Car Audio - Differential balanced to both stock amplifier and aftermarket subwoofer amp

[danweast]

Hi all, I can't for the life of me figure out if there is a good solution to this problem and I don't have the time to get reading on electrical books.

I'm upgrading the bass in my vehicle, I don't have the budget to replace the entire system. In my research the factory amplifier is applying equalization and crossovers before sending power to all the drivers--thus, I want to avoid getting a high signal from the speakers if possible. That means trying to get a signal from the factory pre-amp before the amplifier. In this vehicle, it's a differential balanced connection.

I read somewhere that attempting a connection to that differential line in parallel to my subwoofer amplifier, similar to tapping into a speaker connection, causes 'double termination' and will induce a lot of noise. Their solution was to get their magical harness they designed, which they don't make anymore--nor did it do what I want, which is to connect two of the channels to both the factory amp and my subwoofer amp.

Is there a sensible way of making this connection happen? I'm okay with a minimal amount of noise--this is a car after all, I'm not intending for super high SQ until I replace everything down the road, but if it's mass hissing because of some loop going on then clearly it's not going to work. Thoughts? Thanks!

 

[AudioStudies]

JL Audio manufacturers some devices designed to detect and remove factory amp equalization. Not cheap though, I think in the $400 to $500 range.

 

[preload]

Many JL car amps have differential-balanced inputs, so in theory they would be plug and play. BTW, if you haven't checked out the JL VX-series, they all include a DSP with full parametric EQ, crossover, and gain controls that you can configure with your smartphone (via BT) or via your laptop (via USB). This will allow you apply "room correction" to your sub as well as take up less space (they're relatively compact class D amps and don't already include the DSP "box.")

 

[danweast]

Thanks guys. JL was already my amp of choice, I guess I should have specified that. Their budget JD line now supports diff. balanced. I pulled the plug and got the amp to test, because I wasn't sure if there would be an issue running it in parallel with the stock amp or not--the verdict is, well, I'm not going to use it anyways; apparently the HU is also delegating volume control to the amp over the data lines--in other words, sound was passing through to my subwoofer at full volume even if my HU was muted. Weird stuff.

It seems the rear speakers aren't high-passed when I tried it before I quit for the night, so I'm guessing they will be my best bet to have signal AND for it to follow volume control. Oh well, such is life.