rexpontius

Dont think it is the alternator diode, they dont go wrong a lot (or it must be a 928 issue, but have not ever seen it on other cars).

I also dont think it's the battery, batteries dont induce alteranator whines.

First check the power cables to both the headunit and amp.

Another think to check is if the alternator whine gets louder / softer when playing with the input sensitivity on the amp.
If it does, then try setting the inout sensitivity lower and check if you can still turn up the volume loud enough.

If it doesnt, check if the whine gets softer/louder when you adjust the volume on the radio (best to check with a 'silent' track / mp3.

If that happens, the whine is picked up somewhere in the headunit.

I am curious to hear what you find out.

cheers
Michel

LT Texan

Disconnected the head unit unswitched power (yellow) wire from the splice from the clock and hooked it up with a 10awg cable directly to the battery.

Dead quiet.

No alt whine.

Success!!!!!!!!

I'll rewire both the amp and head unit permanently from the battery.

rexpontius

Great result!!!!! enjoy your whine free sound :-)

rexpontius

Oh and one more tip, make sure to properly fuse the power cable as close as possible to the Battery (NOT at amp or radio)

Cheers

Alan

Good - usually noise induced is due to the power supplies being inadequately sized or connected (power or ground) and also if these are sourced very differently (e.g. head at the front and amp at the back) then differential noise gets coupled into the inputs. Keeping a common power & ground source for the head unit, antenna amp, any active crossovers and the Amp will keep this to a minimum. Best is from the battery (not the alt) and better yet with more local filtering (big parallel cap and local serial supply inductors on the head unit switched and unswitched lines).

Other than that it is down to improving the signal wiring shielding quality and routing as far away from noise producers in the car as was already mentioned.

For most induced noise focus on the supplies first - its easiest to eliminate...

Alan

bill_996

Hi Dan,

I have been having the same problem with my 2001 996 C2. I have tried almost everything to reduce the whine and turning down the gain on the amp does help, but still noticeable with the head unit powered on, but on mute. My yellow wire is connected to the OEM wiring harness. Do you think that going straight to the battery could help in my case? At my wit's end.

Thanks Bill

G8RB8

It's usually a difference of potential in the ground. Ground everything to the chassis except the speakers. I chased a ground loop for months before I found the chassis of the head unit was not grounded as well as the rest of the system. That little screw on the back connected directly to the chassis cleared it right up.