# Issue with Multiple Amps Going Bad in Install



## ChazMichaels (Apr 30, 2010)

Hello All, 

I apologize in advance if this is not the appropriate forum, but hopefully someone might have some thoughts on at least how to debug the issue. I recently had an install done on a ford fusion hybrid. Pretty straightforward install, replaced the front components, rear deck 6x9s, I left the stock head unit in place, and a kicker summing device was used at the output of the stock amplifier (as it turns out the front door and rear door speakers were full range, but the summing device can be used as an LOC so I made the change after the install). 

Here's where things get sticky, I received a call the night of the install stating that the Focal FP 5.500 I purchased was bad. They said when they hooked it up it produced no sound, I wasn't given many other details but they replaced it with the JL HD 900/5. They offered to order me a new Focal and I took them up on it. The Focal worked fine for about four days until the following sequence caused it to fry: 

I have the ability to plug directly into the Aux port of the kicker summing device which effectively bypasses the head unit and any nonsense processing it's doing. The goal was to tune the summing device/amp gains to get it as close to the 'bypassed' sound as possible. I was using a macbook pro plugged into the aux port. The car was in ACC mode. For some odd reason, a lot of noise was on that signal when using the macbook, but with the Ipod there was no noise (standard 3.5mm head phone to RCA connection). I had previously listened to the computer for 2 hours while driving without issue (although the noise was still there). The following sequence happened: I plugged the computer into the aux port, switched the kicker from head unit to aux, a cd in the macbook spooled up and all the sudden all noise went away and the lights started to dim with a steady thump coming through the speakers. 

I looked at the Focal amp and it was constantly going from protection mode (red) to ready mode (green). It was as if it was shorting to ground (resulting in the lights dimming) then protection was clearing the fault, then as soon as it cleared it shorted again. I tried with the car on and no dice. I measured voltages and other than a slightly low (~10V) remote turn on signal, all the voltages were solid (~12.6V in ACC and ~14V car on). No shorts were measured with any of the speakers. They replaced with the JL again, I repeated the exact same test and no failure. 

At this point I'm at a loss, Focal does not have any ideas, the install guys don't have any ideas. Is it possible I was the unlucky recipient of two bad amps?!? The JL has worked fine with several weeks of playing, but I preferred the Focal (little smoother on the mid-high range stuff). Looking at the specs the JL seems to go down to a lower voltage at the power input, and can accept higher voltage RCA inputs but there are so many protective measures on the Focal it's pretty tough to do something to break it. 

If anyone has any thoughts I would greatly appreciate it, if you need more details let me know. The installers are all professional, working for a highly reputable electronics store. Everything looked very well put together.


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## da Vinci (Jun 10, 2009)

The first thing I would do is check the integrity of the chassis ground. If it is not a very good connection it could possibly be drawing ground through the signal cables and frying the amps input section. Perhaps the JL is less sensitive to low voltage... so its worth checking.

You can test the ground point by making some long leads for a meter... one to the ground point, and one to the battery terminal. You can test for resistance at the ground terminal and voltage at the positive one. You can also just test for voltage at the amps +/-, but that can be decieving if it is finding a path to ground through the signal cables it will still show 12v... but as soon as any current goes through it, it's toast. Unplug the signal cables and speaker wires then test.

Next to that, perhaps it is just clipping badly and the Focals are sensitive. Its hard to say over the internet. Someone needs to troubleshoot it.


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## ChazMichaels (Apr 30, 2010)

Thanks for the input, good ideas there. I put an O-scope on the signals and turned the volume all the way up and gained up the kicker device, no clipping was observed (voltage measured around 1.3VRMS). 

I have a pretty low-fidelity multi-meter, but I checked the the ground point and with the longer leads, meter was showing around 0.7-0.8 with a 'direct short' between the leads. At the ground point it was showing around 1.2-1.3. The point was bolted and the paint was sanded off. Not sure if this is reasonable (or accurate for that matter given the 20 dollar meter I have). Max power and 80% efficiency suggest 93A @12V, which at 0.4 ohms would have a voltage drop of 37.2V, probably unlikely to be pulling max power, but even at 30A that's a 12V drop (not including resistance of Positive line connect). Those voltage drops seem extreme so either the >30A is unrealistic, my measurements are bogus, or there's a problem (guessing bad meas.). Long story short, not sure if the measurement made indicates a problem, obviously the JL works fine and plays plenty loud. Next step will be to measure the terminal voltage during regular operation to see if a sizable voltage drop is present. The Focal is rated at 75W vs. 100W for the JL, but that's A/B power vs. D for the JL, so it's probably pretty close to the power draw if not a little more than the JL, so whatever voltage is at the terminals of the JL should be similar to the Focal operation point. I did measure the ground of the RCA cables versus 'car ground' and it showed 6.4k, so I would think it's fairly isolated. 

Maybe the terminal voltage will give some more insight. It's buried a bit so it'll take a little more dismantling to get to it. 

Thanks again.


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