Thread: Terrible Audio Hiss and Engine whine noises - Help

Originally Posted by Red GTi VR6

Check your grounds, most of the time noise like this is caused from a ground loop.

What's a ground loop? Haven't heard of this before

Originally Posted by Red GTi VR6

Where do you have everything grounded? At the same spot? If the same spot wasn't possible, did you try and minimize the numeber of grounds?

My CarPC is grounded "clean". Everything else on the system, i.e. monitor, relay, etc is plugged directly into 12V and grounds coming off of CarPC.

Btw, the sound is not just a hum, its an almost unbearable distorted noise. I think I'll also try seperating the audio and power cables, as they are all bundeled together right now and are running along side each other (could cause distortion)

Originally Posted by sxt173

Before I ask, I did do a

Having problem with audio. Just completed my install and here is what I have:



I built in a manual switch, which controls the 12V going from CarPC to relay, so that I can switch "on" to CarPC, or I can switch "off" to HU.

So, whenever I switch to the CarPC, all I hear is terrible, terrible interference, hissing and engine whine, but it is fine when relay is switched to HU. If I accelerate, I can hear it thru the speakers as whinning. Even the harddrive spinning creates interference sounds. The only time I hear music is if I turn the volume on my carPC up all the way, where it muffles the sounds...

I used radio-shack RCA cables and RadioSHack y-splitters for the section going from relay to CarPC. Also, there is a small section of the relay, where I had to use 22+ gauge wires..

WOuld changing all the wires to shielded high-quality wires work? PLease help

From Deerfield Laboratory:

Ground Loop Noise

Hum and crosstalk are likely to occur when the elements of an electronic system are connected by transmission lines. Ground return paths generally exist which are external to the ground conductor of the transmission line. (The braided shield is the ground conductor on a coax line). Noise energy is introduced into such a loop by way of an equivalent generator in the ground return path, or by magnetic induction into the ground loop. If ground potential differences in the AC power feeds are the cause, then hum results. If the noise source derives from another line, then crosstalk results. Long distances between ground points, poor grounding practices, and inherently compromised grounding environments increase the probability that ground loops will cause interference.

So to correct this problem get a Ground Loop Isolator like this one:

http://www.radioshack.com/product.as...t%5Fid=270-054


Sxt173 I would like to know more about you manual Switch 'cause I really have a good HU and I would like to keep my factory Amp....

Can you post the components and if is possible some links where you got the parts from to build this switch (What relay and more details of you project)

Thanks in Advice....

Thx for the info. Here's my info on the relay and the way I set it up (btw, I got some advice from a professional audio install shop)

The relay is a standard relay from radioshack
Link to radioshack site with item

So, I have FL, FR, RL, and RR speaker cables going to my factory amp. I hooked these up to the relay coming from the headunit to the amp, in the off position. Then I simply spliced a cable coming out of my ATX power supply on the CarPC. This cable + ground (which btw is spliced off of the plug that powers my harddrive) sonnects to the 12V input and ground of the relay. So when computer is on, CarPC supplies 12V constant and switched to CarPC speaker wires going to amp, when CarPC is off, it switches to headunit.
I added a manual switch on the ground wire coming from CarPC to relay, so that I can manually simply throw a switch and switch from headunit to CarPC.

In my setup, the amp is always getting its 12V signal and ground from the headunit, I am simply switching the speaker wires from CarPC to Headunit and back. Important thing is that Relay off position is headunit, and on position is CarPC, where I simply put a manual switch in between, so I'm not forced to get CarPC audio every time CarPC is on.

Let me know if you need more info.

OK, this is what I tried:

1. Plugged in speaker cables directly to iPod, no interference, works great
2. Plugged headset into computer, no interference, works great
3. I plug speak wires back into computer, awful hiss.

Note, when I had the iPod plugged into speaker cables, the relay was still being powered from the PC 12V cables and the speaker wires were still running along the same path as they are when they are plugged straight into the PC.

So, odd problem, my setup works fine when anything but the PC is plugged into it. PC is working fine though, as I tried it with headsets... I'm about to shoot the computer, or the dashboard!!!

This should take care of your problem, Ground your pc case to the ground point on your automobile. I had this problem with my inverter, ground the inverter case, no noise, and one happy camper

that is a great idea, but 1 small problem. My PC case is plexiglass... so maybe ground a metal part of the MoBo? Like the metal part off of the speaker jacks?