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Help: Speaker's hum/buzz troubleshooting

veeceem

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So I noticed there are buzz/hum at random time when I turn the amp on. But tonight I decided to find out what caused such annoying buzz/hum. And I found it.
1/ Amp (grounded) connected to speakers only: turned on, it happened.
2/ Preamp connected to amp then speakers: still happened (only amp was grounded)
3/ I use another amp, it still happened.
4/ So I took sometimes to think about it, what couldve been the cause? Then I recalled, on step1, I still left the rca cables "A" connected at amp's end! Then I picked another pair of coaxial rca cables "B" (shielded).
I then, did a "A" vs "B" test, with them plugged/unplugged into the amp. I replaced them one after another, then turned amp on, I did 3 times each to make sure.
Result:
A: hum/buzz
B: silent
A: hum/buzz
B: silent
A: hum/buzz
B: silent
--------
A: $350 a pair of 1m
B: just something lying around but shielded.
--------
What couldve been the cause? It's not always happened.
My guess is RFI/EMI?
FYI: those are from England and they're red.
P/s: there's a big antena-like device not so far from my house, I can just walk there in minutes (in a straight line). I believe it's something used to re-cast/amplify the signal from the further away TV station. I think so because long ago, the TV station gave me an offer to put such thing on top of my house and pay me monthly in return, but I refused, so they picked another house/location, which is just across the street. Can take a photo of it tomorrow if needed
P/s2: and local TV station is not that far from my house, I can see its attena from the top of my house, approximately 7km max, in a straight line
 
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Doodski

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Seems like you may have a bad cable. Check it with a multimeter and wiggle it around to see if there is a intermittent connection. If the cable is not expensive just replace it.
 

Berwhale

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It sounds like your $350 cables are faulty and the cheap ones you had lying around are not. Best stick with the cheap ones and get your money back on the expensive ones.

Out of interest, did you try changing the direction of the $350 cable? (the shield may be connected at one end only, so you'll ground the shield from a different component if you swap the ends around)
 
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veeceem

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It sounds like your $350 cables are faulty and the cheap ones you had lying around are not. Best stick with the cheap ones and get your money back on the expensive ones.

Out of interest, did you try changing the direction of the $350 cable? (the shield may be connected at one end only, so you'll ground the shield from a different component if you swap the ends around)
I tried switching sides, each cable and both cables connected, ect.... Only the $350 ones had the hum/buzz
 

Doodski

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I tried switching sides, each cable and both cables connected, ect.... Only the $350 ones had the hum/buzz
It happens. There's probably a bad connection at a solder or crimp point. Being a pricey cable they should unthread so you can inspect the connections. Otherwise before you try a repair can you get warranty service or exchange on them?
 
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veeceem

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It happens. There's probably a bad connection at a solder or crimp point. Being a pricey cable they should unthread so you can inspect the connections. Otherwise before you try a repair can you get warranty service or exchange on them?
These were bough more than 1 years ago. Btw, I'll test them again today vs a pair of $1 cables to see if the shielding is the problem.
AFAIK, it does not always happen. I'll be reporting back
 

Doodski

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This is generally what a person can expect if they unscrew the RCA cable connector. If you don't have a lower powered soldering iron I suggest you find somebody that does. Approaching the repair with the a overpowered soldering iron will probably melt the insulation, cause solder to run all over and cause more problems.
19968.jpg

 
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veeceem

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Confirmed: so I tried another cable that I know surely unshielded (the generic one which is less than $1 a pair)
The hum/buzz is loud on 86dB speakers.
Does this mean its RFI/EMI related? And the $350 pair are unshielded?
 
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veeceem

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Same angle, in the wider pic, you can see the antenna of TV station on the far right corner. It's morning here so quite cloudy
 

Doodski

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Confirmed: so I tried another cable that I know surely unshielded (the generic one which is less than $1 a pair)
The hum/buzz is loud on 86dB speakers.
Does this mean its RFI/EMI related? And the $350 pair are unshielded?
Considering we nailed the problem down to a bad cable we can assume all is well.
I wouldn't worry about those cel towers for now or other interference.
Is that yellow and black cable a good or bad cable?
 

direstraitsfan98

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Try a few things. Make sure whatever your amp is outputting to has enough distance from the pre. Make sure the cables aren’t touching each other. Make sure the inputs are secure and tight. I’ve owned plenty of esoteric cables and they tend to have more buzz then just basic $3 Mogami XLR balanced cables. I guess because RCA cables aren’t typically shielded but by their nature balanced cables are.
 

NTK

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You may also try wrapping your unshielded cable with aluminum foil (and ground it if you can) and see if there is any improvement.
 

NTomokawa

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try wrapping your unshielded cable with aluminum foil (and ground it if you can)
Try this. Seriously. A lot of shielded cables are made this way, only they have the foil under the insulation.
 
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veeceem

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1/ everything (amp/pre/wires/ect...) stays apart from each other.
2/ the yellow wire is considered "C" cable, I used it to test if it's unshielded cable that is the problem.
3/ when I get home, I'll look around to see if I can find something else shielded/unshielded to test more
4/ will find something to try shield the unshielded one to test
 

Doodski

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1/ everything (amp/pre/wires/ect...) stays apart from each other.
2/ the yellow wire is considered "C" cable, I used it to test if it's unshielded cable that is the problem.
3/ when I get home, I'll look around to see if I can find something else shielded/unshielded to test more
4/ will find something to try shield the unshielded one to test
Do you have a turntable and use it if you have one?
 
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