Amplifier install - humming noise

[stagea-rs4]

Have installed an amplifier in the back of my Stagea, run the power cable down one side and speaker wires, blue turn on and rca's down the other. Earth is solid and a short run. All was well until I grounded out a speaker wire behind the head unit. I reset the head unit and I now have quite a loud hum with the engine off but it seems to be in a wave. ie not consistent. It's worse with the engine running and gets louder with increased revs.

Any ideas on how to resolve this?

Thanks.

[stagea-rs4]

I've eliminated the fact that the power cable runs the same side as the right side speaker cables (i've run the speaker wires from the back of the head loom rather than wire each speaker individually). I'm going to try an RCA ground loop eliminator next.

[ru']

Was it working fine until you grounded the wire? Sounds like something broke...

[stagea-rs4]

Hard to say. I think I just noticed it after that happened. I didnt have the engine running previously but it's like sitting inside a turbine - the whine is quite loud. I pulled all the wires and started from scratch. Ran temporary pos/neg wires directly to the amplifier with no change. I did read somewhere to use the same earth point for the head unit as the amp but they couldnt be much further away from each other.

[GTR Cook]

You said you grounded out a speaker wire behind the head unit?

[infamous_t]

Originally Posted by GTR Cook

You said you grounded out a speaker wire behind the head unit?

+1
You don't ground speakers, you return them (to amp or head unit).
Personally I don't even ground power, but you definitely don't ground speakers to chassis.

[stagea-rs4]

Oops, sorry for not being clearer. The speaker wire grounding was an accident (a short which put my head unit into protect) when I slid the HU back in.

[ru']

You'll need to take it in stages:

1) If you have any 'speakers running direct from the HU, then disconnect the amp RCA leads/remote from the HU and see if the noise comes out of the HU 'speakers.

If it does it's the HU; see which channels are affected, check wiring and if it's okay bin the HU.

2) With the RCA disconnected at the amp, power it up and see if there's noise through the amped 'speakers.

If there is see which channels are affected, check wiring and if it's okay bin the amp.

3) With the RCA connected at the amp but disconnected at the HU, power it up and see if there's noise through the amped 'speakers.

If there is then try it with different RCA leads maybe? Maybe an earth loop isolator?

4) If the noise is only there (through the amped 'speakers) when everything is connected then the HU RCA out is perhaps faulty.

What HU and amp etc. do you have?

[stagea-rs4]

Thanks to all for the replies.

ru',
1) all ok, I reconnected the the HU to the speakers and it's hum free bliss.
2) RCA's disconnected, amp powered and speakers connected to amp - no noise.
3) To be tested.
4) I think it's either the RCA's or a ground loop problem.

I'll try an isolator in the next few days.

HU is a single DIN Kenwood job with ipod input etc and the amp is a 4 channel Mutant MT2004.

[ru']

let us know how it goes

[agent-x]

i would definately check the earth wire even though you say its solid earth it sum where else

i usually get this problem

the earth wires comes a bit loose and when it moves about makes a noise

ermm cant think what else it could be

ive had quite a few problems in various cars

if i think of anything else ill let you know

[shakman83]

had the same problem a while ago, if you turn the volume down and rev it will be a humming sound.

2 things to try.

1.change ur amp grounding, and make sure its against metal and not paint.
2 it can also be your alternator, not giving enough power, you can get an alternator suppressor from halfords, i think its about a fiver. it goes onto your alternator, that should get rid of the noise or reduce it.

[stagea-rs4]

Thanks for that. I've not got around to installing the ground loop isolators but if that doesnt work i'll try the alternator suppressor.

[Sub Boy]

A ground loop isolator or supressor is unlikely to fix the problem.
You would have blown an earth track in the preout stage in the head unit, If it is a Pioneer they have a fuseable link there.

...This is a job for an audio tech to repair.

[stagea-rs4]

It's a Kenwood. Still worth investigating?