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In Reply to: RE: Digital Cable Redeux posted by double28 on March 08, 2017 at 05:47:43
The important parameter is characteristic impedance matching. You need 75 ohm coaxial cable and can make your own from RG-59 coaxial cable. You can also get RCA connectors that are supposedly impedance matched to 75 ohm for use as terminations for the coaxial cable.
Regards Anthony
"Beauty is Truth, Truth Beauty.." Keats
Follow Ups:
That is below 96khz. You need to take into account the wave length of the signal. At 96khz or below, it's longer than the physical length of the connector. Therefore any impedance mis-match is irrelevant.
Case in point. During the dya of analog NTSC video, with a max bandwidth of about 6mhz, we used 50ohm BNC connectors as well as 50ohm patch bays.
Now when we satarted using digital video at 270mbs or 143mhz, The connector impedance became more critical. Yet you still could get away with 50ohm parts in many cases.
When we got into HDTV digital video at 1.5gbs or 745mhz, true 75ohm BNC connectors became mandatory. Now we are pushing 12gbs around in some cases for UHD/4K.
The reason BNC connectors were only 50ohm for mnay years is that the RF industry is typically 50ohms. And as it mattered there and now with broadcast video, the bulk of connectors manufactures were 50ohm.
The only reason true 75ohm connectors are wide spread today is because of digital video systems.
The issue of a 75 ohm characteristic impedance coaxial cable is valid, while the notion of a 75 ohm impedance matched rca connector is a misnomer. The proper function of an rca connector when used for a 75 ohm termination is to preserve the hopefully precision 75 ohm characteristic impedance geometry of a coaxial cable dielectric when terminated with any given rca connector. The most vital aspect is simply not to crush the foamed/cellular/solid dielectric (insulation) between the center conductor and the braided shield, which will do well to keep the 75 ohm characteristic impedance of the coaxial cable unaffected from end-to-end.
I was referring to specific connectors to accomodate RG-59 cables. To anyone unfamiliar with the requirements of a coaxial cable, they would be otherwise tempted to use RCAs normally for use with a typical "interconnect" cable which of course would be completely unsuitable for accommodating the solid centre conductor.
If you really want to get down to the nuts and bolts of the matter, an RCA is the least preferred connector for interfacing with 75 ohm coaxial cable!
Regards Anthony
"Beauty is Truth, Truth Beauty.." Keats
I know that theoretically the RG-59 is the best, but it is a big pain to switch over. Has anybody done it an felt the sonic benefits are worth the effort?
Dave
Hi Dave
I made my own from Belden quad shielded RG59. Very happy with the results. I've never been one for spending on the Big Name cables because I don't feel the prices charged are justified. I swapped over some of my equipment to BNC connectors, but I couldn't in all honesty say that I heard any signficant difference over my RCA/RG-59 combination. However, as my Big Ben and Grimm CC1 use AES/EBU (XLR) connectors, I have a real mixture of cables now.
The quality of the actual "connection" between the cable and connector (and of course to the socket) are arguably the most crucial connections to get right. The other important point is not to have a tight bending radius.
As to whether it is worth it? Well I didn't spend much in the first place (compared to buying the commercial name brand offerings of course!) and definitely heard an improvement over the cheap 75 ohm video cable I was using as an interim solution.
If you are happy with what you have, I wouldn't worry too much. I know that curiousity about what is "just around the corner" is what drives us to keep tweaking and upgrading, but I'll be honest, once I started doing my own digital recordings and realised that my digital system was about as good as I needed it to be in terms of realism and accuracy, my days of Chasing the "Audio Tweak" Dragon are gone and I prefer to focus on just enjoying the music.
Regards Anthony
"Beauty is Truth, Truth Beauty.." Keats
As i suspected, but the voice of experience is fare more valid than supposition. Thanks for the detailed answer!
Dave
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