What solution do folks use for the dreaded BFD hum? - Page 31 - Home Theater Forum and Systems - HomeTheaterShack.com

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post #301 of 330 Old 05-01-13, 07:57 PM
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Re: What solution do folks use for the dreaded BFD hum?


Welcome to the Forum, Murphy!

You might try floating the ground in the balanced connections (i.e., clipping the shield from the connector at one end), but it sounds to me like your problem is probably “upstream” of the BFD and amp, like maybe a cable TV or satellite dish feed that’s not properly grounded. It won’t do to turn off everything in front of the BFD/amp. It needs to be disconnected from the BFD/amp. I’d first try disconnecting any cable/sat service antenna cables from the system. If that doesn’t isolate the problem, then disconnect each component from the system and then add them back one at a time to see where the noise starts.

Regards,
Wayne



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post #302 of 330 Old 05-11-13, 05:43 PM
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Re: What solution do folks use for the dreaded BFD hum?

Thanks for the suggestions. I disconnected the Lexicon processor, the TiVo unit, the Z-box, the DVD players. We turned off all computers and wireless networks just in case they were adding in anything. The hum was still there. We do not have cable or satellite only off-air antenna and I disconnected that also. The only things I did not disconnect were the other 4 power amplifiers. The equipment is in a equipment closet and to disconnect the other amplifiers is a major tear down. Is there a different unit that can do the same thing as the BFD with adding in the hum?

Getting desperate and annoyed,
Murphy
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post #303 of 330 Old 05-11-13, 09:29 PM
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Re: What solution do folks use for the dreaded BFD hum?

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Getting desperate and annoyed,
Murphy
The simplest ( though not cheapest ) solution is to provide the offending component ( the Behringer unit in this case ) with Galvanic Isolation ( in the form of ground lifted, audio transformers ) .

(i) Here's a set . You should ( hopefully ) only need them on the output of the 1124 .
- Jensen Transformers are TOTL ( spec wise ) & quite transparent in the circuit ( more so than even the Behringer unit that they would follow ) .


(ii) Here's a much cheaper solution at @ 1/5 the price ( though utilyzing the same approach of providing galvanic isolation with ground lifted transformers ) .
- These are just "alright" ( spec wise ) and within a clean circuit ( not yours at the moment ) are apparent ( to the trained ear ) when they are inserted into the signal chain .
- I'd recommend starting with these & then moving on to something better ( if you figure the system warrants the extra monies spent ) .



NOTE : The Urei/JBL 6290 amp ( & the rest of that series ) are pin 3 hot . 6290 OM pdf
- Your Lexicon unit ( like all newer balanced electronics for the last couple of decades ) are pin 2 hot .
- Mixing electrical protocols ( such as you are ) can often lead to hard to trace noise problems / especially with single phase electrical services ( that may already be at a tipping point / current balance wise ) .
- (FWIW ) if those were my amps, I'd modify their front ends & rewire the XLR connectors ( by simply swapping the wires at pins 2 & 3 ).

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post #304 of 330 Old 05-12-13, 12:40 PM
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Re: What solution do folks use for the dreaded BFD hum?


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MurphyLuth wrote: View Post
Is there a different unit that can do the same thing as the BFD with adding in the hum?
So you were not having any hum before inserting the BFD into the signal chain?

Most home theater users get the hum with the BFD because they’re inserting a component with a grounded electrical plug into a system that has only two-prong power cords. Since you already have grounded-plug components in your system (the amps), that suggests to me that you might have a defective BFD, or else used bad cables to make the connection.

A couple of other suggestions: Is there a ground cable for your antenna? If so, it should be connected to the house electrical ground stake.

Also - it sounds like you have your amps in one location and your other electronics in another? If so, there’s a good chance the two circuits in use are on different electrical phases. This is a common source of a hum and noise.

Regards,
Wayne



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post #305 of 330 Old 05-17-13, 09:14 PM
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Re: What solution do folks use for the dreaded BFD hum?

Ok, I spent the money and purchased a Jensen ISO-MAX. I installed it on the output side of the 1124. It did not remove the hum.

Any more suggestions? Please!!
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post #306 of 330 Old 05-21-13, 08:31 AM
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Re: What solution do folks use for the dreaded BFD hum?

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Ok, I spent the money and purchased a Jensen ISO-MAX. I installed it on the output side of the 1124. It did not remove the hum.

Any more suggestions? Please!!
Things to try ;

(i) Locate the 1124 to the location of your amplifiers ( & power the 1124 with the same AC service as the sub-woofer amp ) . Put the ISO-MAX on the input of the 1124 .

(ii) If you bought the 2-chnl ISO-MAX, isolate the input & the output of the 1124 .
- Under those conditions of galvanic isolation , the 1124 should be quiet ( apart from it's inherent circuit hiss ) . If it still produces a loud hum & buzz , then the 1124 either can't work with the AC it's getting ( it happens, but is quite rare ) / or the unit itself is defective ( much higher odds ) .


Last edited by EarlK; 05-25-13 at 06:14 PM.
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post #307 of 330 Old 05-25-13, 01:58 PM
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Re: What solution do folks use for the dreaded BFD hum?

Thanks for everyone's help. I had to get another XLR cable so that is why this replay was delayed.

This is what I did last:
  • I put the equalizer on the same power circuit as the sub-woofer amplifier.
  • The ISO-MAX is 2-channel, so I put the input to the equalizer on the first channel
  • I put the output of the equalizer on the second channel.
The hum/hiss is still there but maybe slightly reduced. So does this mean I have a defective equalizer?

Murphy
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post #308 of 330 Old 05-25-13, 04:54 PM
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Re: What solution do folks use for the dreaded BFD hum?


If you remove the equalizer from the signal chain and the noise goes away, then it is definitely the equalizer.

Regards,
Wayne



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post #309 of 330 Old 01-14-14, 01:24 PM
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Re: What solution do folks use for the dreaded BFD hum?

Hello everyone. I just joined this group recently when I decided to do some upgrades to my home stereo. After years of powering by NHT 1259 subs with a Carver 225wpc TFM24 I decided is was time to pull the trigger on something with more headroom and also apply some room eq using a FBq1000. I don't mean to hijack this tread but short of reading through all 300+ replies in the hope of finding an answer I was hoping someone here might have already come across this. Anxious to get things up and running I set up the new Behringer EP4000 and FBD last night using a Samson S-Converter to get me from RCA to XLR. The signal path is Preamp Sub Out => Samson => FBD => amp. At power on everything worked as it should except for static (digital noise) on the subs. No problem with hum. To isolate the problem I removed the FBD and ....no noise. Has anyone come across this issue before and figured out a possible cause?

Dan

Last edited by Aleph30; 01-14-14 at 04:15 PM.
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post #310 of 330 Old 01-14-14, 04:58 PM
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Re: What solution do folks use for the dreaded BFD hum?


For starters, the FBQ isn’t especially known for its stellar noise characteristics, and you’re merely boosting the noise with the S-convert. There is no reason to use it merely for RCA to XLR conversion; the downstream equipment, both the EQ and amp, will accept unbalanced connections, so you merely need RCA to 1/4" cables readily available at your local guitar shop. Feeding the output straight from your receiver to the FBQ, you might be able to get away with using its rear panel switches in the quieter -10 dB position. If you end up needing a signal boost for the amp, insert the S-convert after the FBQ, and boost just enough to drive the amp to max, and no more. More details in the article on gain structure you can find in my signature.

Regards,
Wayne



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