Odd problems

Hello all, I am a new poster. I hope I can be of help here at The 12 Volt. I hape a pretty good knowledge of all things stereo related, but these problems I'm having leave me quite confused.

The Components:
1996 Chevy Blazer, 4dr., V-6, Black (car)
Pioneer DEH-7400MP (head unit)
2 Pioneer 4x6 (dash speakers) (wired as front speakers)
2 Infinity Reference 5.25 (front door) (wired as rear speakers)
2 Pioneer 5.25 (rear door) (wired as rear speakers)
1 Infinity Kappa Perfec 12.1D (wired in parallel)
1 Pyramid Crystal 1000W (bridged) (not a very good amp)
On order: 1 Phoenix Gold Xenon 400.1

The Setup:
I have all the speakers wired into the factory wiring. The head unit uses the factory wiring. I have the RCA cables run behind the dash to the left, over the steering wheel, down the door jam(sp?), and to the back from there. I have the power wire run from the battery, to the passenger door, and underneath the car.

The Problem:
(1) Seems to be that every time I start my car, change CD's, or just turn the radio on, the amp goes into protect. So what I do is turn the head unit off, then on again, and it works. What the heck's up with that?

(2) After about 25-30 minutes of constant listening, the amp (I'm guessing it's the amp) only puts out half power or less.

(3) Kinda related to problem 2. At times I get a strange hum from my sub. When I use my brakes, it makes another strange sound. For lack of a better description, it sounds like a short fart. Seems like it only does this at night.

My Hypothesis:
I actually have a couple ideas, but I'm not to sure.

(1) The amp is shot, which I know that it is, but that Phoenix Gold amp, I actually have installed it before, and still had problem 1 happen. Which would mean that it's actually a problem with the head unit.

(2) The head unit is shot. Plain and simple. I don't like this theory.

Anyways I'm gonna rip all of the amp wiring out and re-run them and see if that helps any. Doubt it will, but it needs to be done anyways.

Thank you for taking the time to answer these questions in advance.

Paul

you probably have a ground problem, and the head unit may not have enough current on the turn on lead, use a relay that may help

i the second the ground notion, it amazing how many problems you can have with one stupid ring connector....

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I am on board with the ground issue. I would also add a relay to the remote line, just to be better safe than sorry, also I love that little click of the relay triggering the amp:)

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double-secret reverse-osmosis speaker-cone-induced high-level interference distortion, Its a killer

Than you for all for your relpies.

When you say a ground problem, do you mead a ground problem with the head unit or the amp?? And also, for a relay, would you put that on the rempte line?

Paul

Ground problem with the amplifier. If you are running the amp in mono and running it at 2 ohms, this doubles all tasks that the amp must do. Chances are that you are also asking the amp to do something that it was not designed for (this I am assuming as it is a 2 channel amp that is bridged to mono and running at 2 ohms). It most surely will send the amp into protection. Make 100% sure that you have a good ground for the amplifier.

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Top Secret, I can tell you but then my wife will kill me.

The amp is supposed to be 2 ohm stable. I have it grounded to the bolt that holds the backseat to the body, so that should be a pretty good ground, but if not, do you have any other reccomendations as to where to ground it?

Most 2 channel amplifiers are stable to 2 ohms stereo - this is the same as 4 ohms mono. I highly doubt that this amp is stable to 2 ohms mono. If it were then you would also have a 1 ohm stereo rating. The bolt that holds the seat in is usually a poor ground. In most GM vehicles it is best to run a ground wire direct to the battery due to the resistance on the ground return.

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Top Secret, I can tell you but then my wife will kill me.

WO WO WO WO WO WO WO. Rob are you telling him to run the ground for his amp strait to his battery. If you are I am going to have to whole heartedly disagree. Rule of thumb is 3 feet or less for the amp ground. If you wanna run a saftey ground thats one thing but to run the amp ground that far is Ludacris to me. I would use a wire brush on a drill and scrap the paint off a piece of double metal in the vehicle by the amp then use  self tapping screw to ground the amp. Also wouldnt hurt to reground the battery under the hood being the factory grounds usually suck.

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double-secret reverse-osmosis speaker-cone-induced high-level interference distortion, Its a killer

Yup, the reason for it is simple, resistance on the ground return. It is not about the size or amount of metal in the chassis, it is about the resistance through it. Most GM vehicles are a combination of crappy metals, real crappy welds (like the ones that hold seat bolts down) and glued together unibody panels. These all equate to a fairly high ground resistance. Next time you have a GM through your bay make sure you check this reading, most installers do not think to check it. In my years this is something that I learned the hard way, it has blown more amplifiers than I can now remember.

While you are correct with the assumed proper way to gound the amp, you did not mention to check the resistance and no worries dude, most people do not as they were not trained to do it. It is good practice to check it every time. If the ground is above 1/2 ohm and it cannot be made to go lower, bad things can happen when you try and pass current through it. Excessive heat build up, lower power output and in the case of a Rockford amp, pretty much can guarantee a failure if the amp is used on subs and ran hard. I still hook up amplifier how you have mentioned, but I will always check to see what the resistance is and explain to the customer what could happen and why and let the customer make the determination as to where to ground to.

As a side note (not that I did this) start yourself a table of the make, model, year and resistance reading of the vehicles that you work on, you'll find that GM is the worst offender. While I might have jumped to conclusions on where to ground his amp to, I did it based on the knowledge that I have gained on many vehicles just like his.

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Top Secret, I can tell you but then my wife will kill me.

And unrelated to above but an issue since you gave your information in the post:  you have the power wire running underneath the car.  That is not good.  You should re-route it through the interior and into the trunk, and through the firewall...not the door... to the engine bay.

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Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.

Rob, you mentioned checking the resistance of the ground, how exactly would I do that?? And it was also suggested that I move the factory ground for the battery, could anyone make a suggestion as to where I would re-locate it to??

And I'm not a professional installer, just work for myself and select friends, but thank you for the complement.

Paul

To check the ground resistance put one probe of the dmm on the metal of the vehicle where it was suggested to ground, then connect some speaker wire or similar gauge wire to the other probe and connect it to the negative post on the battery. Then set your DMM to the resistance setting and read awayyyy (I've heard you will get a mid 20s reading in ohms on most gm vehicles).

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I do check the resistance on grounds in the vehicles I work on and it is damn hard to find a goond ground in a gm but I cant think of a time yet where I didnt find and acceptable one. My main problem with running the ground all the way back to the battery is the inherited resistance that is going to build up in the wire over a run of that lenghth. Thats why I never do it.

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double-secret reverse-osmosis speaker-cone-induced high-level interference distortion, Its a killer

Ravendarat, on most GM's where is it that you find a good ground at usually? Is it always different car to car, or is one spot on a particular model always good?

Paul

there is nothing wrong with running a dedicated ground to an amp, just like a dedicated power cable...in many cases of vicious engine noise it's essential....

and there really is no rule of thumb regarding the length of a ground cable...many manufacturers make the ground wire 3 ft long as thats the furthest it usually needs to be run...there is however a rule of thumb regarding the recommended impedence needed as a ground potential..... this is roughly less than 1 ohm resistence to true ground, ( battery ground ) regardless of the length of ground cable.... I always try to get less than 1/2 ohm to ground

this should not pose a problem, as if you grab a meter and meter a 4 ga. cable from the negative ternimal of the battery 18 feet to the trunk of a car, you'll usually only have .2-.4 ohms resistence down the length of cable....

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Kevin Gerry
Certified Electronics Technician
MECP First Class Installer

Owner/Installer
Classic Car Audio
since 1979

Good grounds are almost never in the same place from model to model. I have to admit that I have never actually checked the resistance of the ground cable that long, I was always just told it was insufficent. I guess Ill have to try that next time. Does that also mean when adding a second battery you should just reground it to the same point as the battery in the engine bay?

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double-secret reverse-osmosis speaker-cone-induced high-level interference distortion, Its a killer

ATTENTION BEGINNERS READING THIS: In general, a short ground cable (18 inches or less is optimal) connected directly to the chassis as close to the amp as practical is preferred. 

But as Rob stated in many GM vehicles this is not the best choice.  Running a ground back to the battery is also often necessary for Saturn and sometimes for Mercedes and SAAB vehicles in my experience.  I suggest a max ground resistance reading of 1 ohm from the chosen ground point to the battery negative terminal or run a new cable to the battery (or to the engine grounding point.)  I also suggest you over-rate the cable.  I over-rate both the power and ground in all installations by at least one gage size from what is required for the total estimated current, which will help limit the unavoidable heat-related cable resistance.

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Dyohn, if I have time or one of the others do, we should create a sticky for this. This topic comes up way to often.

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Top Secret, I can tell you but then my wife will kill me.

DYohn, so would it be over kill to leave my ground attached to the chassis, but also running it back to the battery? The current is going to take the path of least resistance, so I figure the current will go either thru the chassis or direct, whichever has the least resistance at the time.

Another question, by running a direct line to the battery, would this kill the noise that I'm picking up somewhere down the line?

Thanks,
Paul

It would not be overkill at all, however it does introduce another possible entrance point for noise and a ground loop.  If you have noise right now, try the ground direct to the battery and make sure that if the amp is mounted to metal, unmount it as the screws are also providing a possible ground loop. In 99% of the cases when I have grounded to the battery it has all but eliminated the worst of noise problems.

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Top Secret, I can tell you but then my wife will kill me.

Thanks Rob, I'll do that tonight. I have my amp mounted on two wood blocks so that's not the source of the porblem. I forgot to mention that I have a computer fan attached to the mounting blocks also. I have it running on the power and ground at the amp, but I doubt that's any problem, because I still have problems with it unattached.

Paul

Right, so I got the Phoenix Gold amp in tonight, and I installed it. All my problems just seemed to dissapear. So anyways, turns out I just had a POS amp.

Last time I ever buy anything with the name Pyramid on it again. :-P

Paul

P.S. Thanks for all of your help guys.

Well that explains it all...Pyramid.....enough said...

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Rockford 501bd (500 watt rms)
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---If You Learn Something New Everyday And Teach It To Someone Else, Everybody Would Still Be Dumb As Hell!---

BTW: precision power recommends a dedicated ground wire to the battery for any amp over 300 W on any vehicle.

BTW: precision power recommends a dedicated ground wire to the battery for any amp over 300 W on any vehicle.  This is in addition to a normal frame ground wire.