Thread: Ground Loop
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Scott Dorsey Scott Dorsey is offline
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Default Ground Loop

Bob Simon wrote:
Yes, of course there are other devices that indirectly connect to both the =
audio system and the monitor. A Contour STB, BluRay player, and Fire Stick=
are all connected to an iArk 3-port HDMI switch with the output going to t=
he monitor. 2-channel audio from this switch goes to the pre-amp as well a=
s audio from the STB and BleRay player. The Cox feed to the STB is isolate=
d using a Jensen ISO-MAX VRD-1FF CATV Isolator.


So what changed with them?

I did not include any information on these devices in my original post beca=
use the resolution of the hum issue did not involve them. The only change =
I made to eliminate the hum was lifting the ground to the video monitor. =


Every device needs to have one and only one ground path to everything else in
the system. If you have two paths, you get a hum. If you break either one
of those two paths, the hum stops.

Don't break the path that goes through the power line safety ground. Break
the other one. To do that, you have to find it, and that means drawing out
where all the grounds go and/or disconnecting things to see what things are
in the path of the loop.

In troubleshooting, I found that I could eliminate the hum by either discon=
necting the HDMI cable from the HDMI switch to the TV or unplugging the thr=
ee devices from the pre-amp. None of these configurations are useful but t=
hey led me to lifting the monitor's ground.


Draw it out on paper. Now you know that you have a loop through the HDMI cable
and through the preamp. Now you get to find which of the devices going into
the preamp has the parasitic ground.
--scott


--
"C'est un Nagra. C'est suisse, et tres, tres precis."