Electrical Question ?

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TBass

Electrical Question ?

Postby TBass » Thu Nov 04, 1999 9:32 pm

Hey guys what's up, I have a problem, when listening to music at pretty high volumes with my subs, the amp shuts off till I lower the volume, I thought it was cause i had my amp to a 3ohm load, but now I have only one sub running at a 6ohm load to the amp, and it's doing the same thing, I have my gains really low now, and still doing it, before my gains were almost all the way up, and didn't do it, and also noticed my lights started to dim everytime the bass hits, what could be the problem, I hate to hear it but I think it is the Alternator that's cause the amp to shut off at high volumes, what can I do, I need a new Alternator now, where can I buy one now, what's the best, how many amps should I get, I right now have 90 amps, does low voltage cause an amp to clip??? just checking let me know guys.

T-Bass
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Big Mack
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Postby Big Mack » Thu Nov 04, 1999 10:11 pm

Yes, low voltage can shut off an amp. It won't clip, however. The only time an amp clips is either because of distortion or getting too much signal (improperly set gains). If your head sends a lot of signal, the gains go down. If not, they go up. As for the alternator, they either work or they don't. There's no two ways about it. You can test it right on the car with a meter. Since your car runs off the alternator when it's on, try setting your meter to VDC and see what you get with the car off. Now taking the probes off the amps, turn the car on. Check the volts again. If they went up, you're golden. If not, you're screwed. Just make sure that you set the meter high enough. It should be at 20V or more. This will give you a good reading. Car off should be around 12-12.5. Car on should be 13.8-15, depending. A 90 amp alternator should be good for most systems, unless you're running inefficient amps or just a ton of them. Consider a capacitor to help with lights dimming. You might also want to check and see that 6 ohms is what you are running. Impedance varies with frequency, and if you're bottoming out a sub, it could cause the impedance to dip into dangerous levels. I've seen bridged amps that were run into one single 4 ohm sub get toasted because the owner didn't want to believe that the distortion was a problem. If you want it louder, get more subs and more power. Distortion is your enemy. Hope it helps.
TBass

Postby TBass » Thu Nov 04, 1999 10:59 pm

Well I have 2 caps, one 2 farad for the sub amp, and one .5 farad for the other amp that's being used for my highs. My cap has a voltage meter, and when the car is off, it says 12.4 sometimes 12.8, and when the car is on, is says 14.1, and sometimes, 13.6, I just don't know why it is happening now, but didn't happen before. This is weird, but now my lights dim, where before it didn't. What else can I do, should I try different subs, or could it be that my sub now is damaged and causing all these problems?
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LIV2BMP
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Postby LIV2BMP » Fri Nov 05, 1999 12:30 am

You may need to look at the power cabling. I have seen the same thing with my ZR360 when running bridged. I used 4 gauge to a distribution block & 8 to the amp. I have upgraded to a dual 8 to the amp to prevent the drop in voltage.

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jlaine
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Postby jlaine » Fri Nov 05, 1999 12:41 am

I have encountered this situation with a friends system once. I can agree on the inputs and the fact that clipping cannot occur with low voltage, but with an improper input voltage some amps will start to "haze" at the barrier of shutoff. As for your alternator, I have extensive exposure in this, and I tend to believe that it is not the case. Age and use can reduce the output of an alternator, but it would not go down much more than 30% of its initial rating before it would finally quit on you. The occurrance with my bud was due to a poor ground, which I am sure is not your case, but I would check all of your inputs before you proceed any farther. Excessive voltage fluctuations in a power supply has caused a few amps I have bench tested to quit until I stopped all input and returned the supply to 14.4 And I have seen this happen in a few vehicles. I am not sure of the basis behind this, but I tend to believe that it is due to the low voltage is starving the power supply, and the amp shuts itself off because it cannot keep up with the current demand the inputs are trying to set. If you have an excellent power supply in your car you should be able to test the voltage at the terminals at the amp and when you crank it your meter should stay stable within the 14.1-14.6 volt range. If you can achieve this at the max output of your amp you have plenty of available power. I would tend to believe that your available power is lacking, mainly because of the fluctuations that you can see in your lights. When this is occurring you are robbing other sections of your vehicle of the power it needs to run properly, which leads me to say you need to beef up your available power. As for the use of capacitors, the design behind them is for instantanious and almost infinite current draw. They merely smooth out the current demand and disperse the peaks of power your amp demands into a larger area, taking a lower toll on your alternator(s) and batteries. I would first pick a CD that you think would push your amp to the max, turn all your accessories on... fan on max, headlights, dope lights, A/C if possible, and anything else that might be running in a normal day. Then put your CD in and crank it... testing the inputs as close to the amp as possible, as voltage can (and does) drop through cable, no matter what. That is just a principle of electronics. If you see any major dips you have reason to be concerned, but to see these dips you have to make sure you have a good DMM that has a high sampling rate. If you don't, put in a test CD that has a sine wave that will put out a continuous output through your amp. This will override the low sampling rate of some of the cheaper DMM's by making the current draw continuous. (this also renders your caps useless at such a draw, since they are constantly trying to recharge) If your reading bounces alot.(in my history 12.1-14.8) I would say that you have a very good jump on what may be causing the problem, if you do see this, take your amp in and bench test it.(if you have the equip.) If not get a bud with a large alternator, and hook him to your car with some good jumpers, and see if your voltage settles down then. If your voltage isn't the problem, well I have other hypothesis, but I guess I will leave that for another time. Good luck and hope it all works out for you!
TBass

Postby TBass » Fri Nov 05, 1999 1:58 am

Wow !! When is your book coming out man, now that's what I call a Post Reply, thanks for all the info, I really don't have all the equipment to test everything, but I will try to change the ground and see what happens, thanks for the reply though, I think I am going to go for a high output alternator, where can I get one?
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Big Mack
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Postby Big Mack » Fri Nov 05, 1999 3:22 am

This is a good check for voltage drop, but I'd almost be willing to bet the sub is to blame. Sounds like you've damaged it and could be on your way to damaging your amp. Is the amp excessively hot? Does the protection light come on or flicker like it's going to? If so, you're looking at an impedance problem, plain and simple. Check the voltage first, then while you're back there, crank it for a few seconds and see if the amps' protection lights are coming on. If so, you've found your problem. Good Luck, and let us know what happens, T.
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Postby jlaine » Fri Nov 05, 1999 10:30 am

I definitely agree Big Mack, and that was another thing I was considering... I got my alternator from a company down in Texas, www.alterstart.com. They replied fast, offered me a great deal,$275 for a drop-in 180 amp alternator, and the guy there is willing to work with you... Hope this helps!
TBass

Postby TBass » Fri Nov 05, 1999 11:22 am

There is no voltage drop guys, I just can't make the volume more than half way, then the bass amp shuts off. I've heard some stuff about impedence problems, does this mean my 6ohm sub can be like a 1ohm sub. the amp doesn't get hot at all, it can't cause it shuts off at high volumes. Not that half , just above half way, and trust me guys, the gains are so low that you hear the bass from my 6 1/2s on the door. Is it the sub. I need to know so I can send this back quick, I might get a custom box today, and drop in 2 10" polk dbs. Should I run this amp at 2ohm bridge with these subs, but I'll have the gains really low. This is the first for this type of problem, I thought I went though every problem ever, but I guess I was wrong, and I bet you there are hundreds of more problems that I'm going to go though in this sport.

Thanks agian for your help and follow ups.

TBass
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Postby jlaine » Fri Nov 05, 1999 1:29 pm

Yes a 6 ohm sub could at one point read one ohm, at different frequencies and with different amounts of input. Six ohms is the meadian line for what the speakers general resistance is, the actual figure while it is working is in a constant state of change. I have to back Big Mack on this one, ditch the subs you have connected to your amp right now- and run your amp to a different set, anything that you can beg, borrow, or steal just so they can handle what your sub amp can put out. If you put a different pair on your amp and that doesn't alleviate the problem, I would tend to think that there is a short circuit inside your amp somewhere that is contacting the outputs of your transformers. (which is what would happen if your sub is toast also, they usually dead short themselves.) The protection circuit on amps for a dead short usually do not kick in until your output is at a level that their protection circuit can sense, which would explain why the amp shuts down at louder volume levels. A blown or worn voice coil would not necessairly mean that your sub would not function as it should, but that it will kill your amplifier if you aren't careful. Check out the resistance to each of your subs independently, the reading will not be exactly 6 ohms, but should be in the ballpark (5.3-6.7 in my tests) If it doesn't read that, your sub is cooked. I would find some new subs to try out first though, if one of your coils is gone that would explain why your lights are dimming suddenly. (back to ohm's law... half the resistance- double the current) Amps have set limitations, so you cannot expect to half the resistance and double the output, but if your amp is only seeing a one-ohm load you can be damn sure that before the protection circuit kicks in you will see one hell of a current draw into it, and even with your gain all the way down. That would be because the resistance is so low, and there is nothing to keep the output transistors stable. You have seen that your power is cool, so now check out your subs, that is probablly where you will find your problem. Good luck, hope it helps...

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