On Wed, 28 Apr 2010 07:54:19 +0000 (GMT), QUENTIN COLLIER wrote:
>Sorry to be a pain guys, but as someone who has recently joined this list,
can you please explain what the "pin 1 problem" is ?
It is the improper connection of the shields of external cables where they
enter the rig. The only proper connection is the CHASSIS. Most rigs connect
them to the circuit board on insulated connectors that are insulated from
the chassis. This causes any current flowing on the cable shield to flow on
"ground" or "earth" busses, which then couples that current (noise, hum,
buzz, RF) into the rig, where it is amplified and/or detected.
This defect was named "the pin 1 problem" because it was described in a
reasearch paper presented by Neil Muncy, ex-W3WJE, to the Audio Engineering
Society in 1994, and subsequently published in the Journal of the AES in
June 1995. Largely as a result of that work, Neil was elected a Fellow of
the AES. The connector most used for pro audio is an XLR, and the
designated shield contact is pin 1. I'm told that the guy who first called
it "the pin 1 problem" was Berhard Weingartner, the founder and president
of Neutrik, the excellent connector mfr based in Lichtenstein, who was an
active member of the Standards Committee at that time. He has since
retired, but both management and engineering of that company are still
quite active in AES Standards work.
In some bar conversation at technical meetings, Neil said that "most RFI is
coupled by pin 1 problems." Between 2003 and 2005, I did some research that
proved him entirely correct. My work is also published as several AES
papers. My papers, as well as several tutorials on RFI and other topics of
interest to hams, are on my website.
http://audiosystemsgroup.com/publish.htm
Our work led to several new AES Standards on EMC -- AES48, AES54-1, AES54-
2, and AES54-3. They can be purchased from the AES website.
It's quite easy for cable shields to carry RF currents if they are near a
ham transmitter or broadcast antenna -- those cables are simply acting as
receiving antennas. They will also carry leakage current from the AC mains
when connected between two pieces of equipment that are connected to
different mains outlets. That current is what we hear as hum and buzz. We
call it a ground loop, but it is really mains leakage current. A second
coupling mechanism for this leakage current is as IR drop in the shield of
unbalanced wiring.
Most "RF in the shack" is coupled into equipment by a pin 1 problem. When
you kill RFI by placing a ferrite choke on wiring, you are killing the RF
current on that cable.
73,
Jim Brown K9YC
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