Expert: Cleggsan - 8/22/2008

Question
help!!!  I have a 97 s-10 single cab, w/4 lighting audio 10" subs on a kicker 300.4 on a pioneer head unit. humming sound is driving me nuts. i've tried switching head units, rca's, power wire, and still nothing, even asked the local stero shops and they have no idea. can u help???

Answer
You must find out where the hum is coming from.

It is obviously at the speaker outputs of the amp, right?

But, is it at the input of the amp? (or output of the pioneer head unit?).  Do you know how to check it?  Do you have a vom?  Do you know how to use it?

You can purchase a vom that is good for car audio work at Walmart or Home Depot for under $10.  With it you can measure the ac voltage down to a few tenths of a volt. I don't know if you can measure the input voltage to the amp but try it.  Make sure it is connected properly by listening to music, then with the volume at minimum measure the ac voltage at the input. You may have to open the cover so you can touch onto the input lines to get at the audio signal.

A good test is to turn the volume all the way down to zero. If you still have hum it means the hum is coming after the volume control. If the hum level goes up and down with the volume control it means the hum is infront of the volume control. If there is no level volume control on your external amp then the one in the head unit is the one to use.  If hum goes up and down with volume it means the hum is coming from the headunit or a grounding problem associated with the head unit installation.

Another test would be to put in a substitute amp; connect it in place of the one you have in the rig and see if hum goes away.  If you do not have hum with the test amp that will point to the amp in the car as the trouble spot.

Then, there are many general things to look at.  Here are some good installation ideas from crutchfield.com that might help.
http://www.crutchfield.com/App/Learn/InstallationGuides.aspx

Hope these ideas help you investigate wisely enough to get it resolved, but if not, come back to me with your findings so I can have the additional information to help figure out what is going on.

C