Thread: Noise fix for ATX motherboard

My suggestion would be for you to ground the case to the vehicle's frame. You can do so with a fuse inline or a resistor if you're worried the case may be "live", but chances are it's not.

My company is working on a 12V input, multiple output DC-DC converter that is fully ATX compatible at the moment, but it won't be available for commercial sale for a couple of months I'll keep you posted...

All you need for ATX is a +3.3V output in addition to +5V from your power supply. You could use one of the currently available supplies and add the +3.3V output to it, or build your own from scratch. Maxim ( http://www.maxim-ic.com ) and National Semiconductor ( http://www.maxsemi.com ) are excellent sources for switchmode DC-DC converter components.

You will also need to watch out for the +12V line -- I don't recommend feeding the car's 12V directly to the motherboard & peripherals like many people do, or using a linear regulator (i.e. LM7812) -- the car's 12V can fluctuate from 8-16VDC and is very noisy to a computer. Look into building a flyback converter to convert 8-16V into steady, regulated +12V.

You will need to be able to solder and follow schematics to build a supply though... they don't offer kits or any details other than schematics and electronics equations for figuring resistor values, etc.

DC-DC converters are great because they usually operate at several kHz and therefore don't introduce any audible noise into the audio path.


--Jason
http://jump.to/m2pc

I would recommend grounding the case near the power supply. A good way to do this is to use crimp connectors and find a screw on the case and run the ground wire to somewhere on the car where a good ground is. If you can't find a good ground, you can ground it to the trunk latch (unfasten one of the bolts a little and use another crimp connector) or drill a hole in something metal and fasten it with a screw there.

Yes, doing DC->AC->DC is stupid; a DC-DC supply should draw 2 or 3 amps instead of the 5 or 6 drawn by an inverter. Plus power supply noise wouldn't be a factor anymore.

If you're still getting noise you could try 1:1 isolation transformers on the output from the sound card to the amplifier or even try bypassing capacitors across the DC input to the inverter. I've even heard of people installing an AC line filter across the output of the inverter.

--Jason
http://jump.to/m2pc

Grounding the case shouldn't cause any problems with your alternator or battery. If anything, there is some sort of voltage potential developing in the case of your car PC, and grounding the case will eliminate that potential. Some audio equipment (i.e. head unit, amp, etc.) may not like the case being live, and grounding serves to neutralize whatever stray voltage you have.


--Jason
http://jump.to/m2pc