Alternator whine with new stereo

[Shuvi McTupya]

I understand that a few things could be causing this but where is the most sensible place to start?

The issue started when I installed a power amp. The ground wire goes to a bolt that bolts the seat to the car..Is that likely to be an insufficient grounding point?

Or should i start by ordering some kind of filter ?

The symptoms are a high pitch whine that increases with engine revs.

Edited by Shuvi McTupya on Tuesday 7th January 14:34

[16v stretch]

I'd try another grounding point, you'll want a good bare metal contact. It could just be a case of whatever coating is on the bolt/mounting face is causing issues, and giving them a good scuffing with some sandpaper could resolve it.

If there isn't an alternative grounding point within a reasonable distance, look at ground loop isolators or inline noise suppressors.

[2Btoo]

Ugh. I had this last summer with a new HU and amp I installed in a new (to me) car. Tracing the problem was a nightmare.

Good earths necessary for both amp and head unit. 16v stretch's comments are worth following up. Running them both to the same earthing point can resolve some problems.

Good power cables necessary for both amp and head unit. Again, running them both from the same power lead can resolve issues.

Check that the power cable for the HU doesn't have electrical noise on it. If in doubt then use it to switch a relay which then switches on a supply directly from the battery down a new cable.

Check for interference on the RCA cables. This can defy logic but if you can't get to the bottom of the issue then buying some new RCA cables is not a bad option and the one that solved my problem (after many, many hours of hassle).

All the best.

[Shuvi McTupya]

16v stretch said:

I'd try another grounding point, you'll want a good bare metal contact. It could just be a case of whatever coating is on the bolt/mounting face is causing issues, and giving them a good scuffing with some sandpaper could resolve it.

If there isn't an alternative grounding point within a reasonable distance, look at ground loop isolators or inline noise suppressors.

Thanks, my suspicion was that would be the first thing to check, and the ground loop isolator would just need to get 'spliced' into the ground wire somewhere?

[16v stretch]

Shuvi McTupya said:

Thanks, my suspicion was that would be the first thing to check, and the ground loop isolator would just need to get 'spliced' into the ground wire somewhere?

You'd install a ground loop isolator at the amp end, unplug the RCA cables, insert the ground loop isolator in-between. They're the ferrule style things like what you see on laptop power supplies etc. Here's the kind of thing you'd be looking for

It might be worthwhile seeing if you can find the grounding point for the rear lights, should be a suitable enough earthing point though.

Also, are you using a suitable gauge wiring for your earth? You should be sizing for the power rating of the amp, same for the connector too.

[Dave.]

Did you run the power cable for the amp alongside the RCA/speaker cable?

[Shuvi McTupya]

Dave. said:

Did you run the power cable for the amp alongside the RCA/speaker cable?

They come from different places but end up at the same place so they maybe they do come into contact for a little while. I will check that out too.

[Shuvi McTupya]

16v stretch said:

You'd install a ground loop isolator at the amp end, unplug the RCA cables, insert the ground loop isolator in-between. They're the ferrule style things like what you see on laptop power supplies etc. Here's the kind of thing you'd be looking for

It might be worthwhile seeing if you can find the grounding point for the rear lights, should be a suitable enough earthing point though.

Also, are you using a suitable gauge wiring for your earth? You should be sizing for the power rating of the amp, same for the connector too.

Honestly, I have no idea about the gauge of the earth wire being suitable! That and the power cable (with large inline fuse) came with the amp but it was all second hand.
Maybe some research is required.

[Dave.]

It's less common these days, unless you got really cheap cables or run everything down the same side of the car wrapped around each other.

It's more likely the earth point(s).

[Shuvi McTupya]

2Btoo said:

Ugh. I had this last summer with a new HU and amp I installed in a new (to me) car. Tracing the problem was a nightmare.

Good earths necessary for both amp and head unit. 16v stretch's comments are worth following up. Running them both to the same earthing point can resolve some problems.

Good power cables necessary for both amp and head unit. Again, running them both from the same power lead can resolve issues.

Check that the power cable for the HU doesn't have electrical noise on it. If in doubt then use it to switch a relay which then switches on a supply directly from the battery down a new cable.

Check for interference on the RCA cables. This can defy logic but if you can't get to the bottom of the issue then buying some new RCA cables is not a bad option and the one that solved my problem (after many, many hours of hassle).

All the best.

I installed the new head unit before the amp and had no interference at that point so i can rule that bit out i hope!

As far as RCA cables go there are two sets running from head unit to amp so i can guess i can swap and change them and see if it has any effect.

Its very annoying as it sounds fine so long as the car is stationary!

[Shuvi McTupya]

Dave. said:

It's less common these days, unless you got really cheap cables or run everything down the same side of the car wrapped around each other.

It's more likely the earth point(s).

The RCA cables are pretty substantial and they are certainly not in contact with the power cable for more than a foot or so. I will be checking the earth contact first..The chair mount is painted black and i certainly didn't scrape any paint off it!

[16v stretch]

Shuvi McTupya said:

The RCA cables are pretty substantial and they are certainly not in contact with the power cable for more than a foot or so. I will be checking the earth contact first..The chair mount is painted black and i certainly didn't scrape any paint off it!

I'd try a different grounding point before doing anything else then, you definitely want as much bare metal contact between the ground wire and car body, the bolt should be for securing the ground wire to the body, rather than being the sole grounding point.

If you don't have any other option, pull the seat mount out, clear off a bit of the paint and mount it between the seat mount and the body rather than between seat mount and bolt.

[Shuvi McTupya]

Thanks I will give that a go.

(and thank you to the mod who corrected the spelling mistake in the thread title)

[griffin dai]

I always use one of the rear seat belt points, grind off any paint/coating to bare metal then clamp it down tight.

Also best to use the same gauge power/earth wire if possible, I use 0awg for this from the battery (fused....important!) then run them into a couple distribution blocks (fused for power/solid for earth, I’ve got a decent distro block that does both but you can get one of each for not much cash) then run either 4 or 8 gauge cables into the amps depending on what they take.

As for power wire next to RCA’s sometimes it’s just not possible to keep them apart depending on how your wire runs are, so I make sure they touch as little as possible and cross each other at a 90 degree angle to cut down on any interference.

[griffin dai]

Shuvi McTupya said:

As far as RCA cables go there are two sets running from head unit to amp so i can guess i can swap and change them and see if it has any effect.

Make sure the batteries disconnected before you go swapping cables and double/triple check they’re going in the right place before you power it back up. I killed a lovely Alpine MRV1000 amp a few years ago rushing the job and put them in wrong

[Shuvi McTupya]

griffin dai said:

Make sure the batteries disconnected before you go swapping cables and double/triple check they’re going in the right place before you power it back up. I killed a lovely Alpine MRV1000 amp a few years ago rushing the job and put them in wrong

You killed the amp by putting RCA cables in 'wrong'?? I am surprised by that!

I only blew the fuses in my amp when i put the earth and positive wires in the wrong way round

[griffin dai]

Stupid mistake, I was running an active crossover with 4 v12 amps and cocked up! Gutted!!!

[Penelope Stopit]

I know, ask a stupid question and all that but...........

Has the alternator got a capacitor fitted and wired to its main +ive terminal

2.2 micro farad capacitor https://www.amazon.com/Radio-Interference-Alternat...

Don't know what vehicle the problem is on, may need to check with dealer for the go ahead to fit, shouldn't cause any problems though

Is the Amp power cable connected to battery positive or have you spliced into another circuit?

Are the speaker cables of a twisted pair type?

[Shuvi McTupya]

Penelope Stopit said:

I know, ask a stupid question and all that but...........

Has the alternator got a capacitor fitted and wired to its main +ive terminal

2.2 micro farad capacitor https://www.amazon.com/Radio-Interference-Alternat...

Don't know what vehicle the problem is on, may need to check with dealer for the go ahead to fit, shouldn't cause any problems though

Is the Amp power cable connected to battery positive or have you spliced into another circuit?

Are the speaker cables of a twisted pair type?

I doubt the alternator has one of those things, I am not technical

The car is a 14yr old Peugeot so I wont need to consult with a dealer.
The amp power comes directly from the battery , and the speakers are fed with regular speaker wire.


I have now established that the power cable does not run along any of the other cables at any point.

[Penelope Stopit]

Ok then

Worth fitting a capacitor and having a listen