Just got my DSC4125 and...

[jgruberman 10+ year member]

The "Input Level" knob range on the amp is 6V to 0.2V. Turned all the way down(counter clockwise) is 6V, and up(clockwise) is 0.2V.

Few questions about this(so I can refresh my memory):

1. The input level knob should match the preout voltage from the deck correct? Mine is 4V preouts, so the know should be set somewhere in the range of where 4V is... right?

2. If turning that knob clockwise turns the volume up and makes things louder, shouldn't the 6V be on the high end of the spectrum and the 0.2V be on the low end of the spectrum? Or am I missing a general concept of how the Input Level works on a technical level

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[DarkScorpion 10+ year member]

In theory, yes, you're supposed to match the output voltage of your deck. However, that is almost never the case - the 4v rating is usually attained by the manufacturer when the deck is maxed out and most likely clipping the signal. There are many, many different ways to set your gains; the most common ways are via DMM, oscilloscope, and by ear. All three have their merits as well as disadvantages - you'll have to do some reading and use your own judgement.

The gain knob shouldn't be used as a volume knob. While yes, it does increase the output, it shouldn't be used as such - it should be set once and not touched again unless you're retuning. The reason why 6v is counter clockwise and .2v is clockwise is because if your headunit is putting out a higher powered, 6v signal, you shouldn't need to turn the gain "up" as much versus a .2v signal in order to achieve the same output. The marking on the amp is the voltage of the input signal. A higher voltage signal doesn't need to be turned up, whereas a low voltage signal does, in layman's terms.

 

[jgruberman 10+ year member]

That's some good information right there. That also explains why I seem to have to turn my knob a bit clockwise, because the preamp outs in the car are only 2v until I upgrade this week.