[hairlesshobo]

Originally Posted by jimmydean

Android tablet run to a line driver/crossover then to the amps. You could go headphone to RCA straight to the amp, but the signal from the headphone jack is weak. A line driver to amplify the headphone signal is the way to go.

For conversation sake, I have a question about the line driver portion of your setup. Please read the whole thing first before you think that I am trying to say you are wrong because I am not - I am merely curious.

You are sort of correct when you say that the headphone output is week, at least in relation to a lot of modern head units. In comparison to standard line level, the headphone jack is usually right on par (with the exception of some really cheap players with weak internal amps). Headphone output on these devices is typically ~1 volt RMS, give or take a few hundred millivolts. The only reason that it may seem that the headphone output is weak in an automotive environment is because a lot of head units nowadays have a 2v, 4v, or a lot of times 6v "line" out. While this is a nice feature for sake of minimizing noise in the signal lines, it's actually much higher output than what a real line level is.

The reason that the 6v line level works is because a lot of amps, crossovers, EQs, etc in the automotive world also support it. This variation in "line level" voltages is the main reason that the gain control on an amp exists. The gain control allows you to adjust each amp individually to match with fellow amps, as well as reduce clipping. Remember, gain is not volume control. For example, if you have an amp that is capable of up to 6v line input, and you are using a 6v head unit, if you turn the gain all the way up on the amp, it may "seem" louder, but in all actuality you are just over driving the input and causing the amp to clip.

I say all this to say that with almost all amps and automotive audio equipment, they are prepared to accept a signal input of between 1v-6v for sake of compatibility with all head units. With that in mind, almost all equipment if properly calibrated and tuned, will work just fine with a "lower" 1v input. By properly calibrated I mainly mean that the gain on all amplifiers and crossovers are set correctly.

I am curious to know what gear you are running in particular that wouldn't work to its full potential without including a line driver with the rest of the system.

If there is something here that I am missing or forgetting, please tell me because I don't want to come off as an jack@$$.