I want to make a new cable for AKG K712 which has a trs to 3-pin mini XLR. I’ve noticed that typical trs, like headphone extensions, use 2-conductor cable with the shield acting as 3rd conductor (ground in this case.) I’ve also noticed people using 4-core microphone cable.
Using a shield as the ground would result in a different resistance/impedance/capacitance than the positive signal wires. Doesn’t that matter?
Initially I didn’t like the idea because grounding a shield at both ends introduces a ground loop, but I guess in this application there isn’t a second ground path, but you’re still intentionally making an antenna and using it as part of the ac signal path.
Quad core is meant for balanced cable situations - two + and two - wound together so that noise is symmetrical between + and - and therefore can be better handled by balancing. This doesn’t seem to make sense for 2-channel headphones. You could use the two pairs as R+L but then you lose the claimed benefit Of low noise. If used for 2-channel with common ground, you’d end up with ground loops. More interestingly it seems like more room for jitter (time based problems) since partial signals could arrive at different times/levels if the paths are not identical.
However it’s very difficult to find 3 conductor shielded cable in the proper diameters for headphones.
Mogami’s headphone extension is really a balanced mono extension. Hosa’s headphone extension is 2-core with shield as the ground, and they even tell you the shield is less oxygen free than the cores. But audio is AC so why does that make sense?
« Last Edit: July 27, 2020, 11:26:01 AM by Joe Garfield »
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