Audio Systems: car audio fault finding, bench test, channel amplifier

Question
hey again,
            i havefound out that all the speakers that are connected to my 4 channel amplifier (which are a pair of splits up the front and a pair of 6 inches at the back doors) are all cutting in and cutting back out. they dont completely cut in an dout but just drop off the volume a bit every now and then. when i turn the volume right down i can hear a fuzzy sound coming from the speakers. when the speakers cut out when the volume is on they go a bit fuzzy as well then when it kicks back in it goes back to being perfect. i have tightened all connections at the amp but it still does it. what do u think is wrong with it?

Answer
Let me suggest some isolation tricks:

FIRST:  Try to determine if it is the amp or the head end.  You can do this by momentarily pulling the cables between the head unit and the input of the amps.  Then, feed the amp with a portable cd or cassette player; that way you have a known source going into the amps.

SECONDLY: Then, once you know whether it is the head or the amp you can attack that one.

NOW: I actually suspect the power line voltage is fading for some reason.  Best way to check this would be to pull the one that you are suspecting (head or amp) and bench test it:  Run some wires directly from the battery to the unit on the bench; hook up a stand-alone speaker to the amp, etc.

The above procedure should allow you to get to the bottom of it.  Then let me know if you need more sluething.

Cleggsan