Hi there,

I've recently installed a 4-channel amp in the rear of my '03 Punto in an upgrade from a 2-channel amp that used to drive the front speakers exclusively (rears were run off the head unit... I'm cheap ). Unfortunately I've immediately run into problems.

If I plug in more than two channels at a time, (Ie fronts and one rear/all four/one front and two rears) I get massive engine noise through the speakers. With either rears or fronts exclusively, there's no interference at all!

The amp is driven by an Alpine PXA-H100 Imprint processor which also drives the amp for the subs. For the testing purposes the amps are currently mounted on a plank of MDF in the boot. Each is powered by 4-gauge cable connected to a distribution block with a 0-gauge cable to the battery.

The old amp used to be in the front beneath the driver's seat and never had noise issues. Could it be that I'm using bad grounding points? Each amp is grounded via a short 4-gauge cable to one of the four lower back seat mounting bolts in either side of the boot. They're big fat metal bolts and I'm using chunky 4-gauge ring terminals. The left-hand one (subs) has been installed for quite some time and has never had noise issues. The new amp is mounted on the right-hand side and connects to a bolt on the right, which I recall being slightly rusty.

If it helps, the amp is more powerful in watts RMS per channel than my old one yet seems to top out at lower volumes. Again, I'd love to blame a bad ground 'cuz it's easiest to fix

Image for reference, right-hand side is the new amp.



Any ideas? Cheers for your time.

Where have you earthed buddy and are all earths at the same point. Also i have heard problems like this when earthing things like the Imprint at the front of the car. I think Punto_Matt had a similar problem earthing something on the metal around the HU bay.
I think that your other problems will be something to do with the settings on the processor or the amp.

Thanks for the reply, volxstu. The Imprint IS grounded in the front of the car - I've used one of the bolts that secure the underside of the dashboard trim to the car - just in front of the bonnet release lever (pictured) It's been grounded there ever since installation - the same grounding point that the original 2-channel amp used without problems. Currently, the ring terminal is not mounted around the bolt (the bolt is too large) - could this be the problem? It's never been an issue before, and it's firmly held in place.



The two amps pictured in my original post are the ones that I am now using. The left hand amp powers the subs and is grounded to one of the big bolts mounting the rear seat left-hand hinge to the chassis. Same again with the right hand amp, except on the right hand side - so about as far apart as two grounding points can get without being at opposite ends of the car

Pictures attached - first the left hand amp ground:



And the right:

Am I missing something or have you got the earth and power in one distro block?

As for the ground it needs to be removed from the bolt, you need to sand down an area on the shell to bare metal close to the amp and drill a hole (missing vital stuff like brake lines and petrol tank), use a steel self tapping screw.

Don't forget to use Vaseline to make a good connection with the earth.

The distro block is just power - the silver cable certainly isn't earth Could I not sand down the hinge region rather than making a new grounding point? The left-hand grounding point has been in use for over a year now and has worked brilliantly? I could clean up the right-hand bolt/hinge area if that would be sufficient?

You guys sound like pro's so I feel silly saying something that could be so basic but I was told always to run the power and remote wires down separate sides of the car as it is normally the remote that causes interferance.

And also I was told to earth the amps as close as possible? I use the natural ground used by the rear lights or I have even used the bolt for the spare wheel kit.

Well if I recall the remote wire runs down the left hand side in the mk2 Punto, which is also where the power cable is run. I have routed it such that the power cable is kept as far away from other cables as possible. Audio cabling goes down the right hand side of the car.

Each amp is earthed using under 50cm of 4-gauge cable

The remote and rca's should be ran down the drivers side and the power down the passenger side.


I would only ever ground straight to the shell and not to any boltholes.

Thats what everyone within the ICE scene reccomends and I trust them

As has been said Run RCA and Remote down one side and power down another.
You are getting Ground loop noise ATM due to being earthed in 3 different points. The processor and amps need to all be earthed to the same point in the spare wheel bay.
The reason why you do it here is because a lot of the body panels are held together but cement and this is non conductive so it is difficult to dissipate power through anything else.
Also the rear seat mounts are nor a particularly direct path to Gnd so if you cannot dissipate the amount of power that you are putting in then you are looking at trouble. Although i cant scientifically prove it i have seen plugs, leads and coils totally ruined by bad earthing and theoretically the whole car could blow up.
90% of accidental car fires are caused by people making modifications to the cars wiring system... Badly

Excellent advice everyone, thanks! I don't know that the remote runs down the passenger side, I just assume it does - for simplicity I've used the factory installed remote cable to the now-deceased factory fitted sub in the boot. This sub is fitted on the left-hand side of the car.

So looks like first thing to do is re-ground the amps! Would you recommend a similar arrangement to the power cabling? A 0-gauge from the chassis to a distro block with 4-gauge to each amp?

Whilst I'm at it I would like to do something about the ground wiring in the engine bay - I'm sure I'm pushing the factory ground cable to the battery past safe limits considering the current involved. Would this necessitate tapping a new grounding point in the engine bay to run to the battery and removing the factory cable?

Ok... this seems a little bizarre.

I've switched the new amp over to the sub amp ground cable and still have the whining noise. It also seems that if at least ONE preout for front AND back is plugged in from the Imprint processor, the whine kicks in. So plugging in front left and rear right = whine. But front L/R alone, no whine.

Even grounding the Imprint to the same grounding point as the amp makes no difference.

Here's where it gets interesting. With the whole car turned off, and the new amp not connected to ground or remote (but still connected to power) I can still turn the bloody thing on. Yep - if i bridge the power and remote terminals, the green power light comes on!!

It will fade away after about five seconds. If I then stop bridging remote to power, and re-bridge it - it comes back on.

Using a multimeter I can see the potential difference between the power and remote terminals slowly creeping up towards 12v, where it then remains (this amp is not grounded?!)

If I unplug the preouts from the Imprint processor, this doesn't happen. What does this suggest? There is a current leak between the Imprint and the amp even when everything is turned off?? (Imprint processor remote is controlled via the head unit, which fully turns it and itself off on the ignition) Would making a new grounding point even make a difference here? :bang:

If it's a leak this bad, surely that necessitates a ground-loop isolator?