Thread: The Most Incredibly Un-killable Ground Noise ever...

your sound card will probably only put out 5V if that output is setup as a headphone jack, not line level which is 0.2 to about 1V usually.

Originally Posted by Nola111

Hey Visenri,

Thanks for jumping on board my mess of a noise issue!

Are you sure that all soundcards output that 0V level? This the soundcard I have, which claims a 5V rms output... (scroll to "Specs" at the bottom of the page)

http://www.auzentech.com/site/products/x-fi_prelude.php

We are talking about different things.
All sound cards line outs have a 0 DC output level, but have an AC level (audio) greater than 0V, if not, no sound would be output at all. The 5V rms output spec is the AC level.

Car audio Head unit amplifiers (radio-cd) have normally a DC output level of half the power supply (6V= 12/2), and an AC output that depends on output power.

DC level is the key for turning on your VW power amp.

Originally Posted by Nola111

Awhile back when I first started my car pc hobby, I built myself one of those 6v boxes to turn on my amp, and yes, it does work. Problem I had with it back then is the volume level I would get out of it was way too low when I came straight out of the soundcard into the amp. BUT, that was a soundcard of significantly lower quality than the Prelude so maybe the one I have now would produce different results.

I suggest you to connect now that 6V box you built in the past, if your sound card outputs an AC level o 5Vrms, it could be enough to get the right volume.

Originally Posted by Nola111

On a side note, the Kenwood amp I bought would not turn on my Dynaudio amp??? I basically put the Kenwood in place of the Tio's. There has to be something wrong with it... unless the level I'm sending to the KW input from my soundcard is too low. But the manual says it takes a range of 0.2V - 5.0V. Surely my soundcard can't be putting out less than 0.2V when it claims 5.0V!! Anyway, the Kenwood is probably not the answer anyway.

Thats normal, again, the DC level has the answer, Car audio amplifiers use an internal power supply to get more voltage from the battery, normally a symmetric power supply, for medium power amplifier typically +20V and -20V.
Outputs have a DC level of half the power supply (20--20)/2 = 0V, so they don't turn on your amplifier.

Originally Posted by Nola111

I just spent another 2 hours out there troubleshooting. I feel so defeated. I ran the pc ground to a new ground point just to be sure... I sanded down to bare metal and tapped right into the body of the car. No improvement in the noise. What would happen if I ran the pc ground wire to the ground wire up front that the LCD screen is connected to (which is the ground wire of the car's radio cluster)? Too long a ground wire? Seems it would definitely be at the same potential as the battery, but would the run be too long?

And one final question to add to the other 3: Would a power line noise filter on the 12V from the battery help my issue?

One more time i tell you that a detailed schematic with your current audio signal wiring, from pc to power amp would be of great help.

You have to follow an elimination procedure. Disconnect the input jack of the TIO and short circuit it, short circuit left and right channels with the ground of the jack, and with no other ground. If noise is still there, sound card and sound card wiring has no problem, check your TIO to VW amp wiring, make sure you connected Loudspeaker + and loudspeaker - outputs to the input of the VW amp and not + Loudspeaker and ground, that would not kill the DC level, but would make the output unbalanced and you will get noise. If wiring is ok and you still get the noise, problem is in the TIO, and it gets the noise from the power supply (PC power supply), or from the air, because of radiated high frequencies from the power supply or the PC. PC power supply is not a great power supply for high quality audio, and placing the power amp inside a PC case is also a bad idea, at least without a shielding case.

Does the noise grow with the RPM of your car or not?, if it does, you've got a ground loop anywhere, if it does not, you've got an interference from anywhere (for example: Power supply, radiated or conducted).

Did you mute all unused sound card inputs?

EDIT: sorry, forgot attachment. See next post.

Hi again Visenri.

Thanks again for taking the time to try and help me. You definitely seem to know your stuff.

First things first, find attached the wiring schematic as suggested. I hope it is not too confusing. It's a very crude drawing and I'm NO artist! Let me know your thoughts. There are other things in the mix (satellite radio, HD radio, USB hub, etc) but they are not in the schematic drawing b/c I've disconnected all of them for troubleshooting purposes to make sure none of them were the culprit.

Next, I definitely was confusing DC level and audio level. Thanks for explaining that and that makes much more sense now.

The noise does NOT change with acceleration/deceleration. It's just a constant staticky noise. And yes, I've muted all other channels of the soundcard.

Today I will spend the day continuing to troubleshoot. First thing I will do is your suggestions with short circuiting. I do have one question though about where you say "with no other ground..." Do you mean that I should disconnect the ground of the PSU before doing the short circuit test?

Next, I'll dig up the old 5v box I made to see what kind of levels I can get with just that and no Tio's. If that doesn't work, I'm going to try an old HU I have laying around just for control purposes.

Thanks for your continued help. I'll report back later, and please let me know if you see anything in the schematic.

Here's the schematic.

Originally Posted by Nola111

EDIT: sorry, forgot attachment. See next post.

Today I will spend the day continuing to troubleshoot. First thing I will do is your suggestions with short circuiting. I do have one question though about where you say "with no other ground..." Do you mean that I should disconnect the ground of the PSU before doing the short circuit test?

I mean you have to take a jack and connect it to your TIO input, short circuit every cable in the jack together, and don't let it touch any other ground, chassis. Don't disconnect the ground of the PSU, you need it to get power from the PSU.

In the schematic i see you've got two TIOs, one for each channel, first short circuit every jack independently, each jack live with it's ground, and if you get no noise, short circuit all the jack wires together.

You didn't specify if TIO output wiring is Speaker+ and Speaker- or it's Speaker+ and ground.

looks like you have multiple earthing points too

the pc direct to chassis, and the screen off the loom?

this is the way i have mine hooked up, I re ran the earth and power wires for the HU and screen etc to the main power wire i installed for the amp and pc.

your screen which is earthed at one point in the car is also tied to the earth on the pc.

Visenri - Tio output is Speaker + and speaker -. Ok, I understand now what you're saying... I will try that next (results from today's testing and troubleshooting are below).

Woofnstuff - So you're powering your PC with the 12v line of your radio cluster? The 12v line in my radio cluster is 22 gauge. Too small to power my Opus I'm thinking. Maybe I'm not clear on how you have yours though. I do understand though about grounding the LCD to the same place as the PC. Seems like a long run for a ground wire, no? (front of car to back of car).

Whew, what a long day. I don't know where the time went. First, I removed the Tio's from the mix and connected my soundcard directly to the VW amp via the 5v box I built a while back. As I suspected, it does turn on the amp, but the volume can't get high enough unfortunately. So that's out.

Next, I hooked up my old Panasonic HU. I put it in the trunk, then ran the Front channels of the soundcard to the Aux In of the HU, and the speaker outs to the VW amp. The result was that the noise is still there but it's slightly lower in volume. Definitely still loud enough to be annoying though. The HU made things just slightly more bearable with the noise though (at the expense of the sound quality of the Tio's). The HU is powered directly from the battery and grounded to the same place as the PC PSU.

So, after today, there's one thing I'm 99% sure about: The noise I'm hearing is the hard drive. I can hear the hard drive's activity as I perform tasks on the PC (opening/closing programs, starting up/shutting down, etc). So I'm definitely picking up hard drive noise. Should I wrap my hard drive in aluminum foil????

That's about it for what I got done today. Tomorrow will be another full day of trying to kill the sound that WILL NOT DIE!! The task list will include Visenri's short-circuit tests, among some other tests involving relocating the harddrive away from the pc.

Let me know you guys' thoughts, and thanks again for your time!

Just went and read the 3 or so threads I could find about hard drive noise, dating back to 2005. None of the threads ever concluded with a solution to the issue