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Got myself a home theater kit the other day but my sub makes humming/buzzing noise when powered on. I guess it's the noise from AC network. So for testing I plug it in to the shaver socket as it's separated transformer and most of the noise is gone.
So i need to connect it through isolation transformer of some sort. I would like to keep it as small as possible and sub is only 100w.
Any suggestions?
 
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  • Thread Starter Thread Starter
  • #3
Will it make a difference? It's a class 2 equipment and casing is not connected to any internals I guess?
 
Wave your magic "Volt stick / fairy wand near the cases"...
1x earth may help -near an amp- ( do they do digi / optical inputs on subs !)
..sadly the best speaker to hear any 50Hz hum on..
 
  • Thread Starter Thread Starter
  • #6
I did try with earth to the casing but no joy.
Inputs are RCA but even without anything connected I got hum so it must be from AC.
Basically I need something like THAT but much smaller as only need to pull around 100w and need to fit in the cabinet
 
Just be wary with your "Isolated diagnosis"-Shaver socket
may not have quite been running at normal voltage ....
Hence volume was diminished.
 

Bob Geldoff1234

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Surely,if there's a hum from the sub woofer then it's either A:- a cheap system or B:- faulty.
You shouldn't have to start messing around with transformers etc if it's brand new:confused:
 
You want pure sound? It comes with a price tag.


There is another way, turn the sound up and then you won’t notice the mains hum.

BTW both dad and I had ASBO’s for noise pollution.
 

marconi

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Some suggestions:

1. Use the highest quality LFE(Low Frequency Effect) sub woofer leads with gold plated connectors and keep them short, and un-coiled and separated as far as practicable from mains wiring.

2. Clean surfaces of plugs and sockets.

3. Plug all AV equipment into the same point ie: one high quality socket strip.

Some further trials:

4. With the AV equipment on but not playing turn on:

i) the electric shower;
ii) the electric oven;
iii) the electric kettle;
iv) an electric heater.

Does the amplitude of the mains hum increase with each being switched on?

5. Please tell me what is the homes type of supply - TNCS, TT or TNS? If you don't know from looking please post a photo of your intake including the main supply cable and main cut out and include in the shot(s) where the thick green/yellow earth conductors go to.

6. What kind of lighting do you have in the room and how is it controlled?
 
  • Thread Starter Thread Starter
  • #14
1. Got another cable coming soon, but noise is present without anything connected to the sub except power lead and sub powered on. I start to think it may be internal transformer making that noise.

2. Will try but it's all new, sockets fascia plugs, etc

3. Did that too, did not help, anywhere I plug and power on the sub it make that noise

4. No electric shower or heater but will try with other and report back

5. It's TNS, again all pretty new as I have done lots of work in the house in last 12 months

6. This room have light fitting with 3x CFL bulbs on standard light switch, and most of the house have led spots or other led type lights

Did contact technical as well, maybe they will help
 
  • Thread Starter Thread Starter
  • #15
And there is also free standing light with g9 capsules on integrated dimmer in that room
 

marconi

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For my Item 2 I meant AV plugs and sockets not mains ones.

No doubt you have thought of checking if the hum is worse with the g9 lamps switched on.

Could you measure the supply N-E voltage at the CU with the Main Switch on and then off.
 
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telectrix

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if you're going to play current pop music. the hum will be an improvement.
 

marconi

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We are exploring mains pick up through cabling and connectors, earth loops when AV items are plugged in at different places (- one should use star configurations and linearly linked stars for earths to avoid earth loops), and mains frequency potential differences (differential/transverse mode) - through volt drop along the supply Neutral - between local earth mass and the supply Neutral which results in - electrically - the waggling at 50Hz of the potential of the double insulated sub woofer electronics assembly with respect to its casing which is at ambient/local earth potential - not the same potential as the incoming supply E. For the latter waggling the isolation transformer removes/reduces the galvanic connection to neutral and as reported reduces the hum but does not erradicate it because there is still some capacitative linkage and the lines (L and complement L*) of the shaver output are floating with respect to local terra firma. Sometimes an NTS supply can be used for audio equipment - a bit like an I-T but with the line complement L* connected to local terra firma to make a N* - a neutral with respect to local earth through an electrode in the ground- and this connection used to provided a local terra earth for the cpc of the audio equipment.

(Or something along these lines - being nagged to serve dinner now. Others can correct or amplify.)
 
  • Thread Starter Thread Starter
  • #21
@Midwest
I'll definitely try this

@marconi
N-E shows 0v with mains switch on or off.
None of the appliances affect the noise at all.
Sub is on RingFC up+down.
I also tried the sub with all MCB off except for that 1 socket just to exclude any potential noise from other devices in the house - still no luck.

I will see what the tech support say

In the meantime I'll relax listen some AC⚡DC "noise"
 
I was similarly disappointed with Hum+hiss from a Hi fi loving mates new sub.
(and now fully understand why the diagram has placement of Sub -behind the listener -( and covered in a curtain !))
 

marconi

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Prompted by Static Zaps #22 I pondered the physics of the low frequency sound from your sub woofer. The speed of sound in air is about 350m/s so a 50Hz sound wave has a wavelength of about 7m. This wavelength is much longer than the dimensions of your sub woofer speaker and box meaning the sound it emits is largely omni-directional. However, being comparable to the dimensions of your room there may well be the effects of constructive and destructive interference between sound bouncing off your walls, floor and ceiling. Such interference for a steady 50Hz tone will produce stationary regions/directions of peaks and nulls in sound amplitude. Where you normally sit in relation to the sub woofer may well be in a peak accentuating the 50Hz hum - you said it sounded less in the showroom. I wonder then if you might experiment with the position of your subwoofer in relation to the walls and the listener. Corners will be good reflectors so perhaps try locating the woofer away from them. Lastly, maybe put some sound absorbent material behind the sub woofer - a curtain? - so the predominant sound is from the speaker towards the listener than from reflections off near walls behind it. So, some trials. Top end Hifi buffs will be able to provide their experience on locating speakers and room acoustics.
 

mattg4321

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I've had this on 2 subs now. Neither of which are particularly cheap. One of which I still own and it still does it.

I have a few ideas to try out, but it's not yet bothered me enough to do so.

Mine sounds very similar to yours:
  • Lighting/appliances etc etc make no difference
  • It's done it in two different houses - very similarly
  • The sub is double insulated
  • I've tried plugging all into same lead etc and it made no difference
The only thing that seems to help is if I touch the sub metal casing whilst simultaneously touching the tv metal casing (also double insulated) it gets a fair bit quieter. Unplugging the TV doesn't help! Touching something that is earthed doesn't help. I think touching the bluray player or amp at the same time may have helped a bit too but can't remember now.
 

marconi

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Based on mattg4321's helpful #27 I'd try bonding the casings of all equipments together so they all share the same ambient earth potential at 50Hz.
 

Midwest

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Based on mattg4321's helpful #27 I'd try bonding the casings of all equipments together so they all share the same ambient earth potential at 50Hz.
Marconi much respected, but bits of green/yellow wire looping around ones cinema room, doesn't look particular stylish :D
 
  • Thread Starter Thread Starter
  • #31
@Midwest
Tech support come back today but not much of a help, basically try to plug it in somewhere else to double check and if still buzzing take it back.

Also did not post on the forum from the link but did read lots of post there about same problem and tried few solutions but din not get anywhere.

@mattg4321

Seems like excacly same issue.
Did you try to connect it to isolated transformer or some power conditioner or even shaver for testing purpose?


I may try to link the casing of the amp and sub, in my case is all build in so won't see any cables.

What's bothering me is that this is second unit (first one was from Amazon and did excacly the same thing) and this one was plug in in the store and I could not hear anything. On the other hand they may have all equipment connected through some kind of power conditioner.
 

mattg4321

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The last one I had that did this was about a decade ago and I'm pretty sure I returned it for a replacement and it did the same thing!

I seem to remember the humming stopped on my current sub for a few months maybe a couple of years ago, then started again.

I'm pretty sure it's something to do with earth potentials as @marconi has been alluding to. I'm not sure its a 'fault' with the sub. More that its some kind of design error that makes them do this under some circumstances i.e. supply voltage/quality differences from one place to another.
 
Human hearing is easily distracted ,
( take a sound level meter with you )
.. Shop test only needs to be a little noisier
and in a wide open space !
..could compare by taking it outside..
Power supply is some of cause ...
but it will be a bit ,dangerous + expensive to run from
batteries !
 

Midwest

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@Midwest
Tech support come back today but not much of a help, basically try to plug it in somewhere else to double check and if still buzzing take it back.

Also did not post on the forum from the link but did read lots of post there about same problem and tried few solutions but din not get anywhere.

@mattg4321

Seems like excacly same issue.
Did you try to connect it to isolated transformer or some power conditioner or even shaver for testing purpose?


I may try to link the casing of the amp and sub, in my case is all build in so won't see any cables.

What's bothering me is that this is second unit (first one was from Amazon and did excacly the same thing) and this one was plug in in the store and I could not hear anything. On the other hand they may have all equipment connected through some kind of power conditioner.
In that case (sounds like a product design problem), I'd send it back & claim a refund. Purchase from a different manufacturer.
 
If it hums when there's nothing plugged into it (aside from power), then it's almost certainly defective - or just poor quality. Ground loops from different earthing potentials are created when you're feeding unbalanced audio signals powered from one supply into a sub powered from another. If you're just plugging it in, switching it on and hearing buzz with nothing else connected, then something's wrong!
 

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