What solution do folks use for the dreaded BFD hum? - Page 21 - Home Theater Forum and Systems - HomeTheaterShack.com

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post #201 of 330 Old 05-04-09, 09:34 AM
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Re: What solution do folks use for the dreaded BFD hum?

http://www.jensen-transformers.com/apps_wp.html

Also, I want to add another link to this excellent thread that I didn't notice was here (maybe it is?). This is Rane Notes on the subject, showing all the cabling possibilities. Very helpful:

http://www.rane.com/note110.html
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post #202 of 330 Old 05-08-09, 07:59 AM
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Re: What solution do folks use for the dreaded BFD hum?

I recently just bought a BFD and EP4000 amp and was getting terrible hum and noise problems. I tried an unbalanced stereo isolation transformers with RCA connectors, fixed the problem but introduced a really weird distortion into my subwoofer. So out the door that went. Next was connecting the chassis of the amp BFD receiver together this significantly reduced the hum and noise but there was still hum left which annoyed me when everything was quiet in the room. I then added my panasonic plasma television to the ground loop I made with the amp BFD and receiver and this completely eliminated the hum for me. Now if I can just find a new fan to quiten it down a bit. Apart from these issues the combo kicks ,really makes my DIY 21lw1400 sub sing.
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post #203 of 330 Old 05-08-09, 12:20 PM
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Re: What solution do folks use for the dreaded BFD hum?

Quote:
waldo563 wrote: View Post
I just realized that this AVR has a two-prong power cord and suspect that may have something to do with it. Unfortunately, unlike the Yamaha, the Onkyo does not have a chassis ground post. Do you see any risk in running a ground wire from one of the chassis screws to a ground point on my Monster HT-800 power conditioner? Also, what do you think would be the best way to connect to the power conditioner as it has a plastic case and no ground points that I can see.
Sorry to be slow in answering your questions, I just now noticed your post.

Sure use a chassis screw to get a earth ground connection to your AVR. Might be best to do a little scraping down to shiney metal where the screw head meets the chassis.

As far as the power conditioner ground goes -- can you use the three prong wall socket safety ground where the power conditioner is plugged into the wall socket? Does the power conditioner supply 3 prong power connections? I would think that it would need to. Couldn't you just plug into the power conditioner's power output sockets, a three prong power plug with only the safety ground connected to a wire for getting a ground connection?
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post #204 of 330 Old 05-10-09, 11:23 AM
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Re: What solution do folks use for the dreaded BFD hum?

i didn't read this thread.

i had a hum in my diy subs. turns out that its the comcast cable going to my dlp. i have to figure out the issue. but just unplugging it fixes the hum.
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post #205 of 330 Old 05-12-09, 03:28 PM
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Re: What solution do folks use for the dreaded BFD hum?

bobgpsr,

No problem...I didn't realize until I had posted that I was replying to an older posting but I appreciate your response. I did a quick test by connecting some wire to a chassis screw and then (carefully) touching it to the power conditioner F-type connectors (which I assume would be tied to ground) and did not notice any improvement. However, I did not remove the paint from under the screw head and may not have gotten good contact. I may try it again after doing that. As for the grounding post...after giving it some additional thought I came to the same conclusion that you did to use a 3 prong plug and just connect the safety ground to the wire.
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post #206 of 330 Old 08-07-09, 09:28 AM
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Re: What solution do folks use for the dreaded BFD hum?


Quote:
RazorX wrote: View Post
I just finished eliminating the hum so I thought I'd post an update on what I did to eliminate it.

I gained access to the ground block, and to my surprise, there was a ground wire (loosely) attached to the ground block but the other end wasn't attached to anything. I attached the other end of the wire to a clamp that was already on the main power ground wire which was connected to the ground rod. I tested my system to see if I had eliminated the hum and discovered it was still there.

My next step was to use my Dremel with a soft wire brush to remove the corrosion that had built up on the ground wire from the CATV ground block and the main ground wire. I reattached the ground wire from the CATV ground block and retested. The hum was still there. That is when I noticed the screw on the ground block was loose.

I decided to clean the end of the ground wire connected to the CATV ground block and snug it up. I cleaned this end of the ground wire and snugged it down. The hum is gone. Woohoo!!!

I think the cable TV picture actually looks better now too but this could just be a placebo effect. One thing that was also resolved which I know isn't just in my mind is a hum in our phones that was getting worse and worse over the last year...

Thanks for all the information and tips guys. You ROCK!
Just want to re-emphasize Razor’s experience about checking your electrical service ground.

Recently the transformer on a utility pole that was serving my house and a few others in the neighborhood blew out. After service was restored we were having ground loop problems in our system - significant hum in the audio system that grew louder by the day, and rolling lines on the TV.

To make a long story short, the troubleshooting process eventually culminated at the house ground stake at the service panel, behind the garage. This house was build nearly 30 years ago, and it was a bit distressing what I found.

To start, the clamp attached to the ground stake (for the heavy-gauge ground cable from the service panel) was too large to properly secure to the stake. It could easily be rotated on the stake. In addition, the screw-down terminal for the ground cable wasn't even tight. That's right - a loose clamp with a loose cable. Yikes!

On top of that, the stake had paint overspray all over it, and the clamp had been installed on top of the paint.

But wait, it gets better! The ground stake doesn't even appear to be copper! It looks like some kind of galvanized steel, and shows signs of rust at ground level. It's also really loose and wobbly where it goes into the ground, like isn't going down very deep. I'll bet it's rusted to the point that there isn't much of it left down there. I definitely need to get a proper 8-foot copper stake installed the next time we get a deluge of wet weather.

Taking care of these issues - sanding the paint off the stake, getting a proper-sized cable clamp, and securing the ground cable to the clamp good and tight - eliminated just about all the ground loop problems. The rolling lines on the TV went away, and the hum from the system is just barely audible. That's pretty much the way it was before. I never have got around to installing dedicated circuits in this house for the HT system because it's going to be an ugly job requiring cutting into sheetrock and all kinds of other fun stuff. I hope to tackle that project this winter. Hopefully between that and a new ground stake I'll be good to go with a dead-silent system.

Bottom line, if you have an older house, it would be a good idea to give your electrical ground a once-over. Focus on it first rather than last, as I did!

Regards,
Wayne



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post #207 of 330 Old 08-07-09, 01:52 PM
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Re: What solution do folks use for the dreaded BFD hum?

This is a very common scenario. I strongly suggest that grounds be checked regularly. One should be careful. If there is a problem with the neutral, an open ground cound be a hazard. Not likely, but if things are loose and you fiddle, there could be danger. Best to maintain a ground connection with a second clamp while working on the first if possible if working on the electrical service ground. Not much danger if just working with a cable, sat, or phone ground.

I just did a service call this morning that had a bar rolling through the pix and it was a bad ground on the cable installation.




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post #208 of 330 Old 08-20-09, 10:14 PM
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Re: What solution do folks use for the dreaded BFD hum?

I recently purchased a DSP1124P and, with my luck, ended up with a slight hum. Disconnecting my Dish Network cable into my DVR and using a cheater plug on the BFD pretty much eliminated the hum so it appears there is a ground loop issue associated with the satellite grounding.

So I went to cable entry point and ran some #10AWG solid copper ground wire from the ground rod which was the only ground reference for the satellite/cable coax shielding to a clamp on the electrical conduit going to the breaker box for my A/C unit which should be tied back to the structure ground. As a side note, the ground rod looks like it is steel which may have been copper clad at some point but now is heavily corroded. Unfortunately, the electrical service panel is some distance from where the coax entry points are and I was unable to find the service entry grounding rod. I also replaced the ground wire which was connected between the ground rod and the grounding blocks with #10AWG and cleaned the corrosion from all of the mating surfaces. This seemed to reduce but not totally eliminate the hum so it appears that even a properly (I hope) grounded system may introduce some hum.

Based on some other postings on this thread I then made up a ground wire by connecting only a single wire to the safety ground on a 3-prong plug and plugging it into the surge protector everything else (except the subwoofer) is connected to. This was then connected to the AM antenna ground on my Onkyo TX-SR606 AVR which, amazingly, has no dedicated chassis ground point and is the only device plugged into the surge protector.

The hum from my sub was reduced to an almost imperceptible level after this point but I noticed a slight buzzing from my mains which was annoying.

When I ran the satellite coax through the surge protector (Monster HT-800) coax connections, it cleaned up the buzz coming from the mains.

So it appears that by tackling the root cause of the hum which was the ground plane mismatch between the structure ground reference and the satellite cable ground reference, I was able to virtually eliminate the hum without the need for isolation transformers or a cheater plug. Hope this helps if anyone wants to try to fix the problem without additional equipment.

However, my BFD is still connected using 1/4" mono to RCA adapters and I would like to build some more permanent XLR to RCA cables with the shield attached at the XLR end as suggested by Wayne.

My question is, do these modified cables go between the AVR and the BFD input only and "standard" XLR to RCA cables with the shield connected on both ends and pins 1 and 3 shorted used between the BFD output and the sub? Or would it be better to use the modified cables at both ends.

Sorry for the long post.
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post #209 of 330 Old 08-21-09, 07:19 AM
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Re: What solution do folks use for the dreaded BFD hum?

Quote:
ran some #10AWG solid copper ground wire from the ground rod
Not large enough. Should be #6 or better.

Quote:
My question is, do these modified cables go between the AVR and the BFD input only and "standard" XLR to RCA cables with the shield connected on both ends and pins 1 and 3 shorted used between the BFD output and the sub? Or would it be better to use the modified cables at both ends.
Usually from the receiver to the BFD will be enough to fix the problem.

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post #210 of 330 Old 08-21-09, 03:42 PM
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Re: What solution do folks use for the dreaded BFD hum?

brucek,

Agreed...the #10AWG was what I had laying around so it is a temporary setup but I do need to get some #6AWG or thicker for a permanent installation and to meet the National Electric Code requirements.
Regarding the cables, I suspected as much but just wanted to make sure.
Thanks for the quick reply.
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