Car amplifier noise - help!

[Seraphim]

I've just stuffed an amp in the boot of my car to power the front speakers - I've just this afternoon got everything wired up, and there's noise, and lot's of it!

I get a constant buzzing (with engine off) which is then joined by the typical alternator whine I've heard before when the engine is running. Has anyone got any tips on how I can troubleshoot this problem? I've got the amp grounded to the body at an existing ground point which is shared with something else - maybe the rear cluster... Is this a bad idea? Should the amp have it's own dedicated ground?

I've Googled for all I'm worth and I think I'm more confused than ever. Any help (and I mean any) will be exceptionally greatfully received. It's driving me insane!

 

[monkeyspank]

A dodgy ground might be a culprit. Is there a good connection to unpainted metal. It want's to be as near as poss to the amp.

Got good solid connection to the battery? Well, every connection needs to be good really.

Have you got the power cable running next to your speaker/RCA leads? Are the RCA leads shielded?

It could also be worth checking the wiring under the bonnet - alternator to battery, battery to chassis earth, etc.

Head unit earth might need a proper connection straight to the chassis. It might be dodgy.

Try testing the amp and wiring using a different source - mp3 player, cd player etc. both at the amp end and the HU end. That might show up where the problem lies.

 

[Seraphim]

A dodgy ground might be a culprit. Is there a good connection to unpainted metal. It want's to be as near as poss to the amp.
I sanded the body at the grounding point, so it's a pretty good connection. I could try sanding it more - there's still a little paint on it... Amp is grounded via a 50cm wire of the same gauge as the positive.

Got good solid connection to the battery? Well, every connection needs to be good really.
As far as I can tell, it's all solid - short length of 4AWG to a two-output fuse distribution block (for an eventual second amp) with 8AWG running to the amp

Have you got the power cable running next to your speaker/RCA leads? Are the RCA leads shielded?
Power is running down the opposite side to the audio - and using shielded and unshielded cables doesn't seem to make a difference.

It could also be worth checking the wiring under the bonnet - alternator to battery, battery to chassis earth, etc.

Head unit earth might need a proper connection straight to the chassis. It might be dodgy.

Try testing the amp and wiring using a different source - mp3 player, cd player etc. both at the amp end and the HU end. That might show up where the problem lies.
I certainly will try the amp with different sources tomorrow, and grounding the head unit to the chassis.

Ta for the help, you've given me a few ideas of things to try!

 

[Mickey_D]

Monkeyspank covered most of the points I would have suggested.

Something else to try is if you have a laptop, try pluggin the pre-amp outputs of the HU into the line-in on the laptop and doing a Sound Recorder test of the sound from the HU. If it shows up on the laptop, then you know the pre-outs on the HU are suspect.....

 

[Seraphim]

Ah, top idea Mickey, I'll give that one a go in the morning. It's times like this I wish I had a garage I could work in. Damn these short days!