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.

[TerminatorX5]

your system is definetely picking up the RF portion of the interference - some wire shielding could be in order... have you tried the complete shielding of the signal wires? i remember seeing on some other forums they used a magnetic sheet material (similar to what is used on the printed refrigirator magnets)...

I have not used it myself but you might find it of interest... McMaster-Carr

[oztme]

Hi Mate,

I just tried the amplifier on it's own, with nothing but power and a speaker connected. Still whistles. It's a VERY noisy environment in the trunk space.

I think both the processor, or the amp will pick up the noise...

I still get the noise come through the amp, even without any cables except one speaker, and power connected.

----
I tried putting low ESR capacitors near the alternator to try to suppress some noise at the source. That didn't work. Tried putting some caps on the supply lines in the trunk space; still no good..

Pretty stumped what the hell to try next. Building a bloody faraday cage for the whole thing?

Any ideas please chaps?

Cheers
Scott.

[TerminatorX5]

not sure if you still working on this issue... what you may consider, connect your amp to alternative power, say a stand alone battery not connected to any car, and see if you still have the whine... if you do NOT have with alternative power source, then your current whine comes from the power wires of the amp

if you continue to have whine with alternative battery, then your amp is picking up the whine from the RF... the amp itself might be faulty, or you have power cables running in parallel with audio cable for extended length...