Installed amp, but getting engine noise...

Six6siX

Six6siX

Six6siX

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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 :)
 
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.
 
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.
 
is it decent cable?
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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.

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

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.
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It is a sorta whining noise that increases and decreases with revs, yeah. I'll check all grounds and try different points, thanks.
 
ConfusedTA said:
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.
Click to expand...

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

ConfusedTA said:
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.
Click to expand...

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.
 
mrk1@1 said:
Take an earth cable from each rca to an earth point and that should sort out the ground loop.
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Sorry, disagree, DO NOT do this!

Make sure the amp earthing point is clean and preferrably on bare metal, rather than painted.
 
chipperhead said:
I'm betting you've run your rca/speaker cables next to your power cables, run them down either side of the car.
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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?
 
Durzel said:
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?
Click to expand...

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