So my thoughts regarding input voltage just got trashed, (I think). My head unit is a Sony DSX-MS60 that has an output of 2 volts, thinking higher output voltage would give me louder, clearer sound. the Sony MEX-M100BT provides 5 volts output plus supports FLAC and WAV, so seems like a no brainier.

The amp is JL MHD 600/4, it supports up to 8 volts input, the two position input voltage switch Low/High accepts 200 mV - 2 V and 800 mV - 8 V,

So thinking I install the MEX 100 set the input to high and life would be good. Then I read this statement in the amp manual


Did someone just take a shot at the unicorn?

 

That switch is for high level ( head unit speaker output)

 

Also for high level preamp, So the 5 volts fall between the range 3 volts either side. Will 5 volts going into a 2 volt max input just cause me to reduce the sensitivity on the amp?

I'm glad you guys are here, the more I dig the deeper I get.

 

it was my understanding that higher input voltage = less gain needed which lets the amp do less work

I also thought that a higher input signal would be boosted less and thus you would get a cleaner sound as you're not boosting a lesser dirtier signal (in my mind that works, not sure if that's really the case).

I do know that when I boosted the output with my Line Levelers (same idea as a line driver, and in some cases the DSP's) it sounded better with my TM400x4 than it did with my 600.4. Not sure if there is something magic in the TM400x4 that does something to the signal or not. I just know what my ears hear, this is the only way I can answer it.

 

Sounds like you found a good combination that pleases you're ears.
Time to...

 

Just got off the phone with JL audio, man I had brain fart, the manual spells it out,

High Voltage on the input