# Ground loop hum?



## Guest (Sep 15, 2006)

Bad lightning storm a few weeks ago, and ever since I have a loud humming noise coming through my sub when the BFD is connected. (not conneced no hum.) Sounds close to 60hz (My wife still wants to know how I know that (she calls me a geek))

Anyway - went to rat shack and bought this Ground Loop Hum Filter - http://www.radioshack.com/sm-see-all-needs-and-wants--pi-2062214.html

Only using one of the 2 RCA jacks obviously, but it had little, if any effect. Are both RCA jacks required for this to work? Before I cut the 3rd "leg" off my power cord, aka cheater plug, and see if that helps, anyone have any other ideas? Can a lightning strike all of a sudden introduce such a hum, or did it just fry my BFD?

FYI - I never did program the dam thing, so when Im back in a few days/weeks looking for help, that is why!

Later guys, Jeff

And Sonnie - I got the IB bug too! :holycow: More to come.........


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## brucek (Apr 11, 2006)

Read the section on Connecting the BFD here for some information on hum with the BFD.

The unit you have suffers from poor response and would not be a good candidate to use.....

brucek


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## Guest (Sep 15, 2006)

Thanks Bruce - what do you mean "poor response?" Are some better than others out of the box, or was it likely damaged with a power surge? i had planned to put on ebay, but wanted to make sure I didn't pass on bad goods if it needs to be trashed instead.

Off to read the material you posted - thanks - jeff


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## brucek (Apr 11, 2006)

> what do you mean "poor response?"


I was referring to the frequency response characteristics of the ground loop filter you referenced.

This device is simply an in-line audio transformer and would be quite effective if the transformer was of high quality. Unfortunately, quality comes with a price. 

You'll find the low and high frequency response of this device and most other inexpensive devices such as this to be quite poor. I suggest it will begin to roll off frequencies below 50Hz fairly rapidly, although I've never measured it myself. I'm using the price as the quality indicator. If you find it does the job for you though, then you've got a good solution. 

You don't need any expensive test equipment to check its frequency response. You can do a quick check in your system of its effect, by performing the following test.

With the device installed, and the BFD IN/OUT switch in bypass (green LED flashing), play a single 20Hz tone from a tone CD (You can download tones here. Set the volume control on your receiver to some convenient level and note the BFD's LED front panel LED's indicating the voltage level it's being sent. For example -10dBV.

Without disturbing the volume control on your receiver remove the transformer device and re-check the LED level on the BFD. Did the level rise with the device removed? If so, that's the effect of the device at that frequency. You can do the test for a bunch of frequencies...

Anyway, use a cheater plug as a "tool" only and establish if you have a ground loop or some other problem.

brucek


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