Where do YOU ground your stuff? (1 Viewer)

[Red Beard]

I've been trying to find the best ground for my Mac mini in my cruiser so I can knick this annoying noise over my speakers. I get a slight alternator whine and this weird screech that doesn't change with engine speed.
I posted on MP3car, but they insist I'm going to have a fire.

So, I'd love to know where you ground your stuff, especially your sound equipment. Before, I had my stuff grounded to the chair bolt. Then tried one of those screw receivers for the center console (by the "PERNUNDRL" (P-R-N-D-3-2-L))
Now its grounded to a body mount in the drive side door jamb. Small little screw, best ground so far.

If anyone wants to chime in what the weird screech noise is, that'd be great!
I'm using the factory amp.

 

[ohrly?]

attach to the engine block, and then to the frame


and even the body as well i believe i was told.

 

[IronYuppy]

IIRC having a less than ideal ground will not cause line noise.

I would first check to see if your signal wires are too close to any + wires. If you need to cross them, do so at a 90 degree angle as best you can. Ideally, keep them apart.

 

[-Spike-]

AFAIK, DC current won't impart noise to audio equipment as there's no frequency, although the alternator might put a frequency on the lines for whatever reason, like poor quality components. 'Crosstalk' usually occurs when A/C lines are run parallel to unshielded audio wires, or even unshielded audio wires are run with other unshielded wires, as audio signals are themselves A/C. Quality of grounds is important in auto audio. The vehicle's grounds need to be clean- i.e; there are several ground straps connecting the body , engine block, and negative side of the battery together- these can be loose or corroded and cause audio problems. Also, the bolt you use for the ground needs to have a good electrical connection, clean the contact surfaces of the bolt and the metal around the hole it goes into. I usually use seat bolts myself for large power draw equipment if they're handy, but for something like what you're doing, any bolt into the body should be fine- provided it's clean.

-Spike

 

[Red Beard]

IIRC having a less than ideal ground will not cause line noise.

I would first check to see if your signal wires are too close to any + wires. If you need to cross them, do so at a 90 degree angle as best you can. Ideally, keep them apart.

The ground does matter. While I had the computer on, I changed the ground points, just touching the ground to different spots, and the noise reduced greatly on certain spots. The screech did not.

I'm thinking putting a metal screw into the frame right there under the console, which sits over the Transmission. and grinding down around the hole so it can get full contact. But I'm afraid of rust, if I did this, couldn't I just spray paint it? (not to hijack my own thread, I'd still love to know where people have grounded things.)

 

[-Spike-]

You can use a grease made for electrical connections to rust-proof the grounds.

-Spike

 

[Red Beard]

I usually use seat bolts myself for large power draw equipment if they're handy, but for something like what you're doing, any bolt into the body should be fine- provided it's clean.

-Spike

It being clean as in the bolt being clean or the surface the ring sits on (along with the bolt). The bolt I used was never really touched (still had paint on it) There was paint where the ring was touching, that's what I worry about.

 

[Red Beard]

You can use a grease made for electrical connections to rust-proof the grounds.

-Spike

So you're saying, there's a grease that I apply after I kinda grind off some of the paint and screw in the ring, I apply it over it and it won't rust? I'm for some reason lost.

Looks like we're a little bit behind each other in replying.

 

[Beowulf]

I'm thinking putting a metal screw into the frame right there under the console, which sits over the Transmission.

One of the primary vehicle ground points is under the center console.

-B-

 

[ArmyFJ]

Just to make sure...you are talking about the ground from the power cable right?

Matthew

 

[ArmyFJ]

Also, have you tried it without a ground? Not that I am saying to try that. Just wondering what the effect was if you did try it.

Does the noise occur with the computer on or just plugged in?

What about with CDs in it?

If you can guess what would you say the frequency of the noise is? like 60Hz?

What speaker is the noise coming from?

Matthew

 

[Red Beard]

The alt whine comes through all speakers even when the cable is hooked up to the computer and computer is on or off. More enunciated when on.
The screech is comes on when Mac OS X completely loads up. Never had a CD in it.
When I pump up the volume on the Head unit, the sound gets louder, then gets to a uniform popping.
No idea what Hz it is. :\
Not sure what speaker the "Screech" is coming from.

yeah, we're talking about the ground from the computer's external power supply. Its a DC-DC Regulator.


That illustration, where exactly is that point? Is it a wire or just the metal?

 

[-Spike-]

You need bare metal for a connection. Paint is bad. Hit the mating surfaces with a wire wheel or sandpaper, apply dielectric grease liberally, then make your connection. The dielectric grease keeps moisture out, protecting the metal and the integrity of the electrical connection.

-Spike

 

[Red Beard]

is that grease conductive?

 

[-Spike-]

is that grease conductive?

No.

-Spike

 

[ArmyFJ]

Is it a low freq or a high freq?

 

[Beowulf]

That illustration, where exactly is that point? Is it a wire or just the metal?

Just a guess but I would look under the center console box where there should be several factory wires grounded at that point.

-B-

 

[C6H12O6]

Sorry for the crappy picture, but at the very top, you can see the ground under the center console. Not very big. The white plug with the yellow wire is a 12V ignition-switched power supply, in case you need that.

I used an empty, threaded bolt hole in the rear cargo area to ground my amp. I ground away the paint to bare metal, bolted in the eye on the end of my 4ga. ground wire, then covered the whole thing with dielectric grease. Very effective at keeping it from corroding and keeping everything clean. I like to make my ground wires as big as my power supply.

Are you running your 12V power directly from the battery to the power supply for the computer? If you are pulling 12V from somewhere else, you will get more whine issues. You might try that if you aren't already going straight to the battery from your transformer.

Also, have you been able to operate the computer at all? It might be interesting to see if any changes in the "Sounds" System Preference box have an effect on the noise. You might try looking into the Input section to see what is selected.

Good luck,
Steve

 

[Red Beard]

Thanks for the info. But still for some reason, I can't see where this spot is. Could you take another picture with it zoomed out so I can see nearby things?
The center console I have apart right now is the one over the transmission. The High and Low gear stick, etc.

and I'd say its a low frequency. Sometimes stops for a second then continues.

yes, a line directly from the battery's positive terminal, through a fuse, a 25 amp switch, then it goes to the regulator.

Yeah, the computer works fine, it just has a weird interference.

The FM Radio sounds better than my computer right now, and I don't even have an antenna!

 

[Lugboot]

Hey, Red Beard, sorry to hijack, but how do you have the Mac Mini wired into your truck? That sounds interesting. If you have a different thread or want to reply by PM, that's cool.

Thanks!