Expert: Cleggsan - 7/16/2009

Question
I got a Brutus 2600 watt amp connected to two 15" L7 speakers.  The speakers are in a enclosed case bridged to 1ohm and the amp is also bridged.  I have all this connected to a Optima Yellow Cap battery.  Whenever I turn up the bass pretty loud, after a minute or two, the amp will stay on but it will go into protected mode.

It just started doing this. I am told it could be either the amp is dying or my alternator. What do you think? Or how can I diagnose further?

Answer
I know the Brutus is supposed to drive safely into 1 ohm, but that is pushing them hard.  And, with heavy bass the cap may be discharging after while and the 12v gets dragged down due to the heavy current from the battery and/or alternator.  The impedance of these speakers may drop down below the 1 ohm at points near resonance, too.

So, I suspect you are just plain overloading the amplifier and the 12v system.  You may need to
a) rewire the speakers for 2 or 4 ohm impedance (sound will not change much; maybe not even noticeable).
b) increase the power cap
c) get a stronger battery in the vehicle
d) up the capacity of the alternator
e) increase the size or gauge of the wire from battery to amp.

Hope this helps.

C
PS: It is easy to determine what is going on.  Get a VOM (you can buy one for under $10 as Home Depot or Walmart) and monitor the 12v line at the amp when under heavy bass output to see how much drop you are getting.  And, with the ohmmeter you can check for shorted line or speaker - one of the great causes of protection activation.  You could have a shorted turn in one of the voice coils from overheating and never know it until you check the dc resistance of the coil.  Just compare one with the other.  You should have 4 coils amongst the 2 woofers and the should all read the same resistance.  You must disconnect the wires from the woofer to measure the dc resistance and they should measure just a little less than the rated impedance of the coil.