Range Rover Harman Kardon - Pioneer HU

Hi Guys, Was wondering if anyone can offer some expert advice. I have a 97 RR HSE (series 2), with the HK amps in each doors, and HK Sub in the boot. I have added a new Pioneer H/U, and used the Pre Outs to power the HK amps by making up a loom to attach via the RR 10 way iso connector. The sound is excellent, and the H/U works fine but there is a worrying problem. There is now a high pitched noise, more like a frequency buzz through all the door speakers, obviously more noticeable when the volume is turned down or muted. I am geussing that it is the wrong impedance, or perhaps the voltage comeing out the H/U comapred to what the HK amps need. Can anyone tell me more about the HK amps, or if I need to drop the output voltage of the preout etc? Perhaps I need to run a better ground? Any advice or pointers greatly appreciated. Thanks Nige.

Your post mentions the two possible causes I would start looking at: voltage too high and possible bad ground.  A Land Rover dealer may be able to help you with more information about the amps, but in general OEM amplifiers are designed for max 2 volt input I believe.  You could also try contacting Harmon technical support and see if they will give you the information.Support the12volt.com

Thanks for the reponse, I will try my friendly RR dealer, we have allready looked into the wiring diagrams, and have noticed that as well as the H/K amps in the doors there is another central control model in the stereo wiring loom. This is not to be confused with the under seat Becm, but that could also be looking for a signal of some sort, as they are all interconnect. On the earth front should I run new seperate grounds to each of the amps in all the doors, this would mean 4 for the doors and one more for the subs and amp in the boot. TIA Nige.

Look for a ground (or earth) lead in the OEM wiring harness going between the system devices that has now been interrupted by your modification.  It may be as simple as re-connecting this wire.  The factory wiring diagrams will show this, but they will not generally describe the expected voltage level of the signal.  For this, your dealer may have to contact HK or whomever was the original source of the factory head unit.  Cheers and good luck.Support the12volt.com

Thanks dyohn will try your suggestion.