Annoying headunit audio interference :(

miniyazz · 1 Jan 2013 at 23:12

So a few months ago I installed an ipod docking cable into the back of my headunit - slight alternator whine, but I grounded the ipod adapter unit and all was well and good. Recently got an ipod to 3.5mm jack adapter (yes I know, seems convoluted but is the easiest way!) so now I can plug my phone (or anything else with a normal output) into the headunit. Now this works great except that when I plug my phone in to charge at the same time as playing music, I get an annoying alternator whine - quite noticeable even with phone volume turned on max.
I've already grounded the adapter unit and there's a distinct 'silence' --> 'whine' --> 'silence' when I plug and unplug the phone from the car charger so that's not the problem. I'm not really sure where to look from here to solve the problem.

Any ideas? Is it possible that my cheapo adapter cable has not connected the ground on the 3.5mm jack to the ipod adapter? Would it even play music if that were the case?

Might it be fixed by jury-rigging the 3.5mm ground directly to the car's ground?

Howard · 2 Jan 2013 at 08:46

Is it the OEM head unit or an aftermarket one? Sounds like you've got a ground loop situation going on. You could try either grounding the head unit to a different location or a different USB charger if the charger itself doesn't have a very good ground, causing it to ground through the next best option (through the audio input cable)

Malc · 2 Jan 2013 at 09:40

It definitely sounds like a ground loop problem. The whine should change pitch with acceleration as well.

To save time and tinkering, you could get a ground loop isolator like this one http://www.amazon.co.uk/Kensington-...6?s=electronics&ie=UTF8&qid=1357119274&sr=1-6

I have that one and it works fine. Completely removed the whine.

Liquid_Entity · 2 Jan 2013 at 09:46

I had a similar issue with my new pc build and my external sound card. Got one of those ground loop isolators and no interference at all. Got one on ebay for about £3

Howard · 2 Jan 2013 at 09:58

They, like power conditioners, don't always work terribly well though. But yes if you can spare a tenner or so they're definitely worth a try.

miniyazz · 2 Jan 2013 at 23:01

Hi guys, thanks for the input. The headunit is the stock one, and yes the whine does change with rpm

The charger is one I fitted myself and although the cable is annoyingly cheap and rubbish (monofilament stuff I bought in error), there's very little interference back to the battery - just via a cigarette lighter socket, relay and a fuse so it shouldn't (hopefully) be causing the problem. I'll try plugging it in via the standard cigarette lighter socket though to confirm.
I'll also try a different ground for the ipod adapter though I'm not convinced it's the problem as I can charge my ipod and listen to music (both through the adapter) without problems.

Failing those I'll invest in a ground loop isolater as that seems like possibly a quick and easy fix!

Thanks for the help.