Re: Mackie 400F whine (postponed purchase thoughts)

Scott, I'm very much in the learning process on this bundle of issues.
But based on what I think I might understand so far, I have the
opposite impression from what you seem to be saying.

My take is: You've got audible interference, you're poking around and
listening to the results, and you find that the noise goes away when
you lift a particular AC safety ground. Bravo--you've found the likely
point of entry for interference in a cable shield.

But disconnecting any AC safety ground creates a serious safety hazard;
someone can get injured or killed (for real, not bullshit) by that
"solution." And noise current in cable shields is, as you say, the
order of the day in the modern world. If no further solutions were
available, we'd all have to go around creating safety hazards more and
more often as the world gets crazier with its use of RF devices.

So for an engineer, the next question has got to be: How is shield
current getting converted into audio-frequency signals inside the
equipment? And the answer is often some kind of pin 1 problem. Finding
and fixing that problem makes the equipment far less likely to turn
such current into anything audible. This can be done by using isolating
devices such as input transformers, Neutrik EMC-XLR cable connectors or
Shure A15RF in-line couplers--or better yet, by improving the internal
grounding of the equipment as time permits.

It would be ideal if the equipment manufacturers would catch on and
take care of this as part of their product design, and indeed some
manufacturers do. But I've waited and waited, and somehow all my 20-
and 30-year-old gear just doesn't seem to be updating itself. All the
old installed systems in the world aren't responding like that, either;
I wonder what's wrong.

--best regards

.

Relevant Pages

  • Ground fault clamp thingummy. Sorry, non-political post.
    ... I have some metal-cased equipment whose body should be nominally at ... it's possible that a fault (say in the cable shield) ... could cause the equipment housing to reach an expletive-inducing high ... It's not really a design query; I'm sure we could all come up with ...
    (sci.electronics.design)
  • Re: At what kind of voltage will a mains test screwdriver start to glow?
    ... metal casing of a SCART lead connector on several pieces of ... The whole idea of a safety ground ... on the power system is to NOT have voltage on the shield/chassis. ... Unplug equipment until the voltage ...
    (sci.electronics.repair)
  • Re: At what kind of voltage will a mains test screwdriver start to glow?
    ... on the power system is to NOT have voltage on the shield/chassis. ... Measuring to the power system safety ground may not help if that's the thing that's compromised. ... Unplug equipment until the voltage ...
    (sci.electronics.repair)
  • Re: Scoping a SMPS primary side...
    ... that is the whole reason to use an isolation ... can be easily hooked up to properly grounded test equipment without ... disconnecting the safety ground for any ... reason is a flagrant and dangerous violation. ...
    (sci.electronics.repair)
  • Re: Ribbon Mic picking up Radio Frequency Interference
    ... I think Scott was suggesting you should connect the cable shield to both pin1 ... If the equipment is poorly designed this may very likely result in low ... passively filtering the signal with the inductance caused by the ferrites. ...
    (rec.audio.pro)