Eliminating subwoofer hum/buzz

[kropaske]

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?

 

[The Ghost]

Earth the system?

 

[kropaske]

Will it make a difference? It's a class 2 equipment and casing is not connected to any internals I guess?

 

[Midwest]

Ask these bods, we only know how to install the sockets

Home Cinema Speakers - https://www.avforums.com/forums/home-cinema-speakers.45/

 

[static zap]

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..

 

[kropaske]

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

 

[static zap]

Just be wary with your "Isolated diagnosis"-Shaver socket
may not have quite been running at normal voltage ....
Hence volume was diminished.

 

[Bob Geldoff1234]

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

 

[Midwest]

Happy New Year You filthy Animals

 

[Carl S]

I use a 2kW mains conditioning unit borrowed (permanently) from our laboratory. Something like this but it was free IsoTek EVO3 Mini Mira Mains Conditioner - MCRU - https://mcru.co.uk/product/isotek-mini-mira-mians-conditioner/?gclid=EAIaIQobChMIr5CFrvvM3wIV77XtCh1CFw7lEAQYBSABEgJ4SPD_BwE&v=79cba1185463

 

[kropaske]

I did read about them it may be good idea but bit pricey.

 

[Carl S]

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]

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?

 

[kropaske]

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

 

[kropaske]

And there is also free standing light with g9 capsules on integrated dimmer in that room

 

[marconi]

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.

 

[Midwest]

If it’s making a noise just sat, take round somebody else’s house, see what happens.

 

[static zap]

@marconi Love the bit , Kettle on you RFC ... If broken 2X ,
For when its now a giant induction loop !

 

[telectrix]

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

 

[marconi]

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.)