danlavry wrote on Mon, 04 October 2004 00:45 |
Oh well, I am not the "cable expert of the universe", yet my basic EE knowledge, and that certainly includes careful reading of the "bible" on the subject: "Grounding and Shielding for instrumentation" by Ralph Morrison, plus what the Maxwell Equations (the 5 fundamental laws of electricity and magnetism) suggest otherwise. I quickly read the article you pointed out. I did not see any science in it, just a report about some specific experiment. I was not there to see what they did. So what do they suggest? Are they saying that the whole world is best to remove shields? Including Ma Bell with over 100 years experience?
In any case, they talked about a dynamic mic. It would be good to see what the specific setup was. Did they ground both ends of the shield (that can be a cause for problems).
|
Dan / Roland,
Dr Jahne's (stagetec) statements are quite true but they really
apply specifically to Nexus or a similarly engineered system.
Looking at the technical specs the IO's on Nexus are specced as
transformer isolated. This tells a big part of the story.
Some important issues are:
- Good transformers have very high common mode rejection and
that rejection extends to quite high frequencies.
- Good transformers have excellent RF (radio frequency)
rejection to 'protect' the following active stages.
- Stagetec appears to have a special IP with HUGE CMRR and very
low ground coupling capacitance. They mention up to 150dB CMRR
and 10pF ground coupling c which to me suggests further active
electronics supplementing the transformer. As an example, an
active common mode bootstrapping arrangement could give these
types of figures and could be made to extend well into RF range
if done correctly, there are many ways to do it.
So don't throw away your shielded cables just yet, unless you
are using stagetec equipment. The only exception I would
say is a decent OP dynamic mic into a HQ transformer input
mic pre might be worth experimenting with a single run of
twisted solid core CAT-5 and comparing to your fave shielded
pro cable for grins. But if you hear a difference don't tell
anyone as there should be none
Looking through their website and from feedback from
users about their products it appears Stagetec have some
pretty lateral thinkers on board.
Cheers,
Terry