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diy rca interconnects

post #1 of 13
Thread Starter 
playing with the idea of building my own interconnects to fit better than one i have in place now. thinking of using rg-6 quad shield (probably belden) and digicon compression rca's. searching has lead me to believe that the carnare crimp style are the way to go, will cost me the tooling and dies to do it. how much better are the carnare vs the digicon rca ( http://www.yourbroadbandstore.com/pr...php?pid=716270 ).
post #2 of 13
Are these going to be for analog audio, or digital audio?
post #3 of 13
Thread Starter 
at first analog audio, then i make some for component video followed by digital audio.
post #4 of 13
OK, for analog audio, it doesn't make a pile of beans difference what you use as long as the cable is adequately shielded. The frequencies involved are too low for the cable to function as a transmission line at practical lengths. So, you don't need to worry about maintaining a characteristic impedance like 75 ohms.

For digital audio, or analog video, the connection is designed to function as a 75 ohm transmission line. Ideally, the cable and connectors should maintain this characteristic impedance their entire length. That means using 75 ohm coax, which RG6QS is an example, and connectors. Unfortunately, there is no such thing as a 75 ohm RCA connector. Has to do with geometry and dielectric constants. The best you can do is to use something that comes as close as possible, like Canare's "75 ohm" RCA connector. But frankly, impedance mismatch for the short distance of the connector is likely to have no effect whatsoever that you will be able to detect by listening or viewing.

For digital audio, or analog video, if the cable is less than a significant fraction of a wave length long, you can treat it just like the audio cable. Ever seen the cheap, short RGB/audio cables supplied with some devices? They work just fine.

RG6QS is not a good choice for any of these applications. It is designed for something else. And it is stiff and difficult to work with. A good choice might be something like a good RG59 with a stranded copper center conductor for flexibility (definitely not copper plated steel) and 95% copper braid. 100% foil shield in addition to the braid would be a step up. One of the miniature coaxes might be the best way to go. But it will be more difficult to find the connectors.
post #5 of 13

What Colm said. You really don’t want to use QS for this. In addition to not being terribly rack-friendly because it’s so stiff and gnarly, QS typically has a steel center core and shield, not copper.

RCAs are 25-ohm connectors, so it’s easy to see where the weak link in a digital or video connection is. On top of that, the input and output impedance of the video circuits in consumer products are not tightly controlled. So basically, any decent 75-ohm cable will fit the bill for consumer audio and video applications.

Since you’re already considering the Canare crimp-on route, there’s no reason not to use their recommended cables as well.

Wayne A. Pflughaupt

post #6 of 13
I'll second that (make it third that). Quad-shield is optimized for cable TV frequencies not audio (analog or digital) frequencies.

The impact of the RCA connector mis-match is smaller than the mis-match of the wiring inside the unit (in many cases). But neither is an issue.
post #7 of 13
For DIY, linear compression ends are a lot easier to deal with IMO. Simpler, and you can use the compression tool for all kinds of common ends.

I prefer hex-crimp ends in more professional applications, particularly temporary installations where cabled are being handled regularly and strained significantly. I have greater trust in the ruggedness of the connection, and also I like the boots that you can use at the back of crimp-on ends which also helps with strain relief.

But it's much more PITA to terminate the cable, and it's easy to forget to get all the parts of the connector on there in the right order (always forgetting the boot for instance, etc and the having to waste the connector...).

So I guess it kind of depends on whether you want to go all-out or not.

At least from an ease and quality of connection standpoint, the Canare RCAPs are amazing because of the little spring-contact type things in there.

I also second Wayne and Colm's advice.
post #8 of 13
Originally Posted by Speedskater View Post

The impact of the RCA connector mis-match is smaller than the mis-match of the wiring inside the unit (in many cases). But neither is an issue.

For a direct run I would tend to agree, but I would not at all agree if you are going through wallplates of barreling cables together. The reflections there can make a very significant and visible impact (on video) particularly with long runs if you use RCAs instead of BNCs for example (or if you're going to VGA or something). It's at least something to be aware of, I just don't want people to be entirely dismissive of an impedance mismatch, because it absolutely can become a problem, but it just depends on the situation/context. But otherwise, I would agree I wouldn't worry about the ends of the cable on a direct run so much because whether it's a Canare RCAP or another RCA end it's really not going to be an issue either way, let alone a difference of any significance between various RCA options. Point being: if the RCA connection actually IS the issue, picking another RCA is not going to fix it, you need to be using BNCs in the first place.
post #9 of 13
Good point. I only use RCA connectors where I have to, at the equipment. I use BNC connectors everywhere else for video and digital audio. Note that there are 50 ohm BNC connectors, and 75 ohm BNC connectors. You want the 75 ohm ones.
post #10 of 13
Thread Starter 
so bnc 75 ohm would be the way to go, however somewhere along the way manufactures decided to use rca style for transferring signal (at the consumer level anyways). video signals would be best done by using a 75 ohm cable (like maybe belden 1694a), then the problem arises as what connectors to use. canare rcap seems to be the best bet but what else could be used? canare seem to be the closest to 75 ohm connecter where as the bnc would be a true 75 ohm connector. i'm not doing any long runs all will be used behind the stand nothing probably longer the 4' or so.
post #11 of 13
The wavelength of the highest frequency component of a component video signal is something like 24'. So your cable is about 1/6 of that. Rule of thumb for significant fraction is 1/10. So, best to go with 75 ohm cable and RCA plugs that come as close as possible, like Canare. Might as well use the same thing for all of your cables, even if the digital audio and analog audio cables are less than a significant wavelength long just so you don't have to deal with two kinds of cable and two kinds of plugs.

Here are Belden suggestions for cable applications. 1694a should do just fine for you.
post #12 of 13
You can also go with Belden 1694f, which is more flexible than the 1694a. It's harder to find but alot easier to work with.
post #13 of 13
i need 3 posts to use URL. this is post 3
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