buzz in audio, only while power connected

**gameboy** · 06-04-2005, 11:46 PM

i've got a carputer setup, using a laptop as the brain

no inverter here, laptop will accept 9.5v - 19v directly so i removed the power ac/dc power brick and wired directly.

everything is connected to a common ground(i even have a jumper wire going from the ground on the radio to the ground point of my modulator, laptop, and touch screen.

i get a nasty buzzing / staticy noise thru the audio system only if the laptop is plugged into the car( car running or not no different )

if i unplug the laptop(running of int battery) no buzz / hiss / static / nothing...just clean sound

any ideas? (i did try running a wire from the shielding to the common ground point, and also from a ground inside the laptop(hard drive screw) to the common ground point.... no luck

**kuo** · 06-04-2005, 11:52 PM

try using a ground loop isolator. helped me in one of my installs.

**gameboy** · 06-05-2005, 12:05 AM

i tired one, the ground loop isolator also seem act as a low pass filter

with all the grounds commonly connected (bolted together at the frame(stipped the paint off with a dremel & sanding wheel) i would not think i have a ground loop condition

also, as an after thought, i get some crap on the touch screen while the laptop is plugged in, but clears right up when unpluged(still running ( laptop int. battery)

**Jahntassa** · 06-05-2005, 10:13 AM

Just curious what you mean by 'laptop will accept 9.5v - 19v directly' What's the power supply rated at?

Most likely your problem is trying to go directly to power in the car. The laptop probably isn't getting enough voltage (as most run near 17/18v) and the car only puts out 14 when running. That, and those adapters act as filters to 'filter' the power noise. Go get one of those Targus DC-DC adapters for laptops, match the voltage with the power cord that came with the laptop, and see if that solves your problems.

**Cris** · 06-05-2005, 10:15 AM

Noise can come from many sources, and the first one is not using quality cables.

**Jahntassa** · 06-05-2005, 10:22 AM

If he only has the problem when the laptop is powered off the car...then the first one is his power source. Cables, most likely, have nothing to do with HIS problem.

Most of the rest of the time, it's cables. Which you can figure out by unplugging them until the noise goes away to ID which cable it is.

**gameboy** · 06-05-2005, 10:44 AM

before i used an inverter to power the laptop i had the exact same problem.

i just left the cut out the inverter since the noise was the same with or with out it.

**gameboy** · 06-05-2005, 11:29 AM

for a soundblaster audigy nx. going to try that...
i might also move the ground and V+ lines from the laptop to elsewhere in the car

**Bugbyte** · 06-05-2005, 12:02 PM

In your first post, you mention that you are using a "modulator". Is that for transmitting the audio to your head unit? If so, modulators are easily interfered with. Are the power wires anywhere near the modulator?

The ideal solution, if this is what you are doing, is to use cables. It would also yield better sound.

**gameboy** · 06-05-2005, 08:43 PM

here is another thing i have tried

i've used a ground loop isolator, which seems to rid most of the noise, however it also cuts out about 70% of the mids and highs...not acceptable

In a few minutes i'm going to gut all the wires and **** outta the car, and re-wire everything ( got some new 12 ga ) i will make sure the audio runs are no where near the power runs...only problem with this will be the fm modulator.. will have to think of something about the power wires for it.. i'll run the power related wires thru the center ( pc under pass seat for now ) and run the audio on along the pass door side(that's where i have the audio run for the amp(8 ga power for amp run along drivers side)

will try to keep everyone updated, incase this happens to someone else.