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post #91 of 98
I have recently purchased a brand new AV7701 to go with my MM8077. About a week after I had installed it, I realized that the right surround tweeter is making an intermittent static noise, as if it is picking up interference. So, I decided to perform the following tests:

• I swapped the speaker cable between the left and right surround speakers: the noise remains

• I moved the right surround speaker from its original position to another a few meters away: the noise remains

• I swapped the XLR outputs of the AV7701 between the left and right surround channels, while keeping the same inputs on MM8077 (effectively swapping the rear channels): the noise moved from the right channel to the left

• I used RCA unbalanced inputs instead of XLR: the noise remains

• I moved the XLR output connector on the AV7701 from the right surround position to the right surround back position: I could still pick up a static noise. In fact there is a much weaker version of the same noise on the front right speaker, as well. Both front left and surround left speakers have no such noise.

In addition to the static noise from the right speakers, coming out of the tweeters, there is a constant low-volume buzz coming from all 5 woofers. However, I think that this one is normal.

My speakers are B&W Theatre (685,686). I have already run Audyssey calibration and I have updated the processor to the latest firmware.

Do people have any ideas as to what may be going on?

post #92 of 98
The low frequency buzz from the woofers probably is due to a "ground loop". That's most often caused by poor grounding of a cable or satellite decoder box signal, which people often fix by placing a 75 Ohm isolator in the coax line feeding the decoder box. Sometimes it's caused by different phases of power being used for different devices, which is often fixed by plugging everything into the same surge-protected power strip. (Some strips include the coax isolators, too.)

The results that you describe from your tests of the higher frequency noise certainly are confusing, since they're contradictory and point to the noise originating from different devices. Do you have a different pre/pro or receiver with preamp outputs that you could try?

If you haven't already, you might try unplugging the cable/satellite box from everything, including the incoming signal coax and its power cord. People have reported strange effects which wound up being due to grounding problems. If the noises go away with it unplugged, that certainly would point at the cable/satellite box or its connections.
post #93 of 98
Hi Selden,

Thanks for your reply. I have read a lot about this "ground loop" thing. However, I forgot to mention that before my tests I had unplugged all other devices plugged onto the same wall and had disconnected all inputs to the prepro. I had also plugged in both prepro and power amp onto the same power strip. And I had disconnected the coax aerial cable, too. So, I don't see how there can be an issue with a ground loop.
By the way, I also tried testing the sound with only the power amp switched on, and it was absolutely quiet. As soon as I turned on the prepro, the buzz returned.

As for the high-frequency static, as I said, it only seems to occur on the right channels. The rear right is mostly affected with the front right suffering less from it. I did notice that things become noticeably quieter at night and/or after a few hours of operation; I'm not sure which one plays a role. The left channels are devoid of this problem. Just in case it has to do with the speaker position or speaker cable, I did move the speaker and swapped the cable with no change; It is always the right channels that are affected by this.

I like your idea of trying another preamp. My old receiver is a Sony STR-DG820, which has component stereo out jacks that I can try to connect to MM8077. This may give me a clue. Thanks.

As for those advanced power strips, e.g. Monster HTC, etc., I am a bit sceptical. I would not like to use anything that draws current, i.e. with an RFI/EMI coil, as I have heard that it limits the power going into the equipment with some adverse effects.
I have also tried to rotate the two-prong european plugs but that did not change anything.

One thing just came to my mind but I'm not sure that's it. The coaxial cables that connect my satellite dish to the sat decoder are all running along the right-hand side of my setup. However, the decoder was not plugged in during the tests, so I don't see how there could be interference from those cables. Also, I did say I moved the speaker to another location, so that's not it.

Anyway, I will try connecting my Sony to the MM8077.

Edited by anoutsos - 2/10/13 at 1:40pm
post #94 of 98
Is there any chance some of the noise might be caused by poor connections? You might try tapping on the connectors to see if that makes any difference.

FWIW, I use (industrial grade) TrippLite IsoBars in my primary system. They include inline noise filtering. I've never heard any sonic effects that I could blame on that. The improvement provided by Audyssey is much greater than that kind of subtlety; in my system, anyhow.
post #95 of 98
Thanks again for the info. Well, the connections to the power strip are pretty snug. The two-prong male connectors (C18) at the other end of the power cables (that came with the amps) are not the most reassuring, as they have some slack. I have tried to push them in a bit, just in case, but that's as far as they get. I think that as long as they make contact, they should work fine.

The xlr connectors are all the way in. I pushed them in until I heard them click, so these are fine too.

Yesterday I came across an interesting thread by a guy who claimed that the buzzing sound is normal in separates that have not been grounded properly (http://forums.audioholics.com/forums/amps-pre-pros-receivers/70111-marantz-av7005-networking-v-processor-review-13.html).
He used some wires to connect the chassis of the prepro with that of the power amp and then to a ground. He says that in general it is unlikely that both prepro and amp are at the same potential, so there will always be phantom power that needs to be driven to the ground. I am not sure I want to start wiring the back of my system to cure such a faint buzz (can only hear it a few inches from the mid-frequency driver). If it is just that and not a faulty prepro, I can go to sleep at night knowing that.

I've just finished testing the buzz with the method you suggested. I connected the analog outs of my old Sony DG820 receiver to the unbalanced ins of MM8077, connected the ins of the Sony receiver to my blu-ray player's analog outs, flipped the switch from balanced to unbalanced on the MM8077 and … I still got a buzz through the speakers! eek.gif So, it seems that it is a grounding issue. Well, …

I thought I'd let you know, after a few days of monitoring, that the high-frequency static noise from the tweeter is of a transient nature. E.g. I noticed today that I could pick it up more on the left surround! Very weird. It seems to be some sort of RFI. Again, it is mostly very faint. I only noticed it the other day when it suddenly became audible from about 3 feet away, as it sounded like stepped intermittent hiss: _____

Finally, I would like to ask you about the tripp-lite power strip. Before getting the Marantz equipment, I researched to death whether I needed a fancy, line-filtering power strip. I decided that I didn't need one, as many people say that unless you go for a proper solution, like PS Audio, you are not improving anything. Of course, I would not want to spend that much on power regulation. The cheaper solutions of a filtered power-strip sounded appealing but people either say that it affects the soundstage (weird) or that it makes no difference. Especially with products like the Monster HTS 1000, people have reported lots of problems, incl. buzzing, malfunctioning, etc. Perhaps this Tripp-Lite product is adequate and it doesn't cost very much. (I was once very close to buying the Oehlbach Powersocket 608, http://www.oehlbach.com/en/home-cinema/power-home-cinema/powersocket-908, but I chickened due to the price and that it may not make a difference, after all.)

Thanks for your suggestions.
post #96 of 98
If what you're hearing is RFI pickup, then it's going to be rather difficult to eliminate. Since you're using XLR connections, they already should be eliminating most of the noise. Can you substitute RCA connections? If it's RFI, I'd expect RCA cables to allow even more noise to get into the system. That'd help verify the source.

High-power radio and TV stations often are culprits. Sparking in nearby high-power electrical motors is another possibility. Essentially, all wires act as antennas for picking up the noise. Grounded shielding around all cables sometimes is needed, as well as copper mesh over all equipment air vents, and ensuring all seams are electrically tight. (i.e. making all boxes into Faraday Cages.) Sometimes ferrite filters (aka "beads") are needed in all internal power supply wiring. It can get to be rather expensive.

I use TrippLite because we use them for computers at the research lab where I work and I can make a personal purchase of them from the Lab's stockroom. Unfortunately, when people report subtle audio differences, there's usually no way to reproduce those results in anyone else's system. Often enough the differences can be blamed on "expectation bias" -- i.e. you hear the subtle effects that you expect to hear.

Do bear in mind that Monster sells all of their products at a very high premium. Equivalent products from other companies (like Monoprice or Blue Jeans Cable) usually cost a lot less. My personal opinion is that any company which makes a point of advertising "ultra-pure oxygen-free copper" is charging you for their advertising, not for any anything useful.
post #97 of 98
Just to update you guys AND the new enquirer, Time Warner had to run a new ground and I STILL HAD TO GROUND my receiver to my rack AND powerconditioner. Once done, Hum gone. I stripped out the bare wire to a peice of romex and grounded the AV7701 to the rack and then to the powerconditioner. Its still a major Time Warner issue but I was told in no uncertian terms that it was on me to fix it. At least it was fixable. Next goal is fixing the horrible picture from the TW box over HDMI(another Time Warner problem they are famous for). Still cant upconvert the TW picture to 1080p without a pink distortian washing over the picture. Im going to try to use componet to the AV7701 from TW and let the AV7701 upconvert the sorry 1080i picture from TW. Ill keep you posted.
post #98 of 98
Originally Posted by IdoAV View Post

Just to update you guys AND the new enquirer, Time Warner had to run a new ground and ...

This is wrong. They are supposed to attached their equipment to the existing ground of the house. But most of those install people, cable or satellite, are lazy. Multiple grounds don't all have to be at the same voltage potential, and that's where the group loop comes from.

But you found a good solution, nonetheless. smile.gif
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