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Discussion Starter #1
I just installed one 10" sub today, and it worked for about 20 minutes on decent volume. I wasn't blasting it, but it had a bump to it. Suddenly the sub stopped working, I traced it down to one of the two 5amp fuses on the subwoofer itself (300W boston acoustics G2).

My amp is bridged and puts out 320W with the bridge active. I have the gain set to 5 out of 9, playing it safe. At least I thought so.

Here's a link to a thread with my system info: http://clubroadster.net/vb_forum/showthread.php?t=53222

The only thing not mentioned in there that may be relevant is that I have a 20a fuse on the powerwire from the battery to the amp. This fuse is and has not blown.

Any ideas as to why the amp blew? I would understand if I had my gain up high and was blasting the music but neither were the case.
 

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Discussion Starter #2
I replaced the fuse and turned the gain down a little more.

So far it hasn't blown (another 30 mins of use). I think that may have fixed it as I can't find any other causes for that other than just having the bass turned too high.
 

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brontosaurus
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Two five amp fuses on the amp is means that amp barelly draws any power. A 20 amp inline is too big if the amp itself is only fused 10 amps. The inline one is to save your amp from blowing it's fuses, if it's twice the size as the amp it won't do anything. Your gain was also set to high. Usually most systems from what I have seen and used have the gain set around the lower mid area. It's not a volume control. You can blow any system by having the gain set to high. The gain controls the frequency. If you throw large quantities of power at a driver at frequencies that it can't produce and things will start breaking fast.
 

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Discussion Starter #4
Ok good to know, the 5a fuses were on the subwoofer itself though, the amp has two 30a fuses. So the in-line 20a should be fine no?
 

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brontosaurus
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Sorry, when you were saying fuses I was thinking of the fuses on the amp, not the subs themselves. You just had the gain set wrong. Is that amp powering anything else? Do you have it wired correctly? You might be feeding low resistance poweer into a high resistance system or vice versa. Make sure it is wired correctly for your amps output and total system OHM.

Wiring instruction for different ohm loads

http://www.the12volt.com/caraudio/woofer_configurations.asp

Seems like you probably just have a lot of head room and are over powering the sub. Keep the gain, volume, or both down. A single 300w 10" isn't going to be crazy loud no matter how tempting it is to crank it up. I know every time I ever install a system I always push and push til I blow things many times over. Moderation is the key to longevity.

The amp has 2 30a fuses? Then yeah a 20a inline might even be too small. This isn't relevant to the problem you are having now though. If you were able to draw more power you could have later issues with the 20a inline, but for now if its not blowing just leave it. I think if anything the fuse ratings are an indication your amp is too much for the system.

What is the rms @ what OHM for the amp, and for the sub?
 

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Discussion Starter #6
I'm pretty sure that the gain has solved it, I'm on about 5 hours now of driving without it blowing and I cranked it pretty good for a short amount of time.

Thanks for the information, definitely useful and will be good to know if I expand my system.

Currently the amp is only powering the sub, nothing else.

When the (2 ch) amp is bridged it is 320W rms @ 4ohm, and the sub is 300W rms at 4ohm. I figured out of 9 settings for gain on the amp that ~5 would be ok but I was wrong, at just over 4 (maybe 4.25?) it hasn't blown. So I guess the power incriments decrease exponentially as the numbers go up.
 

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brontosaurus
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Well lets look at the power from the amp.

while car isn't on

Power(Watts) = Current(Amps) x Volts(12)
therefore, Amps = Watts / 12
A = 320 / 12
A = 26.6 Amps
So, a 25-30 Amp fuse would be enough

while car is on

Power(Watts) = Current(Amps) x Volts(13.5) higher due to alternator current
therefore, Amps = Watts / ~13.5
A = 320 / ~13.5
A = 23.7 Amps
So, a 25-30 Amp fuse would be enough

Either way this leads me to believe your sub is just over powered. This is fine as long as you go easy on the volume and gain. Just be sure to remember you have a lot of head room with that amp bridged. The sub having two 5 amp fuses speaks for its power handling ability. 10amp is pretty darn weak.

You can reverse the math.

10amp X 13.5 = 135 watts

This is the true power limit of the sub. If you go over that you will blow those fuses every time. What they are rated at means nothing. When they do testing to get a rating it merely has to hold that power for a split second. Moral of the story, when bying equipment check to see if the fuses can even support its claimed power.
 
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