Originally Posted by Jeremy_84_F41

I feel like this is a stupid question but I've always been curious. Basically, I am wanting to put together a simple system for my daily driver. My head unit has 4v preamp outputs and I have an amp that says it's input voltage sensitivity is 2.5v.

Will I just need to turn the gain way down? Will I have sound quality problems? Thanks guys.

Originally Posted by Jeremy_84_F41

I've seen several amps that state their sensitivity ratings, the amp in question is my old Soundstream USA204 4-channnel amp. I also have been looking at a particular Directed amp and it states a range of 175mv to 8v.

I agree with you, it seems the last thing to worry about when choosing an amp. Perhaps it was used as a selling point from a time when there was no such thing as more than 2.5v from a head unit, I don't know. I've always been under the impression that the more voltage you have, the cleaner the sound going into the amp will be, and that's that.

Originally Posted by Gummie

I’m guessing that higher input voltage leads to better SQ because amps have a lower noise floor than headunits. I’m looking into it (got me curious). I will be sure to post my findings.

Originally Posted by sr20dem0n

(responding to: I would assume that because of the higher voltage, you dont have to have the gains as high, and that would not amp the noise the rcas pick up as much, so that the signal to noise ratio stays higher, thats bout all i can think of)

That's exactly it, the one and only reason why high voltage preouts are "better"

The lower gains don't lower distortion or anything else, they simply lower the amplitude of any noise that was induced in the rcas on their trip from the headunit to the amp. If you don't get audible noise and you're able to hit full output with your current gain setting and preout voltage, you will gain absolutely nothing by moving to a higher preout voltage. Most installs are fine with 1v or greater, if yours isn't then fixing the install would be a better choice than moving to a higher preout voltage (it's like a bandaid fix).

One thing many people don't realize is how little of that preout voltage they're actually using. You only get the rated voltage at your headunit's maximum, unclipped volume, which is often at 90-95% of the range. When people set their gains at 75% which is recommended so often, they're setting their gains with a preout voltage that could be as low as 1/5 the rating (your 4V preouts are now .8V preouts), or maybe even lower. Then they go out and rave about how their 4V preout is so great because they don't get any background noise, but what they don't realize is they could have got the exact same result using a headunit with less than 1V on the preouts by setting the gain properly. Preout voltage is one of the most overhyped headunit specs out there.