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Interference with RCA phono interconnects

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I'm having some audio interference issues with a new amp install. It seems to be a combination of the classic alternator whine (which varies with engine speed) plus a twittering in the background. The noise happens even with the volume turned down.


The head unit has two sets of stereo phono RCA cables, and if I disconnect them at the amp, the noise goes away. I've used Van Damme StarQuad instrument cable run down the passenger side via the door jambs. The screen of this cable is connected to the cold wires at the head unit end only, and unconnected at the amp end. This is as per the recommendations in https://www.rane.com/note151.html

I've changed the amp's earthing point from the light cluster to the battery but there's no difference.


The odd thing was I tried out some old component video cables as lash-up phono interconects with just the 3 wires connected (front L & R and Sub L) and there was no noise, but as soon as I added a fourth spare digital coax cable for the Sub R connection, the noise returned.


Any suggestions on what to try next?




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I have run mine up the A pillar and along the headlining and down the C pillar into the boot after I had simular problems.

No more noise.

A 5 metre run should do it fine.

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Thanks will give it a try.


I did find that the noise went away if I disconnected the cables at the head unit, so was thinking it might be a head unit earthing issue.

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I tried some spare phono cables (since pulling the existing ones will entail desoldering the plugs and it's extremely fiddly soldering in the car) and no matter where I route them the noise persists.

Then I ran some jump leads off the battery and hooked them up to the head unit's power connector, and the noise is still there!


I'm rather stumped now, unless there is an alternator noise suppressor solution. There are various car interference filters on ebay for about £10 but have no idea how good they are.



Edited by mr-b

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