# BFD hum troubleshooting



## Zeitgeist (Apr 4, 2009)

I have an Onkyo PRSC886 with an Emotiva-UPA7 amp..... The Onkyo is connected to a BFD DSP1100 via RCA, and then connected to a powered HSU VTF-1.

With the Onkyo connected directly to the HSU - no hum. With the BFD in the loop - I get a hum. 

I tried a cheater plug for troubleshooting and it made it a LITTLE better but not much (Yes, I'm aware that it's not really a solution)

Other than a direct box, any other suggestions?

Everything is mounted in a M/A Slim5 rack - so I'm curious if the rack grounding could be a factor too. I'm going to unmount the BFD and see if the hum is any different.

Everything except the HSU is plugged into the same power strip. And without the BFD - no hum - so I don't think that there is a ground loop between the Onkyo and the HSU... 

I've read mixed things about different direct boxes - some saying that some are better than others (some attenuate low freqs?).

Thanks in advance! I'm sorry to be creating *another* BFD hum thread...


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## Zeitgeist (Apr 4, 2009)

It sounds like from doing some more reading... that there isn't a loop between the Onkyo and HSU --- but that the loop may be between the BFD and some other component (Cable?).......... Or the BFD and the Receiver. I'm less likely to think that it's between the receiver and BFD since I don't think that it even has a grounded power connector (even though I've read that you can still have a ground loop without it).

I'm going to try with just the Receiver, BFD plugged in to AC and see what happens. It seems like the cable is the culprit for most people.... so I need to check that.


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## Zeitgeist (Apr 4, 2009)

Yeah, OK! Please disregard this thread.

It's the cable. Disconnected the coax, all hum went away. Reconnected coax and then disconnected HDMI from cable...... again, hum went away.

And no, I don't think that the cable is properly grounded!! I need to fix that.


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## Wayne A. Pflughaupt (Apr 13, 2006)

Glad you figured it out; hope checking the cable ground will get it fixed. If it doesn't, there are plenty of other remedies in the ground hum thread you can try.

Regards,
Wayne


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## Zeitgeist (Apr 4, 2009)

Wayne A. Pflughaupt said:


> Glad you figured it out; hope checking the cable ground will get it fixed. If it doesn't, there are plenty of other remedies in the ground hum thread you can try.
> 
> Regards,
> Wayne


Thanks Wayne, I appreciate it!

I knew that I'd figure it out if I kept reading and spent a little time troubleshooting it..

Now I get to see if what happens when I add a EP4000 amp to the mix


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## gdstupak (Jul 13, 2010)

Same problem with my coax cable.
For a month I was tearing everything apart looking for the cause of my very loud hum. Ended up being my cable coax.
My cable coax is grounded but there is still a difference in potential between the coax ground and my outlet ground. My solution (and it worked), I took a piece of wire, around 14 guage, wrapped it around the ground area of the coax cable connector and stuck the other end of the wire into the ground hole of the nearest electrical socked. Now the coax and the wall outlet are grounded together. Whalla, perfect silence.
Now, I just need to get rid of the small hum from the light dimmer.


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## lcaillo (May 2, 2006)

Please do not double post the same info in different threads. See my response in the other thread and refer to the grounding thread below. This is a dangerous way to patch a problem and I strongly suggest tracking down the source of the problem and verifying the correctness of the ground design of your system and its integrity.

http://www.hometheatershack.com/forums/general-service-technical-information/7442-grounding.html


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## gdstupak (Jul 13, 2010)

My cable is grounded to my electrical service outside, but there is still a difference in potential. Will do some investigating and see if I can get it straightened out.


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## lcaillo (May 2, 2006)

Being connected and having an adequate connection are two different things. You could have a grounding problem in your electrical system or in the cable system. Either way, it is always best to find the source of the higher impedance. If it seems to involve your electrical system, please consider contacting a professional electrician, as dangerous potentials can exist if grounds are compromised.


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## gdstupak (Jul 13, 2010)

Don't take this post to say "I'm right and you're wrong, nana nana boo boo!" This is what my experience and training has led me to believe about my situation, and yes there could be a problem somewhere that I haven't found yet. 
As a trained and certified electrician (industrial, commercial, and residential) for over 15 yrs, I haven't found any problems with my house wiring. A certified cable installer checked out the coax system and found variances in signals but all within acceptable limits. Just because you have difference of potential at different points with different systems doesn't mean something has to be wrong. It just means that you don't have a perfectly balanced system. This is not a danger as long as all measurements are within specs.
I believe the difference in ground potential between the cable and electrical in my equipment area is because of installation differences. I designed my equipment area to have all dedicated outlets using 12gauge wire and as short of cable runs as possible, but the cable coax goes up to the attic and splits multiple times and is run who-knows how many feet before getting to my equipment area. 
Several other electricians and cable installers have supported my use of 'local ground supplementation' for my situation. Another possible fix may be to run a dedicated coax from the source straight to my equipment area.
If there is an electrical engineer who still thinks this situation is dangerous, my mind is open to learn.


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## gdstupak (Jul 13, 2010)

lcaillo said:


> refer to the grounding thread below
> http://www.hometheatershack.com/forums/general-service-technical-information/7442-grounding.html


I admit that I know very little about cable installation, maybe you could give your thoughts on my houses cable ground:
1. the ground cable connecting coax to house ground is 12awg solid copper, app. 4' long.
2. this coax ground cable is connected to the app. 1/0 copper house ground cable a few inches above the actual ground rod.

Would my coax be better grounded with a thicker wire connected directly to the ground rod?
I doubt my cable installation buddy's are as well informed as you, don't know how well I can trust them.

As a side note, I was in construction electrical in Orlando from 1999-2005, now I'm out of Florida and construction.....so happy!


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## lcaillo (May 2, 2006)

For 4 feet I see no reason to worry about increasing the size of the wire, though it couldn't hurt. 

I would be more interested in the resistance between your cable ground and electrical ground at the system and why they are different. Somewhere along the way you either have a weak connection in one of the two paths or some extremely long runs if you are grounded at the entry with a 4' ground and the connections are solid there. In most homes you would expect no more than a few ohms between the two grounds. Your ground on the a.c. service must also be at the same potential as the neutral. What have you measured? You suggested that everything was "within spec." What does that mean to you?


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## gdstupak (Jul 13, 2010)

The cable installer checked my system 3 yrs ago and I can't remember everything we did and what he said, but I just went out with my ohm meter and checked a few things.

-At the grounding rod: 0.5 ohms between house ground and ground of coax cable.

-At equipment area: 3.5 ohms between outlet ground and coax ground .... 0.2 ohms between outlet neutral and outlet ground.

-In bedroom: 1.0 ohms between outlet ground and coax ground.

I don't know what is 'within specs.' I had to trust the cable installer. 
I haven't checked in awhile but I think all the cable connections in the attic were tight, maybe I can venture up there tomorrow morning.


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## gdstupak (Jul 13, 2010)

I'm remembering more and more of the testing done 3yrs ago with the cable guys.
They said, since the ground was very good at the ground rod, and the ground was very good in other rooms of the house, and all connections were good, that the not-so-good ground in the equipment area was probably due to a problem with the coax cable going from the attic to the room. But they also said that the ground was still good enough to be within spec to do it's job and that the potential difference of 3-5 ohms is fine for the equipment, just annoying because of the hum. They agreed that my method of evening out the ground potential at the jack is not professional but will work fine.


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## lcaillo (May 2, 2006)

These numbers are good. The ground that you added from the coax to the ground on the outlet is really only dropping the potential due to the 3.5 ohms so it is surprising that this made the difference that you noted. I wonder if there is not some other device in the home creating another loop or something with some leakage current.


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## gdstupak (Jul 13, 2010)

-If I run my system with the cable disconnected from the wall, no hum.
-Connecting the coax cable to the wall (with no alternate ground wire, so there is 3.5 ohms of potential difference) starts the loud humming.
-Adding the alternate ground connection drops the potential down near 0 ohms and the humming stops.
I've tried disconnecting all other cable jacks in other rooms with no effect.
There are light dimming switches that make the system hum a little, but the alternate ground wire does not effect this at all.


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