What solution do folks use for the dreaded BFD hum?

**brucek** · **07-29-08, 09:32 PM**

Quote:

Has anyone purchased this and confirmed this is indeed wired correctly (pins 1 and 3 are bridged) demoting the notorious hum?

The urls you mention show a typical 1/4" TS phone plug at one end and an RCA at the other. There is no pin 1,2,3 on a 1/4" phone plug. The phone plug can be a type TS (tip/sleeve) or a TRS (tip/ring/sleeve).

In the case of a BFD, we want to use the 1/4" TS phone plug (as shown in your url). This essentially shorts the ground and the minus differential amp together, which would be equivalent to shorting pin 1 and 3 on an XLR connector.

This would be the correct connection, but would do nothing to reduce hum if you were experiencing it.

brucek

**myn** · **07-29-08, 10:49 PM**

Quote:

brucek wrote:

The urls you mention show a typical 1/4" TS phone plug at one end and an RCA at the other. There is no pin 1,2,3 on a 1/4" phone plug. The phone plug can be a type TS (tip/sleeve) or a TRS (tip/ring/sleeve).

In the case of a BFD, we want to use the 1/4" TS phone plug (as shown in your url). This essentially shorts the ground and the minus differential amp together, which would be equivalent to shorting pin 1 and 3 on an XLR connector.

This would be the correct connection, but would do nothing to reduce hum if you were experiencing it.

brucek

So the cable I linked (TS to RCA) wouldn't offer me any more value over my existing RCA cable to RCA->TS adapter?

**brucek** · **07-30-08, 07:15 AM**

Quote:

So the cable I linked (TS to RCA) wouldn't offer me any more value over my existing RCA cable to RCA->TS adapter?

In what regard? Do you mean noise immunity?

brucek

**myn** · **07-30-08, 10:16 AM**

Quote:

brucek wrote:

In what regard? Do you mean noise immunity?

brucek

Removing hum.

**brucek** · **07-30-08, 12:02 PM**

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Removing hum.

The only way to remove hum with a cable would be to build a cable that uses a pseudo balanced configuration.

This involves buying a 1/4" TRS plug and wiring it to an RCA connector using two conductor shielded cable as shown below.

See how the positive (+) of the RCA connects to the Tip (+) of the TRS, and the ground of the RCA connects to the Ring (-) of the TRS, and the shield of the TRS connects to the shield of the cable without a connection back to the RCA.

This removes the physical connection between the RCA device chassis and the BFD chassis, which reduces the ground loop considerably. There is still noise rejection realized from the balanced configuration in the BFD, since noise rejection basically relies on matched impedances at the two inputs of the differencial amplifier stage. The impedance of the positive differential amplifier will be that of the previous stages output impedance, while the negative differential amplifier will be at ground or zero impedance. The mismatch still offers decent noise rejection.

Note that you require two conductor shielded cable to use this configuration, and that depending on the severity of the ground loop, this may not offer enough help.

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Name: pseudo balanced.jpg
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brucek

**myn** · **07-30-08, 02:23 PM**

Very thorough explanation. Thanks.

**bobgpsr** · **07-30-08, 06:45 PM**

Excellent post Bruce! One can also use a XLR connector plug instead of the 1/4" TRS phone plug to do the same thing.

**myn** · **07-30-08, 09:46 PM**

So the The easiest way to build this cable might be to buy an XLR to XLR or TRS to TRS cable and then remove one of the XLR or TRS ends replacing it with an RCA connector wiring the RCA connector appropriately as documented in the image above?

This would fit the requirement around having a cable with 2 conductors with shield and you're half there having the cable already bound with either an XLR or TRS connector on one end. I am assuming there wouldn't have to be any changes made to the XLR or TRS end as the main change in wiring occurs at the RCA termination.

Correct?

**brucek** · **07-30-08, 11:18 PM**

Correct..........

**RazorX** · **10-04-08, 12:39 PM**

I bought a Rolls HE18 "Buzz Off" hum eliminator at my local Guitar Center last week and I am very happy with the results.

I had a pretty noticeable hum that I was chasing down and decided to try a hum eliminator. I have read of many people having good luck with the ART Cleanbox II but couldn't find any local. I was able to find one of these in stock so I decided to give it a try. It has completely eliminated the hum and the response curve is unchanged (measured with REW). I also like the fact it has standard RCA inputs/outputs in addition to the 1/4" inputs/outputs.

**thsmith** · **10-05-08, 12:06 PM**

I ordered the DCI product that many people seem to have good luck with here, I currently have a cheater plug I am using on the BFD.

Where does the DCI product go, between AVR and BFD or BFD and sub ?

Thanks

**Wayne A. Pflughaupt** · **10-05-08, 07:27 PM**

From what I see at the DCI web page, it's supposed to be connected in front of the amplifier - i.e., between BFD and sub.

Regards,
Wayne

**thsmith** · **10-05-08, 07:51 PM**

Thanks, that what I thought but wanted to make sure.

**Aminbiz** · **10-06-08, 04:25 AM**

When I ran my Cable/satellite coax into a power/line conditioner first before connecting it to the box it solved my problem, no more hum !

**lcaillo** · **10-06-08, 06:52 AM**

That likely means that your system is not grounded properly. The surge suppressor is just a patch for this and should not be used as a final solution.

http://www.hometheatershack.com/foru...grounding.html

**Aminbiz** · **10-06-08, 04:01 PM**

so what you are saying is that if the line conditioner is grounded and it eliminates the problem then this is wrong ?

**lcaillo** · **10-06-08, 04:12 PM**

No, I am saying that it is only a patch on the real problem. You have tied the grounds to the same potential. This is fine, but you should not rely on the ground path through the line conditioner. You should be sure that the cable and sat systems are properly gorunded to the electrical service ground, and that all of the connections are clean and tight. You could still get a ground loop with everything properly grounded, but it is far less likely. Your protection is compromised if you have a bad (or no) ground on any system coming into the home.

Read the material that I linked to.

**thsmith** · **10-14-08, 09:39 AM**

I am currently using a cheater plug on the BFD until I sort out my hum problem. I ordered the DCI product which made matters worse.

Working with Dave at DCI we determined it is a SAT receiver issue and come to find out DirectTV never grounded the mast or installed grounding blocks for the cables, that has been remimeded this morning.

Anyway, Dave sent me this article. This weekend I tried the cable modiciation describe on the BFD hum forum with no difference but when I tried the one Dave sent it cust the hum in half. When I put the DCI at the sub as recommended the hum was back being louder.

Tonight I will test again with a properly grounded SAT.

**jstefano** · **11-13-08, 07:08 PM**

I just plugged in my new BFD and I have the dreaded "HUM" has anyone come up with any new fixes for this since 10-14-08 "Last Post"? What seems to be best? I checked my grounds they are intact.
Joe

**texfrazer** · **11-26-08, 10:41 AM**

Quote:

jstefano wrote:

I just plugged in my new BFD and I have the dreaded "HUM" has anyone come up with any new fixes for this since 10-14-08 "Last Post"? What seems to be best? I checked my grounds they are intact.
Joe

Hi Joe,

I see that you are using DirecTV as one of your video sources. From what I have seen (and read in this forum), there is a decent probability that your satelite receiver is not properly grounded. I would check that to start with. If that is ok, then I would check your electrical ground wire to ensure that it is tight, with no corrosion.

Let us know what you find.

**NEO Dan** · **12-17-08, 01:40 AM**

Another alternative:
The ground goes to your AVR's chassis/phono/AM ground.

**thewire** · **12-26-08, 04:47 PM**

I sawed off the end of an extention cable and plugged the BFD into it without the ground. I plugged that into a surge protector. Now when I turn my level up higher past -10dB reference I do not hear the hum in the speakers.

**bobgpsr** · **12-26-08, 08:27 PM**

I still think the brucek's way (post #155 in this thread) is the best method.

Do not connect the cable shield at the AVR source end. Avoid making this connection to avoid a ground loop. Connecting a cable shield every chance you get is great for stopping RF leakage but bad for audio hum caused by ground loops.

**NEO Dan** · **12-28-08, 07:03 PM**

Quote:

bobgpsr wrote:

I still think the brucek's way (post #155 in this thread) is the best method.

Do not connect the cable shield at the AVR source end. Avoid making this connection to avoid a ground loop. Connecting a cable shield every chance you get is great for stopping RF leakage but bad for audio hum caused by ground loops.

Bob,
there are lots of folks out there who've already tried the cable connection I've suggested including myself. In my experience it has always been quieter with the shield connected at both ends. Nobody that tried this cable(I sent quite a few out) has ever said that they created a ground loop or more noise with the shield connected at the source. Quite the opposite in fact, most of the people that tried it wanted to buy the cable.

**Wayne A. Pflughaupt** · **12-28-08, 10:56 PM**

Quote:

NEO Dan wrote:

Another alternative:
The ground goes to your AVR's chassis/phono/AM ground.

Not sure how or why that would work. The phono ground lug has continuity with all RCA sleeves. IOW, it's no different than tying the shield and black together on the RCA end. Which is no different than using a plain RCA to mono 1/4" plug. Am I missing something?

Regards,
Wayne

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