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Old 12th April 2015, 06:39 PM   #1
phase is offline phase  United States
diyAudio Member
Join Date: Oct 2004
Default Factory head unit mods

I got a new car recently(2009 Corolla xrs), and was a bit surprised by the way the stock 6 cd stereo sounded. After playing around with some TA8201 based car amps, with an iPad source, I knew that the roughly 10w systems could sound a lot better.
After taking a look around for schematics on the web, and at a dealer that was willing to look, I had nothing, so I got out the magnifier and started to poke around a bit. The njm2115 op amps were probably part of what I was hearing, or not hearing, along with some pretty tiny capacitors for the processor, op amps, and the amp.
Replaced the op amps with some Phillips NE5532 I had left over, decoupled with some wima fkp1 on the pins, and an Elna Silmic ARS 100uf/50v. The digital supply to the processor has a 220uf/50v Cerafine, bypassed with an FKP wima, and the amp has another Silmic ARS as well.
The power pins coming in from the connector have a total of 10k uf and a snubber circuit using a Russian polystyrene.
Sounds amazing at least in comparison to what it started out like, and now I'm hoping the magic won't be lost when I swap in different speakers. I'm willing to bet the eq built in to the stock processor is set to compensate for those wonderful stock speakers...
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Old 15th April 2015, 01:33 AM   #2
phase is offline phase  United States
diyAudio Member
Join Date: Oct 2004
Update; Cerafine has been removed after some burn in, too much odd detail, was hearing some peaks filtered by the effects of those, switched in a Panasonic PX left over from another project, and things are much smoother on the top end with plenty of detail, and a pinpoint punch to the bass notes, better bass detail in general.
Time to refresh the Nakamichi PA300 for use with some infinity 6.5, and old JBL titanium 035 tweeters.
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Old 16th April 2015, 01:52 PM   #3
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Join Date: Feb 2006
Location: Ft Laud. Fla
JL Audio has a product called Cleansweep that dsp-processses out the factory EQ.
If you get further into things, you may want to consider it.
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Old 17th April 2015, 02:03 PM   #4
phase is offline phase  United States
diyAudio Member
Join Date: Oct 2004
Thanks, I did recently see an Audison bit ten for $170 on eBay, it went quick though.
So far just improving the quality is working pretty well with the factory dsp, but I know it would likely be better with a flat eq.
The Nakamichi is sounding pretty good with the bias turned up running on the bench now, and my loc arrived, so it won't be long until it comes together and I will be able and tell if I am going to need to do that or not.
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Old 3rd June 2015, 03:19 PM   #5
phase is offline phase  United States
diyAudio Member
Join Date: Oct 2004
It's all installed and I am working on the passive crossovers now, am cloning the JBL 4408 2-way studio monitors, since they had the same titanium tweets. Using the same JBL design, but with better components, so far is pretty sweet with the modded nakamichi amp.
The 6.5" drivers were from my infinity 62.9, with the original tweeters removed and some better fitting phase plugs installed. Speakers are in the factory locations in the A pillars and doors, with some damping treatment to the doors.
If I were to be anticipating a bunch of upgrades, I would move towards an active setup, but I just want something that will look and work like the factory stereo, but with much better sound.
Sub install to follow the crossover tuning...
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Old 9th July 2015, 07:05 PM   #6
phase is offline phase  United States
diyAudio Member
Join Date: Oct 2004
Well I don't think I will be needing any more processors, the setup sounds great. Those Russian polystyrenes take forever to kick in.
After things had begun to work in a bit, my doors needed some more work, the sheetmetal was the thinnest I've ever seen, maybe even as bad as the Renault R5 from many years ago.
An unused cutting board worked very well attached to the inside of the door struture, tight, clean bass.
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