 2 coax in.

I was just comparing (more exactly trying to test) a 40 euros BC accoustic EX222 (second hand with no remote) against a 400 euros class D (boxem little arthur) i had not listened to any 192khz track since i replaced the coax from my dac to my Pi-hat by a rca, but since i was remebering how superb is the intro of Ridders of the storm is, i pulled it in on MPD, and i got some extremely degraded noise. First i though that my DAC has gone faulty, but then i remmebered that i had been replacing my Coax with a RCA to see if it could work. The idea being that RCA switches are cheap and plenty while Coax ones (digital switches) are marginal products that are almost handcrafted and so they cost way more, i m not complaining about that cost, it is nice to have people proposing solutions and obviously they must make a living.
 

radix

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I use the Inday switchbox. It takes in 4x coax or optical and outputs 1x coax & optic. Works great. I've used at 192 kHz.

An old-style RCA line-level switch box will be hit-and-miss for digital. 192 kHz audio is about 12 Mbps square wave, which could be messed up by too much capacitance or noise if it loses shielding (it's only 0.6V I think).

Marc
 

sergeauckland

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I use a standard cheap audio switchbox for 24/48 and 16/44.1 digital, and it works fine with even any old bit of coax over domestic lengths of cable, as most coax is close enough (50-100 ohms) to 75 ohms for it not to matter. I certainly wouldn't expect that to be reliable for 24/192 where impedance matching will matter a lot more. If you have a 'scope, look at the eye pattern, and you'll see it pretty much closed up at the end of the cable without some attention to impedance matching.


S
 

raif71

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I have no switch box yet, but i may/must get one since it s hard to find a DAC with 2 coax in.

I was just comparing (more exactly trying to test) a 40 euros BC accoustic EX222 (second hand with no remote) against a 400 euros class D (boxem little arthur) i had not listened to any 192khz track since i replaced the coax from my dac to my Pi-hat by a rca, but since i was remebering how superb is the intro of Ridders of the storm is, i pulled it in on MPD, and i got some extremely degraded noise. First i though that my DAC has gone faulty, but then i remmebered that i had been replacing my Coax with a RCA to see if it could work. The idea being that RCA switches are cheap and plenty while Coax ones (digital switches) are marginal products that are almost handcrafted and so they cost way more, i m not complaining about that cost, it is nice to have people proposing solutions and obviously they must make a living.
index.php


The denafrips ares II has 2 coax as well as 2 optical in
 
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Yasser 06

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Yes but it cost 2000euros ;-)

Wish Chinifi would stop making products with low functionnality but good sound ...

I Would immediatly buy a 500 euros toppingsmllokjiegustrad with 2 spdif in 2 coax in and BT Transmission which is 100% more usefull than BT reception
 

raif71

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charleski

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While i was looking for a cheap way to switch between 2 coax someone suggested that i could use a RCA swith (my cables are super short).
Since i had a pair of "quality" rca cables (both are independant) i replaced the coax from my Pi hat to my DAC with a one this RCA.

It probably degraded the sound but i took no notice (i had no way to compare) , but then i fired the monumental "rider of the storm" which is in 192khz (not my deed this is what the Russian distribute) and it was mostly noise (you could still somewhat recognize the song) .

So it seems that rca can more or less carry low bandwidth digital signals (Genesis a trick of the tail in 96 was getting through) but totally failt at 192.

So digital cables do matter, now since a faulty digital signal is unusable cables for digital transmission may have a binary quality instead of a constinuous one. Either the signal goes thought and error correction reconstruct the initial signal or not. So situation is very different from the case of an analogue signal.

Since Coax was designed for Video which require way more bandwidth than audio, it is probably the case than any low grade coax can carry any reasonnable high definition audio (<= 192 khz, i have nothing beyond and don t plan to get any 784 // why not 778 // or 384 khz pcm).

Anyway more information would be welcome, rca work fine with 44khz and seems ok with 96khz but totally fail at 192khz.
S/PDIF over coax should use a cable with a 75ohm impedance. This is pretty standard video cabling and you can find cheap cables that will work perfectly fine. You can get away with using other sorts of cable (like twisted pair) when running short lengths and at the lower sampling rates. But when you get to higher data rates the signal reflections from impedance mismatching can degrade things so the receiver is unable to establish a solid lock on the data rate.
 
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Yasser 06

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S/PDIF over coax should use a cable with a 75ohm impedance. This is pretty standard video cabling and you can find cheap cables that will work perfectly fine. You can get away with using other sorts of cable (like twisted pair) when running short lengths and at the lower sampling rates. But when you get to higher data rates the signal reflections from impedance mismatching can degrade things so the receiver is unable to establish a solid lock on the data rate.
I assume that the lineic impedance is close enough to zero. Similarly, the copper cables in your house do have a resistance oer meter but low enough, but everyone know that with high amperage low section cables can heat, that s why house often have 2-3 different set of connection for law amperage, medum and high.

So if the impedance of the wireis to be neglected then actual impedance of the cable is the one of the connector pair ?

I don t see how it could be otherwise since then cables could be too short or too long.

Anyway PCM at 192Kkz with probably 24 bits could not pass at all into a RCA cable.
 

LTig

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I assume that the lineic impedance is close enough to zero. Similarly, the copper cables in your house do have a resistance oer meter but low enough, but everyone know that with high amperage low section cables can heat, that s why house often have 2-3 different set of connection for law amperage, medum and high.

So if the impedance of the wireis to be neglected then actual impedance of the cable is the one of the connector pair ?

I don t see how it could be otherwise since then cables could be too short or too long.

Anyway PCM at 192Kkz with probably 24 bits could not pass at all into a RCA cable.
The resistance of a cable at DC is not its impedance at high frequencies (MHZ and GHz). For SPDIF Coax you must use a cable with 75 Ohm impedance. Any shielded RF cable for satellite TV suffices. I tested RG59 cable at 44/16 with 16 m length to work fine. I'm sure with approximately 4 to 6 times the bandwidth a cable of 2 m length works fine for 192/24.
 

charleski

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I assume that the lineic impedance is close enough to zero. Similarly, the copper cables in your house do have a resistance oer meter but low enough, but everyone know that with high amperage low section cables can heat, that s why house often have 2-3 different set of connection for law amperage, medum and high.

So if the impedance of the wireis to be neglected then actual impedance of the cable is the one of the connector pair ?

I don t see how it could be otherwise since then cables could be too short or too long.

Anyway PCM at 192Kkz with probably 24 bits could not pass at all into a RCA cable.

Any cable will have a reactive impedance between signal and ground. At high frequencies this becomes significant and will affect the transfer characteristic. Reflection happens when the signal encounters a boundary between two different impedances, and this can cause degradation.
 

wwenze

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Note that your old yellow RCA composite video cable, while you are right in saying video has way higher bandwidth than audio, you forgot that we can often see signal degradation and it still worked with analog signals. With digital signals, signal degradation means noise and nothing else left.

BTW you should see how some computers and even consumer audio devices connect their SPDIF RCA connector at the rear panel to the motherboard. You know those cables used for power switch and HDD LED? Yes, the same kind of cable.

RCA itself isn't a very good 75-ohm connector to begin with, that's why the most you see them used with component video. RGB connectors are BNC as are satellite.
 

Chrispy

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So use an appropriate cable.....good grief so much anxiety over a simple cable.
 
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Yasser 06

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Note that your old yellow RCA composite video cable, while you are right in saying video has way higher bandwidth than audio, you forgot that we can often see signal degradation and it still worked with analog signals. With digital signals, signal degradation means noise and nothing else left.

BTW you should see how some computers and even consumer audio devices connect their SPDIF RCA connector at the rear panel to the motherboard. You know those cables used for power switch and HDD LED? Yes, the same kind of cable.

RCA itself isn't a very good 75-ohm connector to begin with, that's why the most you see them used with component video. RGB connectors are BNC as are satellite.
It is what i wrote, and so a bad digital cable is very easy to detect, you simply cannot use it.

In conclusion RCA cable can be used for coaxial connection as long as you use bandwidth inferior (or equal) to the one needed for a 96x24bit PCM. 192 simply does not pass through.

And so rca switches won t work, they may stop working even before since the switch is likely to add impedance.
 

antennaguru

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I believe you have asked about switching between SPDIF type signals on coaxial cable - 2 sources and 1 output. If I understand this correctly I would just use 75 ohm coaxial cable (RG-6) with F-Type connectors at the switch end, into a CATV 2:1 F connector switch. These are cheap since they are widely used for TV and Cable connections, and they maintain a nice 75 ohm impedance.


Screen Shot 2021-09-26 at 1.31.32 PM.png



 
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Yasser 06

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I believe you have asked about switching between SPDIF type signals on coaxial cable - 2 sources and 1 output. If I understand this correctly I would just use 75 ohm coaxial cable (RG-6) with F-Type connectors at the switch end, into a CATV 2:1 F connector switch. These are cheap since they are widely used for TV and Cable connections, and they maintain a nice 75 ohm impedance.


View attachment 155706


So i just need to cut my rca terminal off the coax cable and replace it by an antenna one ?
 

SIY

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So i just need to cut my rca terminal off the coax cable and replace it by an antenna one ?
Opposite. A 75 ohm cable is what you need. The connector type is far less important.
 
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