What solution do folks use for the dreaded BFD hum?

[NEO Dan]

Apparently there are lots of "quality" AVR's out there that have some difference of potential between the Chassis Ground and the Phono Ground that it makes an audible difference.

I run my EP2500's bridged with the gains full open, and it's significantly quieter with the shield connected at both ends.

[bobgpsr]

The ideal solution is to never have cable shields carrying any ground current. Rather have a seperate wire "star" ground connection from all the audio equipment to a single point ground. Using "cheater" plugs is okay if you then use the cheater plug's ground lug to implement the star ground connection.

from http://en.wikipedia.org/wiki/Electrical_grounding:

Separating low signal ground from a noisy ground
In television stations, recording studios, and other installations where sound quality is critical, a special signal ground known as a "technical ground" (or "technical earth") is often installed, to prevent ground loops. This is basically the same thing as an AC power ground, but no appliance ground wires are allowed any connection to it, as they may carry electrical interference. In most cases, the studio's metal equipment racks are all joined together with heavy copper cables (or flattened copper tubing or busbars) and similar connections are made to the technical ground. Great care has to be taken that nobody places any AC-grounded appliances (heaters etc) on the racks, as a single AC ground connection to the technical ground will destroy its effectiveness. For particularly demanding applications, the main technical ground may consist of a heavy copper pipe, if necessary fitted by drilling through several concrete floors, so they can all be connected by the shortest possible path to a grounding rod in the basement.

The AC ground the article refers to is not the third wire safety ground but rather the AC neutral line which hopefully (but don't bet your life on it!) also is grounded at the mains electrical distribution box. You do not want to involve the AC neutral in any way with the low level audio technical ground. Any audio equipment that only uses a two connector power cable will need a seperate technical ground from its internal chassis or internal audio signal ground "star" connected to the audio main technical ground point.

http://en.wikipedia.org/wiki/Electri...(United_States)

neutral wire is connected to the center tap of the final step-down transformer and is identified by gray or white insulated wire, perhaps with stripes; most commonly bonded to earth for a fixed known path to stabilize the voltages only at the main service panel; many times called the grounded wire. Note that all metallic systems in a building are to be bonded to the panel; e.g., water, natural gas, HVAC piping, etc.

[NEO Dan]

bobgpsr wrote:

Any audio equipment that only uses a two connector power cable will need a separate technical ground from its internal chassis or internal audio signal ground "star" connected to the audio main technical ground point.

Response from popular AVR manufacturers=

[brucek]

NEO Dan wrote:

Response from popular AVR manufacturers=

Perhaps it's boring, but non the less a true statement.

Are you refuting the information, or do you not understand it?

brucek

[bobgpsr]

NEO Dan wrote:

Response from popular AVR manufacturers=

My Yamaha AVR has a nice big knurled screw post for connecting an earth ground and labeled for such.

[NEO Dan]

I am not an AVR manufacturer

My line of thought was that if an AVR manufacturer actually cared there would be a 3pin IEC on the AVR.

You are aware that "star" grounding a BFD to your AVR does in fact connect your AVR chassis to Earth/AC Neutral via your homes breaker box. That is if you are wired to code.

[bobgpsr]

NEO Dan wrote:

I am not an AVR manufacturer

My line of thought was that if an AVR manufacturer actually cared there would be a 3pin IEC on the AVR.

You are aware that "star" grounding a BFD to your AVR does in fact connect your AVR chassis to Earth/AC Neutral via your homes breaker box. That is if you are wired to code.

Sure no problem with that.

The third wire safety ground does not normally carry any current -- but the best way to avoid any AC current induced hum in audio interconnects is to have only one final connection from the star point back directly to an earth ground. Ideally a completely seperate wire going to the ground rod or buried copper water pipe connection. However you can use the safety ground from a given one of the 3 wire outlet power sockets that the audio equipment uses to then ground the "starred" ground point.

Most users just try to use one common power strip for all the audio equipment that uses 3 conductor power plugs, but any equipment that only has a two prong AC power plug should have a seperate wire running from the equipment's gound connection to one of the power strip's safety ground sockets or to the metal chassis of the power strip. Don't have the RCA audio interconnect cable shields providing the only earth ground for any audio equipment (esp the two prong AC powered ones) if you are working to reduce hum pickup to a minimum.

[Sonnie]

Chris mentions the Behringer HD400... this seems like it would be worth investigating...



This ultra-compact 2-channel hum destroyer may be small in size, but there is nothing lacking in its performance. This super-compact solution removes AC hum and noise quickly, easily and reliably. Ground loops are safely broken while the highest sonic quality is maintained. Plus, the HD400 automatically converts unbalanced signals into balanced without any signal loss. The unit carries two 1/4' TRS inputs and outputs for 2 mono or 1 stereo signal.

[bobgpsr]

Sonnie wrote:

Chris mentions the Behringer HD400... this seems like it would be worth investigating...

We would need to be sure that its freq response at the low end is flat to 10 Hz or so. Allow 1 dB down at 10 Hz?

[WaveyD4vey]

i ordered the BFD yesterday and it will be arriving on thursday...i also ordered the cheater plugs for now...ive been reading through alot of this thread but still have a few questions as its still a little confusing...first of all, the way i understand it at least, there is NO other way to get rid of this other than making your own cable as some people (brucek i think) have shown in diagrams how to do...either you make your own cable or you get one of the hum or buzz eliminators...but what about buying a XLR to RCA cable? im talking about one thats an actual cable and not an adapter of any sort...theres a link below to the one im talking about...and one more thing...i have no cable feed coming into my projector...it seems like a ton of people who have the hum with the cheater plugs have this caused by their cable or sat feed...i do have cable internet coming in to this room (obviously)...could that cause the hum as well? i would assume it could...and ONE more while im at it...is it a good idea to get a hum or buzz eliminator box even if i dont get hum with the cheater plugs?

i also must say ive been at AVSforum for a loooooong time...i really like this place alot better...a whole lot less arguing goes on over here....at least from what ive seen so far.

[brucek]

but what about buying a XLR to RCA cable?

It would have to be modified if you required the shield to be open at the XLR end.

could that cause the hum as well?

Yes, and is most often the culprit.

is it a good idea to get a hum or buzz eliminator box even if i dont get hum with the cheater plugs?

Nope. In fact you may not (and most don't) experience any hum at all. I wouldn't use the cheater until I found out if I had hum.

a whole lot less arguing goes on over here

It's against the rules.

brucek

[WaveyD4vey]

well i got it all hooked up and i had no HUM!!! yippie!!! and im ust say, it was VERY easy to set up...i thought it would be a little more involved...ir probly helped that i spent about 6 hours reading and then re reading through the BFD guide here on the forum...once u get one filter set up the rest is a total breeze, especially if u are using REW.

the sound quality from my system is unbelievably better...this almost made as much of a difference as when in spent $2000 on room treatments...im running B&W 683 mains with HTM61 center and DS3 surrounds...basically the entire B&W 600 series system...my subs are HSU VTF3HO with turbo and an MBM...before i EQ'd my subs with the behringer i had a huge rise at 60hz and from 32 hz down to 10 it was about 15 db above 75db which was my "reference" point...the rise at 60hz was about the same as the one from 32hz to 10hz...after i used the BFD and got everything all dialed in i was shocked how much of a difference it made...i did do a slight house curve...i basically raised all frequencys below 35hz by an average of 2 - 4 decibals give or take...but anywho, the difference in sound quality especially while listening to music is just flat out amazing...it made everything sound better...the bass is slightly cleaner and feels much tighter than before...everything just has so much more "definition" so to speak...i can even crank the volume on my receiver higher than before without feeling like the sound is distorting...that surpised me...even voices sound much much cleaner...they sounded just a tad strained at higher volumes on music...they sound much "airier" now...the room treatments and the BFD are definately the 2 best things ive ever done for my rooms sound quality...now its just a question of what my next home theater obsession will be...lol

[bbeck]

Hi everyone. First post here after lurking for quite a while. I don't feel too bad about resurrecting this thread since it's a sticky, so here goes . . .

I'm currently dealing with a low-level hum from my sub (Outlaw LFM-1 Plus) after installing the BFD (1124P) between it and my AVR (Onkyo 805). I have all my components connected to an APC H15 power conditioner/surge protector.

I have tried removing the BFD from the AVR-sub connection chain, which succeeded in getting rid of the hum. I have an attic-mounted TV antenna (not grounded, which I think is OK for those kinds of installations since it sits on a wood floor), whose cable connects to the back of the H15 to be split in two directions, one to a CM-7000 DTV converter box and the other to a TV tuner connected to my laptop for recording HD programming. (The latter connection is rarely used.) Disconnecting the input cable from the H15 did not eliminate the hum.

I then disconnected everything from the H15 with the exception of the BFD and the sub. The hum remains.

What are my options at this point? The H15 has a grounding post, and the Outlaw has a two-pronged plug. Would anything be gained by attempting to ground the sub to the H15? This seems a little risky to me. I know Axiom subwoofers have a ground-lift screw for resolving ground loop issues and wondered if that was a standard (albeit hidden) feature on all subs or just peculiar to the Axiom line. Alternatively, would a modified XBR to RCA cable (as described in this thread) work?

I love my BFD by the way, and am quite pleased at the results I've been able to get with REW and the great help instructions posted on this site. There's just this one nagging problem left to take care of.

[brucek]

Alternatively, would a modified XBR to RCA cable (as described in this thread) work?

It's your best bet. I suspect it will get rid of the hum.

brucek

[bbeck]

Thank you for the quick reply. I don't suppose there's any place that sells these cables custom-made or off the shelf? I have neither a soldering iron nor the expertise to make the cables.

[bpape]

Try www.avcables.com They'll make up pretty much anything you want. That's GEPCO's shop.

Bryan

[Sonnie]

I have also had Blue Jeans Cable make me a few specialty cables. They are friendly and easy to work with.

[bpape]

Sure. If BlueJeans will make up custom things, they're great to work with and reasonable prices.

Bryan

[bbeck]

I might try Blue Jeans. I've purchased some cables from them in the past, and they've been great to work with. I put in an RFQ with AVcable yesterday, but haven't heard back from them yet. I really don't expect a reply at this point, as I'm sure a request like mine is extremely small potatoes compared to other custom jobs they're asked to do.

[bpape]

If you do use AVCables, calling them on the phone is usually the best way.

Bryan

[VERTIGGO]

I was using a 2.5k -40db, BW of 60 filter on the BFD, but after I introduced the Reckhorn B1, I don't think I need it anymore.

The hum was simple to locate using the REW sine generator.

[waldo563]

bobgpsr wrote:
Most users just try to use one common power strip for all the audio equipment that uses 3 conductor power plugs, but any equipment that only has a two prong AC power plug should have a seperate wire running from the equipment's gound connection to one of the power strip's safety ground sockets or to the metal chassis of the power strip. Don't have the RCA audio interconnect cable shields providing the only earth ground for any audio equipment (esp the two prong AC powered ones) if you are working to reduce hum pickup to a minimum.

bobgpsr,
I have been following your postings and I think you may be onto something. I have been fighting a hum issue with my Onkyo TX-SR606 AVR which seems to be HDMI related and have tried disconnecting various HDMI connections, moving my sub power to the conditioner everything else is plugged into, disconnecting the Dish cable from the DVR, and have run a separate ground from the cable ground block to the Air Conditioner junction box conduit. None of these has made a perceptible difference. 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.
Thanks for your informative input to this thread.

[Scooterp7]

Mitch G wrote:

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.

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

Mitch

I find that mostly the humming is because they don't know the lyrics.

[johnvb]

NEO Dan wrote:

Apparently there are lots of "quality" AVR's out there that have some difference of potential between the Chassis Ground and the Phono Ground that it makes an audible difference.

I run my EP2500's bridged with the gains full open, and it's significantly quieter with the shield connected at both ends.

Since the folks here are such big fans of Jensen (myself included, owning several IsoMax units, and diy JT-11 trannys) they should be aware that your proposal is suggested by Bill Whitlock of Jensen in his #AN-003 white paper:


"4 - ABOUT UNBALANCED CONNECTIONS
Please note that, in all the schematic diagrams, connections to the
unbalanced IHF plug (formerly the "RCA plug" or "phono plug") are
shown as the single point to join SH (shield) and LO (signal low or !).
This is very important to absolutely minimize the resistance of
any remaining path used by both signal and ground
currents. If connections are made as shown, the only remaining
common path is the contact resistance of the shield connection
between IHF plug and IHF socket. Use a good quality IHF plug with
high spring force contacts and make sure the contact points are clean
and free of oxides.

With a little extra effort, this small remaining shared path can be
bypassed altogether. Leave signal LO connected to the IHF plug
shield, but connect the cable shield directly to the equipment chassis.
If the equipment manufacturer has thoughtfully provided a binding
post or banana jack marked GND, this will be easy. If not, there is
almost always room to mount one and then use a mating spade lug
or banana plug on the cable’s shield."

[johnvb]

and one more post for a linky :^)

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