Ground loop buzz...CANT FIX IT, HELP!

[droptop93]

Well I am going insane. I just purchased/installed a pair of CDT components for the front, and have been fighting what I'm guessing is a ground loop for days now.

Here's what I'm running:

Pioneer DEH-P6500 head unit
Legacy 800w 4ch. amplifier
CDT Audio HD-62EF components
Polk Audio 12" sub
Stock rear 6x8's
Stock ford amp running the rear 6x8's

With the car off:
I get no whisling/buzzing from the factory rear 6x8's that are run off the factory amp, but get definate interference (no whisling) from the fronts and subwoofer. The only way I have found to cure this is to touch a grounded wire to the RCA terminals on the back of the head unit. This eliminates all unwanted sound and everything sounds great. But should I HAVE to have this little ground wire to get rid of this problem, or is something wrong that needs to be addressed and not just band-aided?

With the car on:
I get no whisling/buzzing from the factory rears, but I do get the same buzzing, accompanied by the whisling that rises with rpm. This is also through both the sub and front stage...and is only reduced when the ground wire is applied to the head unit's RCA terminals.

I have tried a power line filter on the 12v line to the head unit with absolutely no reduction in noise, period. I have checked, and double checked the ground wire to the amp...and am sure it is good. I have also tried another amp I have just to make sure my current amp isn't bad, and it is not. The head unit is only a couple months old, and I cannot understand why it would be bad...but I have not tried another head unit, yet.

The RCA's and speaker wire to the front stage are run down the center of the car away from the 1/O welding cable that goes to my battery in the trunk. I don't think they could be picking up interference, however I guess anything is possible.

Only thing I haven't tried (besides a different head unit) are some high $$$ RCA's, as I haven't fully convinced myself that this is the problem. If it WAS the RCA's, I would expect to get the noise only with the car on, and get no static when it is just on battery power. Am I wrong here?

I don't remember having any kind of this problem with the factory door and dash speakers, and if I did it was hardly as noticable as this.

Any ideas would be greatly appreciated. Next step is to take it to Ultimate Audio, bend over, and tell them to figure it out.

Thanks in advance!

 

[grodgers]

It's the ground to the amp...

Well I am going insane. I just purchased/installed a pair of CDT components for the front, and have been fighting what I'm guessing is a ground loop for days now.

Here's what I'm running:

Pioneer DEH-P6500 head unit
Legacy 800w 4ch. amplifier
CDT Audio HD-62EF components
Polk Audio 12" sub
Stock rear 6x8's
Stock ford amp running the rear 6x8's

With the car off:
I get no whisling/buzzing from the factory rear 6x8's that are run off the factory amp, but get definate interference (no whisling) from the fronts and subwoofer. The only way I have found to cure this is to touch a grounded wire to the RCA terminals on the back of the head unit. This eliminates all unwanted sound and everything sounds great. But should I HAVE to have this little ground wire to get rid of this problem, or is something wrong that needs to be addressed and not just band-aided?

With the car on:
I get no whisling/buzzing from the factory rears, but I do get the same buzzing, accompanied by the whisling that rises with rpm. This is also through both the sub and front stage...and is only reduced when the ground wire is applied to the head unit's RCA terminals.

I have tried a power line filter on the 12v line to the head unit with absolutely no reduction in noise, period. I have checked, and double checked the ground wire to the amp...and am sure it is good. I have also tried another amp I have just to make sure my current amp isn't bad, and it is not. The head unit is only a couple months old, and I cannot understand why it would be bad...but I have not tried another head unit, yet.

The RCA's and speaker wire to the front stage are run down the center of the car away from the 1/O welding cable that goes to my battery in the trunk. I don't think they could be picking up interference, however I guess anything is possible.

Only thing I haven't tried (besides a different head unit) are some high $$$ RCA's, as I haven't fully convinced myself that this is the problem. If it WAS the RCA's, I would expect to get the noise only with the car on, and get no static when it is just on battery power. Am I wrong here?

I don't remember having any kind of this problem with the factory door and dash speakers, and if I did it was hardly as noticable as this.

Any ideas would be greatly appreciated. Next step is to take it to Ultimate Audio, bend over, and tell them to figure it out.

Thanks in advance!

And do *NOT* use "that little ground wire" - because "that little ground wire" will want to become part of the main circuit - and will overload.

1) Where did you ground your amp (i.e. where does the negative wire go?)

2) Is your amp ground of the same size that is feeding it power? (it should be)

3) How LONG is the amp ground? (3 feet or less?)

My first guess is to find another bolt to ground the amp to - wherever you ground it, it needs to be direct to the chassis. If using an existing bolt, did you remove all coatings from the bolt, use a big ring terminal and grind all paint off from around where the ring terminal attaches?

In this case, a DMM (digital multi-meter) is your friend. You can use it to see differences in voltage potential as you check different ground alternatives.

 

[4.6_02_Black_GT]

You might check this out its a problem I had. I too had what sounded like aternator whine that grew with engine rpm. I tried ground loop filters on both my amps and the helped a little

to make a long story short, I found that by reducing the gain on my amps. I elimanated the whine. The tendancy for everyone is crank the gain/sensivity to the max on your amps. People think this makes the amp louder...when in fact all it does is reduce the amount of input to make the amp play louder.

Anyway by reducing the gain you will increase the floor of what the amp reproduces, so low whines and buzzes and hummes are ingored by the amp and only your music is reproduced. (this is because the humms are too low in power, you amp is waiting on a more powerful signal from your head unit to reproduce...so it just ingnores your buzz or humm)

I'm sure I messed up the explantion, but at least try it out it would only take a few minutes to check out.

Reduce that gain, mine is set to about 25% gain. The factory setting was at 50% of the range. You will find that your head unit will require a little more volume to play at the same level as before.

 

[GT2000JAY]

That's exactly what I just found my engine noise to be - the gain. I was banging my head against the wall, checking grounds, changing ground wires, grinding off sections of paint to clean things up for the grounds... All of that helped a *little*, but the buzz/whine was still there.

Took a look at the input sensitivity - it was cranked up pretty good on both amps, just started bringing it down gradually, and sure enough, the whine is gone. Best I can figure is that since the word *sensitivity* is in the name, then it probably makes it more sensitive to noise in the system as well.

All I know is it was driving me NUTS and now it's gone.

Jay

 

[4.6_02_Black_GT]

Yep Jay ..like I said I was doing the same thing, stupid whine was making me go nuts. ...Hopefully this will help DropTop too.

 

[droptop93]

Sorry it's taken me so long to reply...work's been crazy lately and have barely had time to eat and sleep.

Anyway, to answer some questions:

1) Where did you ground your amp (i.e. where does the negative wire go?)

2) Is your amp ground of the same size that is feeding it power? (it should be)

3) How LONG is the amp ground? (3 feet or less?)

My first guess is to find another bolt to ground the amp to - wherever you ground it, it needs to be direct to the chassis. If using an existing bolt, did you remove all coatings from the bolt, use a big ring terminal and grind all paint off from around where the ring terminal attaches?

In this case, a DMM (digital multi-meter) is your friend. You can use it to see differences in voltage potential as you check different ground alternatives.

The Amp is grounded to the same place as the convertible top motor, which appears to be a pretty substantial part of the chassis. I also removed all the paint to insure good contact. I tried the ground wire to several different places, and got almost identical readings from all.

The amp wire is the same size as the power wire (both 8Ga., were part of a Rockford Fosgate amp installation kit I had laying around), and is probably 2-3ft. long at most. Maybe I should try a LARGER power/ground wire? I kinda ASSuMEd since it was a Legacy amp, it couldn't produce close to the 800w's listed...but I'll go check it to see exactly what it is putting out and let you know.

The "little grounded wire" I refer to is not grounded to the chassis of the car, itgoes from the chassis of the head unit to any of the RCA cable terminals. My guess is that the ground inside the head unit from the RCA terminals to the radio/wiring harness might not be that good? I have 3-sets of pre-outs...two (front and subwoofer) plug directly into the head unit, and both produce alternator wine without the extra ground. The 3rd pre-out is for rear speakers, and actually has RCAs coming out of the head unit with terminals that you plug into...as in you don't plug directly into the head unit. I get little if any interference if using this pre-out, which further leads me to believe that the head unit's ground isn't that good?

I did go out and buy some better twisted pair signal cables and ran those instead of the cheaper ones I had, which DID eliminate the alternator wine with the ground wire on the RCA cables. I'm just wondering if my assumption about the head unit's ground being weak is why the extra ground is needed? Is the wire being connected to the head unit going to cause a problem?

to make a long story short, I found that by reducing the gain on my amps. I elimanated the whine. The tendancy for everyone is crank the gain/sensivity to the max on your amps. People think this makes the amp louder...when in fact all it does is reduce the amount of input to make the amp play louder.

Right now the gain on all the channels is set at around 75%...too high? I will definately turn it down and see how that effects things. I guess my amp is probably the weakest part of my setup, being as it's the oldest, and...well, its a Legacy product. Maybe having the amp turned up so high is pushing it's limits? Now that I have been able to get rid of the wine for now, the amp will click over to protection if I crank the radio up. I'll try turning down the gain and letting the head unit do alittle more work (use it's low and high pass filters instead of the amps) and see how that does.


BTW, what's a good 4-channel 800w amp for a reasonable price nowadays?

Thanks for all the input everyone, I'll try out everyones ideas and let you know what happens.

 

[4.6_02_Black_GT]

Droptop...yeah 75% on the gain is too high you will definately have less noise if you reduce the gain some.

 

[grodgers]

The "little grounded wire" I refer to is not grounded to the chassis of the car, itgoes from the chassis of the head unit to any of the RCA cable terminals. My guess is that the ground inside the head unit from the RCA terminals to the radio/wiring harness might not be that good? I have 3-sets of pre-outs...two (front and subwoofer) plug directly into the head unit, and both produce alternator wine without the extra ground. The 3rd pre-out is for rear speakers, and actually has RCAs coming out of the head unit with terminals that you plug into...as in you don't plug directly into the head unit. I get little if any interference if using this pre-out, which further leads me to believe that the head unit's ground isn't that good?

Sounds like you've found the problem - and I'd set the gains properly (using a dynamic CD in the hu, turn gains all the way down and increase volume on head unit until it distorts - then back off the HU volume until it's clean - that's your maximum volume u should use - now, keeping h/u at that volume, turn up gains until amp begins to distort, back off a tad until it's clean - and you're all set. Set 'em and forget 'em.

 

[droptop93]

Sounds like you've found the problem - and I'd set the gains properly (using a dynamic CD in the hu, turn gains all the way down and increase volume on head unit until it distorts - then back off the HU volume until it's clean - that's your maximum volume u should use - now, keeping h/u at that volume, turn up gains until amp begins to distort, back off a tad until it's clean - and you're all set. Set 'em and forget 'em.

Sounds like a good plan to me, I'm going to reset everything tonight when I get home.

Thanks again for all the help/ideas everyone...I really appreciate it!

 

[DJsZincGT]

Sounds like a good plan to me, I'm going to reset everything tonight when I get home.

Thanks again for all the help/ideas everyone...I really appreciate it!

You should try not to take your volume on your headunit past 3/4 volume. Here is a good rule of thumb for tuning your system:

First make sure the gains are all the way down on your amplifiers. Find out what the max volume is on your HU. Figure out where 3/4 volume is in reference to your max volume and set your HU to that volume. Now go to your amplifier and start slowly turning the gain up until you begin to hear a slight distortion and then back the gain back down until the distortion goes away. This method should keep you from cranking the gains up above 50% on your amplifiers. However sometimes it will be necessary to turn them a little farther depending on the amp and headunit in question. Some headunits simply do not have the line level that's needed to run a system efficiently and without a line driver to boost your line level you have to crank the gains a little more than with other headunits.

 

[grodgers]

You should try not to take your volume on your headunit past 3/4 volume.

Interesting theory - buy why? What's magic about 3/4? My Alpine goes from 0-35 - When using pre-outs only, distortion of the unit isn't noticable until around 32-33. Measuring output voltage (flat) using pink noise at 0db, and a fluke DMM with true RMS shows 4v RMS output right at 32 - that's alot higher than 75% (92%) volume.

Given the differences in h/u design, I'd say using a blanket statement wouldn't be advisable.

Of course, that's just my 2¢ and I could very well be wrong.

 

[DJsZincGT]

Interesting theory - buy why? What's magic about 3/4? My Alpine goes from 0-35 - When using pre-outs only, distortion of the unit isn't noticable until around 32-33. Measuring output voltage (flat) using pink noise at 0db, and a fluke DMM with true RMS shows 4v RMS output right at 32 - that's alot higher than 75% (92%) volume.

Given the differences in h/u design, I'd say using a blanket statement wouldn't be advisable.

Of course, that's just my 2¢ and I could very well be wrong.

Reread what I wrote. I said, "Here is a good RULE OF THUMB for tuning your system:", which means for the most part...not all. You also have to consider that most people do not know how to accurately measure their line level and even if they do know how to do it, most don't understand what it means. Granted, using electronic equipment to tune your system to it's maximum potential will always get your system closer to perfect, but we're talking about an everyday stereo here. Why make one piece of equipment do all the work for you? Judging by what I'm hearing from the person who started this thread, his headunit isn't putting out anywhere near the 4V that yours is. Cranking the volume up on a weak headunit is only going to cause more distortion. It only makes since to make your components work together as a system rather than to crank one up and leave the other one turned down low.

I am in no way saying that you can't go over that volume. It's more or less a starting point for tuning an everyday system.