Another noise thread

**BeamRider** · 08-03-2004, 03:06 AM

I've installed my very first setup but I got all noises types from it! I've engine noise and "digital noise" (hd activity, display, ecc) on it.
My setup consist of an 150w Opus, EPIA M10000 and I tried both EPIA's sound card and a Creative MP3+ USB with a 40x4 amplifier. RCA length is about 1m and the remaining lines are all digital, I take power form Opus and the amplifier from the DIN head unit connector (Lilliput is powered by Opus). All the system is installe on the dash and the amplifier is place under the driver seat.

The noise comes only when I connect the 1m RCA cable or just connecting RCA ground to the amplifier (tried with 5cm wire from ground to ground only).
I don't know what kind of solution should I try (ground loop isolator, rewiring, ecc..). I'd move to ground loop isolator but i don't really know if it will work because seems that my problem isn't coming from power lines and the analog audio lines are really short!

Code:

POWER LINES:

                               +---------- lilliput, hd
D         +------ opus --------|
I  -------|                    +---------- epia 
N         +------ amplifier



AUDIO SETUP:

E
P    (1.5m USB)                    (1m RCA)              (1.5m bl/re wire)
I --------------- Creative MP3+ ------------- amplifier ------------------- speakers
A

**rando** · 08-03-2004, 09:57 AM

1) Run dedicated power wires for your Opus and amplifier. Use 4 guage and a fuse at the battery run to a distribution/fuse block. Use 8G from your block (with fuse) to your amp. Use 10G from your block (with fuse) to your Opus. Run 10G ground wire from your Opus to a good ground point (bare metal bolted down). Run 8G from your Amp to the same ground point.
2) Keep your RCA lines as far away from your powre lines as possible (also far away from ANY power lines in the car) Ideally they shouldn't cross the power lines either.
3) Make your RCAs as short as possible. Since your using a USB sound card it should be adjacent to your amp so you can use RCAs that are only a few inches. If you do this step alone and you still have noise, it's almost certainly coming from your power rails directly into your amp. Short your amplifier inputs and slowly turn up the gain. If you hear any noise then it's from your power rail and/or the amp is busted and/or lousy.

**BeamRider** · 08-04-2004, 04:00 AM

Thanks rando, I'm trying to identify the noisy component/line with my laptop (and bridging various ground lines to reproduce the noise) maybe this will help finding the problem. Actually I was not able to reproduce it so I'm thnikning of a ground loop between the ground and the signal ground on the amplifier, should a ground loop isolator on the amplifier power line helps?
The USB sound card is placed next to the amplifier so reducing RCA length is not a problem and obiviously the cable is not crossing any power line. This morning I'll rewire the power lines for opus and amplifier.
Thanks again

**Adam432823** · 08-04-2004, 05:16 PM

The laptop would be running off of its own internal battery, I assume. If the laptop does not recreate the problem (with the engine running!) then it must be the computer or the sound blaster.

You never mentioned wether or not the noise goes away with the engine off. You've got compound issues if you get more noise with the engine running.

I would start by loosing the sound blaster (just for testing purposes) and connect the computer to the amplifier. Take a small peice of wire, about 16 gauge, and ground the chasis of your computer. If that doesn't work (or if the computer doesn't have a chasis) then try the isolator. Ground loop isolators work on the audio interconnects, so connect it between the computer and the amp. I'm almost certain a lot of your noise will go away between these two tests. If so, try using the soundblaster again instead of the built in audio along with which ever method worked.

**BeamRider** · 08-05-2004, 03:08 AM

Hi againg, the laptop is running on its own battery and the sound is clean in every condition. Only when I bridge the grounds the noise come back.
I tried with the internal sound card and the problem is the same as the Sound Blaster.
The noise is composed by a digital component (always present) and an alternator component (only when engine turned on). Actually I'm rewiring everything with a central grounding point, but from first test the problem is still there.
I'll go for a ground loop isolator this morning
Cheers

**BeamRider** · 08-19-2004, 08:42 AM

Finally I've got an isolator and the noise has gone!
Thank you all for the valuable help with my problem.
Cheers

**erazor** · 08-19-2004, 09:36 AM

Isolator? for what? where did you put it?

**BeamRider** · 08-19-2004, 10:31 AM

The Ground Loop Isolator is a small component to be placed between pre-amp output and amp in (on the RCA cable). Its purpose is to decouple ground from the sound source (CarPc) and the amplifier to avoid loops from power ground and signal ground. Power ground and signal ground are on different lines but are joined on both sides (PC and amplifier) so it's possible to have noises caused from current flow and induction when the loop is closed.
The isolator keeps the signal ground decoupled. Mine solved both digital and alternator noise for 15€....worth a try on similar problems!
Cheers

**slasherx** · 08-29-2004, 05:32 PM

Originally Posted by BeamRider

The Ground Loop Isolator is a small component to be placed between pre-amp output and amp in (on the RCA cable). Its purpose is to decouple ground from the sound source (CarPc) and the amplifier to avoid loops from power ground and signal ground. Power ground and signal ground are on different lines but are joined on both sides (PC and amplifier) so it's possible to have noises caused from current flow and induction when the loop is closed.
The isolator keeps the signal ground decoupled. Mine solved both digital and alternator noise for 15€....worth a try on similar problems!
Cheers

So you're saying that from the speaker's negative and positive wires I can hook up an isolator/filter there?