Engine Noise with dual RCA's

[Trls250s]

I need some help to solve a problem with my audio install. I recently upgraded the headunit to a Clarion with 3 pairs RCA outs - Front, Rear & Sub. I run 2 amps a 2 channel bridged for the sub and a 4 channel for front and rear. I was careful to run the power leads down the outside of the car and all RCA, Speaker leads thru the center. My problem is if I use a single RCA and on either the front or rear outputs and split it at the amp I don't get any alternator whine (engine noise). I can use either RCA cable running to that amp with no noise, but using both introduces the noise . I have checked all the earths and ensured the body of the amp is isolated. What else can I try ?

TT2

[Alex B]

Sounds like an earth loop. Tried a diffrent set of RCA's?

[Trls250s]

I have, a friend of mine who is an installer said he wouldn't answer any of my questions until I went out and bought a decent pair of RCA's

[DeeCee]

you are getting an earth loop through your RCAs.. check your grounding on your amps and headunit.

Also, as long as your cables are well built and of reasonable quality then there are no differences between cables.. if they are some ultra budget $2 shop RCAs then there is the possiblity that the insulation is thin and could break causing a circuit, but apart from that, there would be no audible differences between budget cables and something that cost $20/30 - its called snake oil... and a bit of snobbery lol

[sergei]

Get RCA line transformers from jaycar.

[Trls250s]

I have tried some line transformers
I have checked the earth's, I have moved all the earths, (the head unit and amps to a common point and run an earth wire from this bolt back to the main body earth point in the engine bay.

[DeeCee]

what headunit and what amps.. and i assume you have grounded to clean metal?

Sergei - the line transformers are crap.. its better to fix up your electrical system rather than add stuff that is jsut a bandaid..

[sergei]

the problem might be in cheap amp not in bad ground, as I discovered with lanzar amps... If amps have poor ground insulation in input channel they will amplify ground loop noise no matter what grounding you have.
Thats why proffesional gear uses balanced inputs (not RCA). Also thats why high speed networks use twisted pair and not coax.

[Trls250s]

Headunit is a Clarion DXZ-846MP
Amplifier is a Audiobahn A460LT
I have ground it to clean metal.

[sergei]

In my home stereo system I had a big problem with internal sound card: 50Hz hum, + harddrive access noise, I have fixed that by not inserting fully the RCA cables on the amp side (what it does is uses GND wire in power grid as second wire for signal). Than later I bought external sound card with insulated power supply. Now I enjoy 100db SNR.

[DeeCee]

1) seperate your headunit and amp earths - ie no common grounding point..
2) what wire guage are you running for amp and headunit grounds?
3) you say that you are grounding amp and head to a bolt and then running back to the battery.. thought about just using the metal chassis of teh car body as the capcitance for the ground?

also seperate RCA's by 10mm - emf field is created adn collapsed due to AC current running through RCAs.. emf fields created and collapsed next/interfering with each other will cause noise..

also, check: corrosion on battery terminals, ground wire on battery, corrosion on alternator contact points

otherwise.. time to look at your equipment.. that audiobahn may be a prob.. never had troubles with clarion headies..

[Alex B]

1) seperate your headunit and amp earths - ie no common grounding point..

I accualy thought it was reccomened to earth everything at the same point to avoid the chassie becoming a loop? (skimming throu one of ab's tutorials a while back) And at the end of the day the whole car is a common grounding point.

[Trls250s]

1) seperate your headunit and amp earths - ie no common grounding point..

I started with this, a seperate supply for the amps and head unit, I progressed to the common earth trying to fix the problem, I can go back to it though

2) what wire guage are you running for amp and headunit grounds?

4 ga for amps, 8 ga for headunit

3) you say that you are grounding amp and head to a bolt and then running back to the battery.. thought about just using the metal chassis of teh car body as the capcitance for the ground?

I started with this as well, sounds like I have a bit to undo.

also seperate RCA's by 10mm - emf field is created adn collapsed due to AC current running through RCAs.. emf fields created and collapsed next/interfering with each other will cause noise..

I have run the RCA's together, infact I think I cable tied them together.

[Trls250s]

I suppose the thing that I really don't get is why with a single RCA split at the amp (and I have tried both RCA's fed from both front & rear) do I get no noise.

[DeeCee]

Pyro - star grounding is preferred to ensure that there is a common termination point. Overall it is the best method. I'm just trying to figure out other methods for solving the problem.

Trl - you should be able to easily seperate the headunit ground from the amp ground.. so just temp ground it to a clean bolt somewhere seperate from the other bolt.

Also, the emf field creation/collapse is an easy thing to do.. just spread them out a bit.. overall, this is not a common cause when it comes to ground noise.
Corrosion on any electrical termination point or a short circuit with pinched wires is more common than interfering emf fields.

Last time i couldn't find the cause of the whine we ended up removing the alternator and cleaning all the contacts with a wire brush.. same with the battery terminals. Also added new grounds to engine and battery..

What speakers are you running and are you sure it is alternator whine?

Other causes: alternator's rectifier bridge may be poked, output capacitor on ampifier board may be leaking (but that would be a constant hum, instead of the alternator whine - hence my asking whether it is or isn't)

Why is this happening? poor electrical circuit formed, noise loop induced when grounding electricity is taking another route through the electrical circuit (i've seen an ipod hooked directly up to amps and the ipod acting as the ground loop inducer lol )

could be the cables.. pinch wires, bad termination inside the RCA barrel, maybe a short circuit on your speaker wire..

there are basically many things that can produce a ground loop.. hence the reason why i don't suggest line transformers.. because there is a larger problem at hand.

go read this link through: http://forums.nzicemag.co.nz/viewtopic.php?t=4971

you can either sign up to ice and get your fill - but please dont' dredge up old threads (pet peeve..) - start a new thread.

I hesistate to say this, but i doubt that your installer friend would be giving you as much info as this.. tell him that making you buy new RCAs is a rather underhand way of getting info and that if he was a friend he would be helping you regardless.. poke poke..

[Trls250s]

Thanks DeeCee
I'll have a read of the link and go thru your suggestions when I get home.
I'm as upset as you about spending all that extra money on new RCA's.
Your right I want to fix it not disguise it with transformers\filters.
I have to admit I don't know for sure it's the alternator, its an engine noise. I will have a look at the alternator connections I haven't checked these.
Worst comes to worst, I'll run it with the splitter at the amp, haven't changed the fader from 0 since I set the levels on the amp anyway.

[DeeCee]

okay then..
what RCAs do you have for a start?
and the whine - does it fluctuate up and down when you press and depress the acclerator pedal? or is it a steady constant hum?

[Trls250s]

Acoustic Research RCA's
The whine does fluctuate with engine rev's and thinking about it I believe it is more noticeable the more load there is on the alternator ie when the lights are on it's worse.

[DeeCee]

never heard of those RCA's.. but with a name like that they're not likely to be the quality of $2 shop lol

so when the lights are on then you possibly get more noise? hmm.......

What battery do you have and what is the CCA rating of it/age of it..

[Blackrazor]

never heard of those RCA's..

Dick Smith premium brand. Made by Pudney & Lee about 500m from Richies house

As for the whine, the only thing you havent tried is another amp Borrow an amp from a mate, try it out, if the problem disappears you have your answer