Engine hiss through speakers...

Pseudo Nim · 06-25-2005, 11:14 PM

Hey all,

Just wondering (audio newb here...) - why would I get engine noise through the speakers? It happens both from my on-board VIA sound card, and (in a MUCH worse fashion) on an SB Live 24-bit External USB sound card. I'm not using an amp - routing the sound through a 3.5mm stereo->dual RCA cable and into my Panasonic HU.

Is it shielding somewhere? Or crappy sound quality, crappy amp, all of the above, something else?

Any help appreciated.

Cheers,

-pN

homchz · 06-25-2005, 11:15 PM

Sounds like a ground loop issue. (Multiple grounding spots instead of one central) They sell Ground Loop Isolators that help with this. Search Ebay and I am sure you will find a few.

Pseudo Nim · 06-25-2005, 11:40 PM

I see. What is probably not grounded properly, then?

homchz · 06-25-2005, 11:44 PM

It is not that something is not grounded properly as much as you probably have mulitple ground points between your components. In the perfect world (I beleive) everything should be grounded to the same point. If there is space between components than this is not really an option so grounding to the closest point is required. This usually gives you the noise.

Pseudo Nim · 06-25-2005, 11:45 PM

I see. Ok, I'll look around for a ground isolator on ebay - looks like quite a few are for sale. Thanks for the pointer.

On that note - why do people use external USB sound cards instead of the onboard one? Are they THAT much better? I thought it was because of the noise/shielding issue, which is why I picked it up - but doesn't look like there's anything special about it?..

Stealth97 · 06-26-2005, 02:18 AM

Quote: Originally Posted by Pseudo Nim

On that note - why do people use external USB sound cards instead of the onboard one? Are they THAT much better? I thought it was because of the noise/shielding issue, which is why I picked it up - but doesn't look like there's anything special about it?..

Everyone seems to think they sound better, but when I fired up my system for the first time with the VIA onboard sound the other day I thougt it sounded better than my old $1500 eclipse HU... but then again only listened to it for a few minutes.

alti · 06-26-2005, 02:26 AM

The sound quality is the reason some people go with the external sound cards.

depends on the onboard sound though, i have a nforce2 chipset and am very happy with the SQ

Consider rechecking your grounds to, I use a power distribution block to combine all my grounds to one 4 gauge ground wire, as my computer and amp and other equipment are all in the trunk, but if your grounds are not real good it will cause the noise as well. Make sure that you are grounding to bare metal and there is NO PLAY in the grounds.

etown · 06-26-2005, 11:52 PM

A ground loop isolator is a bandaid fix.

When you power anything in your car the circuit will complete itself through the lowest resistance ground it can find. In your case this happens to be your HU. You can ground anywhere you want to, using the same ground point for all your accessories is another bandaid fix. All you have to do is ensure that the ground wire is the lowest resistance path out of whatever item you've grounded.

That means that if you run a Monster cable from your carpc to your amp, your ground wire must be bigger than your Monster cable.

greenwire · 06-27-2005, 08:12 AM

Quote: Originally Posted by etown

A ground loop isolator is a bandaid fix.

When you power anything in your car the circuit will complete itself through the lowest resistance ground it can find. In your case this happens to be your HU. You can ground anywhere you want to, using the same ground point for all your accessories is another bandaid fix. All you have to do is ensure that the ground wire is the lowest resistance path out of whatever item you've grounded.

That means that if you run a Monster cable from your carpc to your amp, your ground wire must be bigger than your Monster cable.

Using the same ground point for everything in a system is not a bandaid fix.. i'm not just talking about audio systems either.. Using a star ground configuration is good design..

Why, when I look at datasheets for switching power supply controllers and other RF circuits does it say things like "ensure all signal grounds connect at one point and only one point on the PCB" etc in the layout notes?

http://www.epanorama.net/documents/groundloop/

^^^ all about ground loops...

evandude · 06-27-2005, 08:26 AM

I agree with greenwire. if you have an amplifier pushing dozens of amps of current through your chassis at some point, the voltage on the chassis at that point is not going to be zero (since there is some resistance, and V=IR) and if you ground some other device near it, the "ground" that it will see will not be a constant voltage, it will vary depending on the current draw of the amp. throw in a bunch more devices, and you see how this effect increases.
and when you shift the ground reference of a device, ESPECIALLY an audio device, things get noisy.

the main point is you have to understand that connecting a device to a low-resistance wire that not carrying current from other devices is different from connecting it to a low-resistance wire that is also carrying current from other devices. the current of the other devices increases the voltage drop on the wire, which effectively makes it "look" like a higher-resistance wire to your device.

therefore, by reducing the resistance of the wire, you can reduce the ground loop effect, but it is much more effective to completely separate the ground paths from each other, that way NONE of the current of your high-current device (ie - amp, etc) is flowing through your computer's ground cable, and your computer "sees" a low-resistance path... this is the "star ground" idea that others are talking about, and a true star-ground system would be the most effective possible way to eliminate ground loops, because there's no way current from one device could enter the ground return of another. not a "band-aid fix"

plunderisley · 03-16-2009, 05:15 PM

bumping this thread
I got my carPC running to a USB audio (Zalman) running then to my amp. When I unplug the connections from the usb card to the amp, the hissing is gone. I also get some engine sound in the speakers. I would guess then the issue is with the pc not being grounded? would the radio shack option be good in this case? Also as I'm out in Europe does anyone know any companies that sell it here?
I don't know why but I just don't get that good of sound out of my usb card as in the house. There seems to be very poor bass, and I did try customizing the levels in winamp but the best I could get sounds like $5 speakers on the pc...