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adelphia83 11th November 2008 03:51 AM

Voice Coil Burning
I had my semi-newly repaired amplifier die today, most likely from shorted outputs. I haven't pulled the amp out to determine exactly what failed, or how. The amp was not being driven hard at the time, and it was only 5-10 minutes after startup, so was not even warmed up.

The protection circuit did not kick in right away, causing rail voltage to go straight to the sub for about 20-30 seconds, enough time to produce a considerable amount of smoke and burning smell.

The subwoofer is an RE Audio SX12, amplifier is an Audiobahn A16000V.

Looking through the vents, the coil wire appears intact and undamaged. The very edge of the voice coil former, near where it meets the cone appears darker, and excessive heat is apparent in that area.

The subwoofer still plays though it's hard to compare the sound output before and after, because I'm using a lower power amplifier. Resistance of the coils measure the same as they did before this incident. The voice coil does not rub on any part of the motor structure.

What are the chances that I damaged the subwoofer? What would be the potential consequences of this sort of overheating?

jol50 11th November 2008 07:01 PM

I've seen them burn together and reduce ohms, or they fry and short. IMO it works or does not, but I don't repair subs either. You think the amp failed itself and not from sub?

How much fuse does that amp have on it?

adelphia83 13th November 2008 12:09 AM

The amp has 80A worth of fuses. It looks like transistor(s) in the output section shorted as the amp powers up completely with the remote signal, just goes right into protection.

The amp was playing along just fine, then all the sudden I didn't hear any sound from the sub. I looked over and the amp power light was on, shortly after I could smell smoke. It took the amp a good 20 secs or more to finally go into protection. Had I not been doing 70 down the interstate I would have shut it down sooner.

The resistance hasn't been lowered any. It measured 1.9 ohm (with VC in parallel), and it's the same after this event.

The sub plays along fine now, but I can't determine if any damage has affected output as I'm using a different amplifier.

I've burned up a few subs (intentionally) so I know what a fried VC looks like. None of the enamel has blistered, but the paper part of the voice coil former is a lot darker than what it used to be. I'm still curious as to whether this has damaged the sub in any way...?

Cal Weldon 13th November 2008 12:24 AM

If the wire has heated enough to darken the former, you may have damaged the adhesive that bonds the former to the cone? Or the adhesive that holds the wire to the former? Or maybe made the former more brittle and susceptible to moisture ingress?

Who knows...

pinkmouse 13th November 2008 12:31 AM

If it works with no rubbing or other problems then fine, carry on using it. However, you have likely reduced its lifetime and power handling capabilities as the VC heating will have left a weak spot that will eventually fail.

adelphia83 13th November 2008 12:40 AM

Thanks for all the replies.

One more question. Will the damage have any effect on sound output (volume)? I don't mind replacing the sub down the road if it fails, but a new sub just isn't in the budget right now :)

impsick 13th November 2008 12:50 AM

it might start doing funny things at high volume. Like Pinkmouse said the lifetime has probably been reduced. But you gonna have to play to find out. ;)

Flyin11 13th November 2008 01:10 PM

I just had a very similar problem...My 2 subs were sounding great and then they just stopped working when I was driving down the interstate. They would cut out at a certain amount of volume level though, different than what is happening with yours I think. I did some testing with another subwoofer I had and found out that that it was the subwoofers and not the amp cause my other sub I tested with would play fine. I bought 2 new subs, the same model and brand cause I liked them so much, and have been good to go and my sound is so much louder and clearer than my first set. So, the previous subs weren't hitting as loud as they use to which I'm guessing that was because they were about to fail due to some problems with the voice coil. I noticed what looked like some oily or dried glue splats on the rings of the subs so I probably did something internally. I screwed up mine on my own had nothing to do with over powering them...I was just stupid :rolleyes:

If you have a extra subwoofer, I would suggest testing that out and see if it cuts out or keeps playing. If it keeps playing with no issues then it's probably more likely your subs.

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