2. home-theater
  3. 1340571655

Hum from my home theater's speakers

Hi,

I finally hooked up all my gears and tested my system last night. This is the first time I hooked up everything.

There is big hum noise from FL, FR, center speakers and subwoofer. I didn't check sorround speakers beause the hum is just too loud from the speakers I mentioned above.

This is my setup:
* Blu-ray player pre-amp Theta Dreadnaught Digital I power-amp 5.1 speakers.
* Pre-amp is also connected to projector through HDMI.
* Connection between pre-amp and power-amp are all balanced cables.
* Connection between pre-amp and sub is balanced cable.

I bought the system several months ago, almost all used (except blu-ray player, pre-amp and projector), and didn't have time to hook them all up until today. But I did tried partially hook them up as following:
laptop playing songs/video pre-amp Theta Dreadnaught Digital I power-amp FL, FR, C and sub speakers
Initially there was hum when I used RCA cables between pre-amp and power-amp, but later I changed to balanced cable and the hum was gone.

Now with the full setup, the hum is back. The full setup is in a different room from the test setup (not sure if this matters because this means things are plugged into different outlets).

Below are a few things I have tried:
* When pre-amp is turned off, there is no hum.
* When I unplugged the power-amp, the hum stops, including subwoofer's hum.
* When I plug power-amp in, the hum starts immediately. There is a power switch at the back of the power-apm (like this one: http://www.wpclipart.com/computer/hardware/.cache/power_switch_OFF.png). Even if the switch is turned off, there will be hum immediately from sub if I plug power amps in.
* I searched and some articles said: if there is only one audio equipment is grounded, there will be no ground loop hum. So I tried to unplug all others with ground connection and leave only power-amp plugged, along with others that doens't have gound connection, the hum remains the same.
* I also tried make the active and neutral on the power-amp's plug contact outlet's active and neutral, and leave ground untouched, the hum is till there.

How could I solve my problem?

Thanks.
deeperblue
rlwainwright
1,904 posts
 
Try to isolate the amp onto a different power circuit and see if that solves your problem...

-RW-
jea48
4,425 posts
 
Deeperblue,

Do you have your H/T system connected to a CATV provider or a SAT provider?

If CATV for a test disconnect the provider incoming CATV RG6 coax cable from the cable box and then check for hum. If hum is gone buy a Jensen coax ground isolator.

If you have SAT satellite dish disconnect the SAT RG6 coax cable from the SAT receiver and check for hum.
If hum is gone.... Post back.... The fix is a little more complicated.....
jwm
918 posts
 
Most subwoofers come with a cheater plug. Place a cheater plug on the sub. A cheater plug can be bought at Home Depot, it turns a three prong plug into a two prong plug thus lifting the ground.
deeperblue OP
8 posts
 
Hi,

Thanks all for the suggestions. Finally I figured it out. It was caused by projector. I have tried a lot of different things when I made the first post, but I forgot to unplug the HDMI cable from pre-amp to projector.

There were two reasons I ignored projector initially:
1. I though HDMI is all digital and should have nothing to do with ground loop. Turned out I was wrong.
2. I have tried to turn off the power switch to projector (not the switch ON the projector, it is the switch that connects to the hot wire of the outlet which the projector connects to), and it didn't help. So I though it is not related to projector at all.

Later I found out that as soon as I connect the HDMI cable to projector, I got the hum. Then I tried to unplug the projector and connect the HDMI cable, the hum was gone.

So I bought this and it solved my problem:
http://www.bhphotovideo.com/c/product/365781-REG/Ebtech_HUM_X_Hum_X_Ground_Loop.html

To Jea48:
I don't have any TV related stuff hooked up to my system yet, although I may do this in the future. I will keep your reply in mind when I do so in the future.

Thanks again for all the replies!
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