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Installed amp, but getting engine noise...

Discussion in 'Motors' started by Six6siX, 7 Jun 2006.

  1. Six6siX

    Mobster

    Joined: 25 Nov 2004

    Posts: 4,787

    Location: Hertfordshire

    I fitted a 4 channel amp in the boot the other day, powering front components and just some rear coaxials at the moment.

    I've run the power cable and remote lead down one side of the car and RCA leads down the other side and used a ground point in the boot on the chassis, but for some reason I'm getting engine noise (ie increases and decreases with revs) - inteference like - when the amp is on. Its only audible at lowish volumes, and can't really be heard when driving normally, but is still annoying.

    The sound comes from both front and rear speakers.

    Any ideas what it could be / what can I do to troubleshoot?

    Ta :)
     
  2. ScoobyDoo69

    Sgarrista

    Joined: 27 Aug 2003

    Posts: 9,697

    Location: West Midlands

    is it decent cable?
     
  3. Sp00n

    Capodecina

    Joined: 18 Oct 2002

    Posts: 18,280

    Location: Brighton

    Were there any other cables on the side that you ran the RCA cables down? Might be picking up interference from another power cable of some sort.
     
  4. Confused

    Sgarrista

    Joined: 18 Oct 2002

    Posts: 8,016

    If it's a whining noise, it's alternator whine/ground loop.

    Usually caused by audio components being grounded in multiple places - ie head unit up front of car, then the RCA leads go to the amp which is grounded at the rear - causing two ground points and voltage differential between them.

    Check your grounds are all OK and as short as possible. Try adding an extra ground wire from the head unit casing to the chassis. If not, try a wire between head unit case and case of amp.
     
  5. Six6siX

    Mobster

    Joined: 25 Nov 2004

    Posts: 4,787

    Location: Hertfordshire

    The power and ground cable are both 8 AWG and the ground from the amp is less than 0.5m away. RCA cables are shielded as far as I know and the speaker cables are decent.

    Thats a good point, never thought of that - I'll have a look.

    It is a sorta whining noise that increases and decreases with revs, yeah. I'll check all grounds and try different points, thanks.
     
  6. RevBillyG

    Wise Guy

    Joined: 18 Oct 2002

    Posts: 1,657

    Location: Neths

    I had the same thing. I moved the Amp's earth and it solved it.
     
  7. Scrutinize

    Sgarrista

    Joined: 4 Apr 2003

    Posts: 7,758

    Take an earth cable from each rca to an earth point and that should sort out the ground loop.
     
  8. monkeyspank

    Soldato

    Joined: 26 Dec 2003

    Posts: 6,360

    Location: cambs UK

    Try something like an ipod as a source, at the amp end. That should help eliminate half of the system.
     
  9. Gav

    Wise Guy

    Joined: 21 Oct 2002

    Posts: 1,376

    Location: Republic of Scotland

    A ground loop is caused by a difference in the resistance between two points. It has nothing to do with voltage.

    Cut the ground from the cars factory plug and run a ground from the headunit to the same point as the amplifier. This will mean both units have the same earth resistance.

    -----

    Have you used the seat belt bolts to earth the amplifier? These are specially treated and dont make for a good ground.
     
  10. Oracle

    Banned

    Joined: 17 Jan 2006

    Posts: 1,971

    Location: Haskins

    Sorry, disagree, DO NOT do this!

    Make sure the amp earthing point is clean and preferrably on bare metal, rather than painted.
     
  11. chipperhead

    Mobster

    Joined: 7 Feb 2004

    Posts: 3,031

    I'm betting you've run your rca/speaker cables next to your power cables, run them down either side of the car.
     
  12. Durzel

    Soldato

    Joined: 10 Oct 2003

    Posts: 5,513

    Location: Wiltshire

    I'm betting you haven't even bothered to read the first post properly. :rolleyes:

    A word of warning, disconnect your RCAs before you start messing about with the ground cable, if you don't they will ground on the headunit which can damage the pre-outs.

    It's possible that you've just got a bad earth wherever you've currently got it. Was it a painted surface? If so, did you scrape all the paint off?
     
  13. AmDaMan

    Mobster

    Joined: 18 Oct 2002

    Posts: 3,988

    Location: Wellington, NZ

    Please read that! I learnt the hard way, one the pre out's are damaged the whining won't go away and then it's new headunit or repair time. :(
     
  14. Six6siX

    Mobster

    Joined: 25 Nov 2004

    Posts: 4,787

    Location: Hertfordshire

    Update on the situation, finally had the time to do something! :)

    I got hold of a new headunit - impulse buy (w00t) :D (only has 1 pair of pre-outs tho - old head unit had 2 pairs) and connected the new one up using the existing wiring and amp to power just the front components. Guess what - no whine!

    Waiting on a set of Y-splitters to feed the rear channel of the amp and I can see for sure if its cured. At this moment its looking like the headunit pre-outs were damaged.

    When installing, I connected the RCA's last, but it was a 2nd hand unit in the first place so may have been inherited damage that never surfaced till now...

    Will update again when fully connected, cheers for the help people :)
     
  15. Six6siX

    Mobster

    Joined: 25 Nov 2004

    Posts: 4,787

    Location: Hertfordshire

    Well, I connected up the rear speakers and there is no humming at all. Problem solved. Must have been the headunit :(