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New HU installation in 94 w/ JBL system

Sscolax

Member
Joined
June 5, 2006
Messages
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City, State
Colfax, CA
Year, Model & Trim Level
94 Eddie Bauer
A couple of days ago I replaced the factory radio in my wife's 94 Eddie Bauer with a new Alpine and retained the use of the factory JBL speakers, amps, and sub. The original setup still sounded great, so I figured there was no point in replacing anything besides the updated radio itself. I thought I'd share how I went about wiring it up.

I researched several online sources in addition to the factory shop manual to get details on the factory wiring, specifically the function of each wire running from the radio to the speaker amp. I discovered that every piece of information I ran across was either incorrect or incomplete. I finally ended up using an oscilloscope to help determine the characteristics, function, and polarity of each of the 8 wires in the grey "signal" harness that carries the audio to the amp. I was pleasantly surprised to discover that the only thing required to properly match the new radio's audio output to the amp's input was a handful of resistors. The "High-Power" speaker outputs from the new radio run at about 3 times the signal level of the factory radio, measured with the amp disconnected. I installed a 100-ohm resistor on the end of each speaker wire on the new radio, then connected the free end of each resistor to the matching amp input wire. I also connected another 100-ohm resistor between the points where each input pair into the amp connected to the previously-installed resistors, which served to attenuate the signal to about 1/3 strength. Finally, I connected the shield from the amp's audio cable to the radio's ground.

I used a 7805 5-volt voltage regulator to reduce the amp-on line from the radio from 12 volts to the appropriate 5 volts that the amp is designed to receive.

The end result was a new radio that sounds just as good as the factory one did, with the added benefit of aux and usb inputs and other modern features. In retrospect, however, I realize that I should have used a lower value resistor, probably around 50 ohms, between the positive and negative signal wires running into the amp to further attenuate the signals because the audio level is significantly higher than the original radio at similar volume settings. This discrepancy is possibly due to the measurements I took without the amp being connected. I may go back in sometime later and replace the resistors, or perhaps add another 100 ohms in parallel to those that are already there.

I'm attaching a diagram showing how all of the wiring was done.
 

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