Whine when connected to carpc, but not iPod

oldirtydillon · 07-08-2009, 05:35 PM

I've searched through the forums trying to find a solution to my issue, but to no avail. The problem i'm having is that i'm getting a stable whine through my speakers when my amp is connected to my carpc from the lime line-out plug. It doesn't fluctuate with rpms. After reading some threads on the forums, I hoped that my grounds were causing this. So I set out to double check. I even went so far as to change the grounds to hopefully rule them out, but the whine remains. For craps and giggles, I disconnected the 1/8 mini plug from the carpc and connected my iPod shuffle, and the whine is GONE! Of course, as soon as I plugged the carpc back in, back came the noise. I was hoping that if I posted my setup and this info, someone could lead me in a new direction to hopefully solve this issue. My setup:

-VOOMPC2 case

-M3-ATX power supply(I purchased this because I read that the M2-ATX was causing interference with the front panel audio connections on my case)

-KINO-690S1 mobo(I was hoping to be able to use the front audio outputs on the case, but I cannot with this mobo because there is no audio out header, so I am now using the lime output on the back panel)

-Monster 200 series stereo RCA to 1/8 mini interconnect

-Alpine PDX-4150

Please let me know if I can provide anymore info, and thanks for attempting to help me out.

Matt

trader007 · 07-08-2009, 10:12 PM

i have heard those power supplies cause radio interference.... i dont know if its actually true but you might try using say an a/c inverter to power a household type supply to see if it changes anything.

DarquePervert · 07-08-2009, 10:19 PM

Quote: Originally Posted by trader007

i have heard those power supplies cause radio interference.... i dont know if its actually true but you might try using say an a/c inverter to power a household type supply to see if it changes anything.

Bunk.
It's all about the wiring.

It's entirely possible that the issue stems from unshielded wiring inside the case. There's a lot of cabling crammed into a small space, so it would be admittedly difficult to track down.
It's also very possible that the PSU needs to be grounded better. I don't know if that's one of the grounds you've examined or not.

csfile · 07-09-2009, 06:32 AM

if you plug in headphones in your carpc, do you still hear the whine?

oldirtydillon · 07-09-2009, 08:54 AM

Thanks to all 3 of you for your suggestions. I will look into all of them and get back with the results.

Woofnstuff · 07-09-2009, 07:48 PM

i made a SINGLE earth point, at the bottom of the dash area, I use on of teh BIG bolts that hold the dash framing in,
took that wire to a distribution point / block, then ran EVERYTHING from that point.

LCD, PC amp, and cd changer hack box, the HD is earthed to that same bit of metal too, via its screws. also check proximity of video cables to audio cables.

having said that my current install has everything cables tied together and is dead quiet (bad noise wise).

also having just typed that, i would check that the m/b is earthed to the case where it should be. and that nothing inside the pc is wrapped around the psu..
also check if mic or line inputs are turned on in the sound mixer.

oldirtydillon · 07-09-2009, 09:02 PM

Quote: Originally Posted by Woofnstuff

check that the m/b is earthed to the case where it should be.

This is something i've never looked into before. How should the mobo be grounded to the case? Through the standoffs? Should I ground the case as well? I won't be able to look into this anymore until Sunday, but again thanks for the replies and keep them comin'.

ptk · 07-09-2009, 10:06 PM

whine means you have a source that is osculating at a certain frequency. Most of the ground loop issue picks up the alternative and hence you will hear whines that changes with RPM. Since you say this is stable, this is likely to be within your setup, likely your PSU.

Try hooking your carpc to a stable power source (eg external battery) and see if the whine persist. if it does, it's not a grounding issue already.

oldirtydillon · 07-12-2009, 08:59 AM

Okay, after looking into this, here are my findings:

-the PSU ground was one that I redid. After reading about grounding the case as well as the psu, I twisted two wires together, soldered them to a ring terminal, and grounded that to a single point. The whine existed before I did this as well as after.

-the lime line-out connection does indeed whine when I connect headphones to it.

-i re-routed the psu wiring in the case to take a different path, however it still exits the case right next to the audio output on the back panel. Could their proximity to each other be my problem?

-could the fans cause interference? The Voom has two front fans, and I have a cooling fan on the processor.

-i am going to check the amp turn-on wire. There are other ways for me to have the amp turn-on, so maybe this is the issue?

-i have not tried any type of alternate power yet. What do you suggest?

csfile · 07-12-2009, 09:17 PM

since the whine is still there with headphones...it's something inside your PC picking something up. You can try grounding the case or moving the PC.

Bad quality soundcards or power supplies can also pick up some EMI. You can try putting in another soundcard or power supply and see if it goes away. I'd start with a soundcard.

oldirtydillon · 07-13-2009, 07:00 AM

Would you recommend a USB soundcard?

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