Alternator Whine...sort of

[spoonraker 10+ year member]

I posted this before, but I got no replies so I'll try again.

First of all let me detail what exactly is going on. I am running a CarPC. All the sound is from the PC, there is no regular head unit anywhere. The PC is located in the trunk. The sound card from the computer outputs to a cable which converts the 3.5mm headphone jack to RCA, and that splits and plugs into my amps. None of the RCA cables are more than a couple feet long. Both of my amplifiers share a common ground point, which is directly bolted to the bare sanded down metal in the middle of the floor under the back seat. From the time I turn the key, it takes about a minute and a half for the computer to fully boot up (this will be reduced to about 25 seconds once I reinstall windows and do lots of tweaks) and during this time there is HORRIBLE alternator whine. The minute the sound card on the PC turns on 100% of the noise is gone.

I know most noise, especially alternator whine is caused by bad grounds. However in my case I don't have noise when everything is on, only when the amps are on but not receiving an input signal.

Do you think the noise is something I can stop by rewiring? If so where should I check, what kinds of test can I try to track down what is wrong. I do have a ground loop isolator and a DMM.

Do you think the noise is unavoidable? It's basically like turning your amps on, plugging an RCA wire in, and then plugging it into nothing. So any radiated noise near the signal cable would be transmitted directly to the amps.

Obviously if I delay the amp turn on until the sound card is turned on that will solve the problem, but how can I do that? The PC and the amps are on the same remote wire so simply putting a switch in the remote wire won't work. I'm not familiar enough with relays to make a delay for the PC, but if you have a diagram for one, post it up. Other ideas?

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[spoonraker 10+ year member]

bump.....

 

[djman37 5,000+ posts]

velleman 555 timer it's a variable delay... there's all KINDS of cool little relay kits and stuff on there.

 

[quest51210 10+ year member]

dude, i have been installing a long time. recently added some PDX amps and new components to my new HHR. i have whine from the passenger tweet....thats it. just the one **** tweeter. not from the mids, sub, or the other speakers. its minimal and only i seem to hear it most of the time so i just turn it up to avoid it.

 

[spoonraker 10+ year member]

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[spoonraker 10+ year member]

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[audioarsonal 10+ year member]

Try moving the rca's around while it is making the sound and see if its picking up the magnetic field of another object.Could be ran to close to a power supply with having short rca's?try that even with a ground loop isolator you woud still get the noise if there is alot of power draw.

 

[sdmtnbiker420 10+ year member]

How do you choose songs while driving?

 

[Megalomaniac 5,000+ posts]

How do you choose songs while driving?

using a frontend software like roadrunner(uses winamp in backend) but skinned or use centrafuse

 

[jco1385 5,000+ posts]

maybe your power supply in the pc is too close to the amps/rcas?

 

[spoonraker 10+ year member]

Well I tried a few things and I think the problem is unavoidable.

I took my laptout out to the car and plugged the RCAs into it, car on, laptop off = no noise. Laptop on = no noise. So that means the noise is simply coming from the CarPC. Once the sound card turns on the noise goes completely away, so I think this problem is unavoidable, I just need to delay the amp turn on, or put a switch on them.

Now in addition to that noise, I seem to be getting interference in the touchscreen monitor in the dash. Again, hooking up to the laptop made the problem go away with the car on or off. I think my CarPC is just a rather noisy shaken to death piece of equipment from sitting 2 feet away from my Fi Q. I'm going to move it all the way into the corner of the trunk and mount it differently with a new fiberglass case and some shock resistant mounts whenever I finish my door panels and hopefully that improves things.