Stereo Intereference

sparkymark75 · 15 Mar 2015 at 10:10

I have a 2009 Mondeo Titanium X Sport. t came fitted with the Sony 6 CD DAB head unit and also Bluetooth + Voice Control.

A few weeks ago I upgraded the Bluetooth module to one that can also handle USB. To fit this I bought the cable from the module to the glove box, the bezel for fitting in the glove box and a USB socket for pairing the USB cable to the bezel. All of these were genuine Ford parts.

This all worked fine with my Sony unit.

Last weekend I removed the Sony unit and retrofitted the NX Sat Nav unit. Other than having to replace the surround fascia, the support cage and add a GPS mouse antenna, it was a matter of plugging all the connectors from the Sony into the NX unit. I had to leave the DAB aerial connection loose as the NX doesn't have DAB.

Now when using the USB socket (I have an 8Gb memory stick plugged into it), I get what sounds like alternator whine. It increases when I accelerate. It's not mega loud but it is noticeable when you turn the volume up, which I have to do as the USB volume is considerably lower than the radio.

Looking online, it appears I might need a ground loop isolator. However I don't know where to get one for USB and where it fits. A friend also asked if I earthed the head unit but there was no "earth" to speak of as such, I connected all the connections (other than the DAB aerial) that were connected to the Sony.

Would something like this worK? http://hifimediy.com/usb-isolator

lord filbuster · 16 Mar 2015 at 14:47

That is a bit strange, the memory stick is powered by the head unit, not it's own power source, so it shouldn't be causing a ground loop.

I'd think it was more likely to be a poor connection to the car's ground. One or two of the wires in the connector block at the back of the head unit will be the ground, so you could try cleaning the contacts in the connector block, or even connecting the support bracket or case of the head unit to a separate ground somewhere.

The isolator you linked to would fix the problem if it was a ground loop, so you could just buy it and send it back if it doesn't work.

sparkymark75 · 16 Mar 2015 at 14:52

The support bracket is plastic so I can't use that as a ground. I might just try that item I linked to and see if that helps. Although if the interference is between the Bluetooth module (that provides the USB port) and the head unit, that may not solve it?

lord filbuster · 17 Mar 2015 at 10:40

Ah sorry, I misread your first post. The Bluetooth module probably does have it's own DC-DC power supply, so it may well be causing a ground loop. For some reason I thought you were plugging the stick straight into the head unit.

The isolator might actually help. You can try connecting it between the memory stick and the USB port, but I suspect you will be better off connecting it between the bluetooth module and whatever it is connected to. You can hide the isolator behind the dash this way too.

sparkymark75 · 17 Mar 2015 at 10:42

lord filbuster said:
Ah sorry, I misread your first post. The Bluetooth module probably does have it's own DC-DC power supply, so it may well be causing a ground loop. For some reason I thought you were plugging the stick straight into the head unit.

The isolator might actually help. You can try connecting it between the memory stick and the USB port, but I suspect you will be better off connecting it between the bluetooth module and whatever it is connected to. You can hide the isolator behind the dash this way too.

The problem with attaching it between the Bluetooth module and the head unit is it's a Ford connection, not USB, so I would need some other kind of device.

lord filbuster · 17 Mar 2015 at 11:14

Yeah, I just googled the parts, I doubt there are any isolators ready made for that. You may as well give the thing you linked to a go, and put it between the stick and the module, it may still fix it.