Imo it´s important to remember that a traditional coax (rca) cable isn´t shielded in the audio frequency region, so it is questionable if it is the best solution in any case; it depends on the type of interference that actually is at work.
STP might be a better solution (as it is already for turntable pickup connections) especially if a diyer is able to optimize the shield connections at both ends.
Coax is shielded in the audio region. The near continuous conductor screens electric fields. The coaxial return current shields magnetic fields. Coax does not rely on skin effect to work; that just adds an extra current path for RF.
Shielded twisted pair works for turntable pickups because they are floating and so a pseudo-balanced connection can be used. Other unbalanced connections cannot take advantage of this.
Shielded twisted pair works for turntable pickups because they are floating and so a pseudo-balanced connection can be used. Other unbalanced connections cannot take advantage of this.
Coax provides no shield for the ground connector at audio frequencies though it does in the high frequency region (due to skin effect, and return current concentrating on the inside of the braid/foil whatever).
So, at audio frequencies capacitive coupled interference into the outer connector of the coax will _not_ be shielded that´s why i wrote it´d depend on the EMI mechanism at work.
You should consider my recommendation of STP in the context of my mentioning of diy possibilities to optimize the shield connections at both ends; and of course that will depend on the EMI mechanisms actually working too...
No microphone cable belongs more often to the "shielded twisted pair" category.
Usual coax is something like RG 58 or RG 59,means a center conductor surrounded by a dielectricum and and outer (foil/braid or even a combination of both) embracing the center conductor, covered by an overall isolator.
Does this have any advantage over coax in an unbalanced circuit where the shield is referenced to power supply 0V?
No, that is normally shielded twisted pair. As a mike is essentially floating you can use a pseudo-balanced or balanced connection.Stuey said:
The ground connection is grounded; it doesn't need a shield. The most it can do is feed interference current into the ground. Coax is used for video, which goes down to audio frequencies.Jakob2 said:
Use coax for unbalanced connections.
Use shielded twisted pair for pseudo-balanced connections into an unbalanced input.
Use shielded (or unshielded if you feel lucky) twisted pair for balanced connections.
Why do people want to use the wrong cable?
As you can tell from all the recent responses from all of those who know everything about cables, you are doing it all wrong with this idea and should perish the thought. Welcome to DIYAUDIO.
Nevertheless, you can do as you like and it won't cause the world to end.
Can´t give any recommendations, as Kimber seems to use nearly every (apart from twisted pair) combination, 3 wire and 4 wire braid and even a 6 wire braid, so it will be a matter of try and error. Capacitance per length will be higher in the versions with 4 and 6 wire braids, so please check if your output stages are able to drive it.
On paper there is magic at work, where it is sufficient to label something as "ground" to realize an infinite sink of zero impedance, but unfortunately we know that it isn´t in reality. "The most it can do...." part is nice, but that might already be enough to evoke unwanted effects.
Coax surely works, but is quite often not the optimal solution for unbalanced audio connections.
No. When I say 'ground' I mean voltage reference point; others may believe the myth of the infinite current sink.Jakob2 said:
Coax is the correct solution for unbalanced connections. If coax doesn't work then you need a proper balanced connection. If using the wrong cable works OK then you never had an interference problem to solve.
It doesn't have to be thankfully, all that matters is that there is minimal potential difference.
But in real existing audio gear we are not talking about "voltage reference points" at rca connectors. The "- lids" are usually connected to a voltage reference "area" via any kind of impedance.
So,it´s actually the other way round, if you don´t have a problem with a simple coax (of course one could opt for triax) then you most probably don´t have an interference problem to solve.
So,it´s actually the other way round, if you don´t have a problem with a simple coax (of course one could opt for triax) then you most probably don´t have an interference problem to solve.
I never said the voltage reference point is at the RCA connector. Generally it should not be there.
If coax fails due to capacitive coupling to the shield then shielded twisted pair will probably fail too, and for the same reason.
In any case, we are getting well away from the foolishness of braided cables - they can only work in the most benign situations.
If coax fails due to capacitive coupling to the shield then shielded twisted pair will probably fail too, and for the same reason.
In any case, we are getting well away from the foolishness of braided cables - they can only work in the most benign situations.
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Well, glad we have the foolishness of braided cables put to rest.
But nonetheless it's hard to know what to use for an interconnect. While I have used braided cables in the past, I try not to use them any more if I can. I now use a shielded cable from cd player to attenuator. It's probably twisted inside, but I really do not know or really care. There's not exactly a plethora of coax cables available, either commercially or for diy.
Here is one that I found from bluejeanscables, the LC-1. Stereo Cables at Blue Jeans Cable
What do you recommend Dave? After all you are the one most vociferous that only coax should be used. Surely you must have some examples of where one can go for them.
I recommend the cheapest coax you can find, provided that it has good copper coverage in the shield. The reason there are not many coax cables around is that a few decent designs cover all possible uses for coax. 75 ohm coax is 75 ohms coax. Differences are in things like RF attenuation (irrelevant for audio), power handling (irrelevant for audio), size (relevant) and flexibility (relevant). For short runs a lapped screen may be sufficient i.e. not even proper coax.
There is a lot of fine print that goes with the lack of shielding at audio frequencies.
Very quickly:
a] For magnetic field it's true, except that because the field affects both the shield and the center conductor, both have the same voltage (common mode) and cancel out at the input stage.
b] For the electric field it's incorrect.
Very quickly:
a] For magnetic field it's true, except that because the field affects both the shield and the center conductor, both have the same voltage (common mode) and cancel out at the input stage.
b] For the electric field it's incorrect.
You recommend using coax cable but cannot seem to recommend anything. Surely you can do better than that.
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