Radio Noise / Whine - Advice Needed

[alan]

Hi Guys,

I have just upgraded the head unit to a new Pioneer DEH-p65BT as this adds support for bluetooth etc.

Prior to this I had an older pioneer head unit which connected to a CD multichanger, surround sound processor and power amp all in the boot. It all worked fine.

The new head unit can not talk to the surround sound processor so I have bypassed it and fed the signal from the head unit into the power amp. All works OK until I start the engine. I then get a whine/crackle which is related to engine speed. I get this on radio / cd / telephone etc and amount of noise / whine is not effected by the volume control - ie turn the volume to zero and the noise / whine is still there.

The odd thing is that turning on electrical loads (headlamps, heated screen, fans) reduces the problem. I have checked for obvious ground issues by running a cable direct from the battery to the stereo but this makes very little difference.

The supply feed to the radio goes through a choke / transformer. The only odd thing is that the power amp is wired direct to the battery whilst the head unit power comes somewhere from under the dash but this is fairly normal and apart from not using the surround sound processor it used to work.

Any ideas - its starting to drive me mad!

Alan

[CNH]

Does the head unit have a seperate ground wire in the harness for shielding purposes other than the one used to ground power? If so hook it up. I would strongly suspect the whinning sound is alternator noise as ignition noise would be a ticking sound. Are you using directional signal cables with a floating shield?

Edited July 3, 2007 by CNH

[KENCO]

Maybe in some way the old sound processor helped with masking the noise, now that it is out of the loop you can hear the noise.

Check grounds, and pull all power to head unit and fire up amps to try and hear the noise, that way you can figure out if its in the head or the amps, or both!

[alan]

Does the head unit have a seperate ground wire in the harness for shielding purposes other than the one used to ground power? If so hook it up. I would strongly suspect the whinning sound is alternator noise as ignition noise would be a ticking sound. Are you using directional signal cables with a floating shield?

Hi,

The head unit only has the ground through the ISO connector. I ran a wire from the battery to the case of the head unit but it made no difference.

Not sure if the noise is alternator or ignition - it sounds like a sequence of very fast clicks. At 2000 rpm thats about 33 ignition events per second. On the other hand alternator ripple sounds possible as the level of noise is related to electrical load. I will try unplugging the alternator to see if the noise goes away.

Not sure what directional signal cables are?

Thanks for the advice

Alan

[98GT3]

Hi,

The head unit only has the ground through the ISO connector. I ran a wire from the battery to the case of the head unit but it made no difference.

Not sure if the noise is alternator or ignition - it sounds like a sequence of very fast clicks. At 2000 rpm thats about 33 ignition events per second. On the other hand alternator ripple sounds possible as the level of noise is related to electrical load. I will try unplugging the alternator to see if the noise goes away.

Not sure what directional signal cables are?

Thanks for the advice

Alan

I think what you are suffering is a common earth loop problem, caused by multiple earths on you system, and even by the internal design of parts of the system themselves. For instance, if the signal wires from the head unit to the amp are two separate screened leads rather than two signal wires with a common screen, this can with certain designs of amplifier or head cause an earth loop. An earth loop is an "area" made by different earthing points acting a bit like an aerial collecting noise generated by engine ignition/alternators etc. and placing this noise on the ground side of the equipment - this is why chokes on the positive side don't cure the problem.

What you need to do is to break this earth loop which can be done in many ways, or minimize it's size - not so easy in a glassfibre bodied car. One other solution is to introduce a high impedance to the noise in the earth screens of the signal wires from the head to the amplifier, there are many units available to do this - a quick search turned up this

http://www.m-99.co.uk/Car_Audio/Noise_Supp...suppressor.html not sure if this particular unit is any good or not, but cheap enough to be worth a try.

Phil

98GT3

[Malc Holmes]

HI Alan,

When I am not doing ESPRITism, I work in Nissan R&D doing Audio and IT design and this issue is something we see time and time again when some after market equipment is added to the cars existing audio system. I agree with Phil, its almost definitely an earth loop issue and many owners of I-pods with an interface to the radio will be aware of the problem when ever they plug the I-pod battery charger into the fag lighter and try to listed to music!

One possible solution is to 'star earth' where all the units come back to the same earth point. I reality this means taking the earth on you amp to the same point that your radio earths to. Also, don't only depend on the ISO connector earth pin, ditch this and take an earth from the radio chassis to the a good solid earth point on the cross car beam that runs under the dash. Connect the earth for the amp to the same point. Keep all the earth wires as think and as short as possible (difficult if your map is in the boot!).

Good luck

Malc Holmes

[98GT3]

One possible solution is to 'star earth' where all the units come back to the same earth point. I reality this means taking the earth on you amp to the same point that your radio earths to. Also, don't only depend on the ISO connector earth pin, ditch this and take an earth from the radio chassis to the a good solid earth point on the cross car beam that runs under the dash. Connect the earth for the amp to the same point. Keep all the earth wires as think and as short as possible (difficult if your map is in the boot!).

Good luck

Malc Holmes

Malc is right, star earthing is a good technique to try, it brings all the equipment earths to the same potential and also removes the loop of area created (wish I could easilly put a drawing up but it's late!). It may cure the problem.....but it also may not depending on the internals of the equipment! You see there could still be a loop formed between the equipment earths and the earth connection joining them together with the connecting screened leads.......earth to head, head to amp via signal lead earths, then amp back to earth again - like a triangle. The only sure way is to try it....best of all, it costs nothing!

Phil

98GT3

[98GT3]

Duplicate post

Edited July 3, 2007 by 98GT3

[alan]

Thanks guys. Whilst the star ground approach sounds like the best solution from a technical point of view I will first of all try one of the ground loop isolators (or two actually - front and rear outputs from the head unit).

Amazon do them for under three quid http://www.amazon.co.uk/High-quality-groun...6636&sr=1-2 and as it will only take 10 seconds to try them out it seems to win out over doing the job properly.

Alan

[CNH]

Hi,

The head unit only has the ground through the ISO connector. I ran a wire from the battery to the case of the head unit but it made no difference.

Not sure if the noise is alternator or ignition - it sounds like a sequence of very fast clicks. At 2000 rpm thats about 33 ignition events per second. On the other hand alternator ripple sounds possible as the level of noise is related to electrical load. I will try unplugging the alternator to see if the noise goes away.

Not sure what directional signal cables are?

Thanks for the advice

Alan

If you are already using decoupler/choke units just before the amp input that should almost eliminate ground loops. Directional signal cables have pos, neg, and sheild with both the neg and sheild hookup to together on the ring at the head unit side and the shield lifted of floated on the receive side.

If it is whinning it is alternator noise, ticking is ignition. I suppose you could have both.

I suppose you put suppresors of the power lines and use additional decouplers on both send and receive side. Decouplers are pretty inexpensive. An easy way to find out if it ground loops is to break the connection to the at the amp side to see if the noise goes away. The touch ring of the connector to the amp case and see if the noise appears.