Stock HU Now Has RCA Pre-Outs! This is no Joke...

tschanrm

Member
In the ongoing saga of dealing with the 2003 P5 Head Unit, this final chapter deals with the most serious problem of the stock HU; lack of RCA pre-outs. Previous discussions are here:

http://www.msprotege.com/forum/showthread.php?t=123617920

and here:

http://www.msprotege.com/forum/showthread.php?t=123618617

Lack of rca pre-outs means that if you want to use an external amp you must go from line-level--->high level--->line level--->Amp (with use of a LOC). By having straight pre-outs you completely bypass the chip amp, giving you a nice clean sound: line-level--->Amp. The solution- add the pre outs yourself! I did this, and am very pleased with the results. If anyone wants try this, PM me (requires good soldering skills though). Basically, I spliced the line-level out from the volume control chip, Mitsubishi M62490FP (data sheet at www.alldatasheet.com). The biggest reason for doing this is to bypass the chip amp's non-linear frequency response. The chip-amp also increases THD (total harmonic distortion) as frequency increases. So at 1w 100hz will have only .05% THD, but 20khz will have .2% THD. By using the RCA pre-outs, distortion will also be reduced to about .03% THD for the entire 20hz-20khz band.

Before RCA Mod:
-Speaker level out---> LOC
Frequency response (from 40 Hz to 15 kHz), dB:+3.29, -1.13


Output with RCA pre-outs
-Straight RCA out
Frequency response (from 40 Hz to 15 kHz), dB:+0.38, -0.54


Ignore the slight .2db hump at 60hz. I had to use a bench power supply that ran off 120 AC house voltage, and 60hz is the oscillating freq. of 120v AC.

Here are some pictures of the unit now. I wanted to keep this as cheap as possible, so I used some RCA cables from another stereo.

Wires about to be soldered into the board:



Back of the head-unit


-It was ironic how there was an open hole in the back of the HU for the wires to fit through.


Conclusion

The saga ends. I have finally created a HU with as good of sound quality as aftermarket HU's, but without the fear of theft. I think the stock HU compliments the interior pretty good as well. Best of all, the 6-disk in dash cd changer and MD player can be kept in the car. I hope you found these posts informative. :)
 
Nice idea....Good job....Now get to doing the How-To...:)
 
sweet. i hate the fear i always have of someone steeling my HU. and i get even more scared when i go out to my car and the alarm chirps telling me that someone set it off.
 
Hmm. This is very interesting. What voltage output do you get from your RCAs? Most high end aftermarket units put out 4v RMS. Is the unit still operational after you perform this mod?

I'd be curious to find out the difference in SQ between this and my Clarion head unit. Granted I get a 3-band parameteric EQ and 24-bit DAC with the Clarion but if the stock unit with these pre-outs sounds good I'd be willing to make some sacrifices. I do miss the red-orange glow of the stock unit.

Edit:
Looking at your frequency response charts, the rolloff is pretty early. My unit handles 5Hz-20KHz +/-1db in . Your chart shows -3db at 30Hz. Could this be caused by a built-in HP filter? If that is accurate, it leads me to think that the stock unit will need some serious bass boost to get a smooth subwoofer response down to 20Hz....or a JL Audio CleanSweep.
 
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Thanks for the comments everybody, I really appreciate it. :) Like I said earlier, if anyone is seriously interested in doing this, please PM me. This is not an easy thing to do, as the motherboard on the stock HU is tight. Some of the connection points used are close to SMD components, and messing up SMD parts would mean the whole stereo is shot (it is hard to get replacement SMD components, and even harder to solder new ones back in!). This is why I fear making a How-to; people getting mad when something that seems so irrelevent gets burned out on the motherboard causing nothing to work.



chuyler1 said:
Edit:
Looking at your frequency response charts, the rolloff is pretty early. My unit handles 5Hz-20KHz +/-1db in . Your chart shows -3db at 30Hz. Could this be caused by a built-in HP filter? If that is accurate, it leads me to think that the stock unit will need some serious bass boost to get a smooth subwoofer response down to 20Hz....or a JL Audio CleanSweep.

Chuyler1,

The datasheet for the Mitsubishi M62490FP chip claims to have a max voltage output of 2.2v RMS. That's not stellar, but still pretty good considering this is a stock head unit.


Also, the RMAA frequency response chart does not show a -3db drop at 30hz, it shows a -2db drop or better at 20hz (please see below for further explanation). Granted, this HU should not be used for SPL competitions, but this HU still provides impressive numbers. Keep in mind that manufacturer claimed specs are far from reality. Look at this freq. response for the Alpine CDA-7892. It claims 5-20khz with +/- 1db:


-By looking at the bottom of the picture, you can see that it is already -.8db and -.6 db at 20hz. Not shown, but at 10hz it has dropped down to -3db and -2.9db. This test was done with a professional sound card too, an Echo Layla 24/96. The tests with the stock HU were done with a consumer sound card, a Yamaha DP-U50 USB.

For a comparison, here is a close up shot of the rca out for the stock HU:


If you read the bottom, it shows the exact numbers: -1.8db for left and -2.1db for right channel at 20hz. In reality, the Mitsuibishu chip in the stock HU can do better, see below:


This is with a high decoupling capacitor (100uf), and shows only a -1.1db and -1.3 db drop at 20hz. I did not choose this capacitor value because I felt the DC offset was too high. DC offset can damager speakers. The value chosen, .47uf, keeps dc offset low and still provides less than a -2db drop at 20hz. I also do not plan to have a sub in my car so anything below 30-40hz is of no concern to me. So it was in my implementation that caused the .5db lower response, not the chip itself. If you wanted to improve the frequency response even more, and have a safe dc offset, an opamp would have to be modified into the system. This is a much more difficult task than what was done.
 
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Now you're getting into some technical jargon beyond my undergrad physics minor. Anyway, I may have been reading the diagram wrong. It's obvious that this mod can be used to get some serious SQ out of the stock unit. Most people who would attempt this would do so only as an alternative to purchasing an aftermarket unit. As long as you add plenty of disclaimers I think it would be safe to post it here. After all, it's not like people can hunt you down if they screw up their own head unit.
 
Merry Christmas & Happy Holidays Everyone!

Somebody asked for help performing this mod. It took some time to research and write up the procedure, so I figured why not share it with everybody. Hopefully this will go into the how-to section soon. Anyway, here's your Christmas present Mazdaforums!


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After having this in my car, I think you will need a line driver. I think the head unit is designed to put out less than 2v at full volume.

Disclaimer: I assume no responsibility for damages you may cause to your head unit or other any connected equipment to this HU by performing this modification. This guide is written to the best of knowledge, and is written in goodwill.

There is one other thing that is of some concern. From doing some research on forums it seems there may be more than one version of this headunit. This may mean that the internal parts may be different than mine. Here is the best thing I could find on the subject:
http://www.msprotege.com/forum/showthread.php?t=23494&highlight=panasonic

Mine is the Panasonic Version.

With that out of the way, on to the fun!

You should get the following things to perform this modification (Most are available at RadioShack):

1.) 20-30 watt soldering iron (make sure it has a fine tip on it for working with motherboards)
2.) 2 pair of RCA female connectors -Easiest thing to do is buy a cheap RCA audio cable and cut it. So you could buy two of these and cut them in half:

http://www.radioshack.com/product/i...&cp=2032058.2032228.2032256&parentPage=family

3.) 4 (four) - .47 uf 50v capacitor (get an extra or two, they are cheap, about $ .60 only) DO NOT GET NON-POLARIZED CAPACITORS.
-I am not positive on the value for the capacitors because of DC offset. Ideally you want 0v dc offset. With a .47uf capacitor Dc offset is between 2-4mv. This is what value I chose keep in mind. This is still very acceptable though. Anything under 5 mv is generally consider OK for source components. You may want to go with a lower value, like .22 uf, but this will cause a larger rolloff around 20hz. The capacitor value really depends on the gain and the input impedance of the amplifier(s) you are using. If you are worried about this, PM me back and I'll try to do some research.

4.) Some heat shrink tubing (this should be small enough tubing to shrink down and fit snugly against the capacitor wire leads)

5.) Rosin Core Solder (do not get fulx solder, it can etch out the board over time)
6.) Wire stripper
7.) 12V bench power supply or car battery charger.
8.) Small hook up wires, like gator clips (for the power and other temporary connections done in this guide) I bought these, and they worked pretty well:

http://www.radioshack.com/product/i...&cp=2032058.2032235.2032304&parentPage=family

9.) Optional: Heat gun or Hair dryer for heat shrink tubing. You can also use the end of the soldering iron too, but it takes much longer for the tubing to shrink.

I think thats all you need, OK let's get started.

Here is the basics of the RCA cable (in case you didn't know):

This is very similar to what you will see when you strip the rca cables (to be done later).


What you will be doing is connecting wires to two chips on the motherboard by using through holes already on the motherboard. The through holes makes the modification much easier to do. The ground wires will all be a single common ground (they will all be connected in one place), while the signal wires will all be independant (Front Left, Front right, Rear Left, Rear Right). You will be connecting the common ground to the ground input of the amp chip, and you will be connecting all the signal wires to the volume control chip.

To start, look at these two data sheets:

-AN7560Z- Amp Chip
http://www.alldatasheet.com/datasheet-pdf/pdf/13492/PANASONIC/AN7560.html

Look at age 2. You will be connecting the signal wires to pins 14,15,22,23.

and this one
- M62490FP - Volume Control
http://www.alldatasheet.com/datasheet-pdf/pdf/1341/MITSUBISHI/M62490FP.html

Look at page 9. You will be connecting all the ground wires to pins 20 and 22.

Let's go over the order of events:

1.) You should cut the RCA wires in half, so you are left with 4 even length RCA female cables. The length of the cables is up to you, but it is probably easiest if the cables are all 1ft in length.

2.) Strip the outer plastic sheathing off. You will be left with an outer wire braid and another small inside insulated wire. Twist the outside wire braid so it is seperate from the white inside wire. Now strip this inside wire as well. It should now look like this (your connectors should be female though):



3.) Now Take apart the head-unit so you are only left with the motherboard as shown below. You will need the faceplate for later on, so keep it nearby. If you need further assistance with taking the head-unit apart, message me back and I'll write something up.


4.) Now, find the Mitsubishi Chip. It is this chip on the motherboard:


5.) You will be splicing into the through-holes around this chip. The inner wire on the RCA cable will be connected near the Mitsubishi Chip, while the outside wire will be connected to common ground. Here's the pinout of the chip to help you out:





6.) You should now solder the capacitors to the inside signal wire of the RCA cables. Keep in mind the distance between the signal wire connection point and the ground wire connection point (ground point shown in the second picture in step 6). Make sure to heatshrink the end of the soldered capacitor lead, so it doesn't ground out on the head unit cage. Also, make sure polarity is followed ( the negative marking lead should be connected to the rca signal wire). This picture should help you out:


Here is where the ground through-hole is, to help you get an understanding of the distance between the ground connection point and the signal wire point (The connection point locations are explained just below in detail).



At this point you should also solder all ground wires to a solder lead. You may need a small wire for the ground connection and the signal connections to reach their through-holes. It's easiest to buy an extra capacitor, and cut off one of its lead. Then, use this lead and solder all four ground wires to it. Heat shrink this or use electrical tape to cover any bare wire showing. You need to use a wire lead as you will be using a through hole for the ground point as well. (the outside braid wire of the rca cable). Study this pinout, it is the chip amp pinout. You will be splicing into pin connections 20 & 22 (common ground in):


There may be another point to use for ground connection, but I figure that this given connection is clean because the chip amp uses it for the ground.


7.) In this step you will be making temporary connections to ensure proper through hole connections. Now would also be a good time to pull out the bench supply. You should also run all RCA wires through this hole on the heatsink BEFORE you make any connections. You will not be able to fit the RCA's through this hole once they have already been attached and soldered:



The rear pinout for the head unit is shown here:

http://www.msprotege.com/forum/showthread.php?t=8940

You will also need the faceplate to hookup up to the motherboard.

Look above for pinout numbers for the signal connection (Mitsubishi chip), then match these through holes with the pinout number:


Some comments on the picture. Pin 22&23 holes are located just next to the chip, as you'll notice. My HU was already put back together, so I did not get a chance to take another picture. Either way you will see the two.

To test the holes, place the lead of the capacitor through the hole, then connect the ground to any common ground point. Connect the faceplate back to the motherboard, and power up the HU. Connect an amp to the HU and turn up the volume. Play with the balance and fade to make sure each connection is right. You may also want to use old speakers, because if the ground connection is bad you will get lots of noise.

Now you can connect the ground point. Look at the above photo of where the ground point through hole location is. In order to find the through-hole, look on the bottom of the motherboard where all the chip amp pins are soldered in. Follow pins 20 & 22 until you find the through-hole right next to the regulator chip. Use the picture from above to help you get a feel where the ground connection is. Make sure to test this connection by powering up the head unit and hooking up this ground connection and one of the signal wire connections.

8.) Now that you've found the connection points, you can solder them in (finally :) ). Make sure to leave enough lead wire on the capacitor so that it can be folded down onto the motherboard. If the capacitors are soldered in facing vertical, you will NOT be able to put the head unit cage back on. You must make sure they are folded horizontally on the motherboard. Double check to make sure none of the signal wire connection points will ground out. Also make sure the ground connection itself does not touch any other wires. The last thing you want is for the ground wire to short out another component on the motherboard!

9.) Test again. Power up the head unit motherboard and re-confirm that all four rca connections work. Don't forget to clip off the extra lead wire from the bottom of the motherboard.

10.) Re-assemble the HU. You may have to loosen up or unscrew the rear heatsink again to get everything to go back together. It also may be a good idea to tape down or hot glue all the wires on the motherboard. This prevents them from getting yanked out. IMPORTANT: There is a small folded down piece of metal on the cagepiece where the MD deck goes. This folded metal is right were the volume control chip is. You need to fold this piece of metal back flush with the rest of the cage. If you do not, you run the risk of having one of the capacitor leads touching this metal piece, causing a short.

11.) Your Done! (cabpatch) If you've made it this far and double checked your work, you should now have a working stock head unit with RCA outs. If you have any questions about this, please PM me back.
 
amazing. I want to buy a stock head unit (the CD player on mine stopped working) and maybe attempt this. I too miss the look of the stock head unit, and my Alpine CDA 7894 is getting old.
 
I revamped the How-To after performing this mod...
http://www.msprotege.com/forum/showthread.php?t=123620193&highlight=stock+head+unit+line

The output level is too low for this to be an end-all solution. However, I'm curious now if there is a better place to tap into the signal. Perhaps imediately before the amplifier circuit instead of directly after the volume control circuit. Now that my unit is back together I probably won't be pulling it apart anytime soon though.
 
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just did this mod....and sq is definitely better...
however, i now have massive alternator whine where i had none before with the exact same setup using a navone loc.
did you guys use shielded RCAs?
 
I did not use shielded RCAs. double check your connections. If one of your ground wires is not connected it will introduce alternator whine.
 
so it turns out my wiring was ok....but i realized that i didnt have my headunit pushed all the way back into the cavity. pushed it in hard and it clicked into place. started my car and the alternator whine was gone.

is the middle screw in the back the ground connection? ie it has to touch the metal bracket behind the headunit? mine probably wasnt before, allowing it to ground through either the RCAs or the antenna.

anyways i just have to stress again the major improvement in sq. thanks to tschanrm for figuring this out. just goes to show how good the stock headunit can sound...as long as the interior amplifier is not used.
 
Did you have enough output voltage to power your amp(s)? Mine was really low and even my stock rear speakers were playing louder than my 85w/ch amp.
 
all this info being thrown around, i knew there was a reason i should have paid attention in school:( think ill still to my in line converter as a source of out puts. even this is over my head
 
chuyler1 said:
Did you have enough output voltage to power your amp(s)? Mine was really low and even my stock rear speakers were playing louder than my 85w/ch amp.


This is one caveat that I forgot to mention. Some amps will not be able to provide enough gain to match the stock amp gain. It all depends on the gain level of your amp. Some manufacturers reveal the gain specs, some do not. In my case, I used an Aura amp, which has a max input level of only 2v! With this amp, it is no problem for me to match the rear and front speaker volume levels. YMMV I guess....

Unfortuately, there is simply no room inside the HU to add an output stage for the rca pre-outs. You can try adding a line amplifier to increase RCA's pre-out level, but I think that will add some noise. I was going to add a line amplifier if my amp couldn't provide a high enough gain level. There is also no other place to splice into the signal wires. All input routing is done through the Mitsubishi chip, and then sent straight to the amp stage. Hope this helps.
:)
 
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