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building a digital rca coax to mini cable.. questions - Page 3

post #31 of 41
6/20/11 at 9:50am
Thread Starter 

thanks.. I've never heard any rumors, but i also know nothing about digital cabling, or much about reflections in cables or anything like that.  I just know how to make a cable, and thats about it.

 

beyond interferance though.. as far as the music actually working.. its all or nothing right?

 

also.. if a cable has these specs, would that be considered negligible resistance, or at least "probably ok" for the cables i want to make? :

The ohm resistance is 0.085 ohms per foot of each inside conductor. The outside shield is 0.093 ohms per foot

 

btw i updated the OP to reflect the fact that I plan on making 2 cables - one mini to rca digital, and one mini to mini digital.

 

 


Edited by Br777 - 6/20/11 at 10:13am
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post #32 of 41
6/20/11 at 1:17pm

You're going to be just fine.  With toslink, you can 99% of the time get away with a cable that's not 75 ohm.  I wouldn't sweat it.

 

The rumors I'm speaking of are people talking about HDMI cables, and how a $3 cables to go will perform as well as a $30 ____ brand HDMI cable.  Will you see a picture, will you hear sound, will it pass edid?  yep.  Is it as accurate as a well made cable that follows appropriate standards, with proper shielding?  No.  But people will still flap their arms and yell that they are smarter because they bought a cheap cable.  Good for them.  A lot of this comes from the blind test someone did years ago, where they proved that a listener couldn't tell the difference between a set of expensive Monster speaker cables and a coat hanger, it was funny to be sure, but a lot of people have applied this logic to other cables that just don't make sense.

 

Sorry to be confusing about what I was saying, sometimes I get too bogged down in details to give a straight forward response.

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post #33 of 41
8/7/11 at 5:15pm
Thread Starter 

ok - more questions... say my cable is 2 feet or longer, and I want to do my best to make it 75ohm.

 

can you measure the overall resistance of a cable with multimeter.. probably right?

 

so if you can is the bottom line ideal to have it measure 75ohms?   do you just put one lead on one connector tip, and one on the other and test for 75ohms?

so lets say you get some 75ohm coax wire..but you get plain vanilla connectors.. not 75ohm.. how much is it really gonna throw it off?   if it does throw it off a bit could you just compensate with a higher resistance wire?

 

i dont know if it works this way but i'm curious.

 

thanks

 

 

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post #34 of 41
8/7/11 at 5:22pm

Ok, first of all, ignore all the wrong information above your post. The 75 Ohms we are talking about is characteristic impedance, not something you can readily measure. I've measured square waves through a 75 Ohm Canare cable with non-75 Ohm RCA plugs and there was only the slighest distortion of the square wave, far from enough to cause a problem with any DAC, let along signal loss.  The problems wont be anywhere near as bad as what is caused by Toslink connections and they work just fine. So as I suggested before, just use 75 Ohm cable and whatever connectors and don't worry about it.

 

Direct output of the device is in white. Cable output is in green.  Ignore the spurious distortion in the lines as I was using an unshielded measuring device.

 

75-Ohm-cable-with-RCA-plugs.png

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post #35 of 41
8/7/11 at 5:47pm
Thread Starter 
Quote:
Originally Posted by Currawong View Post

Ok, first of all, ignore all the wrong information above your post. The 75 Ohms we are talking about is characteristic impedance, not something you can readily measure. I've measured square waves through a 75 Ohm Canare cable with non-75 Ohm RCA plugs and there was only the slighest distortion of the square wave, far from enough to cause a problem with any DAC, let along signal loss.  The problems wont be anywhere near as bad as what is caused by Toslink connections and they work just fine. So as I suggested before, just use 75 Ohm cable and whatever connectors and don't worry about it.

 

Direct output of the device is in white. Cable output is in green.  Ignore the spurious distortion in the lines as I was using an unshielded measuring device.

 

 



 

nothing spells convincing like a good old fashioned chart!  thanks.. thats great news!

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post #36 of 41
8/7/11 at 6:16pm
Thread Starter 

ok new question.. what type of coax?

 

this kind?  if so -  the main center wire is the signal, but what do you solder to the ground?

 

or do you need 2 conductor coax? if so anyone know where you can find 75ohm 2 conductor coax as thin as possible?

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post #37 of 41
8/7/11 at 9:15pm

When i've wanted thin 75-ohm coax, i find the thinnest stuff just by dismantling a multi-coax video cable such as this one. You also get lots of colours to choose from :)

Now i've just linked to a product on the same site you mentioned, this isn't the same cable as i've used.

 


Edited by DingoSmuggler - 8/7/11 at 9:17pm
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post #38 of 41
8/8/11 at 4:13pm
Thread Starter 
Quote:
Originally Posted by Br777 View Post

ok new question.. what type of coax?

 

this kind?  if so -  the main center wire is the signal, but what do you solder to the ground?

 

or do you need 2 conductor coax? if so anyone know where you can find 75ohm 2 conductor coax as thin as possible?



anybody on this?  specifically how to solder the signal and ground if only one wire is present?

 

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post #39 of 41
8/8/11 at 9:23pm

signal => single conductor

ground => shield

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post #40 of 41
8/9/11 at 7:33pm
Quote:
Originally Posted by Currawong View Post

Ok, first of all, ignore all the wrong information above your post. 



Ouch?

 

Impedance of cables and connectors does matter, some signals will show issues more so than others.  Toslink, you could probably make the cable out of bread ties and it would work, HDSDI at 1080p + Embedded audio run at 100 meters, it better be 75 ohms all around.  Even then, cross your fingers and toes.

 

As I said, I went off on a tangent, but definitely not "all wrong".  Feel free to pm me if you want to argue about it, and avoid confusion due to mucky details.

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post #41 of 41
8/9/11 at 9:38pm
Thread Starter 

this just cant be simple can it?  frown.gif

 

I guess i'm gonna just have to make a few cables, see which one sounds best, and be blissfully ignorant if i have made something less than perfect. 

 

Given that I am going to need either rca to mini, or mini to mini, i dont believe it is poissible to find 75ohm connectors, especially since one of them will have to be 4 conductor trrs.

 

oh well..  it will be a fun experiment anyway.  Not to mention all of this cable business hinges on the fact that my JH3A will actually ship in this lifetime.

 

 

 

 

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