Home Theater Forum and Systems banner

What solution do folks use for the dreaded BFD hum?

103K views 329 replies 74 participants last post by  Andre 
#1 ·
I'm a big believer in standing on the shoulders of giants. :)
In this case that means I would like to know what solution folks use for addressing The Hum.

Right now I'm using a cheater plug, but I would like to solve the problem the right way. I saw the links to Jensen and Ebtech stuff, but Jensen has a bunch of different products, and the Ebtech links are qualified with words like "possible."

So, what are you audio giants using to address The Hum?

Thanks,


Mitch
 
#2 ·
The right way is to convert the balanced connections on the BFD to unbalanced that are required by most AV systems using a transformer. You can get them at radio shack for about $14. Using the cheater plug is OK for testing and may never cause a problem, but why not do it right?
 
#7 ·
I've never heard of this problem before, my BFD doesn't hum, then again im in Australia on 240v, not sure if that has anything to do with it or not.

I've had a look at the links posted in this thread, could one of those be used to eliminate the ground loop caused by a laptop on mains power?


Harry.
 
#8 ·
could one of those be used to eliminate the ground loop caused by a laptop on mains power?
Most likely, if it's in the audio chain.


I would like to know what solution folks use for addressing The Hum
In the BFD GUIDE, under the first section "Connecting The BFD", it discusses the solutions to this problem, including several of the products already mentioned. Some use transformers, some differential amps - take your pick... The DC1 that stitz mentioned seems to be a good price and get good reviews. I've never tried it myself.

You want to stay away from inexpensive devices for this application, since their low frequency response are quite poor. The Radio Shack product is particularily bad in this regard.

brucek
 
#9 ·
Just so people don't think I'm a complete idiot, I did see the suggestions in the BFD guide, but there appear to be a hundred Jensen products and the other products are listed in the guide as "possible solutions."
Hence, I wanted to hear some first hand accounts of what people are using.



Mitch
 
#11 ·
The cheapest solution I found, which also worked the best/easiest, was to buy XLR ground-lift adapters. I think they were $7/each (one per channel as necessary, not all channels since I still want the ground level between my processor and amp to be equal) from Sweetwater.
 
#13 ·
I see that sweetwater has a plethora of adapters and couplers that might work if a ground lift works. Could you attach a rca(f)/xlr(m) adapter to a xlr(f)/xlr(m) ground lift coupler into the BFD and use the 1/4" jack/rca(f) as the output to the sub woofer? It would be a cheaper option compared to a transformer/humx? if it works...... Will the amount of different attachments screw with the signal?
 
#14 ·
Could you attach a rca(f)/xlr(m) adapter to a xlr(f)/xlr(m) ground lift coupler into the BFD and use the 1/4" jack/rca(f) as the output to the sub woofer?
Well, you always have to remember a basic rule in electronics, that no signal can flow in an open ended circuit. You need to create a loop for current to flow. In an unbalanced interface, there is only a single unbalanced line that requires a return path, and that's the ground. You can't break that path - no amount of adapters can break that rule. The shield in a balanced circuit isn't a return path, so you are allowed to lift it. Not the case with a single ended circuit.

I suspect the Hum-X to be ineffective. You really need a device that is placed in the audio circuit itself, such as the DC1...


brucek
 
#17 ·
Gotta question your quick assumption there Bruce given that we all know that lifting the power line groung with a cheater solves the problem
Yeah sorry, I answered quick because I have concerns over these devices. I have no doubt it likely does the job. But we all know there is no way to eliminate that ground loop hum at the plug/receptacle without lifting the safety wire or inserting components into its path.

Those components have to be able to support the entire 120volt AC current to ground in the event of a failure in your equipment. They must support that current until the breaker trips. This requires quite high wattage components. Do they fit into that little device? Does the device have UL certification? If so, where are the specification sheets on their site. All I read is advertising hyperbole.

I'm more comfortable recommending line-level components.

brucek
 
G
#18 ·
Hmmm, I thought as Dundas did not having to insert something in the signal path would be preferable, and so have been using the HumX with great success, but...after reading bruceks' comments may need to rethink this.

Any thoughts on the suggested converting BHD balanced out to unbalanced RCA?

RG
 
#19 ·
Any thoughts on the suggested converting BHD balanced out to unbalanced RCA?
Can you explain what you mean? The BFD has both balanced and unbalanced capability on the output already. If you have a hum, you could try the DC1 that was mentioned..

Again, I have no experience with the HumX, so I was just asking questions about its safety. I couldn't find any testing reports or specs on the site or otherwise....

brucek
 
G
#23 ·
Can you explain what you mean? The BFD has both balanced and unbalanced capability on the output already. If you have a hum, you could try the DC1 that was mentioned..

brucek
I was referring to lcaillo's post, the second in this thread, where he suggests this to be the proper way to cure the problem, apparently with some type of adapters or cables of adaptive nature. This would seem preferable to line source measures that utilize filters or whatever. Would this cure the problem? Apparently lcaillo believes so. Any drawbacks to this? Anyone else tried this approach?

Regarding the HumX, I agree without some data how are we to evaluate the product. Upon recieving the product, which does not include any additional data, I was left wondering if I had in fact just purchased the worlds most expensive cheater plug! :dunno:

RG
 
#20 ·
I was reading some other stuff about ground loop hums and one suggestion was to ground your cable TV service to the same place as the power ground.

My humming is clearly related to my cable TV because once I disconnect the cable TV, the hum goes away. My cable TV service is grounded outside where it enters the house. But, that ground is not the same as used for power.

So, I was considering adding a coax grounding block where the cable enters the house and then running ground wire to the water pipe where my power ground is. My coax entry and my circuit breaker box are basically colocated. So, it's not as if I'm running the ground wire any further than the power ground wire.

If I understand the root cause of ground loop hums, this seems like it will remove the voltage potential that is causing the hum. But, I would like to hear from the experts before I pull the trigger on this.


Mitch
 
#22 ·
I was reading some other stuff about ground loop hums and one suggestion was to ground your cable TV service to the same place as the power ground.
Not only is it advisable, it is a violation of electrical codes anywhere in the US to not ground the cable to the a.c. service ground. You should have a ground block at the entry point connected tot he same ground rod that your electrical service is grounded to, not a water pipe. This will likely improve your problem.

You don't have to do it yourself. Your cable provider is REQUIRED to do it. If they refuse contact your county inspector's office or state professional certification board and let them know that they are not properly grounding their installations. You'll get action.
 
#21 ·
If I understand the root cause of ground loop hums, this seems like it will remove the voltage potential that is causing the hum.
In some cases it will. It never hurts to ground the cable at the service panel. Any difference in potential on the safety grounds at your equipment can cause a hum.

Even though the safety ground is a cold conductor, it can and usually does, develop a small potential, through mutual inductance, wire resistance and various other reasons that can be quite different at each receptacle in your house.

When you plug a power amp into one receptacle and a preamp into another receptacle, the metal cases of these two units can have a small potential difference in their safety grounds which means that this equipment's metal cases are at a slightly different potential. When you connect a single ended (RCA) cable between these two devices, a small AC current can flow in the shield because of the potential difference. This unwanted signal is in the signal loop circuit and can cause a hum. An interconnect circuit has a loop path (completed circuit) that flows through the centre conductor of the interconnect cable and back on the shield. If there is an AC signal on the shield flowing because of the ground difference potential, you'll hear a hum. Breaking the safety ground of one of the two devices removes the potential and the path for the unwanted signal flow...

Exactly the same situation can occur, except usually worse, when you introduce a new ground into the system from cable TV or a satellite. Their ground on the shield may possess a different potential than the ground in your system and current will flow in all the interconnects. Usually by centralizing and bonding all external grounds to the common house ground you're at least giving yourself the best chance of reducing this problem.

With cable, sometimes it's necessary to use an isolator device like this one. They usually work - not by magic, but by using an RF balun or similar device. They are quite safe, albeit a bit expensive.

brucek
 
#27 ·
I was referring to lcaillo's post, the second in this thread, where he suggests this to be the proper way to cure the problem, apparently with some type of adapters or cables of adaptive nature. This would seem preferable to line source measures that utilize filters or whatever. Would this cure the problem? Apparently lcaillo believes so. Any drawbacks to this? Anyone else tried this approach?
Robert,

I'm don't see where lcaillo's post refers to adapters or cables. He said the proper way to eliminate the problem is with a transformer - and he's correct. I backed this up in my post where I suggested any of the in-line solutions suggested in the Guide would work by using transformers or differential amps. You do have to be careful to not purchase a transformer that is so cheap that it suffers a poor low frequency response.

Either the DCI-ALHI or the Ebtech Hum Eliminator would be fine. Personally, I like Jensen transformers. Some people just make their own with Jensen transformers or they purchase them in a box like this or this.
Jensen supplies this type of proper spec sheet. Why can't the others? I suppose that's why Jensen products are so **** expensive.
MarkerTek for $120.....or mono MarkerTek for $95............... :)

brucek

EDIT: I should be mentioning the Jensen isolator for subs which has better low frequency response.
 
#29 ·
The HDMI connection is just one of the ground paths that exist in your system. Look for a solution elsewhere by improving the ground at some point or isolating one. Chances are that the problem is something else and breaking that connection is just one of several that relieves the problem.
 
#30 ·
Upon recieving the product, which does not include any additional data, I was left wondering if I had in fact just purchased the worlds most expensive cheater plug!
The HumX patent application appears to be number 20040264712 which can be seen at:
The patent documentation shows the device to be exactly as I indicated before. It uses the standard method of inserting (parallel back to back diodes) in series with the safety ground. Using the fact that the flow of current that causes hum is usually quite low, it is easy to see that if you place a device in series that inhibits that flow until a small breakdown voltage is reached, then no current will flow and the hum problem is solved.

A single diode has a breakdown of 0.7volts and two would have a breakdown of 1.4volts, etc. You need two sets in parallel with opposing polorization, since this is required to pass AC current.

This is the standard principle used in marine galvanic isolators to block AC and DC currents from reaching a boat connected to shore power. It eliminates corrosion of the boat hull etc.

Anyway, this is great as long as those diodes are rated to pass a steady state current long enough to trip a breaker on the hot line. A 120voltAC dead short can pass enormous current. It can easily be a few hundred amps depending on your service. The breaker should trip fairly quick. It must trip before those diodes blow. Most high current diodes are the variety that require bolting to a heat sink to achieve their rating. But then, they must pass that current for long periods of times. The diodes in the HumX only need to pass that current long enough to trip a 15 or 20 amp breaker. Hopefully the diodes that are jammed into that little device are spec'd to achieve that. I'd feel confident if it had a UL or CSA sticker on it. Either way, the HumX is sure better than a cheater plug.

You also have to realize that if the BFD is connected to a device that has a safety ground, then the shields of the interconnects will pass the current in the event of a BFD failure and trip the breaker. In fact, that's long been a trick to eliminate ground loops and its resultant hum. Choose a central device that everything is connected to (such as a processor), and then cheat every other device except the processor. The theory being that the interconnects will provide the path to safety ground through the one device that is safe. This is a horrible idea though, since some unsuspecting person may have the interconnects pulled off and a fault may occur and electrocute them. Don't use this method.

The best and safest method is to plug in the three prong plug to the wall and if there is a hum, solve it at the line level.........

brucek
 
#31 ·
I'm going to buy an isolation transformer for this purpose very soon.

Is the Ebtech Hum Eliminator significantly better than the Art Cleanbox II?
 
#32 ·
I haven't any experience with these two products, but the specs they publish show the low frequency response of the Art CleanBoxll to be better. That's important for a sub application.

The HUM Eliminator shows down 0.5dB @ 20Hz. We don't know what the 10Hz value is.
The ART shows 0.5dB @ 10Hz.

These transformer based hum devices generally would use an "input" type transformer. This is evidenced in the ART spec with it's large insertion loss with low input impedance loads. This would mean it is a good idea to install it very close to the load amplifier. Probably a good idea anyway, because since it allows balanced or unbalanced connections. I would run a long balanced interconnect from the BFD to the ART box and then a very short RCA unbalanced interconnect to the power amplifier (unless your amp is balanced input - then use that)...........

brucek
 
#33 ·
I have a balanced interconnect from the BFD to a Carvin amp. No problem there.
The noise is in the connection between the Denon receiver and the BFD.
I should install the Cleanbox close to the receiver, right?
 
#34 ·
The noise is in the connection between the Denon receiver and the BFD.
I should install the Cleanbox close to the receiver, right?
Well, since you'll be running balanced from the cleanbox to the BFD, and unbalanced from the receiver to the cleanbox, you would think that the distance from the receiver to the cleanbox should be shortest, but I don't feel that it would be best here.

My reasoning being that the output impedance of the cleanbox demands that the output cables be the shorter ones, although the worst that will happen with long lines after the cleanbox is that it will act as a low pass filter and lower transient response.

Either way, your BFD must be located close to the reciever, no?

brucek
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top