Hey Guys,
I just wanted to add my
to Matt's write up so it's part of this thread for people that may be thinking about upgrading the factory bose setup with navigation. I had a slightly bumpy road, but ultimately was able to upgrade successfully - and want to share how I got there.
I was part of Matt's "California Builds" recently - and wanted better quality audio all around, while retaining my factory nav/head unit. I quickly found out that I didn't have any options w/ swapping the head unit for reasons noted above.
So I opted for an MTX LOC which was reasonably priced (MTX RE-Q5) as the interface between my Bose head unit and new amplifier (Alpine PDX-5). We bypassed the factory amp and went straight to the RE-Q5 and then to the Alpine. We DID encounter problems w/ the MTX unit (faulty harness) - so I had to get another one mid-install. Definitely not fun scrambling to find one locally, but I was able to. The alpine amp was powering Image Dynamics components (door speakers/tweeters), and an Image Dynamics Sub.
This is where the problems began - alternator/engine whine. If you've never had to deal w/ this - it's a gnarly constant whine that persists whether the stereo is on or off...and amplifies as you accelerate. It can quickly drive you up the wall!
Matt double checked all grounds, but that was not the problem. Upon research, we found that many MTX RE-Q5 users experienced the same thing. Whether a higher end unit (JBL MS-8; Rockford Fosgate Three-60) would have avoided the whine - I can't say for sure. I would, however, recommend one of those higher end units as they would be MUCH easier to tune the system...but more on that later.
So finally, I had to use trial and error to find/resolve the source of the engine whine. I initially tried an inline power noise filter at the battery terminal (the MTX was fed directly from the battery). That didn't work. Next, I tried an inline power noise filter near the MTX; along with a ground loop isolator. I also separated any power and audio cabling w/ simple ducting. VOILA - engine whine gone!
I was happy at that point, but still a little unsettled w/ the overall tuning of the system (didn't feel the bump in the sub and front speakers were too loud relatively). I increased gains at the amp, played with the crossover frequencies and gains on the RE-Q5, and fine tuned w/ the factory audio controls - and FINALLY, I felt very happy w/ the result. As mentioned earlier, a higher-end LOC would have probably made the final audio adjustments easier (MTX has simple/cheap knobs you adjust w/ a screwdriver). That said, I have a hunch I would have still had to deal w/ eliminating engine noise which stems from having to amplify the factory Bose levels, which as Matt mentioned, are output at odd levels.
Matt and I ventured into this knowing we were entering uncharted waters...but I'm thrilled to finally have an upgraded system w/ the factory nav/Bose system. Significantly better clarity, imaging and bump
. Hope this helps anyone looking to upgrade...
-Lohit