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I have an A/V system which takes two balanced audio inputs, two DC inputs (8.4v and 12v), and outputs HDMI and IEEE-1394.

We frequently plug and unplug the system. Each of those connectors is at a different physical location on the rig. It would be nice to plug and unplug a single cable.

I was thinking of cutting the ends off the existing cables (25 ft) and using a multi-pin circular connector, but I'm worried that using this type of connector will degrade the high-speed interfaces. I know another poster had no problems using other connectors for USB.

HDMI has a max pixel clock rate of 165MHz up through revision 1.2. IEEE-1394 uses a 98.304 Mbit/sec half duplex data transport (roughly 98Mhz per channel?).

Is the inductance and capacitance between pins of an HDMI cable assembly mostly a function of the cable itself, or do the connectors play a significant role?

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  • \$\begingroup\$ The clock for HDMI may be up to 165MHz, but the data lines will be 5x faster (so 825MHz+). For more recent standards that can be much higher. \$\endgroup\$ – Tom Carpenter Aug 18 '15 at 22:10
  • \$\begingroup\$ You say, "We frequently plug and unplug the system". The datasheet for the connector you reference lists: Durability: 250 matings and unmatings. Will that be enough over the lifetime of the equipment? \$\endgroup\$ – tcrosley Aug 18 '15 at 23:26
  • \$\begingroup\$ @tcrosley - Good catch, thanks! 250 might be cutting it a bit close. I'm also looking at this connector from AMP. That one looks like it's tested for 500 connections. \$\endgroup\$ – watkipet Aug 19 '15 at 16:05
  • \$\begingroup\$ I find it interesting that the "receptacle" has pins, and the "plug" has sockets. I guess its based on which side is screwed into the other. \$\endgroup\$ – tcrosley Aug 19 '15 at 16:20
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    \$\begingroup\$ @tcrosley - AMP sells both configurations (pins on the receptacle or pins on the plug). In my case, the plug is actually providing DC power to the rig (relatively low current). So I like having sockets on the plug (I wouldn't want something falling into the plug and bridging the pins). \$\endgroup\$ – watkipet Aug 19 '15 at 16:33
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High speed cables use shielding, twisted pairs and separation etc to mitigate intereference. Each standard has a maximum length that helps ensure that it can deal with exepected background noise over that distance. So, assuming that you are not using long cable runs, the connector you choose is a low loss type and you try and maintain as much of the original shielding/twists etc( eg do not expose 30cm of cable at your join) it will probably be ok. But until you make the connector you are probably not going to know.

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I have passed high-speed signals of various types through miniature circular connectors with little problem. I have used the Hirose HR30 series in particular.

Pay attention to how you assign the pins in the connector. Keep balanced pairs on physically adjacent pins, and don't skimp on ground connections.

As BenG says, pay attention to how you dress the wires when you assemble the connector, too. Be prepared to waste some cables in the experimentation.

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  • \$\begingroup\$ When you mentioned ground connections, were you thinking of making sure there's a low impedance path for return current, or separating adjacent lines with a ground to reduce crosstalk? \$\endgroup\$ – watkipet Aug 19 '15 at 15:33
  • \$\begingroup\$ All of the above, but mainly impedance. Crosstalk is more of a problem along the length of the cable itself than a problem in the connector. \$\endgroup\$ – Dave Tweed Aug 19 '15 at 15:48
  • \$\begingroup\$ Dave makes a really good point re balanced signal pairs, this is a very effective method of removing common(ie it affects both lines) noise. Also be aware that some cheap cable manufacturers will substitute copper wire, particularly on the "unused" pairs and that can make a huge difference to throughput. \$\endgroup\$ – BenG Aug 20 '15 at 19:38

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