When is a ground loop sound not a ground loop?

[TheSensFan 10+ year member]

I am looking to eliminate noise within my system and needs some help. When I turn on the head unit (Pioneer DEH-P4800MP) I get a sound similar to noise / high whine sound. I believe I have pretty good grounds (sanded down right to the shiny metal and using large cables).

The noise I have can be heard even when the key is turned to accessories (car not running). If I had another deck around I would plug it in and try it.

Could this still be a ground loop issue?

Or could this simply be noise coming from the head unit itself through the RCA?

When is a ground loop sound not a ground loop?

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[snoopdan 5,000+ posts]

Ahh, Pioneer head units....they are teh suk. There have been 3 people on my team that have had the exact same problem, including me. Pioneer's seem to have a standard problem with the grounding methods their head units use, that loose their grounding point on the op-amp output stage of the board inside.

Ive tried a couple of ways to successfully eliminate about 90% of the noise, but you just cant beat it.....What I did is I used a bar choke filter from radio shack ($4.50) thats labeled for CB use, and wired it in series to the 12+ constant lead to the head unit. Additionally, I cut both RCA cables and tied a wire to the outer sheathing ground on them, and wired that to the frame of the head unit. Then after that, the real trick is getting the head unit in your car and not letting it come in contact with any grounding surfaces of the vehcile. Luckily in my jeep, all the radio mounts are plastic, so that wasnt a problem...however there was a little peice of metal for mounting in there that was grounded, and every time the head unit's chassis came in contact with it, the loop noise would return. So I just electrical taped the metal peice and wah-lah...90% less noise. I also bought one of those RCA to RCA in line noise adapeters from Radio Shack ($15) and that got alot of the noise out of it too. I used all of these methods, not just one to get less noise.

I hope this helps ya, it took hours of dicking with grounding scenero's to figure that out on my own.

 

[MegaHurtz 10+ year member]

Good grounds do not mean you will not get ground loop noise. The two are completely different balls of wax. No matter how much you sand the surface, no how good your connectors are, no matter how tight it is bolted down, you are still going to have ground loops. Having a ground loop does not necessarily imply having ground loop noise in your system. A ground loop is created by grounding two or more circuits to the same common ground. Ideally, both grounds should be at the same potential, but due to resistances created in wiring and the physical connection to the ground, this can result in different potentials being created, which can cause an unwanted current to flow through your system, which is literally what you hear when you hear ground noise. The best solution to this is to ground everything at your battery, where the chances of equal potential will be at their highest. There is still a chance that you will get ground noise there, but it is the most ideal spot for a number of reasons, equal potential being one, and the least resistive point being another.

There is a way to "hear" the potential in different parts of your vehicle. I was told this in a conversation recently, and while I don't remember it exactly, I get the gist of it. I will ask this person again about this method and post about it. What he told me about checking for ground noise was to take an old cassette walkman, remove the magnetic pickup that reads the tape, put it on the end of an approx. 36" long stick, run the two wires to a pair of headphones, and then turn your car on and touch the magnetic pickup to different metal areas of your vehicle. What should happen is that you will hear the stronger electromagnetic field at certain points, which would be your ground noise. You simply could have picked a noisy spot in your vehicle to ground to. You would take your high falutin magnetic stick and test different areas of the vehicle for noise until you found the quietest place, and that's where you ground your equipment.

Of course, you could do all of this testing, and it would make no difference if you were using faulty equipment to begin with, so try and eliminate that possibility first, and then work on finding the best spot for your ground //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

 

[TheSensFan 10+ year member]

Wow very in depth and very informative responses, greatly appreciated. I will attempt to tackle this step by step to see if I can eliminate enough noise to a point where in which I (my ears) feel conformable. First step will be to pick up a ground loop isolator and see if I notice any difference at all. If not I can always return it.

I have done a little more tinkering around and I think the noise is coming directly from the head unit (RCA) and not so much a ground loop. When I unplug the RCA cables from the cross over, so nothing is being fed into the amps or cross over. The noise is gone. This leads me to ask;

If it were a ground loop causing the noise would or should I still hear the noise when RCA’s are unplugged?

Or by unplugging the RCA cables, has truly not accomplished anything?

Thanks again!

 

[TheSensFan 10+ year member]

Ahh, Pioneer head units....they are teh suk. There have been 3 people on my team that have had the exact same problem, including me. Pioneer's seem to have a standard problem with the grounding methods their head units use, that loose their grounding point on the op-amp output stage of the board inside.
I hope this helps ya, it took hours of dicking with grounding scenero's to figure that out on my own.

Out of all your steps in attempting to eliminate the noise, what did you find helped the most?

 

[snoopdan 5,000+ posts]

Putting the rca loop isoloator helped a bunch, but remember I cut the sheathing on each RCA onnector near where it plugged into the back of the head unit, and ran a wire from the sheathing to the grounding / mounting screw on the center of the back of the head unit.

I, as you, identified the head unit as being the main source of the noise. In my setup, I have a Audiocontrol Overdrive, and a Audiocontrol EQX that is in line between my amps (which could induce more noise) ... but that wasnt the case. What I did is I grabbed one of those $10 portable cd players from walmart and got a miniplug to RCA converter for it, so I could just plug my signal processor's (the audiocontrols) inputs into the cd player instead of the head unit.....the result? Absolutely no noise whatsoever. The **** head unit is what was at fault.

Like I said, ive seen this problem with fellow team mates with similar pioneer head units, and some people dont have the problem at all.....its like a craps shoot it seems if weather you get a head unit that does it or not. Funny thing is I pop my old Sony xplode cd player from years ago in place of the new pioneer deck, and its perfectly quiet...haha.....oh well.....im throwing this Pioneer in the trash next week anyways - where all Pioneer head units belong.

 

[TheSensFan 10+ year member]

Putting the rca loop isoloator helped a bunch, but remember I cut the sheathing on each RCA onnector near where it plugged into the back of the head unit, and ran a wire from the sheathing to the grounding / mounting screw on the center of the back of the head unit.

Right... I shal try this too if the isolator does not help.

What I did is I grabbed one of those $10 portable cd players from walmart and got a miniplug to RCA converter for it, so I could just plug my signal processor's (the audiocontrols) inputs into the cd player instead of the head unit.....the result? Absolutely no noise whatsoever. The **** head unit is what was at fault.

Great idea for a test! I am going to test this with my CD player and IPOD. If I can not get the noise down to a reasonable amount I may end up buying a new head unit. Crappy thing is I only bought this about a month ago. Oh well, live and learn.

Thanks a bunch.

 

[toaster 10+ year member]

isolators and chokes are band aids for poor installs. in 21 years of professional installation, ive never seen an instance where the true problem couldnt be found, and power and voltage robbing devices such as those eliminated.

 

[VereChronicus 10+ year member]

Never, or it would not be a ground loop sound.

 

[JohnnyChuttz 10+ year member]

I have a Pioneer 7800mp and have no noise what so ever. I discovered a neat little trick to eliminate noise, I have the ground to my amps daisy chained together.

Shiny metal---->One 8ga cable--->Sub amp(4ga terminals)--->8ga cable----> Comp amp. 99 Ford Ranger

 

[helotaxi 5,000+ posts]

There is a way to "hear" the potential in different parts of your vehicle. I was told this in a conversation recently, and while I don't remember it exactly, I get the gist of it. I will ask this person again about this method and post about it. What he told me about checking for ground noise was to take an old cassette walkman, remove the magnetic pickup that reads the tape, put it on the end of an approx. 36" long stick, run the two wires to a pair of headphones, and then turn your car on and touch the magnetic pickup to different metal areas of your vehicle. What should happen is that you will hear the stronger electromagnetic field at certain points, which would be your ground noise. You simply could have picked a noisy spot in your vehicle to ground to. You would take your high falutin magnetic stick and test different areas of the vehicle for noise until you found the quietest place, and that's where you ground your equipment.

Doesn't work. That was a little gadget that was described in Car Audio and Electronics in an article back in the mid 90's for finding emitted/radiated noise. Won't tell you a darn thing about ground suitability. If you were listening for current to find a good ground spot, you would want the area of highest current for your ground anyway. Electricity takes the path of least resistance which is exactly what you want in a good ground. The spot where the most of the current is flowing is the path of least resistance. Richard Clark tried using a device that created an audible tone to explain why you shouldn't ground to the battery, but his theory was flawed, because the device was measuring the difference in potential and changing the pitch of the tone in relation to the potential. His explanation was that the tone was highest at the battery and that was because the most noise was there (BS!) when in reality it was indicating that the battery and the chosen ground point had a very high difference in potential and that the ground point chosen was really poor. I don't have a link to the article describing the whole thing but you could use a like device to find an area with low ground potential. You could also save yourself the rouble and spend a little more on wire and just ground the amps back to the battery.

 

[TheSensFan 10+ year member]

Well I continued testing today I believe this issue is not a ground loop but rather the Pioneer head unit emitting noise from the RCA outputs. I disconnected the RCA input from the amps, connected my ipod using the RCA -> mini adapter, turned the car on, and turned the head unit on. No noise what so ever. Turned ipod on and played music and it sounded great.

The one last thing I could try (be a big pain) would be to run a ground wire from the head unit to the trunk where the common ground is for all the amps.

I sure do miss my old Clarion head unit…

 

[helotaxi 5,000+ posts]

The Poineers have well documented problems with ground noise. The common fix has been to ground the outer barrel of the RCA plug.

 

[snoopdan 5,000+ posts]

isolators and chokes are band aids for poor installs. in 21 years of professional installation, ive never seen an instance where the true problem couldnt be found, and power and voltage robbing devices such as those eliminated.

True problem was explained by my post....the fact is that the problem was identified, but he couldnt just pop over to best buy and buy another head unit just to get rid of his noise, some people cant afford to do that right away - those bandaids you speak unhighly of will work for now just fine.

Well I continued testing today I believe this issue is not a ground loop but rather the Pioneer head unit emitting noise from the RCA outputs.

snoopdan = right. //content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif

 

[VereChronicus 10+ year member]

As Helotaxi stated, it's just a thing with Pioneer head units...not saying that others don't share the same problem, but Pioneers have most definitely been known for it. If you simply ground the RCA outer portion to the same ground the head unit uses itself.....the noise should go away. So apparently some cheap components within the head units...that DIDN'T use to be so cheap years ago....is going bad....some do it the second you hook them up...others do it a few weeks down the road. The last 3 vehicles I've worked on had this exact same problem...and on the first one...where I looked to EVERY OTHER POSSIBILITY FIRST...since the head unit was "brand new"....took me a while to track down. I was begining to thing that my wiring was faulty and that I was no longer doing something right...when in all reality, I was doing better and better wiring on every install since the first day I started doing this crap in '89. You can imagine the quasi-epiphany I thought I was having. All to come to the truth that Pioneer is just not making head units like they used to. It was a relief, however, to find that I wasn't just getting senile. Ground the ground barrel of the RCA to the same ground wire your head unit uses and it should dissappear.