Right, I've been doing some checks with my system and have come up with some results...

But first a recap for those who don't know it!

I have a Sony CD MX-8800 HU connected with 2 amps, one powering the 8 mid/high speakers and 1 driving the twin 12" sub. The main power for the amps is coming straight from the battery (Thanks to the grommit behind the glovebox) and the ground is located in the boot. I have what can only be described as alternator whine on the system.

The following tests have been done...

1) Changed grounding on the amps

2) Used the same earth as the HU

3) Used the amp's earth for the HU

4) Used the same 12v+ connection for both amps and HU

5) Used +12V and GND for both amps and HU

6) Changed HU

7) Changed RCAs to the amps

These all result in no change to the noise. I've tested the amps and cabling by putting an mp3 player into it, resulting in no noise! Yay!

After this I changed the ignition connection to the +12V from the amps and used +12V for the HU as well. The noise still existed.

I'm not at the stage where I need help. The boys on Talk Audio don't seem to want to respond to my questions.

What do you all think? What would you do next?

which way have you routed the rca and power cable

which way have you routed the rca and power cable

RCAs down the passenger side, power down the centre

do the RCA's run next to any power cables for any considerable length anywhere?

it sounds like you are picking up interference in the RCA's to me.

do the RCA's run next to any power cables for any considerable length anywhere?

it sounds like you are picking up interference in the RCA's to me.

Just the ignition one (part of the RCAs). The RCAs are shielded though. I can re-run the ignition cable to see if it makes any difference, but I have done this previously with the old HU and it made no difference.

I think the earth is of poor quality. No good solid earths exist on these cars, period. And don't even try and tell me seat mounting bolts, seat belt bracket bolts, light wiring earths etc are... :eek:

You need a good ground in the boot fella, and earth everything including the head unit it to that. I recommend a grounding post with 2 bolts through the boot floor, nice and clean bare metal, lots of protective grease etc...

how random, are you able to get the car close to another car so you can plug your stereo into another set of amps to see whether its the HU giving out the noise?

I think the earth is of poor quality. No good solid earths exist on these cars' date=' period. And don't even try and tell me seat mounting bolts, seat belt bracket bolts, light wiring earths etc are... :eek:

You need a good ground in the boot fella, and earth everything including the head unit it to that. I recommend a grounding post with 2 bolts through the boot floor, nice and clean bare metal, lots of protective grease etc... [/quote']

really tom?

my seat belt mounting point seems to be quite solid and provides adaquate solidity for my 0awg earth cable and i get no earth faults from my system which is running about 2000W rms roughly.

I'm afraid I've no access to another car with an amp, but it does give me an idea which I'll look into at the weekend.

I can also try the "seat belt" earth!

@bengie - any chance of a picture so I can copy your design ???

really tom?

my seat belt mounting point seems to be quite solid and provides adaquate solidity for my 0awg earth cable and i get no earth faults from my system which is running about 2000W rms roughly.

Its not ideal mate, no.

If that dont work mate I have a ground loop isolator I can send you to try.

Its not ideal mate, no.

How is a metal bolt though the boot floor any different to that though. The seat belt anchorage is an M12 bolt straight into a captive nut welded into the body.

If that dont work mate I have a ground loop isolator I can send you to try.

I have one! It helps somewhat but doesn't get rid of the noise altogether

I think the Seat belt bolt trick will help, hopefully

as ross said the seatbelt bolt is a dirty great big thing welded into the fricking body if the car, how much do you want it?

what i did mate was loosen the bolt that holds the buckle to the body and just stuck the flat part of the lug betweent he body and the bottom of the buckle assembly and tighten the hell out of it

its never come loose and has served me very well so far

as ross said the seatbelt bolt is a dirty great big thing welded into the fricking body if the car' date=' how much do you want it?

what i did mate was loosen the bolt that holds the buckle to the body and just stuck the flat part of the lug betweent he body and the bottom of the buckle assembly and tighten the hell out of it

its never come loose and has served me very well so far [/quote']

Did you sand down the area around the bolt?

I had this problem in my old car. Tried everything inc changing the ground. Only thing that solved it was repacing the HU.......:thumbdwn:

I assume that you get no interference when the engine is off?

yep i did mate

I had this problem in my old car. Tried everything inc changing the ground. Only thing that solved it was repacing the HU.......:thumbdwn:

I assume that you get no interference when the engine is off?

Yup, engine is off, there is no noise.. and I've already replaced the headunit with no joy.

@bengie - Ta, It'll give me something to do over the weekend ...

:P Sorry, should have read your first post correctly!

Were are the amps and are they mounted? Only thing I can think of is getting the interference through them:confused:

I remember reading somewere that amps attract interference, but I maybe wrong. If I am someone will soon put me right!

:P Sorry' date=' should have read your first post correctly!

Were are the amps and are they mounted? Only thing I can think of is getting the interference through them:confused:

I remember reading somewere that amps attract interference, but I maybe wrong. If I am someone will soon put me right! [/quote']

Amps are mounted on MDF one each side of the boot and are linked via distribution blocks on power, ignnition and ground.

An Update!

Still happening I'm afraid. I've done more tests including replacing the HU with a mp3 player resulting in no issues with sound. I've also run a -'ve cable directly from the cable to the amps which made it worse.

I'm at the stage that I'm looking from some professionsal help, preferably someone on here, as I'll be in the UK during the last week of August / first week of September.

Any takers / ideas ?

Just a thought, but do you earth your amps separately or at a joint earth? Combined earths are supposed to be the way to go iirc. So the earth lead goes from each amp to a non-fused distribution block, and then to a single cable (the same size as the main power cable) to an earthing point. Also just out of interest, where abouts are you earthing the amps?

Heres a useful guide from Talkaudio, if you haven't seen it already Tracing Alternator Whine

An Update!

I'm at the stage that I'm looking from some professionsal help' date=' preferably someone on here,

Any takers / ideas ?[/quote']

Hello! No need to go to the UK for that i'll have look at it for you at RR, i might just know a thing or to about sound

http://www.maplin.co.uk/Module.aspx?ModuleNo=33172&criteria=ground%20loop&doy=17m7

Try one of those

I had the same, seat belt bolt made very little difference.

What I did was to drill a hole in the boot floor near the light cluster. Dremmelled it until it was clear of all paint then put an M10 bolt though and a nylock nut and washer under the car to hold it nice and secure et voila, the noise went away. Seems drastic I know but it was all I could come up with. Just glad it worked