On Thu, 28 Apr 2005 09:11:08 -0500, "Chad Wahls"
wrote in :


"Frank Gilliland" wrote in message
.. .
On Wed, 27 Apr 2005 10:22:40 -0500, "Chad Wahls"
wrote in :

snip
Most often, even wahat you consider "high end" cards do not have the audio
sheild grounded properly.


Very good point. Some cards have shield connectors that are DC
isolated from the chassis to prevent ground loops with other audio
equipment. In such cards the shield is coupled to chassis ground with
caps, but line noise can be a problem (and the cap must be shorted)
because the caps may not large enough to fully shunt low frequencies.
But the caps do shunt RF very well, and if they can keep the local AM
broadcast stations out of the soundcard then the neighbor's legal CB
radio shouldn't be a problem.




Problem is that they don't do all that well with AM Broadcast. When I was a
conglomo radio engineer we had a 50K FM and a 500W AM in a residential area.
I would get complaints-o-plenty of the AM coming thru computer speakers,
cheapo HT systems and phones.


Sounds like we had similar jobs -- do the daily checks, fill out the
daily reports, then spend the rest of the day making cables, cleaning
cart machines and waiting for something to break?


Of course we had to do what we could to
eliminate the problem and usually I would pull the sound card, DC ground it
with 1 ohm 1/4W resistors and the problem went away. 90% of my problems
called in were ratified with proper grounding. Fortunately most of the
construction in the area is newer as that tower used to be outside city
limits but due to urban sprawl it is no longer.

As for my personal soundcards I use pro models with a separate breakout box
that's balanced. The other card in that computer and other computers in the
house are SB audigy models with the mini jacks removed and XLR whips out in
their place. This whip then goes to a breakout box with 6 Jensen
transformers in it 4 for output and 2 for input. The mic input is shorted
down permanently. I have zero noise problems, if you have an Audigy card it
does sound good! You just have to help it out


I use the Extigy -- it's great because you can locate the box some
distance away from the noisy computer and ground it directly to the
mixer.

But for complaints to the station, I got them to order a huge box of
4" jumpers that have pigtails to the shield. Just plug them into the
soundcard (or whatever audio equipment is getting the interference),
screw the pigtail to the chassis, and 'presto' -- problem solved. No
invasive surgery, and you're out of the house in a matter of minutes.


The transformers....... When radio engineering and upgrading EAS systems in
all the stations I found that all the old receivers that we were throwing
out were loaded with Jensen transformers! What a salvage find!!!!!


No kidding!


I had
many-o-dumpster diving missions, then adopted a Chad's gotta pilfer it pile.
Lots of transformers and power supplies were gutted


Those old Bogen and Rauland paging amps have some pretty sweet
transformers, too. One of these days we gotta exchange inventory lists
of our scrounge bins.






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