sorry to post on the sub section but no one ever posts on the hu section. i am considering 2 hus a pioneer deh-p660 and an alpine cda-9825. the pioneer has more features but only has a 2 volt preamp output and the alpine has a 4 volt. please explain the importance of a preamp output and the difference it makes and recomend a hu.
There is a pretty big difference between the 2V Pioneer and 4V alpine head units. There is less chance of introduced noise into the system when you have a higher preout voltage, but the impedance is important as well. It just isn't as noted as voltage is. Inductance can occur with RCAs since your car contains numerous electrical devices, and a higher voltage is more resistant to inductance. Also use high quality twisted pair RCA cables. A higher voltage also lowers the noise floor, basically it allows you to set the amp gains lower, meaning the amp won't introduce as much noise into the system. It's important, but not the end all be all of choosing a head unit. You can run 2V lines and still not have noise in the system (at least not noticeable noise), if features and ergonomics are more important to you, then choose according to that. If utmost SQ is your priority, you'd be better served with the Alpine more than likely, not just because of the preouts though.