Car Stereos: alpine MRP-F600 amplifier, sony head unit, volt range

Question
hi
i got my alpine MRP-F600 amp installed professionally at the same time as my new sony head unit. the amp is running 2 6" alpine R series speakers which are bridged across channels 1/2 and 3/4. after about a month of using the sound system, the front speakers would start to cut out for a about a second or two and then cut back in. i had a look at all the wiring in the car from the battery all the way to the head unit and then to the amp and then to the speakers but couldnt find any dodgey connections. the gain on the amp is running on the minimum it will go. what could be the problem?

Answer
Hi Sam,

I'm not certain what's causing the problem, but I'll try to speculate a bit.

It doesn't sound like the issue is caused by a problem in the signal chain wiring (by which I mean the wiring that carries the actual sound).  The left and right channels are separated at the head unit's RCA outputs, and they're driven separately by the amplifier.  If you had a problem with the RCA or speaker connections, I doubt that you'd be getting problems with both speakers at once.  I could see a bad RCA or speaker connection causing a dropout on one speaker, but not both simultaneously.  

It seems more likely that the problem originates with the amplifier or the head unit.  Of the two, I'd suspect the amplifier.  It's possible that your problem is occurring because of a voltage drop on the power line to the amplifier.  If the voltage drops too low, the amplifier shuts off for a second until the reduced current load causes the voltage to rise again.  This is especially likely if the speakers are cutting out on musical peaks, or at especially high volume.  

One way to troubleshoot would be to use a multimeter to monitor the voltage on the amplifier's power terminals while the music is playing.  If you're seeing the voltage dropping down to the 10 volt range, then I'd repeat the test at the battery terminals.  If there's not a significant voltage drop at the battery, then there would have to be a point of resistance somewhere along the power line.  The most likely trouble spots would be the amplifier's chassis ground connection, the fuse and fuse holder, and the battery terminal connection itself.

On the other hand, if you don't find a significant voltage drop at the amplifier's power terminals, then I'd suspect a defective amp.

Hope this helps!

Brian