Just got a new amp for the front stage, its slightly bigger than the old one. and now I get alternator whine!! :~(

if I unplug the RCAs, its quiet, so Im guessing its due to the RCAs being close to the power line

the problem is, my battery is in the boot, so its pretty much unavoidable.

Currently using jaycar twisted pair RCA connectors.. would changing to a shielded one make any difference??

one word: Grounding

I upgraded the bat-> chassy ground and whine dissapeared. I used a single 10cm long 0g ground. sanded down to metal on chassy, bolted it down and paitned over it. no more whine. Do the same for your amp ground. should fix it

Grounding is it.

If your grounding point is OK, you probably have a ground loop. Get a Jaycar isolation transformer, and run it inline between your headunit and amplifier.

amp is grounded on the battery (battery is in boot)

edit:
battery grounded to chassis with 15cm 0 Gauge and 15cm 2 gauge (same point)

[ August 10, 2003, 19:44: Message edited by: rheetard ]

am re-doing my install, and recently ran into alternator whine myself. after several hours fiddling around with some help from a mate, all that was needed was to move the RCA lead into the amp an inch or two away from the power feed to the cap. now all is silent play around with the routing of your RCA's, sometimes just a little shifting is all that is needed (and no, new RCA's wont necessarily solve your problem, i found in my case a cheaper RCA was quieter!).

your battery gets ac current from the altinator, ground your amp to the chassis or your car,its more bedder!

Check your rca leads with a multimeter you might have a earthing problem with them.

Something I noticed with my system was I'd get alternator whine, but not until i drove for about an hour or so. Turns out the rca's were dodgy, and when they got warm from the back of the headunit, they somehow induced noise. I moved these rca's to the sub-out because that uses fly leads, and walah, noise problem no more.

Well, I have the feeling that my RCA leads are EDIT: not broken, since a lot of noise can be induced by a broken shield lead, but its not that bad (still horrendous tho)

I will try to relocate the rcas.. it will be hard tho, cause theres no room.

and as for grounding, I cant think of any reason why the neg terminal for the battery is worse than the chassis, since they are basically right next to each other and connected by a short piece of 0gauge.

if anything, the grounding of the headunit is probably where the problem is at, but that will take a lot more effort to fix :/

I'll move the amp around a bit tomorrow.

[ August 11, 2003, 23:28: Message edited by: rheetard ]

Two things not thought of are:

Alt's build up carnbon deposits from the brushes on the comutator. Blow some are through the alt to see if clearing it helps.

When an alt is wearing out the diodes can start to die, this will cause a whine and is a sign the alt is on the way out.

Phil K

hmm
it COULD be
but the whine started coming through when I changed amps.
and I thought it might have something to do with moving battery to the boot (seeing that the headunit's power would be drawn from the alt and not the battery now)

but i'll move the RCAs over and see what happens.

technically this is more of an install topic, than a sound quality topic - but ill leave it here cause the ideas seem to be flowing, haha

hehe, I spent $150 deadening each door, only to have the bloody alternator whine!!! argh!!

So far the symptoms:
alternator noise, does not get louder with volume.
was not there before I swapped amps.
I have an eq, the system layout is this:
HU front speakers -> EQ -> amps -> speakers
if I unplug the RCAs from the amp, the noise goes.
battery is in the boot, so amps run straight off the battery's earth, where as the headunit is closer to the alternator than the battery.
I also get whine in my CB Rx, which was always there, even before I had whine through my system. This has a connection to the front distrobox, and earthed at the same chassis as the headunit
I have turned the amp around and the RCAs are not running past the +ve power anymore, it is however near the ground wire only. BUT, the noise hasnt got bigger or smaller.
I might actually plug the speakers into the rear speaker out RCAs (not using those atm) and give that a try.

any more ideas I can try?

isolation transformer.

well, when I go into work on thurs I will have to fiddle around with the isolation transformer and see if it helps.
although I cant see why it would be what I need since I havent had alternator whine in the system before?

Ground loops are funny things, partly because they're caused by a combination of power ground and signal ground. Ideally, the resistance to ground through the RCAs and through the power ground will be the same.

But, power ground is running through the chassis, signal ground via the RCAs. The signal ground and chassis ground, in non-car audio, are kept 100% separate (power ground via the earth pin in the power cable, signal ground from the rectified AC signal). But that can't be done in cars.

And different devices deal with ground differentials in different ways. The amplifier is a critical part of the chain and can decide whether or not a ground loop will create noise.

Basicly a ground loop becomes a problem when the amplifier has two ground references that are different. End result is a shift in what voltage it considers 0 volts. That's a bad thing. An isolation transformer "disconnects" the deck ground and amplifier ground from each other, eliminating the problem.

if all u have done is change amps, check to see how the new amp changes the location of the RCA plugs, perhaps no they are closer to something else. if everything is the same and it is the only thing u changed, that is where i'd focus - helped me recently

On the old amp, the RCAs are on the same side as the power cable, on this one, its on the other side
so theoretically, it should be better!!
I'll definately give the ground loop isolator a go tho, but I was hoping thered be a better solution than that?? (isnt it a compromise?)

Hmm
Well the isolator didnt help

If I plug RCA into isolator and isolator into amp, noise remains
unplug rca from the isolator and leave it plugged into the amp, the noise also remains
unplug the isolator, no noise.
hmm :/
unless somethings wrong with the input stage or the isolator was acting like an antennae??

You have a very strange problem!

Sure the amp is ok?

I would hope so :/
bought it off a member of caa a week ago..
sounds like something to do with the potential at the rca inputs..
the amp runs fine, its got power, just annoying when the volume is low

OK, the manual says:
Never use a U.S. amp with a ground loop isolator or an isolated input signal
U.S. Amps are input isolated at teh factory and require an input ground for proper operation

Does that make any more sense??
Should the shielding on the RCAs be grounded or something?

That's the strangest thing I've ever heard, it makes no sense.

It implies that it has built in isolation - "input isolated at teh factory"

But says it needs an input ground for proper operation? All an isolation transformer does is cut out any DC component in the signal. A ground is only a 0 level signal relative to the actual music signal.

As for grounding the shield - usually signal ground and power ground are kept totally separate. But I don't even know if that is possible in a car where everything is DC to start with.

Basicly, its a really wierd problem, that shouldn't occur if all your equipment is functioning correctly. I'd try testing the amp in another car. Its input stage may well be faulty.

I added another ground lead and gave it another power lead, and then adjusted the gains again.. the whine went down quite a bit.
I dont understand what the manual is implying either, I just thought it means that theres an input isolator built into the amp.

Anyway, I'll have a play around with it a bit more soon and we'll see what happens.