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Speaker interference - advice please


BlueStringPudding

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47 minutes ago, WotEver said:

Then it’s not an earth loop. 

 

Try the suggestions above, and good luck :)

How do you work that out? More likely to be an earth loop with 12v stuff. 240v power supplies are normally galvanically isolated. 12v ones aren't and have continuity between the input and output -ve connections.

 

BSP. I have a spare isolating transformer in my box of bits, which you're welcome to.

 

MP.

 

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12 minutes ago, Boater Sam said:

I'll say it again another way, its the switch mode power box feeding the 12v TV.

It probably is, but if internal to the tv then not easy to change, and we still don’t know if it is radiated interference or on the 12v supply cables.  So I still suggest she tries my earlier test.  Then if D.C. then ferrites on the 12v supply to the tv and amp may be enough, but before jumping ahead let’s wait for her to do the test.

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1 hour ago, MoominPapa said:

How do you work that out? More likely to be an earth loop with 12v stuff.

An earth loop involves an induced 50Hz signal circulating around the earth cables. That’s why it’s a ‘hum’ as opposed to a ‘buzz’. Sometimes you get harmonics resulting in 100Hz and 200Hz on top, but the 50Hz is always predominant. 

 

DC has no 50Hz to create the hum in the first place. 

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Does it go,  Hummmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmm, like a Hornet or Buzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzz, like a Bee. :closedeyes:

My solution would be to only watch war films like The Dam busters or 633 squadron where the Hummmmmmm, would blend in with the drone of the aeroplanes and be unoticeable.

Edited by bizzard
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5 minutes ago, bizzard said:

Does it go,  Mmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmm, like a Hornet or Buzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzz, like a Bee. :closedeyes:

Don't mention the Bee, the sting from the weekend will flare up again and there will be another attack of the vapours

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3 minutes ago, tree monkey said:

Don't mention the Bee, the sting from the weekend will flare up again and there will be another attack of the vapours

Busy bee,

Busy bee

Sting someone else

But don't sting me.   Arther Askey.

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2 hours ago, WotEver said:

An earth loop involves an induced 50Hz signal circulating around the earth cables. That’s why it’s a ‘hum’ as opposed to a ‘buzz’. Sometimes you get harmonics resulting in 100Hz and 200Hz on top, but the 50Hz is always predominant. 

 

DC has no 50Hz to create the hum in the first place. 

Not necessarily. The root cause to significant (and varying) currents in the signal earth connection between two pieces of equipment. The non-zero resistance of the connection converts this into a varying voltage added to the wanted signal. The current might be 50Hz, but it might be from the input to a switching power supply. If you have have two pieces of equipment, each connected to the negative supply and, also connected to each other via an earth connection, then some fraction of the power supply to one of the peices of equipment might be flowing via the negative connection of the other and the earth connection between them, depending on the relative resistances of the various paths. This situation is much more likely with 12v supplies than with AC, almost all AC PSUs have a transformer and do galvanic isolation. Almost no 12v supplies do.

 

The spare transformer I'm offering BSP was bought to fix a noise problem connecting the audio-out of a laptop to a car stereo. When the laptop was running on a 240v supply, there was no problem: when running it via a 12v supply, you could here the switch-mode converter in the supply changing frequency as the load changed.

 

MP.

 

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5 hours ago, Chewbacka said:

It probably is, but if internal to the tv then not easy to change, and we still don’t know if it is radiated interference or on the 12v supply cables.  So I still suggest she tries my earlier test.  Then if D.C. then ferrites on the 12v supply to the tv and amp may be enough, but before jumping ahead let’s wait for her to do the test.

Thanks for your suggestions. I'm going to try to cover several of the questions/suggestions in one go here:

The tele power cable has a little box on it that says "INPUT 12-32v OUTPUT 12v" so I think that means it's very much a 12v tele. That box hangs a good 2ft below the tele and amp, if relevant.

When I connect my phone to the amp with the tele on stand-by, and hold both the amp and phone as far from the tele as possible (just under 2ft) there's little interference noise. As soon as the tele is switched on, the interference noise returns at the same volume and pitch as it did when the amp was situated 3 inches below the tele on the media cabinet.

So to summarise the various scenarios:

My first trial of the amp, as described in a previous post, had the amp and the tele plugged into DIFFERENT 12v circuits.  That trial had the amp situated about 2ft from the tele in a thick OSB cupboard with the tele in the neighbouring cabin.
The interference noise was present when the tele was on.

My second trial of the amp had the amp and tele plugged into the SAME 12v circuit. The amp was situated below the tele on the media unit. The interference noise was present when the tele was on.

With the amp located CLOSE to the tele but plugged into my phone, the interference was present as soon as the tele was switched on.

With the amp located FAR from the tele but plugged into my phone, the interference was present and at the same volume as before, as soon as the tele was switched on.

For info, the speakers are built in to the wall so immovable. The tele is on a wall-mounted bracket immediately in front of the speakers. That cannot be relocated because it's near to the aerial and electrics and the rest of the furniture is built around having the tele and electrics in that location.

The speaker cables do run close to the tele - there's little room to put them anywhere else.

The amp needs to be situated on the media unit below the tele because that's what the furniture is built for. The satellite box similarly sits on that unit just a few inches below the tele (but causes no interference).

Phew! Is there anything I've forgotten?

4 hours ago, bizzard said:

Does it go,  Hummmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmm, like a Hornet or Buzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzz, like a Bee. :closedeyes:

My solution would be to only watch war films like The Dam busters or 633 squadron where the Hummmmmmm, would blend in with the drone of the aeroplanes and be unoticeable.

It hums like Aled Jones with his nuts in a vice. 

4 hours ago, tree monkey said:

Don't mention the Bee, the sting from the weekend will flare up again and there will be another attack of the vapours

Vapours!!!!!? You're lucky I read that after you just left my boat, Mr Monkey

Edited by BlueStringPudding
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1 hour ago, MoominPapa said:

Not necessarily. The root cause to significant (and varying) currents in the signal earth connection between two pieces of equipment. The non-zero resistance of the connection converts this into a varying voltage added to the wanted signal. The current might be 50Hz, but it might be from the input to a switching power supply. If you have have two pieces of equipment, each connected to the negative supply and, also connected to each other via an earth connection, then some fraction of the power supply to one of the peices of equipment might be flowing via the negative connection of the other and the earth connection between them, depending on the relative resistances of the various paths. This situation is much more likely with 12v supplies than with AC, almost all AC PSUs have a transformer and do galvanic isolation. Almost no 12v supplies do.

 

The spare transformer I'm offering BSP was bought to fix a noise problem connecting the audio-out of a laptop to a car stereo. When the laptop was running on a 240v supply, there was no problem: when running it via a 12v supply, you could here the switch-mode converter in the supply changing frequency as the load changed.

 

MP.

 

Thanks Moomy? Do you know what connectors your isolator thingy has on it, please?

Edited by BlueStringPudding
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17 minutes ago, BlueStringPudding said:

Thanks Moomy? Do you know what connectors your isolator thingy has on it, please?

 

3.5mm stereo jacks (like headphones) on each end. Nothing that a small attack of the soldering irons couldn't change though.

 

ETA. Reading your information post above, I'd bet the remainder of this winter's pine-needles that the problem is an earth loop because the TV and the amp are both connected to the 12v negative, and the transformer will fix it.

 

MP.

 

 

 

Edited by MoominPapa
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20 minutes ago, bizzard said:

A lead shield between telly and amplifier is needed. Lead flashing from Wicks or from a church roof. If it can stop nuclear radio active rays getting through it it should stop a hum.  Strontium 90 is good for you.

She’s not having my tin foil hat. 

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26 minutes ago, WotEver said:

She’s not having my tin foil hat. 

I think she ought to get used to ''attuned'' to the hum, then after a while she won't notice it at all. So just before telly time she should take a long run out  in a conveyance such as a Hummer or an old Humber Hawk with a worn out differential.

Or indeed ''home cure'' regular use of an old toy tin humming top.

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59 minutes ago, bizzard said:

I think she ought to get used to ''attuned'' to the hum, then after a while she won't notice it at all. So just before telly time she should take a long run out  in a conveyance such as a Hummer or an old Humber Hawk with a worn out differential.

Or indeed ''home cure'' regular use of an old toy tin humming top.

I remember those humming spinning tops! The speaker noise isn't dissimilar, now you mention it. 

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From post #35, there seem two possibilities. As the hum is still present when amp is connected to the phone, and not the TV, it has to be either radiated from the TV, or travelling via the power supply. (More likely, IMO) A different 12V circuit will still have a common negative connection. Is it possible to temporarily power the amp from a separate battery or power supply, without a common negative?

If this cuts the hum, it might be worth trying connecting the TV to 12V without its "black box".

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2 hours ago, Tony Brooks said:

Do digital telles need any form of time base circuit? If so maybe that is one source of interference.

 

I bet Cello do not use LED back lighting (check the manual) so the inverter for the back light tubes may be another source - TV engineer required!

I think all their teles are LED these days, aren't they? Mine is only a couple of years old. 

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When I was watching my old analogue telly I always new when it was frosty outside without looking outside. Railway is only about 100 yds from us and every time a train went by I got a narrow fuzzy band at top and bottom of the screen, top band caused by the trains electric pantograph travelling along the catenery wire and scraping through the frost. the bottom band would have been the return through the wheels on the track I suppose.  Apart from this alerting me to a frost outside it also told me  that a train was going by, also without going outside to look,  magic.  I did compile a log of all the times of trains going by in an excercise book and by this method in conjuction with a timetable got from the station  compared the times and could determine whether each train was running early or late, mostly late.  All this from my armchair, watching the telly and not even looking out of the window,  magic. Since I had to renew my analogue telly with a digital one sadly this tremendous and joyful pastime has finished.  I'm instead beginning to create a log of the planes taking off and landing at Stansted airport because their radar make my digital telly pixels break up a little bit and can tell in conjuction with Flightradar24 on my lappop whether or not a flight is early or late without looking at Flightradars departure or arrivals board,, but, sadly with the digital telly it doesn't tell me whether or not its frosty outside without me having to get up to look from my window.  I sinserely  hope that this absorbing and exciting kind of hobby will be of interest others, its nice to have hobbies.  :mellow:

Edited by bizzard
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Its the switched mode power supply in the brick connected to the TV putting hash back onto the 12v supply.

To prove it, connect the TV power lead to a seperate 12v battery that is connected to nothing else, the buzz will not be there.

How do I know this? Because I had exactly the same problem.

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8 hours ago, Iain_S said:

If this cuts the hum, it might be worth trying connecting the TV to 12V without its "black box".

Only connect the TV to 12V without it's "black box" if you are absolutely sure the 12V is indeed 12V. A cigarette lighter style socket on the boat batteries will vary between 14v+ (engine or solar running) and 10V or less (as the water pump or fridge kick in)

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18 hours ago, Iain_S said:

From post #35, there seem two possibilities. As the hum is still present when amp is connected to the phone, and not the TV, it has to be either radiated from the TV, or travelling via the power supply. (More likely, IMO) A different 12V circuit will still have a common negative connection. Is it possible to temporarily power the amp from a separate battery or power supply, without a common negative?

If this cuts the hum, it might be worth trying connecting the TV to 12V without its "black box".

It's a great idea Iain, thanks for the suggestion. But unfortunately I don't have the means to run it from a separate battery. 

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13 minutes ago, BlueStringPudding said:

It's a great idea Iain, thanks for the suggestion. But unfortunately I don't have the means to run it from a separate battery. 

Got a spare bit of cable? Try disconnecting the TV negative and running a temporary negative cable from the TV all the way back to the batteries as a test. 

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It might be caused by the hummmmmmmmmmm's abuzzzzzing all around in the steel boat with no route for escaping, in which case you could try opening all the doors and windows when you've got the telly on to give them all a chance to escape and disperse, which would be nice and a human kindness towards them.  Failing that I'm afraid the telly will have to be moved and watched outside in the fresh air where all the Hummmmmmmm's have a chance to beat it.  Much healthier out there too, in the lovely fresh air.    For inclement weather a dainty little ''Goggle Box'' cabin or Gazzebo could be erected on the after deck, but the door might still need to be left open to allow all the Hummmm's to evacuate the space. On second thoughts perhaps a structure more comely and stout like a sentry box that shouldn't blow away in a gale of wind would be better because of there not being a door, yes, a sentry box would be ideal, for sitting in to watch the box and guarding things at the same time.  They can be viewed for design purposes ouside  Queen Lizzies drum at the end of the Mall in London.   Hope this helps. :giggles:.

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