Audio interference

[Dieseldonkey]

Can anyone help resolve some audio interference in my E-class W210? I've recently installed a boot-mounted DVD and Video player to keep kids quiet on those long journeys - and it certainly does that. Images are played through headrest-mounted screens, with audio run through comand (and the option of wireless headphones for the kids, if wife and I want to listen to music - the interference doesn't come through car when listening to regular audio sources). A comand interface lead also enables images to be played on comand so we can watch when parked up, if required.
All is fine when engine not running. Start the engine and alternator-type whining comes through speakers and headphones when watching DVD or video. It's only occurred since adding this kit - which is Necvox/Centurion screens, vid and DVD plus Phillips headphones.
System is powered direct off battery, but with required fuses of course, and also earthed back on battery. I've replaced all standard RCA audio and video leads with shielded higher quality items than those supplied as standard, but to no avail. All images are perfect, though faint horizontal interference does drift across all three screens, according to changes in engine speed.
I'm open to suggestions. Has anyone else encountered similar problems and found an easy fix? I could go on guessing to resolve the issue, but not sure what to try next......
Thanks for any help you might be able to provide.
Regards
Geoff.

 

[neil.b]

hmmmmm, normally alternator whine is caused by an earth loop but in this instance that doesnt apear to be the case, could always be a faulty unit thats been fitted, i would suggest going back to the place you bought it and getting them to have a closer look

 

[JimmyTD]

I had similar audio interference when I fitted a set of speakers in the tailgate and ran them from a boot mounted amp. I tried running the RCA down both sides of the car, found the solution was to run the cables down the centre away from all other electrical cables. On the C-class the main + cable runs down the passenger side.

Might be worth a try.

 

[Dieseldonkey]

Thanks guys for your thoughts.
I forgot to mention that its an E320Cdi, so don't be tempted to suggest 'wrong spark plugs'.... That said, the car isd bristling with electronics and there's a mass of them under the rear seat, which is where my power comes from.
Power only runs from beneath seat into boot. And the only cable that runs forward through the car is a triple RCA that delivers left and right channel audio, plus video signal into comand. It's buried beneath trims on nearside, crosses the passenger footwell and into the rear of comand.
Though trying different cable routes at the rear might be a good starting point.
Has anyone any experience with after-market suppression kits, which in-car entertainment dealers seem keen to promote?

Cheers

 

[JimmyTD]

Seriously, try routing the RCA cables differently. Even if you temporarily lay them down the centre of the inside of the car.

I had this with mine and its a diesel too, I tried fitting suppressors to the alternator all it did was varied the pitch of the whining.

 

[neil.b]

where are you drawing the power from for them?

 

[Dieseldonkey]

All power comes directly off the battery +, under rear seat - but split via individual low amp fuses for the screens, the DVD, video and wireless headphone transmitters.
But the bulk of my wiring is contained under the seat - which could also be an issue.
I'm also going to try disconnecting power to all but the DVD source (I'm informed it has its own integral suppression), then run the engine and see what happens - just in case the headphone system or video player is causing the problem.

 

[joe bloggs]

Dont earth your new kit at the battery, this is an exellent earth point, trouble is it is better than the command earth point, this produces a small difference in voltage at the two points and the difference tries to even itself out along your various connecting leads.

Ideally earth everything at the same place.

 

[alan ainsworth]

First thing to establish is whether the interference is line borne (being fed along the cables) or radiated (transmitted). A real easy trick is to power the entire DVD system from a seperate battery not connected in any way to the vehicles own electrics. Firstly disconnect any common features between your added system and the vehicle ie. command controls etc. THIS IS IMPERATIVE TO PREVENT ANY DAMAGE TO THE VEHICLE. If the problems cease then your interference is being fed via your supply cables (neg or pos). You can purchase electronic noise filters to clean up the supply but make sure you buy the electronic version not the cheaper models. Kenwood and Alpine both make excellent noise filters. They are available in differing current ranges depending on your load.

If the above makes no improvement then your problem is more than likely a tricky little thing called "secondary radiation". The only real solution for this one is to re-route cables and re-position your equipment as best you can. It really is a "black art". Try running braided ground cables between all your equipment and then to the command ground point.

Best of luck!

 

[ian_stephen]

Hi-Fi Interference

I've had a very similar problem after having a new Sony stereo fitted to my ML320.
There is no interference when the ignition is turned to stage 1, but as soon as it as at stage 2 (with or without the engine on) there is interference through all 4 speakers.
Originally the speakers were wired directly from the back of the stereo but now an adapter has been fitted to take the output from the RCA connetions (ie via the amp?).

Does anyone know where I can get a noise filter? And do you think that this will help?

Also, I cannot get a MW reception whereas my old Audio 10 unit was fine with MW and did not have any interference.

Very frustrating but I'd like to stick with it so I can access CDs / MP3s etc.

Any advice? Thanks

 

[alan ainsworth]

Re: Hi-Fi Interference

I'm not totally familar with the antenna on the ML but if its the "bee sting" type i.e. short stumpy and nornmally black then your MW problem may be due to losing a 12v feed to your antenna. Some manufacturers build an antenna amplifier into the radio itself (VW is one) so if you change from the original radio you will need to add an antenna amplifier (Halfords sell them for VW but will be ok for a Mer.) I would think your problem is more than likely to be the lost feed to the antenna as it very common for installers to forget to wire the antenna matching coils back up when changing head units.

Electronic noise filters can be purchased from any approved Kenwood dealer.

I've had a very similar problem after having a new Sony stereo fitted to my ML320.
There is no interference when the ignition is turned to stage 1, but as soon as it as at stage 2 (with or without the engine on) there is interference through all 4 speakers.
Originally the speakers were wired directly from the back of the stereo but now an adapter has been fitted to take the output from the RCA connetions (ie via the amp?).

Does anyone know where I can get a noise filter? And do you think that this will help?

Also, I cannot get a MW reception whereas my old Audio 10 unit was fine with MW and did not have any interference.

Very frustrating but I'd like to stick with it so I can access CDs / MP3s etc.

Any advice? Thanks

 

[Dieseldonkey]

Cracked it. At last. Thanks for all your help and suggestions - but the addition of a noise filter on the main positive feed to the DVD player and headphones transmitter cured the whining, along with a ground loop isolator and RCA noise filter on the left and right channel audio for good measure.

The only small problem I have left is a huge difference in audio levels - which I had before fitting the filters - CD & radio volumes played at a comfortable listening level become very quiet when switching to the TV mode to listen to a DVD (even at full volume, the audio level through TV mode is quite quiet). I might need to add an amp to the DVD's audio output, as I don't know where else to get some additional volume from.....

The car has a speed-related auto volume feature: the faster you go, the louder it gets, the slower you go the quieter it gets - but I don't know how to adjust this setting either. It's not listed in any of the handbooks that came with the car. Has anyone else suffered a similar problem?

Thanks

Geoff.