On 7/13/2012 9:46 AM, Pete Smith N4ZR wrote:
> Interesting point on phono plugs. I wonder if it would be useful to use
> one of the Caig Labs chemicals on those shells to enhance their contact
> with the jack.
Better to buy and use proper connectors. Switchcraft makes EXCELLENT
phono and 3.5 mm plugs, and the lower cost plugs and jacks made by
Neutrik's Asian subsidiary are pretty good. I buy them from Full
Compass, a very good audio distributor in Madison, WI.
But there's another more fundamental issue than the plug itself -- 99.9%
of the time, the shell of the phono JACK built into the equipment
doesn't go to the shielding enclosure, but instead goes to the "common"
on the circuit board and wanders around for a while before it finds the
chassis. This serious engineering mistake is a major cause of RFI. In
the pro audio world, it's called "The Pin One Problem." And because
it's a passive network, it both sends and receive RF trash. Now, it IS
possible to terminate the cable shield to a properly implemented "ground
layer" on a PC board, but as Henry Ott has observed both in his EMC
seminars and in his classic text on EMC, any signal traces that cross a
break in that layer can render it useless, putting RF trash on those
external cables.
Another point -- improper shield termination can also introduce
instability in the circuit, because current doesn't flow where the
designer hoped it would flow. Henry Ott's text is required reading.
73, Jim K9YC
_______________________________________________
UR RST IS ... ... ..9 QSB QSB - hw? BK
|