Expert: Ernesto R - 2/3/2011

Question
I have a 2003 Toyota 4runner with the JBL Synthesis Stereo System.  This is a 10 speaker system, that is controlled via factory amplifier located near the rear of the truck.  The amplifier is supplied by a left and right preamplified signal from the factory head unit.  I am attempting to add an aftermarketed 4 channel amplifier to run the factory subwoofer and front door speakers, while preserving the factory amplifier to power the other speakers in the system.  To do this, I spliced into the Preamp output of the head unit and ran this to my high level inputs on my amplifier.  After some investigating, I see that this will not work, because it is a preamp signal and not high level output. The voltage on the preamp output from the HU seems to be VERY low....like 5 millivolts when measured.  My question is this:

Is there a way for me to use this signal? Does it sound typical that the output voltage of the preamp is really only a few millivolts?  Can I convert these wires to RCA cables and run them directly to my amplifier low level input, or will I first need to increase the voltage somehow?

Thank you

Answer
No don't do that, thea to  radio sends a very small fix signal and it also sends data
to the amplifier to adjust the signal,

it is best to get the signal after the amplifier, use 2 hi/low one from the front channels the other on the woofer channel you can link l and r from the same output ( bass is mono )

use 2 of this  http://www.oemautosound.com/pc-575-132-pie-2-channel-high-to-low-converter.aspx

the signal from one blue cable one can turn on both amplifiers