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Thread: 75ohm coax

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    I want to make my own cable for CDP -> DAC, I've ordered some 75ohm coax, but what RCA's can I use with it? or doesnt it matter? and do I still need to earth it like a standard analouge interconnect cable?
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    Post imported post

    Ideally you'd use 75 Ohms BNCs, because most phono connectors characteristic impedance varies all over the shop - there is no standard, so I doubt it matters much what you use - they're much of a crapness.

    Maybe Eichmann bullets?

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    i_should_coco wrote:
    Ideally you'd use 75 Ohms BNCs, because most phono connectors characteristic impedance varies all over the shop - there is no standard, so I doubt it matters much what you use - they're much of a crapness.

    Maybe Eichmann bullets?


    funny you should mention those, as I have a set of bullets lying around, I just thought I'd check before hand. I'll use them and see how it goes, if I wanted to use 75 ohm BNC's, is it best to solder or use crimp type connectors? and does it effect the ohm rating if you use BNC - RCA adaptors?

    Cheers again.
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    Post imported post

    Hi there,

    Give the bullets a shot - can't hurt! and yes, using adaptors will mess up the termination impedance.

    It annoys the fcuk out of me that manufacturers fit shitty phono connectors where they should use proper RF connectors, such as BNC. Maybe because they don't gold plate the sodding things.

    The cable manufacturers are no better - I doubt that more than a handful of the poncy audiophile cables are designed with the correct charteristic impedance.

    At the (RF) frequencies involved, impedance matching *is* important to minimise reflection which interfere with signal edges.

    Cheers,
    Pete

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    Post imported post

    Iv made several cables using pure silver solid cores for both + & - all the crap about being 75 ohm is not what it's cracked up to be Iv had many commercial cables and they simply cannot sound like my diy cables! they are 2 dimentional and shut in.

    Get some pure silver pair of wires and twist them together solder each to phonos check+ - is correct ideally Bullets as vastly superior to standard ones or use WBT next gen expensive but worth it for a decent cable like the Mithril I use also this has got it's own shield which I leave floating ie: unconnected.

    Sit back and enjoy 3D imaging like never before,both me and several mates Iv made cables for have been simply gobsmaked and the best bit it needn't cost more than £20 -£80 depending upon wire and plugs used.

    2 meters of silver wire should cost around £10 ebay etc and bullets £12 for a pair and you get free silver solder from the missing link simple to order too.

    Or buy 1 meter Mithril £40 and WBT next gens £40 and the wow factor will be even more so!

    No rocket science as we are leadto belive just fact that can be herd plain and simple.





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    Post imported post

    i_should_coco wrote:
    Ideally you'd use 75 Ohms BNCs, because most phono connectors characteristic impedance varies all over the shop - there is no standard, so I doubt it matters much what you use - they're much of a crapness.

    Maybe Eichmann bullets?
    I believe there is only one manufacturer making true 75ohm RCA's and that's Canare but only in their 'crimp' fit range, so not suitable for most DIYers.
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    hifinut wrote:
    Iv made several cables using pure silver solid cores for both + & - all the crap about being 75 ohm is not what it's cracked up to be Iv had many commercial cables and they simply cannot sound like my diy cables! they are 2 dimentional and shut in.

    Yes, impedance matching DOES matter. Just because it works when it's mis-terminated doesn't mean it won't work better when properly terminated.


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    I believe there is only one manufacturer making true 75ohm RCA's and that's Canare but only in their 'crimp' fit range
    ..and I'm suspicious about those. Characteristic impedance is set almost exclusively in coax cable and connectors by the ratio of conductor diameters. Since these are fixed for the RCA phono standard, a true 75ohm phono is impossible.

    Even if you managed it for the plug (with a locally-massaged speed-of-light perhaps) the socket wouldn't be!

    So - you've got what you've got, SPDIF via phono. Use a plug as good as you fancy paying for

  9. #9
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    felix wrote:
    I believe there is only one manufacturer making true 75ohm RCA's and that's Canare but only in their 'crimp' fit range
    ..and I'm suspicious about those. Characteristic impedance is set almost exclusively in coax cable and connectors by the ratio of conductor diameters. Since these are fixed for the RCA phono standard, a true 75ohm phono is impossible.

    Even if you managed it for the plug (with a locally-massaged speed-of-light perhaps) the socket wouldn't be!

    So - you've got what you've got, SPDIF via phono. Use a plug as good as you fancy paying for
    So does that also apply to BNC's from your perspective?
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    If you mean impedance skt:plug, then no; the BNC mating pin design is different from the way RCAs go together and keeps the diameters nearly constant. Good enough for 4Ghz anyway I am told*

    From a cost POV - definitely!

    *by a clever mate paid to worry about such things!

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    felix wrote:
    If you mean impedance skt:plug, then no; the BNC mating pin design is different from the way RCAs go together and keeps the diameters nearly constant. Good enough for 4Ghz anyway I am told*

    From a cost POV - definitely!

    *by a clever mate paid to worry about such things!
    And I'd also say that the best BNC's you can get (VFM) are also Canare, so I'd be happy with either. If you don't believe in cable differences then Belden or Canare coax and Canare plugs are probablythe best you can buy;)
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    i_should_coco wrote:
    hifinut wrote:
    Iv made several cables using pure silver solid cores for both + & - all the crap about being 75 ohm is not what it's cracked up to be Iv had many commercial cables and they simply cannot sound like my diy cables! they are 2 dimentional and shut in.

    Yes, impedance matching DOES matter. Just because it works when it's mis-terminated doesn't mean it won't work better when properly terminated.

    How are my cables mis terminated Im using WBT next gen phonos on my cable the only ones that advertise to be 75ohm's,also if you go onto the zerogain forum and read about digital cables thats where I got the idea from using 2 silver matched cores for both + & - by using a coax for the - it probably slows the signal down and has losses too some info was missing via several cables I tried on my 3 box cd front end it is crittical to cables and Iv removed grain and digital hash by trying things out.

    Simply put if you dont try you dont know what you are missing out on and given that most digital cables are only 0.5 or 1 meter signal transfer is very quick without problems,I do not wish to argue the ins and out's Im just telling a good diy recipe that works and can be tried for as little as £25 in fact if anybody wants to try out a cable Id happilysendyou one all it will cost is postage Iv got 2spare diy digitals a 0.5 & 0.6 PM me and pay postage you wont be disapointed .;)

    Id never have such superb sounding hifi if Id never tried it the Mithrill probably embarass £1000+ cables yet cost me peanuts in comparison.
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    Post imported post

    Hi Hifinut,

    Unfortuntely it's not just a case of the connector being 75 Ohm, to be a properly terminated transmission line, the cable must also have a characteristic impedance of 75 Ohms, not just the connectors. At the frequencies involved, the cable acts more like a waveguide than a conductor. Have a read up on transmission line theory to see what I mean.

    Now, I'm not saying that your cables don't sound fantastic, they may well do. However from an engineering point of view, the impedance mis-match will cause reflections along the transmission line, and this blurs signal edges increasing jitter and such.

    My point was really about manufacturers who have engineers that know about impedance matching and it's benefits, yet still persist in ignoring it by fitting phono connectors.

    Cheers,
    Pete


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    Post imported post

    Unfortunately the argument could even go on to say about what happens to the signal when it travels across the circuit board between components ie: cheap phono sockets most kit has etc have they been soldered properly etc.

    The best way to send digital signal is probably via glass optical not necessarily Toslink but the highend glass links some kit has then it does go at the speed of light and cannot get any rfi emi effecting the delicate signals.



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    Post imported post

    hifinut wrote:
    Unfortunately the argument could even go on to say about what happens to the signal when it travels across the circuit board between components ie: cheap phono sockets most kit has etc have they been soldered properly etc.
    Yes, indeed, and in mission critical, e.g.military applications, I expect it is accounted for, but then it get very expensive....


    The best way to send digital signal is probably via glass optical not necessarily Toslink but the highend glass links some kit has then it does go at the speed of light and cannot get any rfi emi effecting the delicate signals.
    That is one solution, but of course the process of converting to light and back is not without it's own set of compromises...


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    In my past life I was a CCTV Consultant and engineer. We use RG59 coax cable which is 75ohm. Use the crimp type BNC connectors as they are the easiest to use. All you need is a Hex shape crimp tool. You can also buy a coax wire stripper that custs all the cores to the correct lenths with one twist.

    you can get all the tools from any CCTV supplies company as they are the most used tools.

    A company I have used are Digital videos. They supply to the public and you can buy online. http://www.digitalvideos.co.ukThey sell the crimp tool for £18 and the BNC connectors for 24 pence each.

    I hope this was some help. PM me if you want.
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    The easiest BNC connector to try is the screw on type. All you do is strip the Coax down to the right lenths of core and shield then screw on the BNC. It may ne worth a try to see how you get on terminating cables.
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