On 1/12/2011 2:49 PM, dalej wrote:
> How would I cure a pin one problem in a particular piece of equipment. Would
> I look at the input XLR or TRS and put that pin one directly to ground or the
> chassis somewhere close to the receptacle?
Let's stop confusing things by using the word "ground" when we talk
about a connection to the chassis, or to circuit common. The key info
here is that common mode current, usually, but not always shield
current, needs a complete circuit (or an antenna). Our objective is to
provide a path that does NOT include circuit common, thus keeping it
outside of equipment.
Low frequency current usually finds a path to the earth, or to the power
system equipment ground (Green Wire), and NEC REQUIRES that the the
Green wire go to the chassis of equipment, and to the earth at panel
where power enters a building. Thus, a connection to the CHASSIS (or
more correctly, the SHIELDING ENCLOSURE) for all cable shields, return
of power cables, solves that problem. That is, all the common mode
current stays outside the box.
> What about the PCB? Some of those doggone connectors are mounted to PCB
> and not that easy to find the pin one connection. I like the theory, but
> implementation is another matter, in some cases.
YES, that's exactly the root CAUSE of most pin 1 problems, and because
of the way stuff is built, they are usually VERY difficult to fix
without rebuilding and rewiring equipment (and perhaps causing more
problems than you solve). In those situations, the best solution is
usually to simply kill the current on that cable, either with a common
mode choke, or by diverting the current to a lower impedance path.
Common mode chokes are most effective at RF, while diversion is usually
most effective at audio and power frequencies. Both are typically needed
on telephone equipment (including voice phones and DSL modems).
RF current is on those cables because they are acting as receiving
antennas. At high frequencies, no earth connection is needed to provide
a return path for that antenna current -- the local wiring within a ham
shack, or an A/V rig, or even the chassis of equipment may be large
enough as a fraction of a wavelength to be the other half of the antenna.
There is a lot of tutorial material on my website about this. The Power
Point on Ham Interfacing, and the Solving Problems In the Shack chapter
of the RFI tutorial, address the audio frequency solutions. The RFI
tutorial also includes lots of detail about how ferrite chokes work, and
how to use them to kill RFI coupled by pin 1 problems.
Two sets of people need to understand all of this, and the two must
react to it differently. Those of us who USE equipment must usually
work around those problems with band-aids like diversion and ferrite
chokes, and by making sure that our stations and systems are properly
bonded together, to the earth, and to the power system. Those who
DESIGN and BUILD equipment must BUILD IT DIFFERENTLY! In 1994, when the
pro audio world was first alerted to the Pin 1 Problem by Neil Muncy
(ex-W3WJE), a very good pro audio mfr called Rane acknowledged the pin 1
problems in their gear, and over a period of about five years made
running production changes to all of their more than 50 products to
eliminate them. When that transition was complete, they found that their
customer support costs, most of which addressed problems with hum,
buzz, and RFI, had dropped by 90%!
73, Jim Brown K9YC
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