Amp Current Draw with one sub

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lensam69

Copper - Posts: 63

Joined: April 11, 2004

Location: United States

Posted: August 21, 2004 at 6:03 PM / IP Logged

I just got a JBL GTO1200.1 amp today.

I have an Infinity perfect sub (DVC wired in parallel @ 2 Ohms), that's been sitting around useless for about 2 months.

The sub is rated at 350W Rms, and the amp is rated at

1100W rms @ 2 Ohms

750 W rms @ 4 Ohms

I was planning on adding one more sub eventually, wiring the voice coils in series, for 8 ohms, to get both subs in parallel for a grand total of 4 ohms.

Right now i only have one sub conected to the amp. But it's drawing too much current (i think).

I was trying it out with a 60A fuse and it blew at moderate volume. The thing is that the sub never gave any indication that it was playing too loud.

The way i see it, the amp drew more that 60 amps, so the fuse blew. If it drew that much current, then i'd guess it was probably putting out more than 350W RMS.

Why is it that the sub never even distorted? And don't say it's because it's infinity. It wasn't even playing (too) loud.

forbidden wrote:

Wrong advice young grasshopper, go back to square one and do not pass go.

zane9000

Copper - Posts: 69

Joined: August 07, 2004

Location: United States

Posted: August 21, 2004 at 6:32 PM / IP Logged

im not fimiliar with that sub so i may be giving completly usless advice but.... is each voice coil 2ohm or 4ohm? because if they are 2ohm them wiring them in parallel would bring it down to 1ohm and that may be why your amp is blowing fuses.

wether this is the case or not you may want to try wiring the voice coils in serries to raise the impeadance. even if they are 4 ohm coils that means the total load will be 8ohms and with the kind of output your amp has, it should be no problem to push your sub.

hope this helped,

Warren

I had Cheetos and wine for dinenr.

forbidden

Platinum - Posts: 5,352

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Joined: November 01, 2003

Location: Alberta, Canada

Posted: August 21, 2004 at 6:41 PM / IP Logged

Ahhh, young grasshopper, we solve probrem. Your sub did not distort because the amp was not clipping. I am going to summise that this one sub you have wired as a single 8 ohm driver, correct? Thus this would knock the amps power back to a more respectable 375w @ 8 ohm load and it would still give you a tonnage of headroom. Think of it this way, your redline is at 8000 rpm and the sub is being run at 1500 rpm. Now, just because it is a low power setting does not mean that it will not draw a large amount of current. As you use your amp, the longer you use it the hotter it gets, this all relates to a higher current draw. Same with the type of music being played, some tracks might have +10db boost added at 50hz recorded in the track, this again will increase an amps current draw. There are very few reasons for a fuse to blow. I am again going to summise that this is the fuse at the battery that is blowing. This fuse is to protect the vehicle, not the amp, the amp has it's own fuses. If the current draw is too high from the amp for too long a period of time, the fuse will blow. If the power wire is short circuiting, the fuse will blow. You have one of these two issues, my bet is on the current draw. Get a bigger fuse or keep the volume down some.

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

lensam69

Copper - Posts: 63

Joined: April 11, 2004

Location: United States

Posted: August 21, 2004 at 7:06 PM / IP Logged

Ummm... The sub has a pair of 4 Ohm coils wired in parallel. -> 2Ohm. (I did write it in my post Amp Current Draw with one sub -- posted image.

and the fuse that blew was in the dist. block (The one closest to the amp).

I was however, playing a test track (Chemichal Brothers - Under the influence) which probably has that +10Db boost. But i hadn't been playing for more than 3 minutes, and as i said before, the volume wansn't too loud.

My question is if the amp drew that much current, it should've been outputting a big number of RMS Watts into that 2 Ohm load. How come i never heard them?

(And yes, the sub is in phase :P)

forbidden wrote:

Wrong advice young grasshopper, go back to square one and do not pass go.

forbidden

Platinum - Posts: 5,352

Joined: November 01, 2003

Location: Alberta, Canada

Posted: August 21, 2004 at 7:16 PM / IP Logged

Rewire the sub to a series wiring configuration from the parallel connection that you have now. There is nothing wrong with what you have done other than you will using more power than the sub was designed to handle. This could lead to a melted voicecoil if the sub is ran for too long at too loud a volume level. You know I read your post and just blocked out what you had done, sorry dude. A difference in power levels of double what you had would give you an increase in output of 3 db. You did hear correct, there is a point that a sub just cannot get any louder. This is due to box design, speaker limitation, power output of an amp, vehicle and other matters as well. What have you done with the ground wire on the new amp? Suspect an issue here.

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

lensam69

Copper - Posts: 63

Joined: April 11, 2004

Location: United States

Posted: August 21, 2004 at 9:35 PM / IP Logged

I guess you'd have to hear it to understand. The Sub is an infinity perfect 12.1 DVC, rated at 350WRMS.

I have it in a sealed enclosure of 1 Cu. Ft. (Which is what infinity recommends i think).

I believe that the sub isn't playing as loud as it should be. And as for power cables, I'm using 4ga cable for power and ground to a distribution block, and from the block, to the amp i'm using 8Ga (But it's only a 1 foot distance).

I will rewire it though. Even if it's not playing loud it's sure drawing a heap of current. I just drove the car, and my headlights are dimming a lot. I expected to upgrade the alternator after i got my second sub.

It's weird... for all the power it's drawing i can't feel it. Are there any Infinity owners out there??? Opinions?

forbidden wrote:

Wrong advice young grasshopper, go back to square one and do not pass go.

kfr01

Gold - Posts: 2,121

Joined: April 30, 2003

Posted: August 21, 2004 at 10:36 PM / IP Logged

Try running your amplifier at a low volume for a while and see if your fuse still blows. If it does, there is a strong possibility something is wrong with your amp or there is a short somewhere. It should not be blowing a 60 amp fuse at low volume. Pros, correct me if I'm wrong on this.

New Project: 2003 Pathfinder

stevdart

Platinum - Posts: 5,816

This member consistently provides reliable information

Joined: January 24, 2004

Location: Pennsylvania, United States

Posted: August 21, 2004 at 11:42 PM / IP Logged

Let's look at what Ohm's Law tells us about this: I = sq rt ( P X R ). So that the amperage drawn through the fuse is equal to the square root of wattage output times the resistance of the driver. Going by what you have written, you were not playing the system at a loud level when the 60 amp fuse blew. And you didn't hear crap or distortion from the subwoofer. Using the Ohm's Law formula, and knowing you have a 2 ohm resistance load...to get to 60 amps would be out of the question here. If we presume 100 watts of power in this case, the current draw would be just 14 amperes.

If you were outputting 200 watts, which would reasonably seem toward the loud side, the amperage draw would be only 20. If the output were 300 watts, reasonably loud, the amperage draw would be just 24.5 amps. And if the wattage were 400 watts, more than the RMS of the speaker, the amps drawn would still be less than 60. Just 28 or 29, actually. And at that point the speaker would be overdriven, and the sound would be noticeable.

So, from that, current draw can be eliminated as the culprit for the main fuse being blown.

Which leads to another cause of the problem. As zane, forbidden and kfr01 have all pointed to, there is an short happening here.

Rob asked about the grounding issue. Take it apart and redo it. Also reconnect the power and ground at the amp and be sure there are no stray wires hanging out. You most likely have a DMM, so measure resistance on the ground, too. Make sure it is a nice low reading of less than half an ohm to the battery negative. And check the complete length of the power wire to make sure it is insulated and sound, particularly at the spot where it goes through the firewall.

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

pimpincavy

Silver - Posts: 880

Joined: May 20, 2004

Location: United States

Posted: August 22, 2004 at 12:14 AM / IP Logged

You should upgrade that one foot of 8G wire to 4G. Thier is no point in running 4G through the rest of the car if you end it with 8.

evnldr

Member - Posts: 36

Joined: December 28, 2002

Location: United States

Posted: August 22, 2004 at 2:39 AM / IP Logged

8 awg should be plenty the reason for the use of 4awg is the length of the wire run ....the internal amp wires are probly only 10awg at best.

my .0000002

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