What solution do folks use for the dreaded BFD hum? - Page 4 - Home Theater Forum and Systems - HomeTheaterShack.com

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post #31 of 324 Old 10-04-06, 10:15 AM
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Re: What solution do folks use for the dreaded BFD hum?

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?

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post #32 of 324 Old 10-04-06, 10:56 AM
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Re: What solution do folks use for the dreaded BFD hum?

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)...........

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post #33 of 324 Old 10-04-06, 12:30 PM
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Re: What solution do folks use for the dreaded BFD hum?

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?

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post #34 of 324 Old 10-04-06, 12:49 PM
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Re: What solution do folks use for the dreaded BFD hum?

Quote:
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?

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post #35 of 324 Old 10-04-06, 12:59 PM
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Re: What solution do folks use for the dreaded BFD hum?

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.

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post #36 of 324 Old 10-04-06, 01:23 PM
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Re: What solution do folks use for the dreaded BFD hum?

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.

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post #37 of 324 Old 10-05-06, 06:43 PM
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HELP!

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!

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post #38 of 324 Old 10-06-06, 12:01 PM
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Re: What solution do folks use for the dreaded BFD hum?

Quote:
brucek wrote: View Post
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.

Last edited by tdamocles; 10-16-06 at 10:16 PM.
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post #39 of 324 Old 10-06-06, 12:38 PM
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Re: What solution do folks use for the dreaded BFD hum?

Quote:
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?

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post #40 of 324 Old 10-06-06, 01:22 PM
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Re: What solution do folks use for the dreaded BFD hum?

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.


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