Ground Loop Problem

[ee904age]

I've just finished making a DIY AUX cord for the Bose H/U in our Mazda Atenza. It works semi-okay, except when using an Ipod, it has a horrible high pitched screech when you touch the Ipod, which almost disappears when you let go but not quite. When playing through the Mrs Galaxy phone the sound is just awful, no screech (possibly because it's a plastic body as opposed to the aluminium Ipod) but just an awful muffled sound with almost no vocals.

The cord is just a basic 3.5mm stereo extension around 1m long, with terminals soldered on the end connected directly to the pins on the head unit.

When connected to the Ipod, if the wind is blowing at the right angle and you hold your tongue just right, the sound is perfect for a few seconds, so I've counted out the possibility of an issue with the input of the head unit, and put it down to the cable.

Any Ideas what would be causing this?

[MrOizo]

Not getting any conductivity across the pins of the 3.5mm jack?

[sergei]

Remove one end of the shield from ground on the 3.5mm cable (leave only one end grounded).
As you already have a ground connection from charger to ipod.

[ee904age]

Weird! I've solved the problem by a fluke. I found if you hold the Ipod while touching the head unit the sound is remarkably better, so I changed some pins around and voila! Now I have what seems to be Left+ to Left+, Right+ to Right+, and common -ve to head unit earth, not signal -ve as the instructions say. It's not how the tutorial has it wired but work for me. Can't believe we've spent 18 months listening to FM when I could have done this right away!

[sergei]

Weird! I've solved the problem by a fluke. I found if you hold the Ipod while touching the head unit the sound is remarkably better, so I changed some pins around and voila! Now I have what seems to be Left+ to Left+, Right+ to Right+, and common -ve to head unit earth, not signal -ve as the instructions say. It's not how the tutorial has it wired but work for me. Can't believe we've spent 18 months listening to FM when I could have done this right away!

Signal negative was causing the loop.