Computer audio noise from Intel 2 ghz mini

dogpilot · 11-13-2007, 07:19 PM

Well I went for a 2ghz Mini to install in my Vanagon Syncro. I managed to get a Carnetrix P1900 with the extra 5V output to drive a USB hub. This all is connected to a Lilliput 841 mounted on the ceiling. The touchscreen interface is working just fine. I have got it running Routebuddy with a Etrex Vista Hcx going in through the USB hub.
I have connected the audio output to my Panasonic 8304 stereo's AUX input.

Unfortunately, I get computer noise in the audio on the Panasonic. I isolated each output, screen, hub, and screen power (by installing a relay on the secondary output of the 1900, and running it on its own power supply).

So any suggestions on getting the noise to go away. Would it get better if I perhaps went to a USB sound output?

iamgnat · 11-14-2007, 12:19 PM

Sounds like you have a ground loop. Check over in the Audio forum (or maybe it's in the FAQ section?) for a great write up on finding and fixing them.

The jist is that you need to either try moving your various ground points around or pick up a ground loop isolator (though they don't always work).

-dave

dogpilot · 11-14-2007, 10:57 PM

Well ground loop is defiantly a possibility. I am getting more computer noise feedback. I need to check the ground on the power cable shield as well.

I did a little trip to Fry's Electronics today and picked up a few essentials, a better shielded audio cable and a Creative USB audio output. I can locate it closer to the Audio amp, and it will be isolated from the computer's generated noise that can be generated out to the audio line.

More experimentation tomorrow.

BTW, I did read that thread, sometimes there is other wisdom to be gained from the community as experience grows.

monsho · 11-15-2007, 03:30 AM

Interested to see your final set up in the Syncro, I'm just pulling everything together to install into my 89 Westy...

hondaluder · 11-15-2007, 08:26 AM

If you did not use the mounting plate (metal thin cover for ports) you probably are not fully grounded. On my jetway had to solder a wire on the metal connectors in the back (USB, Firewire Etc) to each other and then ground. Solved all my noise problems

dogpilot · 11-15-2007, 10:23 AM

I have some photos of the early version of the install using a G4 Powerbook. It just didn't fit anywhere without some kind of issue. That coupled with the fact it had to be started with the lid opened, then you could close it, made it a poor choice.

I just had the van painted, so the windshield was off. That gave me an opportunity to have some holes drilled in the back side of the glarescreen so the wires where neater. I had temporarily mounted the Mini on the heater box in the same position as the G4, but there is an issue with shifting on the Syncro. So, I have bought a spare glovebox assembly and am in the process of mounting it in there.

The least fun of this whole project was pulling the VGA cable down the A pillar. I had to cut and solder it besides maneuver it through a maze of thin openings and sharp metal edges. The noise thing is irritating, but I mainly put the system in for navigation. I will have to do some more EFI steps on the Mini. Sounds like the Cold War all over again, I will have to make it 'Tempest' safe.

If your interested in the Syncro, there are some pics of the Kitchen unit mod I did, and scroll down the page to the computer part and the recent paint job.

http://homepage.mac.com/greystoke.eng/PhotoAlbum12.html

dogpilot · 11-17-2007, 09:20 PM

Well by improving the shielding on the power cord all the way to the plug and incorporating a metal foil tape over the remainder of the exposed wires. This was all encased in adhesive heat shrink tubing. Noise went down substantially. I also got a very high quality patch cord for the line out to the AUX in to the Panasonic Stereo.

I picked up a Creative USB Audio output port. I thought the line out direct sound was great (when no noise was present). Well I was wrong. It is hard to describe, but the sound has a lot more depth and almost all the noise was eliminated. It was worth the experiment. Output sound is now better than when sourced with CD's or XM.

It seems that most of the output lines will radiate a bit of noise from the P1900. So I will go back with some shielded wire we use in avionics installations to eliminate any possible remainder for the power button line.

monsho · 11-19-2007, 06:31 AM

cool, some interesting stuff you're doing with the install...

I thought about cutting away the passenger side of the dash to make a mounting place for the mini, but my new westy is very very original so don't really want to start chopping it. Getting a VGA lead up the pillars has definitely put me off a roof mounting

dogpilot · 11-19-2007, 09:41 AM

I really wanted to avoid cutting up anything as well. I finally found the solution for the cable in the pillar. I used a rather stiff piece of household electrical wire to snake down the pillar. I took off the button for the interior light. I could push through this small hole to push the wire over to the hole the door wiring goes though and grab it. Once that was in place I pulled down some strong nylon flat web, about 1/4" wide. I first pulled the cut VGA cable, which also carried a USB cable internally as well. Then I pulled power for the screen. I left a piece of the nylon in place so if I decide to pull anything else, its already there.

I bought a spare glovebox assembly, complete for $15 shipped off ebay. I will modify this to hold the Mini, Mounting on the heater box was just too close to the shifter. There is loads of room under the dash, in front of the glovebox to mount power supplies and other expansion items.

jb510 · 11-20-2007, 09:03 PM

I'm interested too in how this works out for you. I was just starting to think about putting a mac mini in my 86 Syncro Wolfsburg Weekender.

How is it having the liliput mounted the the ceiling where you do? It seem a little hard to see and work with for GPS navigation. I like having my GPS on top of the dash pod. With a PC in the van to drive GPS I was thinking about a 7" screen just left of the ash tray, but I haven't really researched that yet.

Also why put the mini in the glove box (which seems totally reasonable to me) rather than under either of the seats (which seems equally reasonable, if not preferably). Just wondering what your thought process was?

Finally how are you running power to the Mini? 110V AC or something else? This was always the reason I've leaned towards using a laptop.

Looking forward to more reports on your progress and results

-Jon

dogpilot · 11-20-2007, 09:52 PM

Well, the reason for the ceiling mount. It is accessible to both passenger and driver. I really don't like anything obscuring the view over the nose. I do a lot of off road, it seems that anything you put on the dash either is in the way blocking vision, or moves around soo much as to be unusable. Personally, I am used to getting info from the overhead, common spot to mount equipment in an airplane. I don't need to stare at it very often, I am not shooting approaches with it or anything like that. It folds up and out of sight, a good deterrent to theft. If you put anything on the dash it is like in a display case at a store, especially in the Syncro. I do have an Etrex Vista or I use the Garmin 295 I mount up there in the factory mount. I have found that they do wag a lot off road.

Glovebox mounting. Almost all the connections I need are there. There is loads of room in front of the glovebox for power supplies, hubs connections to GPS, stereo and access to the A pillar. I can also still actuate it with the IR remote, the signal makes it through the crack. You can actually pop it open an put a DVD or CD into it while in motion, by sight, not feel. I also do not think it is actually high enough for the mini under there. I do have Recaros in mine and the adjustment bar would also make access harder. I do remove the Mini from the van when I don't use it, and it needs to be easy to access.

I am making up a mount for a 7" Lilliput to put in my Range Rover. The Mini will go in the glovebox with it as well. The 7" fits perfectly where the factory POS navigation system went. I need nav that has contours, not just roads. I am a geologist, that does remote sensing with aircraft and I do go in the field to do ground truthing. The instrumentation does lie.

As for power. I tried my own design at first, but it was too noisy, it put noise lines in the video. So I took the path of least resistance, the P1900 power supply. I do not have it wired to do the turn off and on of the mini at this point. I do it with an external switch. I did make a 5 volt power supply for the usb, but it was easier to just add the third output to the P1900. I do run the lilliput off a relay driven by the secondary power output. I put a 12.5 Volt power supply at the head unit That way there is less load on the P1900. It is power output limited, and I am running the 8.4" monitor, which uses more power than the 7".

If they still made the MacBook Pro in the 12" size it would work well. The only problem I had using the laptop was you had to turn it on with the lid open, then close it and put it away. The 15" was a little awkward in size to put away. I have a 17" Macbook Pro and it is way too big to use in the car, especially off road. I have had a laptop do a screen-ectomy once in the past, a financial disaster do not want to repeat.