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 said
05:44 PM Jun 14, 2022
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.
Hylife said
11:36 PM Jun 14, 2022
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 said
08:46 AM Jun 15, 2022
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.
Aus-Kiwi said
10:04 AM Jun 15, 2022
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
oldbloke said
11:37 AM Jun 15, 2022
I had the same issue. Just plug in a 3w rechargeable speaker. Abt $15. Does the job.
Mike Harding said
01:16 PM Jun 15, 2022
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.
oldbloke said
05:13 PM Jun 15, 2022
Yep, it was easy. Lol
Brodie Allen said
07:41 PM Jun 15, 2022
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 said
07:25 AM Jun 16, 2022
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 said
02:40 PM Jun 16, 2022
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.
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 said
11:10 PM Jun 22, 2022
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 said
07:33 AM Jun 30, 2022
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.
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
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.
Belkin make quality ready made lengths of audio cable with 3.5mm plugs. Visit JB HiFi.
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.
Ea
Double check the 12V connections as I suggested and if that yields nothing the above is probably the easiest solution.
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.
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
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
Thanks Linwood.
Will see them as soon as I get home. Thats a likely solution, I'm told.
(Presently in outback Qld).
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.