What solution do folks use for the dreaded BFD hum?

[lcaillo]

brucek wrote:

Can you explain what you mean? The BFD has both balanced and unbalanced capability on the output already.
brucek

The BFD manual states that the outputs are balanced and recommends using balanced devices. The BFD is no different from any other balanced device, in that you can ground one side and use it with unbalanced devices, halving the impedance. While this may work fine in some systems, others will have problems with it. The only certain way to avoid ground loops due to kludged unbalanced connections is to use a balancing transformer or an active device designed to modify the output configuration. Transformers are the logical choice for low frequencies like we use with subs.

[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?

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.

[Dundas]

Bruce,
The HumX patent application appears to be number 20040264712 which can be seen at:
http://appft1.uspto.gov/netahtml/PTO/srchnum.html

In addition to the BFD I also have a hum problem with an HDMI connection between my Panasonic projector and Denon receiver. I have not seen any signal path solutions for HDMI.

[lcaillo]

Dundas wrote:

Bruce,
The HumX patent application appears to be number 20040264712 which can be seen at:
http://appft1.uspto.gov/netahtml/PTO/srchnum.html

In addition to the BFD I also have a hum problem with an HDMI connection between my Panasonic projector and Denon receiver. I have not seen any signal path solutions for HDMI.

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.

[brucek]

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

[Ayreonaut]

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?

[brucek]

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

[Ayreonaut]

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?

[brucek]

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

[brucek]

Actually, after rethinking this, I would definitely place the Cleanbox close to the BFD and run the longer unbalanced lines to the cleanbox from the receiver.

The cleanbox's job is reject noise. Even though the line feeding it is unbalanced, the common mode rejection will be very high since transformers tolerate the mismatched source impedance very well.
The short lines on the output of the cleanbox will offer the lowest distortion and overall insertion loss.

brucek

[Ayreonaut]

I guess it's a useful discussion for others, but silly for me to debate.
My BFD is sitting next to my receiver, literally touching it.
Two 18" cables will do the trick.

[Ayreonaut]

HELP!

I bought the ARTcessories CleanBOX II and hooked it up. It made a terribly loud hum!

I connected my recievers subwoofer pre-out to the CleanBOX II with a cable that has an RCA jack on one end and an unbalanced 1/4" TS jack on the other. I connected the CleanBOX to the BFD with a balanced 1/4" TRS cable. I powered up the amp and it hummed very loudly. What did I do wrong?

The connections on the CleanBOX II are confusingly labeled in that one side is labeled input and the other side is labeled output, but a painted line seems to indicate that the inputs are connected, which seems not to be the case as I have tried connecting the cables all ways.

Help!

[tdamocles]

brucek wrote:

Most people use RCA unbalanced though..... Can't lift that ground

How about this duo? This combined with a cheater plug?

Will this work? I've found the gfci elsewhere for about $12. $12+cost of a cheater plug could be a cheap solution to eliminate ground loop hum.... Any comments?

What I found is that the GFCI works the same as the ground(3rd prong) with one difference....If there is a ground fault, you won't know until you touch it and get a slight shock before it shuts power off. If the BFD isn't bypassed with the cheater plug a ground fault would blow a fuse or circuit immediately without touching it.

[brucek]

I connected my recievers subwoofer pre-out to the CleanBOX II with a cable that has an RCA jack on one end and an unbalanced 1/4" TS jack on the other. I connected the CleanBOX to the BFD with a balanced 1/4" TRS cable. I powered up the amp and it hummed very loudly. What did I do wrong?

The connections on the CleanBOX II are confusingly labeled in that one side is labeled input and the other side is labeled output, but a painted line seems to indicate that the inputs are connected, which seems not to be the case as I have tried connecting the cables all ways.

This is a stereo unit, so there are two inputs and two outputs. The funny line between the two seems dumb for sure.

Anyway, since we presume this is a transformer device, you can remove the ground reference at its input and simply use the differential input.

Does the sub amp hum with just the BFD and cleanbox connected without the receiver connected?

Are you able to make your own cables?

brucek

[Ayreonaut]

Thanks for helping, Bruce.

There is no hum at all if the receiver is not connected to the input of the CleanBOX.

I don't make cables, but I could always order a custom one from a local shop if I needed to. What could be wrong wtih the way it's hooked up now?

(Maybe some bonehead bought this unit and fried it with an amplified signal and then returned it to the store. ???)

Here's what I tried and got the very loud hum.

[brucek]

The cable that goes from the receiver to the ART is an RCA to TS. It has the center pin of the RCA connected to the TIP of the TS plug, and it has the shield of the RCA connected to the SHIELD of the TS plug. This grounds one side of the input transformer in the ART.

The standard remedy for this is to float the input side of the transformer with a cable called an XLR ground lift adapter. It is a cable with XLR's on both ends with the sleeve connection lifted on one end, and so the signal goes to the transformer which is now floating without the ground loop passed through.

You can make your own single solution with an RCA connector and a TRS connector and a piece of shielded wire.

Of course we don't have a schematic of the ART, but it's a good quess...

The schematic would be like this:



Make any sense?

brucek

[Ayreonaut]

I don't have it with me but there is a schematic on the back of the package of the CleanBOX II. On the input side, the tip and sleeve are connected to the transformer. On the output side, the tip and ring are connected to the transformer.

[brucek]

On the input side, the tip and sleeve are connected to the transformer

Mmm, doesn't make sense to me, since it accepts balanced inputs, it would have to have the tip and ring connected to the input of the transformer and the sleeve to transformer ground.....

Take a picture of it so I can see....

brucek

[Ayreonaut]

I won't have a chance to scan it, I'm leaving for vacation tomorrow morning and I have to go home and pack tonight. But I remeber what it looks like pretty well, I was studying it very hard last night.

It looked something like this:

[brucek]

When you return you'll have to take a picture and then we'll sort it out because that makes very little sense with regard to the ability to feed a balanced signal to the device - there is no ring (-ve) connection on the input?......

brucek

[Ayreonaut]

Despite what I said, I took a "break" from packing to scan and post the CleanBOX II schemaitc. Here 'tis.

[brucek]

Oh well, call me surprised. They are only allowing unbalanced inputs when the information says, "Connections, 1/4" balanced/unbalanced jacks".... I would take that to mean the input or output would accept balanced or unbalanced.

OK fine, the input accepts unbalanced and you can use the RCA to 1/4" TS plug connected from the receiver to the ART that you used before.

On the output you can use the balanced 1/4" TRS cable except you need to lift the shield on one end. You can make your own cable or modify the one you have (if it doesn't have molded connectors). I've never seen TRS ground lift adapters - only XLR ground lift adapters..

brucek

[Ayreonaut]

I went back to Sam Ash today to get a cable that I can mod if necessary.

While there, we hooked up my CleanBOX II to make sure it was working properly.
We used an RCA-to-1/4"TS adapter cable for input, and a 1/4"TRS cable for ouput, just like I have at home. No problem at all.

Why am I having this problem at all? Am I haveing to lift the ground because of a problemm with my BFD? Do the other people using the CleanBOX II with the BFD have to lift the ground too?

Tonight I'll try my new cable with the ground lifted from the CleanBOX II and see if it works.

[brucek]

We used an RCA-to-1/4"TS adapter cable for input, and a 1/4"TRS cable for ouput, just like I have at home. No problem at all.
Why am I having this problem at all? Am I haveing to lift the ground because of a problemm with my BFD? Do the other people using the CleanBOX II with the BFD have to lift the ground too?

No, you don't have a problem with your BFD. You established that when you answered my question and said, "There is no hum at all if the receiver is not connected to the input of the CleanBOX."

This says the ground reference of the BFD and the Carver amp are close and not creating a hum producing ground loop. When you hook up the Receiver, the hum begins. This is where the potential difference exists. This problem requires we convert the unbalanced signal of the receivers output to balanced (using the ART), so that we are then able to lift the line-level ground (completely safe, as opposed to lifting an AC safety ground).

Note, we couldn't lift the ground on a single ended unbalanced signal, since the ground shield itself is required for proper signal flow. This is the beauty of balanced signals (that the ART is supplying) - we are able to lift the line-level ground because the signal is carried on two difference signals from the transformer. Sometimes you get away without lifting the ground on a balanced signal, and sometimes not. In your case it would seem not.

Lift the shield between the ART and the BFD and you should be fine..........

brucek

[Ayreonaut]

Thanks 1,000,000 Bruce. I'll let you know what happens.