check out the new remote control Jockey Wheel SmartBar rearview170 Beam Communications SatPhone Shop Topargee products Enginesaver Low Water Alarms
Members Login
Username 
 
Password 
    Remember Me  
Click here for the Grey Nomads website -> The Grey Nomads Forum -> Techies' Corner -> Hum in aux speakers from TV audio out
Post Info TOPIC: Hum in aux speakers from TV audio out
Brodie Allen


Guru

Status: Offline
Posts: 725
Date:
Hum in aux speakers from TV audio out
Permalink  

Here's one for the techies:

My van radio has an aux in, which is connected to the 3.5mm audio out of the TV.

I use this for better quality sound since that from the TV speakers is awful.

There is an objectionable hum in the system, which varies according to picture content !

Since everything is on 12v it can't be mains hum.

BT headphones from the same 3.5mm outlet fine thru double plug.

Is there anything that I can do about it!

 

Sphere TV, Fusion tuner/amp.

 

Brodie



__________________
Whenarewethere


Guru

Status: Offline
Posts: 7579
Date:
Permalink  

LED lighting noise or cheap Chinese cables. I had a humming noise years ago & replaced with Van den Hul cables. It is usually the shielding on the cheap cables is pathetic & not earthed to the cable plug.



__________________

Procrastination, mankind's greatest labour saving device!

50L custom fuel rack 6x20W 100/20mppt 4x26Ah gel 28L super insulated fridge TPMS 3 ARB compressors heatsink fan cooled 4L tank aftercooler Air/water OCD cleaning 4 stage car acoustic insulation.
Hylife


Guru

Status: Offline
Posts: 637
Date:
Permalink  

Buy quality shielded cable, and if you're getting serious interference, a ferrite toroid (4 or 5 wraps through close to the radio input).
Belkin make quality ready made lengths of audio cable with 3.5mm plugs. Visit JB HiFi.

__________________
Mike Harding


Guru

Status: Offline
Posts: 4706
Date:
Permalink  

Brodie Allen wrote:

There is an objectionable hum in the system, which varies according to picture content !

This may be a clue: when the picture changes it's quite likely the 12V supply current required by the TV will change and it's possible the radio is also seeing this current change, as a voltage change, on its power input, ie. conducted interference.

Ensure both TV and radio have the best 12V supplies possible - pay special attention to connectors - add extra grounding to both if feasible, ideally feed both devices independently directly from the battery/fuse carrier.

In reality it probably won't be trivial to change the 12V wiring so the next thing to try is a common mode choke and/or capacitors across the 12V supply as close the TV and radio as possible, do some Googling on this first.

I doubt shielded cables will help.



__________________

 

"I beseech you in the bowels of Christ think it possible you may be mistaken"

Oliver Cromwell, 3rd August 1650 - in a letter to the General Assembly of the Kirk of Scotland
Aus-Kiwi


Guru

Status: Offline
Posts: 7642
Date:
Permalink  

Try twisting the wires ? So the ground shields . Route wires away from each other . Preferably saddled to metal chassis or frame ? There is a noise suppressor which can be fitted .
Ea

__________________
Whats out there
oldbloke


Guru

Status: Offline
Posts: 2061
Date:
Permalink  

I had the same issue. Just plug in a 3w rechargeable speaker. Abt $15. Does the job.

__________________

Sta
Mike Harding


Guru

Status: Offline
Posts: 4706
Date:
Permalink  

oldbloke wrote:

I had the same issue. Just plug in a 3w rechargeable speaker. Abt $15. Does the job.

Double check the 12V connections as I suggested and if that yields nothing the above is probably the easiest solution.



__________________

 

"I beseech you in the bowels of Christ think it possible you may be mistaken"

Oliver Cromwell, 3rd August 1650 - in a letter to the General Assembly of the Kirk of Scotland
oldbloke


Guru

Status: Offline
Posts: 2061
Date:
Permalink  

Yep, it was easy. Lol

__________________

Sta
Brodie Allen


Guru

Status: Offline
Posts: 725
Date:
Permalink  

Thanks all, but i don't understand how I have mains hum (if that is what I have)
since everything is 12v.

And why does picture "strength" vary the volume of the hum?

It seems likely that I might have to get professional install instead of the home
grown job that i have managed.

There's stuff-all cables involved - the HDMI to TV from fox decoder is about it!

Thanks all.



__________________
Linwood


Member

Status: Offline
Posts: 9
Date:
Permalink  

Hi Brodie,

It is very common to get hum when you connect the earth of one device to that of another thus setting up a ground loop. The easiest way to get rid of it is to use an isolation transformer for each stereo channel. Jaycar Electronics sell a stereo pair that they call a Ground Loop Noise Isolator (Stereo).


"CAT.NO: AA3086
Used to eliminate ground loop problems in audio installations. The unit has a 3.5mm stereo sockets on both ends."

This integrated pair of transformers retail at $12.95

Glenn



-- Edited by Linwood on Thursday 16th of June 2022 07:26:02 AM

__________________
dorian


Guru

Status: Offline
Posts: 4181
Date:
Permalink  

Perhaps you are hearing some artefact related to the refresh rate of the TV (along the lines of what Mike suggested). The refresh rate is typically the same as, or double, the mains frequency.

I was reading an article which stated that some TVs fake 120Hz support by ignoring every second frame and pulsing the backlights instead.

https://www.tomsguide.com/opinion/tv-refresh-rates-how-to-see-through-the-tv-industrys-biggest-lie

 



__________________

"No friend ever served me, and no enemy ever wronged me, whom I have not repaid in full."

Lucius Cornelius Sulla - died 78 BC 

 
Brodie Allen


Guru

Status: Offline
Posts: 725
Date:
Permalink  

Linwood wrote:

Hi Brodie,

It is very common to get hum when you connect the earth of one device to that of another thus setting up a ground loop. The easiest way to get rid of it is to use an isolation transformer for each stereo channel. Jaycar Electronics sell a stereo pair that they call a Ground Loop Noise Isolator (Stereo).


"CAT.NO: AA3086
Used to eliminate ground loop problems in audio installations. The unit has a 3.5mm stereo sockets on both ends."

This integrated pair of transformers retail at $12.95

Glenn



-- Edited by Linwood on Thursday 16th of June 2022 07:26:02 AM

 Thanks Linwood.

 

Will see them as soon as I get home. Thats a likely solution, I'm told.

(Presently in outback Qld).

 

 



__________________
jegog


Senior Member

Status: Offline
Posts: 245
Date:
Permalink  

Brodie Allen wrote:

Thanks all, but i don't understand how I have mains hum (if that is what I have)
since everything is 12v.

And why does picture "strength" vary the volume of the hum?

It seems likely that I might have to get professional install instead of the home
grown job that i have managed.

There's stuff-all cables involved - the HDMI to TV from fox decoder is about it!

Thanks all.

Firstly, do you have an inverter? If yes that could be the source of the problem.

If not, is it an unbalanced output. That is, is one wire connected to earth?

Are you using a shielded pair(two conductors plus shield) or just a shielded single conductor connection?

The easiest way to solve this is to run the TV and the Amp from separate DC supplies, using plug packs.

 

 



__________________
Linwood


Member

Status: Offline
Posts: 9
Date:
Permalink  

I have yet to see the audio output from a TV not being unbalanced. Caravan radios are also powered from the 12V battery supply. I can't see the above advice having any application.

__________________
Page 1 of 1  sorted by
 
Quick Reply

Please log in to post quick replies.
Click here for the Grey Nomads website -> The Grey Nomads Forum -> Techies' Corner -> Hum in aux speakers from TV audio out
Tweet this page Post to Digg Post to Del.icio.us
Purchase Grey Nomad bumper stickers Read our daily column, the Nomad News The Grey Nomad's Guidebook