I'm an idiot...

[knoted]

After spending around 12 hours over a week, borrowing oscilliscopes and other test gear from work, I finally figured out where the incredibly annoying whine was coming from in my new install (even with the engine turned off).

I was going round and round in circles, the problem was somewhere in the RCA cables. Replacing, re-routing, nothing worked.

Of course, it's a good idea to earth or remove any un-used built in remote lines on RCA cables...

Note: It's not an alternator whine, something completely different.

[knoted]

I lie, remove unused remote lines, still no luck

[commy92]

prob with head unit maybe??

[knoted]

Nah, had the CRO on it with a test tone CD, perfect sine wave.

Think I might go through the tutorials around the place again, as I'm getting a tiny amount of alternator whine (not a priority right now), but it's definitly a problem with the RCA's somwhere. I'm getting perfect HU output, and plugging an mp3 player direct 3.5mm --> RCA cable to the amp works perfect.

Wierd

[semi]

try singling out each different component to teast them. Find something like an mp3 player, something with RCA outs (you can buy a lead that goes from the headphone jack to RCA's) and plug that into the amp to see if it does it. Then plug it through the RCAs in your car to the amp.

If it makes the noise when plugged into the other source, its a problem with the amp. If it does it with the RCA's in the car, its an RCA problem. Otherwise its a HU problem

[knoted]

Thanks, but

I'm getting perfect HU output, and plugging an mp3 player direct 3.5mm --> RCA cable to the amp works perfect.

...

[StoneX]

What happens if you earth the outside of the RCA's plug at the head unit end while it is plugged in? What brand head unit is it?

[knoted]

No change. It only seems to make the noise when I plug the sub channels RCA in now, pull subs out stops completely. Just had a go at re-earthing the amps better, no change.

HU is just a phreddy mod factory unit.

[knoted]

A bit of a summary, this is really bugging me, any more help would be greatly appreciated.

It's not alternator noise, it's a fairly random squeel that goes up and down and all over the place in pitch, only seems to come from the front speakers. HU RCA output is perfect (tested with oscilliscope), and music, when I turn it up over the squeel (noise doesn't change with HU volume) is great.

When I d/c either end of the sub channel RCA (passthrough on the jaycar amp) the noise stops.

Note: I've been doing most of my fiddling with the battery connected, and changing the RCAs around with the HU turned on. I've since gathered this isn't the best thing to be doing... But I have tried earthing as many RCA's as I can, and it doesn't go away, in fact, it gets worse (louder, higher pitch). Do I need to get all 6 earthed at the same time? Does it have to be earthed directly to the HU earth point or anywhere on the chassis will do?

(I'm actually in the electronics field, but this auto electrician seems very hit and miss )

All of this is with the engine turned off.

2004 VYII Acclaim Wagon

Phreddy modified HU
Alpine MRD-301 mono amp
Jaycar 50Wx4 4 Channel amp
2 x Alpine SWS-1241D 12" subs wired for 2ohms
Alpine S type 171A 6.5" splits front
Alpine S type 6.5" coax rears

4awg to 2x8awg power cables
8awg earths (4channel to seat bolt, sub to centre rear seat belt bolt, both sanded back)
Somewhere around 16awg Speaker cable
Temporary remote lines running everywhere...

[Patrio7]

hold up, if you said the HUis putting out singal no worries, and mp3 to amp is fine, have you tried mp3 down the HU's rca's to amp? or testing headunig from the amp end of the RCA's though i suppose you have. the fact its doign it with engine off is weird imo.

maybe theres some kind of weird mis-match between the headunit and amp, so they work indipentently but not together? </whimsical suggestion>

[semi]

Thanks, but ...

yeh, you must have posted while i was typing

[semi]

recconect those unused remote lines and earth them if you can, might make a difference but cant be stuffed going into why

[knoted]

I kinda removed them completely

[semi]

damn. got any 12ga or something small lying around?? use a few cable ties and run it along the length of the wire, tying it on, tehn earth it at each end. Doesnt matter if its tiny shitty wire too much, wont really be taking any current

[knoted]

Earthing at one end produces a louder constant noise, earthing at both ends seems to cancel out that louder noise, back to my original position

[knoted]

Gave it a go semi, didn't make any difference. I also tried using an RCA splitter on both front and rear channels. Whichever channel (front or back) had both speakers and subs, produced the noise. I also tried earthing both amps to the same point, didn't make any difference.

I'm starting to think the amp is screwed, but I only bought it a month ago. I have a mate with exactly the same model that I'll try and swap them over and see if it makes any difference, but he's away for another 2 weeks

I don't really want to take it back and have it gone for a month if it's not definitly the problem

[HoZy]

Do you have a battery polariser, brocky polariser, rust preventer anything like that.....

I've seen too many installs turn to shithouse because of them putting out a wine at the start of the power cable in the engine bay, trust me, i used to runa 4wd polarizer on my battery, suprisingly enough i rekon this one works but meh people say whatever they want, Just if you have something of the sort, remove it.

Cheers
MaT

[knoted]

It appears as if there is some wierd earth loop happening. Plugging the RCA's only half way in on the sub cable at one end stops the noise.

Now to make it permanent and so it doesn't fall out...

I tried just cutting the outer steal bit off then wrapping tape all around the top with the inner nipple sticking through, but the noise comes back. Are there any more sophisticated ways of making a broken earth cable than sticking blue tack all over it? I can't figure out how to pull the connector appart.

[Patrio7]

It appears as if there is some wierd earth loop happening. Plugging the RCA's only half way in on the sub cable at one end stops the noise.

Now to make it permanent and so it doesn't fall out...

I tried just cutting the outer steal bit off then wrapping tape all around the top with the inner nipple sticking through, but the noise comes back. Are there any more sophisticated ways of making a broken earth cable than sticking blue tack all over it? I can't figure out how to pull the connector appart.

though i doubt its effects but maybe the center post on the cable is too long?

or perhaps the outer ring isnt getting the right conduction when fully on, suggesting maybe the amp terminals might be a little mal-formed?

[naf33n]

try limiting the amount of earth loops. try mounting your amp on wood or something that isnt metal. had to do it the otherday in a VR. sovled the same problem

[semi]

ahh, thats a pretty clever idea naf. good stuff

[garfa]

yup mount the insulate the h/u, amps and any external processors. pain in the arse!

[knoted]

Well it wasn't the amp earthing anywhere.

I've given up trying to find the problem, and just wired both front and rear speakers off the front RCA, subs off the rear, and using the amp gain controls for fader

Too much bloody hassle