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My Macbook modified DC adapter doesn't work - now what?


greg sextro

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I tried doing some searches for the problem I'm having, but have come up short.

Alright - so the DC adapter I bought and modified with a 4 pin XLR works in that it powers the computer, but once in place on the cart with all the connections I get this really awful "digital noise" that is present thru my system.

Everything is powered thru a PSC powerstar - (minus a Motu 828mk3 - currently on AC)

If I unplug the power connector to the computer - the noise goes away.  If I unplug the firewire connector that goes to the 828, the noise goes away.  With everything connected and the 828 turned off, the noise gets louder!

Of course - if I run the laptop of regular AC - there is no noise.  Though I generally will have AC on set - I know there will be times when I will have to be full DC - so I need to get this laptop hooked up properly.

So now what?  I have an inverter coming in the mail today (Exceltech XP 125) which I got just to convert and power the 828 off of DC.  I'm very much hoping that connecting my laptop thru it as well will work. 

I've read that some other people on this site have made DC to DC connections with their laptops.  Has anyone encountered the same problem?

Any advice is greatly appreciated!

-Greg-

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Could a capacitor be used on the negative pin of circuits that serve AC devices to serve as a noise filter?

My electronics class is somewhat forgotten...

It kind of makes me wonder what (if any?) filtering PSC, Remote Audio and the rest use in their power supplies, and how expensive it might be to add.

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Might not be practical, but you might want to isolate the computer power from the rest of your equipment by using a second gel cell ( or whatever battery you use ) and run the computer off that. I've read posts from others using even hard drive recorders like the DV824 running into this.

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