Amp overheating with subwoofer (this problem defies all logic)

[xenofactor07 10+ year member]

Ok guys here's the deal. Perhaps I was a moron buying a 2 channel amp and bridging it to run one subwoofer rather than buying a mono block... If so, I give all of you permission to call me a *******. With that said, let me continue.

I just bought a Boston Acoustics GTA-802 (80W RMS x 2 @ 4 ohms) to run a JL Audio CS110-WXv2 subwoofer (200W RMS @ 4 ohms). By bridging the 802, the spec according to Boston Acoustics, becomes (260W RMS x 1 @ 4 ohms). With 260W, I figured this was enough above the rated RMS wattage of the subwoofer to warrant purchasing it.

The main reason I bought this particular amp was because I have the GTA-704 powering my speakers, so I just wanted matching amps in my trunk. They look great by the way.

Here's the problem: the 802 runs so hot that it's almost too hot to touch with it bridged. It runs so hot it will enter protection mode. I thought maybe it wasn't getting enough ventilation, so I tried letting my seats down and letting the amps breathe better. The 802 still overheated and shut off the subwoofer.

So the solution is.... What? Buy a mono block amp?

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[drockstar 10+ year member]

Wow, I surely am in a bit of a quandary. My guess is bad ground.

 

[JoiNt- 10+ year member]

is it a class ab amp? class D amps are more efficient in terms of overheating, i dont think what channel it is has much to do with it, ur running at 4 ohms so its not like ur pullin that amp for all its worth, like the above guy said possible weak ground wire

 

[mylows10 5,000+ posts]

Wow, I surely am in a bit of a quandary. My guess is bad ground.

this ^^^^^ or maybe cheap wire or gains set too high

 

[xenofactor07 10+ year member]

With regards to gain, when it's bridged, I can hear it clip at 21 (out of 35) on my HU.. With it unbridged, it clips at 25.

It is a Class AB amp. I know that D amps are more efficient and put out less heat.. But this series of amps does not come in class D.

If it is bad ground, what can I do to make the ground better? Right now it's a ring terminal bolted underneath a bracket in my trunk. It's in direct contact with the car body.

 

[mylows10 5,000+ posts]

never bolt to brackets or seat mounts ,just not good enough area .go direct to the body sand the paint off and drill a hole and use a bolt

 

[drockstar 10+ year member]

With regards to gain, when it's bridged, I can hear it clip at 21 (out of 35) on my HU.. With it unbridged, it clips at 25.
It is a Class AB amp. I know that D amps are more efficient and put out less heat.. But this series of amps does not come in class D.

If it is bad ground, what can I do to make the ground better? Right now it's a ring terminal bolted underneath a bracket in my trunk. It's in direct contact with the car body.

What kind of car? Does it have a frame or uni-body?

 

[BrownVanMan 10+ year member]

gain set incorrectly?

 

[xenofactor07 10+ year member]

Ok here's an update. I checked the ground. The washer that was on the bottom of the bolt holding the bracket to the chasis was actually made of paper! So after realizing that, I moved the ground wire to a new bolt with an actual metal washer (sanded off the paint on both the washer and on the chasis) and bolted it down on there. I then set the gain using a 40 hz test tone.

On my 45 minute road test, I played the volume at what i call "not too loud, but not too quiet" (which was about 23 out of 35 on the head unit). On the road test, I believe the subwoofer performed better.. Meaning, as time went on, it seemed like the sub was putting out the same amount of sound. I rode with the seat down to let the amp breathe. It never went to protection mode.. However, I think it was hotter than it's ever been. To the point where it WOULD burn your hand..

So what do you guys think? Should I return this amp and get a mono block? Buy a cooling fan for this amp and try my luck there? Or is there something I'm missing with regards to my current amp install.

 

[goingdef 10+ year member]

Ok here's an update. I checked the ground. The washer that was on the bottom of the bolt holding the bracket to the chasis was actually made of paper! So after realizing that, I moved the ground wire to a new bolt with an actual metal washer (sanded off the paint on both the washer and on the chasis) and bolted it down on there. I then set the gain using a 40 hz test tone.
On my 45 minute road test, I played the volume at what i call "not too loud, but not too quiet" (which was about 23 out of 35 on the head unit). On the road test, I believe the subwoofer performed better.. Meaning, as time went on, it seemed like the sub was putting out the same amount of sound. I rode with the seat down to let the amp breathe. It never went to protection mode.. However, I think it was hotter than it's ever been. To the point where it WOULD burn your hand..

So what do you guys think? Should I return this amp and get a mono block? Buy a cooling fan for this amp and try my luck there? Or is there something I'm missing with regards to my current amp install.

might just want to look for a class D mono block larger then you need and run it at it's highest rated impedance to obtain your desired wattage it will run cool and ask for very little current wise to do the job, as for class a/b amps about 45 min is as long as I can get one to run full tilt on sub duty even at 8ohms bridged they just get hot when ran hard not much you can do about it.

 

[THATpurpleKUSH 5,000+ posts]

still sounds like the gain is set too high

 

[goingdef 10+ year member]

still sounds like the gain is set too high

well I am assuming when he said he set the gain with a 40hz tone that he did it correctly, but having them too high would speed up the process leading to thermal protect.

 

[Epic0318 10+ year member]

idk if its possible but after going into thermal protection a few times could that have done some damage to the amp internally?

 

[goingdef 10+ year member]

idk if its possible but after going into thermal protection a few times could that have done some damage to the amp internally?

at some point I have had to use three different rockford amps(both power and punch) bridged some at there lowest impedance levels (2ohms bridged)and I drove all of these into protect a million times and never had an issue with them afterwards but i do suppose the protect is a electrical/mechanical switch so anythings possible.

 

[xenofactor07 10+ year member]

I sure hope I didn't damage the amp... The way I set the gain was the following:

1. Turn the gain on the amp to the minimum value.

2. Turn the volume up on the head unit playing a 40 hz tone until I hear clipping from the sub.. The way I determined if it was clipping was if the pitch seemed to jump from one volume notch to the next.

3. At that volume where clipping happened, I go one back. Now turn the gain on the amp up until I hear the clipping from the sub again.

4. Go back a tad till it is eliminated.

5. Done.

So did I do it right? I've been reading about impedances online.. Isn't it possible that the sub is rated for 4 ohms but often falls under that during normal operation? I read that impedance varies with frequency.