symptoms of a bad ground? pls help

[Farside 10+ year member]

I'm having an intermitent problem with my setup (Alpine 12" w. coustic 400W amp). Its hard to decribe but I'll try my best...It seems as if the power output of my Sub fluctuates. sometimes when it hits a note it'll be really hard and others it will be soft for the same notes, but it seems to be random...this only started a few days ago and I've had the setup for at least a few weeks in my new car.

I'm using 4GA wire for PWR and GND and I'm grounding at a large bolt that goes through the floor of the hatch. Just to be safe I cleanned the bolt and the hole off as best I could. Could this be a Grounding problem ? Has anybody ever heard of these symptoms? what else could it be? thanks.

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[boister77 10+ year member]

could be a grounding problem. however, it seems that your electrical system can't provide enough current that the amp needs. you may want upgrade the big 3, alternator, or battery. you could get a cap, however it isn't the best long term investment.

 

[forbidden 10+ year member]

Bad ground or bad amp.

 

[Farside 10+ year member]

OK, I disconnected all my connections and cleaned/tightened them up so I'm sure theres no bad connections. I cleaned the battery terminals (they looked ok but I did it just to cover all my bases) and used a grinder on the ground connection just to make sure its a bare metal to metal connection.

I'm still getting a power fluctuation there's no mistaking it now, my subs power output is definitely fluctuating. I have installed a few subs into cars over the years and I have never had this problem before.

I'm beginning to suspect my charging system (Alt). System doesnt seem that big 400WRMS, do I really need a Cap? I thought they are necessary only on really high power applications?

PLS help if anybody can make anymore suggestions, I'm getting desperate b/c its really annoying to drive like this after spending a fair amount of money on this setup.

Thanks.

 

[supa_c 5,000+ posts]

check your voltage output on the dash(if you have one). if that fluctuates its the electrical system. if it stays the same, prob your amp.

 

[Farside 10+ year member]

unfortuntely I dont have a voltage guage on my dash, but if I measured it at the bat or amp I think it would show the same result, I'll give it a try thanks

My car is a 93 civic cx so it doesnt exactly have the biggest battery or alt. If it is my electrical system would you suggest getting a bigger Alt or battery?

If it is my electrical system then wouldn't my headlights be dimming when the base hits?

 

[pavengmike6 10+ year member]

If you measure it take the reading at the amp. It should read 12 - 14 volts. Take it with the car running stereo off, and then again with the stereo playing. take it for a few seconds to get a reading over a time period.

 

[Farside 10+ year member]

ok, first let me say thanks for the replies.

I measured the voltage at the amp with the car running and stereo off (14.5 volts) and with the stereo running (14.5 - 14.4 volts dipping a little with bass) soit seems that my voltage is fine.

My headlights dont dim when the stereo is on either.

Its strange how the subs power fluctuates only when I'm driving, it never seems to happen when its running in the driveway. It doesnt happen all the time either, it seems intermittent.

Would this mean I got a bad amp (its only a couple months old and worked fine in my other car)? or could it be a bad deck?

 

[sumone 10+ year member]

engine noise? alt whine?

 

[BIG_SUPERMAN72 10+ year member]

I think i know what you mean. My SX was not hitting as hard in a few notes. i rewired everything and it works really good now. Try re running line to sub and amp. Check all ur stuff. Check ur RCAs make sure they are in the amp good. My SX loosened the wiring off one of the voicecoils. I didnt even notice. Sometimes stuff like that happens

 

[pavengmike6 10+ year member]

Well with what you are saying it sounds like a loose connection. But you said you checked all of them. (even the ones to your subs?) If so where is your amp mounted? It is mounted to the floor of the car? If so try this, and do not do it for long as you may disrupt airflow. Put some padding under the amp and try to take up some of the vibrations, and see if it goes away.

With the car in your driveway stereo playing wiggle your HU and see if it makes the same problem. It almost sound like there is a loose connection inside your amp or HU.

 

[Farside 10+ year member]

My amp is mounted on my sub box, is this a bad idea? could the vibrations be messing things up?

I tested it by wiggling the amp/sub power connections with the stereo playing and the subs power output didnt fluctuate. i'll try it with the head unit as well i guess.

I've dissconnected and reconnected all the amp connections and I tested the DC resisitance of my sub coils 4 Ohms exactly ( I have the two 2 Ohm voice coils in series), however I'm not going to rule out the possiblity of a loose connection inside the box.

 

[pavengmike6 10+ year member]

I would check inside the box too. But I would figure it would do it no matter if you were driving or not with all the air that is moving in that box.

As for mounting your amp to your sub box, that is a common thing people do. I would not say it was bad or good, it just depends on your amp. NOT THE MODEL, it deals with the fact did they solder the conections good or not. I had an amp that when laying flat it had a problem but when you picked up one end about 10 degrees the problem went away. (no matter the amount of vibration or not). It only worked with one end tilted up. (BAD AMP)

If you have enough wire try disconecting the amp from the box and laying it on the floor. Drive around and see if the problem goes away. The only other thing I can think of is this. If you chasie grounded your amp and for some reason when you drive you are not getting a good chasie to battery - connection (because of rust or whatever) it takes power away from the amp. I would bet this is not the problem since just more than your amp and subs SHOULD not WOULD be messing up, or getting faulty readings.