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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:

LIFT copy.jpg

Make any sense?

brucek
 

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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.
 

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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
 

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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:
 

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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
 

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

 

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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
 

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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.
 

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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
 

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

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I'm sorry to report that lifting the ground did not help. I desoldered the ground from the sleeve in the TRS connector plugged into the CleanBOX II, and the results were unchanged. It still generated a loud hum. Wierd.

The hum I'm trying to get rid of is very low level. I can hear the hum start when I rotate the receiver volume dial up from "---" (muted) to "-70" dB. Could it simply be the noise floor of the sub pre-out of my Denon AVR-1905?

I did come up with something that reduced the level of the hum by -10dB, so that its pratically inaudible at the listening positions now.

I had the BFD input set to "-10 dBV" as instructed. But I had to set my reciever's sub pre-out to the minimum -12dB and it still clipped the input of the BFD with "The Haunting" in DTS at reference level. So I switched the BFD to the "+4 dBu" setting and was able to increase the receiver's pre-out level to -2 dB without clipping, and dial back 10dB on the amp. So now the hum is being amplified 10dB less, and its barely noticable. It doesn't bother my wife at all, and I only care because I tend to obsess. :coocoo:
 

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I desoldered the ground from the sleeve in the TRS connector plugged into the CleanBOX II, and the results were unchanged. It still generated a loud hum. Wierd
Then it's not a ground loop. That's what this exercise was supposed to remove. The hum is in the signal from the receiver. No amount of gizmos will remove that unfortunately...

brucek
 

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Well, my DMC-1 and MPS-1 are both plugged into the same outlet, and if I completely decouple the grounds between the two, I have crazy noise. I found that depending on the arrangement of XLR pre-outs to amp modules, the amount of noise (and the channels, since different channels are going to different modules now) would vary. I had to decouple only some of the XLR connection grounds.

So, I didn't have a ground loop either, it would seem, based on extensive troubleshooting on my own, with AV123, and from discussions with a Furman engineer. However, I did have noise that I was able to remove by lifting the ground on selective interconnects.
 

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The hum is in the signal from the receiver. No amount of gizmos will remove that unfortunately
Note that I'm talking about two different hums.

1. Without the CleanBOX II there is a very quiet hum. It might be the receiver.
2. When the CleanBOX II is introduced, there is a very loud hum. I don't know how this is being generated.

The quiet hum may be generated by the receiver, but I wanted to try the isolation transformer to see if it would be eliminated that way or not. Unfortunately, the isolation transformer is introducing another problem altogether and I am no closer to a definitive diagnosis of the original problem.
 

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I may try the original CleanBOX instead of the CleanBOX II.
It converts RCA inputs to XLR outputs.

Will the BFD convert an XLR input to a 1/4"TRS output?
 

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When the CleanBOX II is introduced, there is a very loud hum. I don't know how this is being generated
Makes no sense to me........

Will the BFD convert an XLR input to a 1/4"TRS output?
Yep, both connectors are active

I may try the original CleanBOX instead of the CleanBOX II.
I think they're the same except the Cleanbox introduces some gain with an active stage (requires plugging in an AC adapter).

brucek
 

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Inserting the CleanBox II seems to be exactly what I experienced when I completely disconnected the processor and amp grounds from each other. I had to leave ground between at least one channel, or else everything was kaka.

Have you tried rearranging which outlets your receiver and BFD plug into? Trying combinations of different outlets and same outlets might do something. It didn't do anything for me, but you might try it.

One thing I was doing before with a Yamaha RX-V1400 and Outlaw Audio 7100 and Alesis DEQ-830 was to wire the chassis together using 12awg copper and then stick the last end of the copper into the ground of an empty outlet on the same power strip used by all three components. That reduced my noise by a few dB.
 

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I'm thrilled to report that I eliminated the receiver hum completely.
No, I did not solve the CleanBOX II mystery.

I messed around with the BFD filters some more. I used the old fake lowpass trick by inserting a filter at 1.00 kHz, 120/60 octaves wide, down -30 dB. This obliterated whatever noise the receiver was generating, all of which was above the subwofer band.

The CleanBOX II will go back. It never made sense to me either, Bruce.
 

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by inserting a filter at 1.00 kHz, 120/60 octaves wide, down -30 dB. This obliterated whatever noise the receiver was generating, all of which was above the subwofer band
Interesting that your receiver is outputting a noise around 1000Hz.

When I look at your filter (in green) I see it has almost no effect on your existing filters. That's good.
The phase (in red) only effects the crossover area by about 5 degrees, so that's good.

Too bad you had to go to so much trouble to track down the problem, but that happens sometimes.




brucek
 

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The noise isn't centered on 1.00 kHz, it seems to be made up of many frequency components and I couldn't track them all down by ear. The broad cut was my attempt to kill all components of that noise wherever they were in one fell swoop, and it worked.

Thanks for showing me the phase too. (Note that my filter width is two octaves and it looks like you simulated for one.)
 
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