Alternator Whine suppression

[oztme]

Hi Guys,


I have engine speed dependent whine coming out of my aftermarket alpine stereo.

I'd appreciate it if anyone has solved similar problem and can educate me? This isn't the usual grounding problem; I think it's distributor noise that I need to suppress at the source.

Setup: I have an alpine PXA-H800 processor, and an Alpine PDX5.100 amp. I'm not using any of the factory kit at all. The noise is present, even when I have all processor inputs disabled (except optical), and inputs disconnected.

Diagnosis:
I have tried all sorts of things to fix problem, relocating Processor+amp, ferrite chokes on all power lines, many grounding configs (amp is now 10cm above battery!), many RCA configs etc..

So, to test if grounding was an issue, I mounted proc + amp on a sheet of wood, got a separate 12V battery , and connected it to the proc + amp, using short cables. The amp + proc are now completely electrically isolated from the whole car, both supplied by a small 12V battery off 20cm leads.

I used an oscilloscope, and can see that there is the whine signal coming directly out of the processor, even when it is disconnected from everything else except the battery...There is no ground loop (problem is present with single processor on its own! ie: the processor, and a separate mini 12V battery!)


Summary: Pretty sure the processor circuitry is picking up distributor noise/trunk electrical noise through EMI/RFI; not through power wiring (there is no power wiring connected at the moment!).

I had a look at the signal with an oscilloscope, on the 12V line on the firewall and it's quite noisy. perhhaps 100mv of noise. The battery lead in the trunk shows similar noise.

Has anyone solved this problem? I'd like to suppress the noise at it's source but not sure how to do it. In the old days, people put condensors on alternators, but not sure if that's still the done thing..

Can supply wiring diagrams/photos/CRO screenshots if that might give anyone a hint?

Cheers + thanks,
Scott.