# BFD HUM



## rudra (Feb 2, 2008)

I dont get any hum when the I connect the BFD to the subwoofer. 

Amp->BFD connected by RCA to XLR
BFD->Sub connected by XLR to RCA

Used the interconnect guide from rane http://www.rane.com/note110.html
to do the interconnects.

When everything is connected, there is no hum from the sub. When I play either music or movies the sub hums:dizzy:. When watching movies especially during a quiet scene I can cleary hear the hum from the sub. If I switch off the BFD and turn it back on the hum disappears. All the components are connect to belkin PF60 power console.

I dont know what else to do:scratchhead:


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## brucek (Apr 11, 2006)

You didn't tell us about your cables that you reference from the Rane site. Did you use one or two conductor shielded cable? What pins on both ends?

brucek


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## rudra (Feb 2, 2008)

My apologies bruce.

2 conductor shielded cable ( BELDEN® 1800B)

for the interconnect from http://www.rane.com/note110.html
AMP- BFD followed #17 RCA-> XLR
BFD->SUB followed #6 XLR->RCA female + DIY 'Y' connector(using BELDEN® 1855A cable and gold plated RCA connector) into the sub


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## brucek (Apr 11, 2006)

Do you have the pin-3 to pin-1 short on the XLR in diagram 6 ?

brucek


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## rudra (Feb 2, 2008)

yes I have shorted pin 3 and 1


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## brucek (Apr 11, 2006)

This connects the AC ground of the BFD itself to the BFD's output of its negative differential amplifer. This ground then passes on the black wire to the outer case of the RCA at the other end, which in turn is the AC/DC ground of the sub.

It would be wise to remove this connection from pin 1 to pin 3, and you will then break that un-needed possibility for a ground loop. This will then be equal to the situation you have with your input cable. It will preserve the floating nature of both the plus and minus input and output differential amplifiers in the BFD. The shields are still connected to case (pin 1) in both situations, but no connection is made with the external source or sink device. The devices themselves are safe since you have not interfered with the third prong safety ground on the AC plug of any device.

Anyway, give that a try and see if it helps. If that's the source, it will clear it. If not, it won't.....

brucek.


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## rudra (Feb 2, 2008)

I did have the short removed but made no difference. The hum is there if I play a movie at around -35db level on the receiver. When I switch on all the equipment there is no hum. Btw I have a pioneer 2016AVS receiver if that is of any help. Thanks for the help bruce.


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## brucek (Apr 11, 2006)

> When I play either music or movies the sub hums





> If I switch off the BFD and turn it back on the hum disappears.





> The hum is there if I play a movie at around -35db level on the receiver


Now that we've eliminated cables we can try some other stuff.

I guess you must know how very unusual those quotes I listed appear......

Do you happen to have a rather large gain filter in the BFD that is exacerbating a hum that already exists in the source equipment?

Have you removed the BFD and listened real hard for the hum at any level?

Have you temporarily tried a cheater plug on the BFD?

Does your receiver have any sort of Auto-EQ system that is on?

brucek


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## rudra (Feb 2, 2008)

> Do you happen to have a rather large gain filter in the BFD that is exacerbating a hum that already exists in the source equipment?


As far as I know I have not set any gain filter. Just taming the peaks. Unless REW set gain filters I was not aware off



> Does your receiver have any sort of Auto-EQ system that is on?


Yes the pioneer has got a 9 band MCACC auto eq system.



> Have you temporarily tried a cheater plug on the BFD?


I did not use a cheater plug(I dont know If one is available in australia). I removed the ground pin and connected. The result wasnt what I expected. I got a huge thud which I did not get before. I have set the subwoofer to switch on 10 secs after the BFD switches on.

even after turning off the amp the hum still persists. When I turn on all the components there is no hum:gah:

I did notice that if I do a mono connection the hum reduces. If i connect in stereo the hum is more pronounced.


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## brucek (Apr 11, 2006)

Do you have cable TV connected to the system? Does disconnecting it temporarily change anything?

brucek


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## rudra (Feb 2, 2008)

I dont have cable TV. I do have a sat installed. Disconnecting it does not make any difference.:surrender:


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## brucek (Apr 11, 2006)

You never answered the question of whether the hum goes away with the bfd removed?

brucek


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## rudra (Feb 2, 2008)

I have been busy. Got a chance to look at the problem in the weekend. You were right :clap: It is a BFD filter issue. When I bypass the BFD the hum is not there. I will have to see what filter setting in particular is causing it. What would be the best to approach the problem. I dont have the filter files with me.


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## brucek (Apr 11, 2006)

> What would be the best to approach the problem


You haven't given much information on your filters and how you set them (i.e. REW recommendations or test tones etc).

Generally with a BFD you select a program slot for your filters (i.e. #4), and set all the 12 filters in both channels to OF mode. This ensures you don't inadvertently have one filter set to feedback destroy. 

Then one by one you add the filters you need by placing it in PA mode (parametric) and set the parameters for that filter.

If you've done this already and you have a strange hum, then simply turn each PA mode filter to OF mode until the hum goes away. Then decide why the hum is happening with that filter (i.e. gain too high, etc.)

brucek


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## rudra (Feb 2, 2008)

The filters were set by REW. I will try what you suggested and will let you know how it goes


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