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In Reply to: Re: I'm Not posted by Roland on April 02, 2002 at 07:04:57:
So here's how I have the Neutrik A2 set up:Generator impedance = 200 ohms, (No 150 ohm setting unfortunately)
Generator frequency = 40kHz (as high as it goes for this set!)
Measurement input impedance = 600 ohmsA quick try of a handful of standard values available to me right this minute gives a 2.4dB drop a 40kHz when I strap 27nF across the line. 27nF = 27,000pf which at 150pF per metre, is equivalent to 180 metres.
-At 150 ohms source impedance, the drop off would be lower still, so it definately seems to disagree with getting a -3dB point at 16,xxxHz with only 100 metres of cable...
As for personal use, there are a number of factors governing this kind of stuff. I have always used starquad-type cable for individual mic runs in noisy environments, -Bundling cables produces a de facto improvement in shielding, but sometimes it all gets a bit to big, so a good multipair snake is a better choice as soon as outside dimension becomes a limiting factor.
On the subject of digital cable, -I have a few hundred metres of it (Clark Wire & Cable part # 801 and Gotham GAC-2) here and I've been forced to use it in a pinch for analog connections... -it's about as microphonic as anything I've ever tried. -Now I realise that other people might make a decent 110-ohm digital cable which is softer than this stuff, and may well be a little less ill-suited, but trust me... you wouldn't want to use this for analog connections -ANYWHERE!!!
-If anyone has any other types of 110-ohm cable, I'd be interested to know if they can hear anything when they flick the cable with their fingernail...Technically yours,
Keith
Follow Ups:
...In fact the math using a more correct source impedance of 150 ohms gives a -3dB point at 67kHz using the starquad at 158pF per metre, and a -3dB point of 246kHz for the Belden. -Now that seems more like it!!!-Certainly, the lower the capacitance the better, but for short runs in hostile environments, the Starquad -or similar- always gets my vote. -We have an account with Clark, so I normally go with their 'mink-4' cable, which is also a quad.
Frequently overlooked in installations (in addition to the very valid point of spacing cables where possible) is the grounding scheme. -Sometimes you have to star ground with far-end shields lifted, sometimes this forms a nice little antenna-array, and you have to take some of the far-end shields to ground with a small capacitor... sometimes you have to connect both ends... sometimes you're connecting unbalanced sources to balanced inputs, sometimes it's the other way round... Some manufacturers (Like MCI!) used to make the decision for you by installing the shield capacitors on the unit!
-An expensive cable will do you no good at all if the grounding scheme isn't properly worked out... -In fact a friend of mine recently invited me over to hear his new home system. -It took me less than three seconds to tell him that the whole thing was 'out of phase'... -We checked the connections... everything looked good... -finally I got the trusty ol' fluke meter out of the car. -Turns out that one of his (rather expensive, hand-made audio-salon type) speaker cables had a polarity flip... -He'd been listening fairly happily to the system for some weeks... -I'll never trust an opinion from him again!!! ;-)
Technically yours,
Keith
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