Car Stereos: amp switching to protect, ohm subwoofer, load impedance

Question
Hey Brian, I am having a problem when I turn the volume and bass up.  My amp switches over to "protect" and that kicks off the subwoofer.  It seems to do it only at higher volumes.  I already went through and checked all of the wires and connections and even replaced the ground wire with a new one.  could you help me troubleshoot this?  I appreciate it.
My setup is:
Stereo - Pioneer DEH-P4000UB
Amp - Jensen KA-2
Sub - Pioneer TS-W302R (brand new)

Thank you

-Blake

Answer
Hi Blake,

Usually, when you have an amplifier going into "protect" mode, it's caused by a problem with the sub, or subwoofer wiring.  In most cases, either the load impedance is too low, or the sub has an internal short. This causes too much current to flow through the amp's outputs, triggering the protection circuit.  The problem can also be caused by sloppy speaker wiring--if there's a strand or two of wire that's crossed over between the terminals, at the amplifier or the sub, that can send the amp into protect mode as well.

In your case, the load impedance should be fine--you have a single voice coil, 4-ohm subwoofer, and it should match up very well with your Jensen amplifier in "bridged" mode.  It's possible that there's an internal short in the subwoofer--sometimes there's a fault that doesn't cause a problem until the sub's cone reaches a certain point of excursion.   This can make it very difficult to troubleshoot the problem, because there's no practical way to test a sub's voice coil for shorts all the way through its excursion range.

I'm also inclined to suspect the amplifier, simply because I ran into a similar problem with a Jensen KA-series amp a few months ago, and a defective amplifier turned out to be the cause.  

In a case like this, all you can really do is try to substitute components. If you have another 4-ohm, single voice coil sub available, you can try connecting that to the amplifier and see if you get the same results.  In my shop, I have "dummy-load" 4-ohm resistors that serve the same purpose.  Or, you can try the sub on a different amplifier.  I'm doubtful that your problem is wiring-related (although you might want to double-check the speaker wiring); it's likely to be a defect in the amp or the sub.  My hunch is that you have a bad amp, but the only way to tell for certain is to try a different one.  

Hope this helps!

Brian