Hisssssssssssssss

[S80_UK]

Hi,

You say you have an equalizer - I am not sure where that comes in the signal part from the Phatbox - often the equalizer is connected to outputs from the headunit and then feeds to an amplifier.  In that case, adding the isolator between the two will probably not help (but no harm to try).  The place that you generally need to put the isolator to elimiate digital "hash" on the audio, and to eliminate alternator whine, etc, is between the Phatbox and the audio component that it connects to (the head unt).  This wiki page is specific to a Volvo installation, but using a VW Phatbox, so some of it may help you.  Note that the power and audio pins on the 26 way connector are the same, but the control signals will be on different pins in your case.

http://wiki.phathack.com/VW_Phatbox_to_Volvo_Transplant_%28How_To%29

Note that you may need to provide alternative power supply grounding arrangements for the Phatbox.  I think in VWs it is normally grounded via the head unit cable and the isolator will break the audio ground, and maybe the power ground.  You will need to check.  Operating the Phatbox with +12V applied and with the control signals connected to the head uniit but with no ground might cause damage, so after installing the isolator I would check the grounding before applying any power and then add a ground wire for the Phatbox if necessary. (That is how I have my Volvo wired.)

Good luck!

[ajrobson]

Well I don't know for sure that the source of the hiss is the Phatbox or not. It could very easily be the HU itself. Lacking any specs on it, I would not be surprised if the signal to noise ratio isn't very good.

Yes, the EQ is installed after the HU and I will try the ground loop isolator there before I try anything more ambitious.

But since the HU (and Phatbox) both share a common ground while the remainder of the system share a different ground (in the trunk for the amps) maybe the ground loop isolator will work.

However, I have experienced ground loop problems at home when connecting the output from a PC to a stereo at the other end of the house. The noise was not hiss, but a definate "hum". So I am a bit surprised that this hiss would even be considered a ground loop problem.

[S80_UK]

However, I have experienced ground loop problems at home when connecting the output from a PC to a stereo at the other end of the house. The noise was not hiss, but a definate "hum". So I am a bit surprised that this hiss would even be considered a ground loop problem.

That depends where the hiss comes from.  If it is just from component noise, then sure, it's nothing to do with ground loops.  I found that the digital operations in the Phatbox and hard disk generate their own noise on the power supply ground.  For the most part that can also sound like a hiss, but it may have tones or some kind of rhythm on top (from the processing loops).  Interestingly I found that this problem when I was debugging my installation and I had the PB grounded via the cable to the head unit (as I think VW do).  Grounding like that solved the alternator and injector noise, but replaced it with the digital noise.  In my case grounding the PB again locally and fitting the isolator got rid of both.