Ground Loop - Unable to find source - diyAudio
Go Back   Home > Forums > General Interest > Car Audio

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 28th May 2008, 03:33 PM   #1
phuz is offline phuz  United States
diyAudio Member
 
Join Date: May 2008
Send a message via AIM to phuz
Default Ground Loop - Unable to find source

Hey guys...I want to pick your brains before I just go out and buy an amp to replace my factory amp.

Car is a 2006 Volvo S60R. I just did a CarPC conversion and I am getting some noise in 4 of the 5 channels. The 5th channel (center speaker) is now driven off a separate Alpine amp because the original Head Unit used to drive that speaker directly. I do not get noise in that speaker, and I use a simple stereo --> RCA cable to the amp for the Line-In.

My soundcard is a USB Sound Blaster 5.1. I was advised that avoiding on-board soundcards is better for noise reduction. I used to have an obnoxious amount of noise, until I isolated the power supply case from the PC casing. I no longer have the "whine" associated with engine noise, etc., but I still have a high-pitch noise that is quiet, but still noticeable when the music is OFF. Since my battery is in the trunk, that is my grounding point. The Alpine Amp, Factory Amp, and DC-DC PC Power Supply grounds are all tied to the negative terminal.

The tricky thing about my factory amp is that it uses a 5-wire input. One wire for each channel, and then one common Audio Ground....so for the outputs from the PC, I just tied all the grounds together and coupled it with the Audio Ground into the amp, but did not tie the Audio Ground wires to an actual ground.

I tried ground loop isolators for all 4 channels but that didn't really do much for me. Somewhere there is still a loop, but I am unable to figure

I already took a look at this thread...
Grounding scheme in a Car Audio Gainclone???
  Reply With Quote
Old 29th May 2008, 01:52 AM   #2
diyAudio Member
 
Join Date: Mar 2007
You said you connected the grounds from the PC to the ground of the amp, have you tried grounding them? Have you tried grounding the ground going to the amplifier and leaving the grounds from the PC unattached?
__________________
If it ain't broke Don't fix it
  Reply With Quote
Old 29th May 2008, 12:05 PM   #3
phuz is offline phuz  United States
diyAudio Member
 
Join Date: May 2008
Send a message via AIM to phuz
Quote:
Originally posted by I Am An Idiot
You said you connected the grounds from the PC to the ground of the amp, have you tried grounding them? Have you tried grounding the ground going to the amplifier and leaving the grounds from the PC unattached?

Yes, the PC Power Supply AND the amplifier grounds are all tied together at the Battery (-)....which is ground.

I did try floating the ground to the PC power supply, and it didn't fix the audio noise, and it actually created a whole bunch of noise in my in-dash LCD.
  Reply With Quote
Old 29th May 2008, 03:42 PM   #4
diyAudio Member
 
tsmith1315's Avatar
 
Join Date: Jul 2003
Location: Doerun, GA
Quote:
I still have a high-pitch noise that is quiet, but still noticeable when the music is OFF.
What kind of output voltage is the PC card?

Early Volvo factory amps (80's-90's) by Clarion and Alpine expected a fairly low voltage. Higher voltages would cause noticeable hiss at low volumes, and a significant impedance mismatch can cause all sorts of noises. I may still have some info on those somewhere.

I have no idea what the newer Volvo products are like, but it sounds like they are still using a 5-pin DIN input.

Where is the factory amp mounted? Have you tried unbolting it from the chassis?
__________________
Tim
  Reply With Quote
Old 29th May 2008, 03:54 PM   #5
phuz is offline phuz  United States
diyAudio Member
 
Join Date: May 2008
Send a message via AIM to phuz
Quote:
Originally posted by tsmith1315


What kind of output voltage is the PC card?

Early Volvo factory amps (80's-90's) by Clarion and Alpine expected a fairly low voltage. Higher voltages would cause noticeable hiss at low volumes, and a significant impedance mismatch can cause all sorts of noises. I may still have some info on those somewhere.

I have no idea what the newer Volvo products are like, but it sounds like they are still using a 5-pin DIN input.

Where is the factory amp mounted? Have you tried unbolting it from the chassis?

The PC sound card output is around 1volt, which is what the factory amp takes.
  Reply With Quote
Old 29th May 2008, 06:53 PM   #6
diyAudio Member
 
Join Date: Mar 2007
Sorry for the confusion, I was talking about the shields of the audio cables and the shield going to the amplifier.
__________________
If it ain't broke Don't fix it
  Reply With Quote
Old 29th May 2008, 07:15 PM   #7
phuz is offline phuz  United States
diyAudio Member
 
Join Date: May 2008
Send a message via AIM to phuz
Quote:
Originally posted by I Am An Idiot
Sorry for the confusion, I was talking about the shields of the audio cables and the shield going to the amplifier.

Yes, I did try grounding the shields...made no different. I didn't think it would, since the distance of my line level cable into the amp is less than 18 inches long.
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
ground loop Jamh Chip Amps 10 2nd November 2007 07:18 PM
Fix a ground loop! sorenj07 Digital Source 2 1st October 2007 06:39 AM
hum,ground loop,earth loop problem with your answers please frank2395 Pass Labs 2 17th May 2005 06:46 PM
does connecting mains ground with circuit ground create a ground loop? jarthel Everything Else 0 25th June 2003 12:55 PM
Ground loop hum jag Pass Labs 20 25th November 2002 05:32 PM


New To Site? Need Help?

All times are GMT. The time now is 06:22 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2