setting gain with oscilloscope

My guess would be to test your Headunit outputs first and see where they clip and go down a few notches, then hook the headunit up to the amp and turn the gain up until the output almost clips. But im sure there is a far more detailed method. 2003 Chevy Avalanche,Eclipse CD7000,Morel Elate 5,Adire Extremis,Alpine PDX-4.150, 15" TC-3000, 2 Alpine PDX-1.1000, 470Amp HO Alt.

if the rca outputs are clipping than you will be able to tell by hooking up the scope to the amps outputs...they will be clipped also

The quick way to set unity gain with an oscilloscope: start with scope connected to amp output and input gains all the way to minimum.  Play your test tone CD and slowly turn up HU volume until you start to notice the waveform being clipped.  This is your max HU volume setting before the onset of clipping.  (Note that some high quality HUs today will not clip their outputs at all.  In this case, simply set the HU to about 80% of whatever it's max might be.)  Now slowly increase the input gain setting on the amplifier until you reach the target output voltage for the amp's power rating into your speaker load, or until the waveform starts to clip whichever comes first.  You can actually go a bit past this setting and introduce a small amount of clipping (no more than 10%) as most people will never hear this and it will allow a bit more usable output from the amp.  If you want to be more precise, you can also scope the line level outputs from the HU and set the volume for max rated voltage output level before you scope the amp.  After you have set this basic level, change the CD to play some frequency sweeps or pink noise and re-check the amp output.  If you notice significant clipping, reduce the gain setting until it clears.  The real power of using a scope comes from being much more precise than a volt meter, and also a scope makes it much easier to adjust settings to match the output levels from multiple amps.Support the12volt.com

Wow DYohn -- That's a great explanation. Very helpful. I was wondering how this worked and that cleared it up!