21 replies to this topic

[Tornado99]

Just installed a new amp in the boot due to a failed previous amp. Now I have a high pitched whine that gets higher pitched with engine rpm. Was not happening with previous amp, same wiring throughout. Happens on all sources, CD, radio and bluetooth, even with volume all the way down. Does not increase or decrease with headunit volume.
Where to start troubleshooting?
Is it normal practise to isolate amp chassis from car body? I've got it mounted to boot firewall with machine screws so it will be grounded at the four screws.

[Spider]

Most likely from the Alternator. Temporarily disconnect it to be sure.

First check all the connections to it are tight and also the Earths. Check your Battery connections too.

 

It could be a sign that your battery is on the way out. I know my car does this and within a couple of months of it starting to do it, the battery dies.

If everything is OK then look at fitting a suppressor to the Alternator. Sometimes a basic capacitor on it's output is all they need but sometimes, they need something a bit more heavy duty.

[Tornado99]

Thx. Been doing some research and apparently can be several causes. But one obvious issue is some amps do not like to have their chassis in contact with vehicle ground, so rec is to use a no-conducting/wooden mounting board to insulate from ground contact. Something to do with creating a ground loop,sets up a whine in some amps, depending on their designs. Will try that first.

[stuart bowes]

I've never earthed any amp to the car body in that way, the amp has a dedicated earth terminal and that should be connected obviously or it won't even turn on.. but my amps are usually screwed to a wooden sub box and even then I put little wooden 'feet' under each point to space it away from the surface a bit and let air flow behind.  (for that reason alone it's worth putting some spacers under the fixing points, amps get hot)  just 4 bits of wood the size of a matchbox will do

 

that's not to say it is the reason for the humming but it doesn't cost anything to try taking it off the metalwork

Edited by stuart bowes, 21 March 2022 - 04:40 PM.

[Tornado99]

OK, amp now mounted on wood...and whine is still there 

Always present if  head unit is turned on, doesn't change level with volume knob. Also noted a rapid clicking sound as soon as I go ign on, not yet started, shuts off with my electric fuel pump shut off switch. So clicking from fuel pump electrical noise affecting amp. Ign/alt e-noise also getting through. 

 

None of this happened with previous amp in same location...but different brand (Planet Audio, Class A or B I believe, vs now a Cerwin Vega Class D). 

 

So looks like I now need to learn about noise filtering setups. Any suggestions?

[stuart bowes]

are you using all the same power leads and same sound signal wire and everything else exactly the same, except literally just the amp has been swapped?

 

i.e should we be able to rule out a wiring issue.  

 

for example I know that signal wire (phono cables) should be run as far away from power leads as possible because you can get a hum from that similar to the way an induction loop works (or that is my admitedly limited undertanding of the reason which may be wrong... but the fact remains it does happen)

Edited by stuart bowes, 23 March 2022 - 04:10 PM.

[Tornado99]

Yup, same cabling to battery, same RCA shielded cables from HU. It was as you say, direct amp swap out. I've found multiple videos of guys dealing with hiss/static/rpm whine on new installed HU and amps, via simply grounding the rca output socket to HU chassis. Might try this and also confirm all ground connections amp/hu are in good nick.

Where is the engine to chassis ground point? I'll try to inspect and clean that if easy to reach.

[Shaun78]

Hi,could it be just a faulty noise suppressor on the head unit wiring.

[Tornado99]

Hi,could it be just a faulty noise suppressor on the head unit wiring.

AFAIK, there is no noise suppressor on power lines into HU. 

[stuart bowes]

you could try sticking a ferrite core on the power lines to the head unit and amp?

 

https://www.amazon.c...,aps,77&sr=8-12

 

usually they give them away with dashcam wiring kits to stop interference causing fuzzy picture

 

or pop back to that car audio place you went to before and ask them if they can think of anything to try or ways to test where exactly it's coming from

Edited by stuart bowes, 25 March 2022 - 01:58 PM.

[Tornado99]

Fixed! Just did this:

 

 

 

 

Grounds out the RCA outer contact by wrapping with copper wire around the radio RCA out jack, slipping the rca cable into place to hold, then attached free wire end to a good ground on the m=etal of the radio body. 

Fully killed the horrible fuel-pump clicking and rpm whine on my car. 

Could be a poor ground elsewhere that created the problem but have not located that (yet).

Edited by Tornado99, 27 March 2022 - 01:47 AM.

[bpirie1000]

Did you run the rca leads and the remote feed for starting the amp down the same place?

These should be separate... split them up... see how you go..

Link added. See step 6..

https://www.wikihow....stall-a-Car-Amp

Edited by bpirie1000, 27 March 2022 - 07:19 AM.

[sonscar]

Controversial?buy an amp with better internal power supply and shielding.Steve..

[Tornado99]

Did you run the rca leads and the remote feed for starting the amp down the same place?

These should be separate... split them up... see how you go..

Link added. See step 6..

https://www.wikihow....stall-a-Car-Amp

pre-amp and speaker wiring run left side to boot, blue power on signal line runs right side to boot.
Again, all was fine previous amp and no wiring was changed when new amp installed. Must be some design differences making new setup more prone to getting this interference noise. So glad the grounding of RCAs solve it easily.

[stuart bowes]

I would lean towards agreeing with sonscar to be honest, assuming the wiring is unchanged and hasn't suffered some sort of damage in the mean time which is causing a fault

 

still if the adding of earthing has cured the issue then thumbs up, enjoy your tunes and move on :)

 

glad you found a cure

 

interested to see the amp spec if you can stick a link on here at some point, just purely out of curiosity

Edited by stuart bowes, 28 March 2022 - 11:58 AM.