Hi Dave,
-> Bonnie -
->
-> The other day you recommended an isolation transformer as a solution
-> to a hum problem I encountered when I hooked up cable to TV and tuner
-> then connected the TV to the pre-amp. I stopped in at Radio Shack and
-> found them, but now have even more questions.
 My reply was a little short to you in a couple of regards, hopefully,
this will clarify some.
 Ground loops (the usual cause of hum) can be caused from many things
and sometimes can be difficult to track down. When hooking to cable TV
as an example, which I believe was what you were asking about, many
times the ground loop is caused from connecting directly to the cable.
Remove the connection and the hum goes away. If this is the case, then
an isolation transformer between your cable and reciever should solve
this. This is the kind that Radio Shack has and should solve your
problem.
If the hum is still present when the cable is disconnected then this can
get much more difficult to find and solve. Ground loops are where there
are more than one path to ground at different potentials. Ground isn't
necessarily ground. In the US as an example, primarily for shock safety,
ground is referenced to the electrical ground, which isn't necessarily a
true ground, but for shock purposes it is. Almost every device made has
a three prong grounded plug which creates an effective ground between
all units plugged into the wall. Unfortunately, every two wire audio
signal also is referenced to ground, which isn't necessarily at the
electrical ground which can cause additional noise problems by providing
a signal ground that may float around the electrical ground, and a
seperate line to carry it. Assuming that every electrical device has a
grounded return to the electrical ground providing basically what is
called a "star ground" from each device to the ground, the cable from
your tuner to your preamp doesn't follow that grounding and can create a
ground loop or difference in potential from that electrical ground.
How to solve these problems can be very frustrating. Using a three to
two prong AC adaptor placing it in line with the AC of an item may
illiminate the noise, and many of the power distribution boxes that are
commercially used has the ability to selectively lift the power ground
from active devices in the system.
When you first mentioned your problem, it is quite common to have an
interaction between the ground coming from the cable (also at a
different potential than your electrical ground and system ground), can
cause the noise, that's why I suggested the isolation between the cable
and your cable box/tuner. These are usally called baluns and a 1:1 ratio
should be fine. Get one with two outputs if you intend to connect to
your audio reciever and TV reciever as cable sources.
As far as books on  audio, there are many, many fine books, on this
topic I have at least one that is great called "Grounding and Shielding
Techinques in Instrumentation" which has helped me out on some very
difficult problems in the past, but the above synopsis will usually get
you by.
In home audio you always have a ground along with a hot lead any time a
signal goes from device to device. Also, the AC usually has a brute
force ground which resembles a star grounding system. The signal grounds
effectively make a ground loop in such a situation by making a loop
between all of the devices in the star creating the difference in
potential and thus the noise. Or as I believe in your case, it is coming
from the difference in potential between the cable ground, the AC ground
and your system ground requiring isolation of the ground on the incoming
cable like originally suggested.
 I have so many books on various aspects of audio that it is difficult
to suggest one that will cover most things and yet be easy to understand
by someone not electronically versed.  Perhaps someone else has some
good suggestions from the consumer orientation.
 Bonnie *:>
P.S> Thanks for your comments. I intend to support this echo as long as
there remains a Fidonet.. There's getting to be a number of folks that
have experienced newsgroups and are coming back to the echos because
they suit them better. Something like how vinyl is making a
retrocomeback for some people.
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