HU has 5V preout and amp has 4V input?

[squeak9798 5,000+ posts]

My HU has 5V preouts, but my amp says input is 100mv to 4 volts, will this cause damage to amp

You are fine.

Listening to music at any reasonable volume level, your headunit will never output a full 5v. On highly dynamic music at very loud volumes, it may reach close to 5v for milliseconds.....not enough to cause any problems.

I used an 8v deck with an amp that had a maximum input level of 1.5v with no problems.

 

[jer_stud56 10+ year member]

Hook it up, you'll be fine.

Good question, never thought of it before, but you shouldn't have an issue.

 

[helotaxi 5,000+ posts]

Only time you need worry is with the volume maxed (and probably the bass as well) playing a test tone. That is the only time you even see rated voltage out of a deck.