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 Post subject: Buzzing sound from speakers - normal?
PostPosted: 17 Feb 2016, 18:18 
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Hi!

I recently did some changes to my surround setup at home. One of them being that I introduced a power amp to drive the "new" stereo speakers in the front. When it is powered on, I do hear a buzzing sound coming from the speakers. It stays constant. It isn't loud, but I can hear it from my sofa three meters (~10 feet) away if there is no or very low sound input. This can't be 50Hz hum, since I do hear the same buzzing in both the mid-range and tweeter too.

The speakers are adjusted to 75 decibel using a SPL-meter set to C and slow. Speaker distance is measured and added to the AVR configuration. All speaker wires are 2,5mm2 (~13 AWG). The power amp gets the signal from the left and right (RCA) pre-out on the back of the AVR.

A list of the equipment:
Yamaha RX-A2020 AV receiver
Cerwin Vega CXA-8 (power amp)
Cerwin Vega VE12 (stereo front)
Cerwin Vega XLS-6C (center speaker)
Cerwin Vega XLS-6 (surround back)
Cerwin Vega XLS-15S (active subwoofer)

I've unplugged everything, leaving just the power amp connected. It was the only thing powered on with only the speakers connected. I removed the RCA inputs to the amp as well. No change. I connected the speakers to the AVR and had no buzzing then. So something is going on with the power amp. The curcuit breaker trips very often (almost every time) when I power on the amp. That is a different issue, though. The buzzing is also slightly lower on the right speaker. I have tried moving around the speaker wires, having them at least 1 meter away from any mains, but it didn't change anything.

The electrical installation is from the 80s, so it isn't grounded. It is also an open installation, meaning the wires go on the outside of the wall. Not sure if this buzzing would go away if the amp were grounded.

Is it normal to have some buzzing coming out of the speaker when using a power amp? If I crank the volume all the way up on my AVR, I do get some hiss from the tweeters in the other speakers. This is, as far as I know, completely normal. What bothers me is the buzzing from the stereo speakers.
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 Post subject: Re: Buzzing sound from speakers - normal?
PostPosted: 17 Feb 2016, 18:36 
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you have some noisy switch mode power supplies on the same breaker? A plasma TV would do this.
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 Post subject: Re: Buzzing sound from speakers - normal?
PostPosted: 17 Feb 2016, 18:40 
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I did disconnect everything, leaving only the amp plugged in. Can go and double check, might be something I missed. A computer network switch or something. The circuits are a bit messy for some reason. The one in the hallway might be on the same as the living room.
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 Post subject: Re: Buzzing sound from speakers - normal?
PostPosted: 17 Feb 2016, 20:02 
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Still getting the buzz?
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 Post subject: Re: Buzzing sound from speakers - normal?
PostPosted: 17 Feb 2016, 20:09 
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Found out that the outlet under the stairs on the other side of the wall is on the same circuit. That one has a network switch AC adapter connected to it. Unplugged it and still get buzzing.

Could hook up the oscilloscope to the speaker output on the amp to get an indication on what kind of signal I'm dealing with.
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 Post subject: Re: Buzzing sound from speakers - normal?
PostPosted: 18 Feb 2016, 15:32 
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Hooked up the scope today. I'm not that experienced with troubleshooting and interpreting signals. It does look a bit noisy, though. The scope was set to 10mV/division, 5ms/division and AC coupling. It is connected to the amplifier output (speaker disconnected).

Have to correct my self a little bit. The noise does get slightly louder when volume set to full. Below that, it does appear to stay constant.

Volume set to full:
Image

Volume set to half:
Image

Volume set to lowest:
Image
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 Post subject: Re: Buzzing sound from speakers - normal?
PostPosted: 19 Feb 2016, 22:55 
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Are you (or anyone else in your house or getting power from the same transformer) using the powerline for computer networking? That's been known to give problems, especially where things aren't earthed.
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 Post subject: Re: Buzzing sound from speakers - normal?
PostPosted: 20 Feb 2016, 01:11 
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Well, I do have my fair share of different networking stuff. Different switches around the house. Also actually have a media converter for fiber optical networking that are dug between my and my neighbors house. What other neighbors have, I don't know. The reason we went for fiber is because the high-voltage power distribution line is in the ditch outside the house.

Could be possible that other equipment for some reason creates noisy power eventhough it isn't on the same circuit. Or a neighbor has something that affects my house too.

I'll try and pull a really long cable to a grounded outlet. In old houses only bathrooms and kitchens are grounded. Just a shame the nearest one is on the other side of the house, lol. Maybe giving the amplifier proper grounding might help. Worth a try at least.

Replaced the circuit breaker today at least. Finally I can power on the amplifier without tripping it!

I do also have a theory that the amplifier might be poorly designed. Transformer not shielded properly or something. It does have active cooling, in other words fans. Those might create some electrical noise too.
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 Post subject: Re: Buzzing sound from speakers - normal?
PostPosted: 06 Apr 2016, 19:05 
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Sounds like you may have a ground loop issue. A very simple test can be done using a cheap RCA plug ground loop isolater that can be bought on ebay for a few bucks..
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 Post subject: Re: Buzzing sound from speakers - normal?
PostPosted: 06 Apr 2016, 22:00 
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Can't really be a ground loop when there isn't any grounded outlets.
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 Post subject: Re: Buzzing sound from speakers - normal?
PostPosted: 06 Apr 2016, 22:35 
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samaron wrote:
Can't really be a ground loop when there isn't any grounded outlets.


I'm presuming you don't have any other components connected to a potential ground (like a cable television coaxial cable through a cable box, ethernet port, grounded antenna, etc)?
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 Post subject: Re: Buzzing sound from speakers - normal?
PostPosted: 07 Apr 2016, 01:28 
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Have taken it somewhere else and powered it up to see if the same noise exists or has gone away would then eliminate your home or surroundings.

Does the noise change when playing maybe a sine wave tone into the amp or does it stay the same?

Have you tried tapping the amp with your hand to see if it goes away.
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 Post subject: Re: Buzzing sound from speakers - normal?
PostPosted: 07 Apr 2016, 11:44 
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I've tried disconnecting everything on the circuit the amplifier is on. No change. I've also used a really long extension cord to a different circuit and hooked it up to an outlet that is grounded. No change. The noise isn't audible if I play music or whatever, unless the volume is really low.

Got a guy with more experience than me to look at my oscilloscope pictures. Theres a 100 Hz signal there which is probably from the rectified 50 Hz mains. There's also another signal which is about 15 times higher in frequency.

I've also tried tapping the amplifier with no luck.
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 Post subject: Re: Buzzing sound from speakers - normal?
PostPosted: 24 May 2016, 13:04 
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I finally managed to convince the hi-fi store I bought the amplifier from to take it in for service. It is normal to hear some noise when putting the ear right next to the speaker, not 1 meter or more apart. Hopefully I'm not struck by Murphy's Law this time too. I bought a Denon blu-ray player a few years ago from the same store. When playing a movie, it would suddenly glitch up the image, freeze and make some awful mechanical noises. I used two (!) years to get it replaced. Everytime I brought it to the store, it suddenly worked fine... Hopefully that is not the case with this amplifier too.

I can also add that I found pieces of cut cable ties behind the fan grill when I took the amplifier out of the packaging. Not exactly a good first impression to find junk inside the amplifier that I had to fish out when it is brand new...
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 Post subject: Re: Buzzing sound from speakers - normal?
PostPosted: 25 Jun 2016, 11:42 
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Finally got the amplifier back after a month. Apparently some repair were done to the input of channel 1 (left). I don't notice it, buzzing as it did before the repair... I actually think it is worse than it was, as the right channel also have some buzzing now. Not as intense, but I don't need to put my ear right up to the speaker anymore. Can hear it maybe 1 meter apart. The left channel I can hear from my sofa still, which is 3 meters away.

For being an amplifier that costs over 700 USD, I'm not very impressed. I've heard 50 USD amplifiers that makes a lot less noise...
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 Post subject: Re: Buzzing sound from speakers - normal?
PostPosted: 21 Dec 2016, 14:46 
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Have had the amplifier in for repair once more, but still got buzzing noises. I brought it to the store after the 2nd repair, tested it and confirmed the noise there. I got a text message from the store on Monday saying that I could come in and replace the amplifier with a new one, which I did. All good now! Guess it were faulty after all, and the actual problem never got fixed when it were in for repair the two times.

Eventhough the buzzing wasn't really loud, barely enough for me to hear it from my couch which is three meters away from the speakers, it felt like a dead pixel. Once you notice it, it is always there. Good to finally have it working properly now!
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 Post subject: Re: Buzzing sound from speakers - normal?
PostPosted: 21 Dec 2016, 14:55 
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Glad you finally got it sorted - quite a saga
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 Post subject: Re: Buzzing sound from speakers - normal?
PostPosted: 22 Dec 2016, 02:40 
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Just a thought, but it looks like it repeats every 4 divisions = 20ms which is the period for a 50Hz signal. Mains in Europe. Faulty reservoir caps can send this signal straight to the speakers. I did a repair like this last week.
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 Post subject: Re: Buzzing sound from speakers - normal?
PostPosted: 22 Dec 2016, 12:56 
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Yeah, I had a theory the mains somehow got through, but there's also a signal that is 15 times higher in there as well. Got noise through all speakers (tweeter, mid and woofer). Thankfully I got a new one on warranty. If not, I would probably have started to tinker inside more. A bit weird if the caps were defective out of the box (and not noticed on the two repairs it were on), but I guess it isn't impossible. It is just a really big hassle to get anything checked/replaced on warranty since it is pure waste of money for the seller. I used two years to replace a faulty blu-ray player with a mechanical fault on warranty once as well.
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