On Tue, 02 Nov 2004 02:54:57 GMT, James Harvey
wrote:

Hi,

I have been recording vinyl LPs to my computer the past few days with a
grounded phono preamp. I had no problems until today. I am now picking
up serious hum and buzz, and I can hear broadcasts from an AM radio
station that has a powerful transmitter located in my city, while using
the recording software. WTF?

Hi James,

The proper usage is
"WTF, Over?"

Is there any way to stop this bs? I have tried various isolation
transformers, grounding schemes, and shielded cable configurations to no
avail.

What you describe is a ground loop. I bet you have had a weather
change in the last day or two. (I know, that is almost certain, but a
recent rainfall, or cessation of raining often introduces these
problems.)

I have complained to the station, but got no response from
engineering.

It's not their problem.

Any ideas on what to do? Practical advice appreciated.

Plug ALL of your electronics into the same power strip and plug that
into the wall. Strip out all wires that go to other equipment (like a
modem, printer, T1/network connection, scanner, you name it...) make
sure the monitor shares that same power strip. You say "grounded"
phono preamp. This is probably antediluvian equipment (a two wire AC
plug with a dangling wire or knurled nut in back for ground). There
is every chance that your ground wire is going to an open ground lead
(did you check the outlet for inverted hot/neutral, hot/ground,
neutral/ground, open ground?). Is this two wire AC plug polarized?
You may have a potential suicide adapter - be careful. You might be
more successful in simply connecting the Phono output directly into
the sound card Microphone input. If it makes a hellacious hum during
the connect process, then YES you do have ground problems - you also
stand the chance of that problem going away when the plug finally
seats though (my guess is that this has always been the case, and it
just got more noticeable).

I see you have tried isolation transformerS (why the plural?). If
you neglect wires that trail off to foreign connections (already
listed above) this will do nothing but confuse the situation (it only
takes one wire).

There is a working solution and to find it means starting with a
minimal working system. Add your system axillaries one at a time
until it breaks and examine THAT item and notice how it is powered,
and how it finds ground. If it isn't obvious, it may be working, but
it may also be broken in the sense of a safety violation (a chassis
screw punctured a PC board and hit a power land - or a connector shell
nut fell off and the ground is floating).

The added clue of the AM station suggests that there is a POOR
connection somewhere. The sense of poor is that it is corroded (this
creates a crude radio detector circuit and the amplifiers do the
rest). The solution here is to break ALL connections and clean them
and reassemble. Often simply twisting connectors that twist will
clear the problem, or unjacking and rejacking connector jacks does the
same thing. Tightening screws that hold ground leads is the same
thing. Corrosion will be obvious, if in doubt, abrade surfaces until
you observe bright metal. Tarnish offers the same problem. Use a
typing erasure or toothpaste to clean the metal (mild abrasives).

73's
Richard Clark, KB7QHC