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Old 13th December 2013, 11:03 PM   #1
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Default STP analog audio interconnect ex-Firewire

I am planning to build an analog audio interconnect, from a disused piece of firewire (6 to 4 pin) cable. This cable contains two STP (shielded twisted pairs) inside another (isolated) outer shield.

My question is what to do with the shields. Leave them unconnected at one or both ends, using just the inner twisted pairs for signal transmission? Are there advantages or disadvantages to connecting up the shields?

It's intended for line level, unbalanced analog audio signals.
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Old 14th December 2013, 01:16 AM   #2
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And you expect that somehow this will be as good an interconnect as a well chosen co-ax cable? And just how will you attach the connectors?
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Old 14th December 2013, 01:49 AM   #3
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I will attach the connectors with solder. Some people claim better quality with twisted-pair interconnects, rather than coax. But those people typically use unshielded twisted pair, hence my question.

If the goal is to decrease cable capacitance, then I suspect ignoring the shield is the way to go. But perhaps leaving the shield connected at one end only might be a good idea, for extra RF rejection (not that it's much of a problem at line level).

Would an *unconnected* braided shield still help to filter out RFI?

Last edited by fyzygy; 14th December 2013 at 02:05 AM.
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Old 15th December 2013, 05:44 AM   #4
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Update. I went ahead and made the lead, using the twisted pairs but ignoring the screen/shields. The lead is only 2 metres or so in length. I can only compare it - subjectively - with a generic interconnect almost twice as long. To my ears, no RFI issues with twisted pair as opposed to shielded cable. The firewire hack is noticeably brighter - impression of added high-end sparkle. But I will try and improve on these subjective listening tests, and report back if mistaken. Will try and do some objective comparisons. But so far, so good.
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Old 16th December 2013, 03:00 PM   #5
DF96 is offline DF96  England
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An unbalanced twisted pair will pick up some RF interference. This can add 'sparkle' to the sound. An unconnected screen is likely to increase this pickup, so if present the screen must be grounded unless you like some RF with your music.
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Old 17th December 2013, 10:22 PM   #6
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Thanks for the tip - I will try grounding the screen for comparison.
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