Expert: Cleggsan - 8/20/2008

Question
I'm having problems with the stock system in my 2003 Mazdaspeed Protege.  Kenwood KDC-MP919 head unit, Kenwood KAC-529S amp, and stock sub. The sub is not working. I originally diagnosed the problem as a bad RCA connection. I pulled the head unit out and reattached the cables and everything seemed to be working fine, but then after about 10 minutes of driving it gave out on me again (no weird noises, the sub just stopped working.) I then pulled everything apart, checked the sub connection in the box, checked the fuses, power light in the amp is on...everything seems to be fine. I went back to the original problem, RCA cables. I tested the system with a new set of RCA cables and everything worked fine again so I installed the new cables. The system worked fine in my driveway for a few days and then when I took it out for a drive, it stopped working again after a few minutes of driving.

(RCAs are connected to the correct NF cables behind the head unit and the NF button is ON)

Any ideas??

Answer
Yes.  I don't like the NF cables nor Monster nor Noel Lee the president as they are not good cables.  Switch to conventional el-cheapos and they will do you better.  The ones you get at the dollar store are just fine for car audio purposes; of course, they must be long enough to do the job.

The amp may be going into protection mode.  This amp supports a 2 ohm load, supposedly.  Have you checked the impedance/resistance of the sub? And have you checked for shorts in the speaker wiring or connections.  The main reason for sub amps going into protection mode is either a speaker load too low for the rating of the amp or a shorted voice coil or wiring.

And, the amp may be voltage unstable. If you have a VOM you can check the voltage getting to the sub amp; make sure it is staying over 11v during normal operation and should go to around 13v or more with engine running at road speeds.  If the voltage drops too low (like when strong bass signals are being pumped to the subwoofer) the amp can dropout.  If the power wire coming from the battery is too small the resistance can cause too much voltage drop.  Solution on this one is to use bigger wire; 6 or 8 gauge.

Check your battery voltage when car is on the road, also, with the VOM.

Also, have you tried an alternate subwoofer to see if it fails in the same way with the alternate?

Let me know more of the story after checking these items.  I'm sure we can get to the bottom of it.

C