How-To: Stock head unit with RCA outs (P5)

Antoine

Administrator
* Created by tschanrm

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/index.jsp?productId=2103844&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/index.jsp?productId=2062233&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.<!-- / message -->
 
I took some time over the long weekend to perform this mod. I took pictures throughout the process so I could refine this how-to for people who aren't as electrical-savvy.

I will post my full results this evening (photos are on my home computer) but here is a summary:

Pros: Better bass response from 100Hz down (factory amp chip creates a very sharp rolloff that this mod fixes perfectly). Fairly flat RTA curve at 85-100% volume. No distortion or hissing with amps at full gain. Sound detail is significantly improved over using a LOC.

Cons: Whether using a LOC or this Line-out mod, the factory unit does not have a constant RTA curve at all volumes. As you turn the volume down the mid-range dips (I will post TrueRTA results). The output voltage is too low and a line-driver is required. With my 85w/ch amp at full gain I barely got my front stage louder than the rear speakers connected to the factory amp.

Ideally to make the most of this mod you should consider a 1/2 din eq that has a volume control and a built-in line driver. That way you can run the stock unit at full volume (with a flat rta curve) and use the eq to adjust volume. You can get a cheap 1/2 din PEQ or GEQ for under $100 and install it below the ashtray.
 
Let the bidding begin.... :)


o8ufsx.jpg
 
LINE-OUT HOW-TO FOR MAZDA DOUBLE DIN HEAD UNIT (TAKE 2)

DISCLAIMER

This mod requires experience working with circuit boards and soldering irons. If you are not familiar with this then I suggest you find some tutorials on soldering before continuing. I accept no responsibility if you break your head unit or can't figure out how to put it back together again.

BACKGROUND

You should familiarize yourself with the following circuit diagrams before attempting this modification. Myself and other MazdaForums memebers have done the leg work but if something doesn't appear the same, you may have a different model head unit and a multimeter may be necessary to find the correct soldering points.

Volume Control Chip

http://www.alldatasheet.com/datasheet-pdf/pdf/1341/MITSUBISHI/M62490FP.html
You will be making connections to pins 22 (Front Left Out), 23 (Rear Left Out), 14 (Front Right Out), and 15 (Rear Right Out).

Amplifier Chip

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

You will be making a connection to pins 20 and 22 (ground).

MATERIALS

Available at www.partsexpress.com



240-540 RCA DUAL EXTENSION CABLE 6' (2) $1.40 $2.80
020-1186 0.47uF 50V AXIAL MINI ELECTROLYTIC CAPACITOR (4) $0.24 $0.96
080-614 3mm HEAT SHRINK 3:1 BLUE 6"x8 PCS (1) $2.95 $2.95
080-624 6mm HEAT SHRINK 3:1 BLUE 6"x5 PCS (1) $2.95 $2.95
Total: $6.71
TOOLS



* SOLDERING IRON AND SOLDER
* MEDIUM HEAD PHILLIPS SCREWDRIVER
* SMALL HEAD PHILLIPS SCREWDRIVER
* SMALL FLAT HEAD SCREWDRIVER
* WIRE STRIPPER / WIRE CUTTER
* HEAT GUN OR LIGHTER
<table border="0" cellpadding="0" cellspacing="10"><tbody><tr> <td align="center" valign="top"> </td> <td valign="top">Step 1

Remove trim panels from the unit and set them aside.

</td> </tr> <tr> <td align="center" valign="top"> </td> <td valign="top">Step 2

Take off the top cover to the unit by removing the screws found at each corner.

</td> </tr> <tr> <td align="center" valign="top"> </td> <td valign="top">Step 3

Remove the large screws holding the CD player unit in place. There should be two on each side. These screws are larger than others so remember what they look like for when you reassemble the unit later..

</td> </tr> <tr> <td align="center" valign="top"> </td> <td valign="top">Step 4

Lift the CD player out of the unit's chassis. You may need to use a flat blade screw driver to get it started.

</td> </tr> <tr> <td align="center" valign="top"> </td> <td valign="top">Step 5

To take off the face plate you need to remove a screw on each side. These are diffent screws from the others so remember where they go and what they look like.

</td> </tr> <tr> <td align="center" valign="top"> </td> <td valign="top">Step 6

Take off the plastic piece which is hiding the clips from the bottom of the face plate. It is just glued on. Using a flat blade screw driver gently pry off the top and bottom until it comes loose.

</td> </tr> <tr> <td align="center" valign="top"> </td> <td valign="top">Step 7

Take off the front plate by loosening the three screws in the center and one in each corner. The bolts in the center require a smaller phillips head screwdriver. Put them aside so you remember where they go.

</td> </tr> <tr> <td align="center" valign="top"> </td> <td valign="top">Step 8

Your unit should now look like this. Next we have to remove the plate shown in the photo.This one took me the longest to figure out.

</td> </tr> <tr> <td align="center" valign="top"> </td> <td valign="top">Step 9

Take off the right side clip by removing the two screws. Thes screws are flush mount. Put them aside so that you remember where they go.

</td> </tr> <tr> <td align="center" valign="top"> </td> <td valign="top">Step 10

Remove the hidden screw shown in the photo.

</td> </tr> <tr> <td align="center" valign="top"> </td> <td valign="top">Step 11

Take off the heat sink by removing all the screws on the back side. One is smaller than the others so remember where it goes. Watch out for the white thermal compound used between the heat sink and amplifier chip. It can be real slimy if you touch it. If you accidentally wipe it off you may need to reapply some.

</td> </tr> <tr> <td align="center" valign="top"> </td> <td valign="top">Step 12

Now that the heat sink is off, you should be able to lift off the metal plate, remove the side pieces, and lift the circuit board out.

</td></tr></tbody></table>
 
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<table border="0" cellpadding="0" cellspacing="10"><tbody><tr><td align="center" valign="top"></td> <td valign="top">Step 13

Next we will create our pre-out cables. Take an RCA extension cord and cut off about 12-14" from the female side.

</td> </tr> <tr> <td align="center" valign="top"> </td> <td valign="top">Step 14

The RCA cord I have is a coaxial where the ground wire is wrapped around an insulated signal wire in the center. Remove about 4" of the outer sheath but be careful not to damage the wiring inside. Separate the ground wire from the signal wire for each channel.

</td> </tr> <tr> <td align="center" valign="top"> </td> <td valign="top">Step 15

Repeat steps 13 and 14 with the second RCA extension cord then twist all of the ground wires together.

</td> </tr> <tr> <td align="center" valign="top"> </td> <td valign="top">Step 16

Clip off about 2" of the ground wire since it will only have to travel a short distance inside the unit. Solder a pin (just use the end of a capacitor or resistor) onto the end so we will be able to connect it to the circuit board.

</td> </tr> <tr> <td align="center" valign="top"> </td> <td valign="top">Step 17

Place heat-shrink-tubing around the ground wire and leave about a 1/2" exposed. Use a heat gun or lighter to shrink the tubing. Now is also a good time to label both sides of your signal wires. I just numbered them 1, 2, 3, and 4 but you can do FL, FR, RL, and RR to be more specific.

</td> </tr> <tr> <td align="center" valign="top"> </td> <td valign="top">Step 18

Add a large piece of heat-shrink-tubing around all the wires to group them together. This will be an added layer of protection for when they pass through the heat-sink later and it protects the end of the ground wires.

</td> </tr> <tr> <td align="center" valign="top"> </td> <td valign="top">Step 19

Strip about 1/2" off each signal wire. Take four .47 uf 50v capacitors and clip one side to about 1/2". Solder a capacitor to the end of each signal wire. Be sure to put heat-shrink-tubing on the wire before you solder the capacitor but don't heat it up until after you are finished soldering.

</td> </tr> <tr> <td align="center" valign="top"> </td> <td valign="top">Step 20

If you haven't already, you need to feed your new wires through the heat sink. Use the hole below the antenna jack.

</td> </tr> <tr> <td align="center" valign="top"> </td> <td valign="top">Step 21

Solder the ground wire to one of the ground holes by the amplifier chip.

</td> </tr> <tr> <td align="center" valign="top"> </td> <td valign="top">Step 22

Any one of the three holes that are linked to the pins on top row, second and third from the left in this photo will work.

</td> </tr> <tr> <td align="center" valign="top"> </td> <td valign="top">Step 23

The signal wires will be soldered to holes near the volume control chip. This chip is located in the center of the board. All soldering should be done on the bottom of the circuit board but it is much easier to find the holes in relation to the top of the board. Be sure to leave plenty of slack on the wire so the chassis can be placed back on. Before you solder anything to the circuit board you might want to do a test fit.

</td> </tr> <tr> <td align="center" valign="top"> </td> <td valign="top">Step 24

In this series of photos, the heat sink is towards the top. Solder channel 1 (front left) to the first hole directly above the chip.

</td> </tr> <tr> <td align="center" valign="top"> </td> <td valign="top">Step 25

Solder channel 2 (front right) to the hole off to the lower left of the chip.

</td> </tr> <tr> <td align="center" valign="top"> </td> <td valign="top">Step 26

Solder channel 3 (rear left) to the second hole above the chip. Be careful with your soldering. You don't want to short out the two channels when you power the unit up.

</td> </tr> <tr> <td align="center" valign="top"> </td> <td valign="top">Step 27

Solder channel 4 (rear right) to the hole off to the upper left of the chip.

</td> </tr> <tr> <td align="center" valign="top"> </td> <td valign="top">Step 28

Here is a shot of the leads coming through the bottom of the circuit board. After you solder, clip off the extra lead so it does not short out on the chassis when you reassemble everything.

</td> </tr> <tr> <td align="center" valign="top"> </td> <td valign="top">Step 29

Place the bottom of the unit back on and test fit everything. Make sure the wires do not snag on anything. Reassemble the unit by following the disassembly instructions backwards. I ended up putting on and removing the heat sink several times before I got everything back together.

</td> </tr> <tr> <td align="center" valign="top"> </td> <td valign="top">Testing the Unit

I was unsure about the results I was going to get with this modification so I made a point to perform some thorough tests. Unfortunately I don't have the greatest test equipment. I used a 10a 12v power supply and an RCA-to-1/8" jack converter to connect everything to my computer's Sound Blaster 16 card. I dropped in a CD with a pink noise track and loaded up TrueRTA.

I couldn't get anything remotely resembling a flat signal so I ran some tests on my Clarion DRX9575rz head unit. I know the unit has a fairly flat response curve but it wasn't displaying well through my system either. After hours of tweaking and calibrating I decided to simply compare the factory head unit's response relative to the response provided by the Clarion unit. This turned out well and gave me some curves that made a little sense.

</td> </tr> <tr> <td align="center" valign="top"> </td> <td valign="top">Test 1 - David Navone LOC

The David Navone LOC is a pretty good unit for converting speaker level outputs to high-voltage line outputs. The factory amplifier chip picked up a 60Hz spike from the power supply so ignore that. The three curves shown are the factory head unit at 1/4 volume, 1/2 volume, and 3/4 volume. As you can see the response curve is absolutely horrible at 1/4 volume almost as if there was some sort of loudness affect. At 3/4 volume the response curve smooths out but the bass response plummets below 100Hz. Without some sort of bass boost using a LOC will not give you desirable results.

</td> </tr> <tr> <td align="center" valign="top"> </td> <td valign="top">Test 2 - New Pre-outs

In this graph you can see that the frequency response at 1/4 and 1/2 volume still sucks. However, we see a great improvement at 3/4 volume. We have a flat response down to 40Hz and a reasonable roll off after that.

</td> </tr> <tr> <td align="center" valign="top"> </td> <td valign="top">Test 3 - Direct comparison between Pre-Outs and LOC

Here are the 3/4 volume results placed side by side for comparison. Clearly the pre-outs take the cake with bass response.

</td> </tr> <tr> <td align="center" valign="top"> </td> <td valign="top">Conclusion

Although this mod addresses the bass response issues with using a LOC connected to the speaker level outputs, it has one flaw. The signal strength obtained directly from the volume control chip is not strong enough to power aftermarket amplifiers. A line driver would be required to make the most out of your system. During my in-car tests, the factory rear speakers were just as loud as my front speakers being powered by an 85w x 2 amplifier and the bass was barely audible. Even when I turned the gains up all the way the amplifier could not produce enough sound to drown out the rear speakers being powered off 10w from the factory head unit.

The best solution to fix this and the response changes at different volumes would be to get a 1/2-din eq and mount it below the ashtray. You could set the factory head at 3/4 volume and use the eq volume instead.

As far as sound quality is concerned, the mod provides a much cleaner signal that is better suited for amplification. I listened to a few high-fi recordings and the mix was very transparent and the highs were much more detailed than with the LOC. The staging and imaging is not comparable to my Clarion unit with it's 20-bit DAC but I would put it on par with most entry-level aftermarket head units. I used to get noticeable hissing from my LOC but the line-outs do not produce any hissing even at full volume with my amplifier gain at 100%.

</td></tr></tbody></table>
 
Chuyler,

I haven't checked this post in a while and just wanted to say thanks for posting all those pictures. My How-to was an afterthought request when I had just finished putting my headunit back together, so the only pictures I had were reference points for myself.

Also, as an addendum to this How-to, refer to Chuyler's frequency response graphs, specifically "Test 2." You'll notice that at 1/2 and 1/3 volume levels the skewed frequency response increases the bass and the treble. Yet, after 3/4 volume, the frequency response is back to normal. Anyone have any clue why? Well, Chuyler was right, it's a loudness feature!

The Mitsubishi volume control chip has two internal switches, switch A and switch B, controlled by pin 7 on the chip. These two internal switches decide whether the chip should enable or disable the loudness feature. The data sheet makes reference as how to configure these switches to disable loudness, but does not tell you how to flip the switches on and off!!!!(pissed)

So, sometime before September I'm going to take another hard look at that Mitsubishi datasheet and figure out how to disable loudness. I'll post in September (or sometime before) and let everyone know if you can disable loudness.
 
Well, that was quick, I already figured out why they don't list how to change the switches. The MCU on the headunit controls the loudness feature. I'll have to look into the MCU stuff now and find out how to disable loudness.
 
Cool tschanrm! At first I thought I was going bonkers because my graph looked nothing like yours. The loudness isn't such a bad thing, but you have to account for it when you set gains on your amps. I'd much rather you devise a how-to on creating a line driver to boost the signal to 4v. :)
 
tschanrm said:
Well, that was quick, I already figured out why they don't list how to change the switches. The MCU on the headunit controls the loudness feature. I'll have to look into the MCU stuff now and find out how to disable loudness.

dude, i didnt even notice there was a loudness control in this chip...that would definitely account for the screwy frequency responses at lower volumes.

but...looking at the datasheet for the M62490FP, wouldn't it to easier to modify the external RC circuit for loudness instead of trying to figure out the MCU data input? i mean if the RC circuit was bypassed wouldnt that effectively remove the filter and then the frequency would be the same whether the loudness is on or off?
 
Chuyler,

I know I mentioned it in the other thread, but I'll say it in here too. As you know, space is really limited in the headunit. Because of this, there may not be enough room to add an output stage to 4 channels. The other issue is getting the right voltage/amperage. Panasonic most likely designed each voltage rail with just enough amperage to power each chip. Adding an output stage with opamps could overdraw the one of the voltage rails, causing the unit to malfunction. There is also the issue of the headunit not supplying an appropiate voltage. So, is it possible to get a 4v output by making an ouput stage? Yes, of course, where there's a will there's a way. However, I don't think making an internal output stage is necassary because:

1. As said before, limited space.
2. Line amplifiers do the same thing.

Yes, a line amplifier does the same thing an output stage does: boost the signal. Why go through all the extra effort to disassemble and re-mod your headunit, when you can just wire up a line amplifier. I think a line amplifier is the best choice because space is not limited, meaning you can use whatever premium parts you want. Anyway, that's my line of thinking. I have never used an off-the-shelf line amplifier, so I have no idea how much noise/distortion they add. I can tell you making a home-made line amplifer would be just as effective, and probably could sound better than adding an internal output stage.

Feelander,

If you bypass the loudness control, you lose zero-cross detection, and also bass/mid/treble control. I have looked into it, and I am still looking into it as a possible option. I like the MCU option because it requires no new hardware modifications, and you can still keep bass/mid/trable control. I will keep both options open as I try to disable loudness.
 
Here's some info I posted in the other thread that should help explain why some people have volume issues:

The main determining factor for how loud you can get the hacked pre outs from the stock headunit depends on the max input voltage of the amp(s) you are using. Ok, lets create a sceneario that should help explain:

Lets say that you have a 50w/channel amp that has a max input of 8v. In order to get the full 50w/channel going to your speakers, you would need an headunit that can push 8v. Now, many headunits cannot do 8v, so what does an amp manufacturer do? They add a gain level to the amp's channels, which can increase or decrease the incoming voltage of the headunit pre-out. This way, if you have a headunit that can only do 4v max, you can increase the gain level on the amp so you can harness the full 50w/channel. Make sense so far?

However, the amp gain can only amplify the voltage by so much. For instance, if you had a headunit that could only output 1v max, the amp gain may not be able to amplify the signal enough to reach 8v. Lets say at the headunit's full volume and max amp gain level, you can only reach 6v. This means that you could never get the amp to push 50w/channel-remember, the amp needs 8v to reach the full 50w/channel. This is not a universal rule however, as amp manufacturers have different levels of max gain. So, there *may* be an amp with an 8v input that can amplify a 1v preout signal to 8v.

Now, lets you have an amp that can reach the full 50w/channel at a lower voltage, say a 2v signal. In this case, you could easily apply enough gain to the 1v pre-outs to reach 2v, and push 50w/channel out of the amp. In my case, I have an amp that reaches full power at 2v, so it is not a problem for the hacked pre-outs to match the stock amp level.

Overall, the main problem with the headunit is that I think the volume control chip is programmed for too low of an output. The MCU inside the the headunit controls the volume control chip, and while the volume control chip is capable of outputing 2v RMS at max volume, I think the MCU keeps the max volume at less than half that. If this scenario is not the case, (which I am pretty sure it is, considering Mazda enabled the loudness feature) than the only other explanation I can think of is that there is an impedance mismatch between the hacked pre-outs and the 10k ohm input of most amplifiers. Hope this helps. :)
 
My question wasn't specifically targeted towards an internal line driver. External would be fine, but I think I found something that would work perfectly....

http://www.davidnavone.com/linedrivers.htm

The first item on the page is designed for boosting the output of MP3 players up to 2v RMS. It's not a high-end 4v signal but I think it will give me a little more gain if I need it.
 
chuyler1 said:
My question wasn't specifically targeted towards an internal line driver. External would be fine, but I think I found something that would work perfectly....

http://www.davidnavone.com/linedrivers.htm

The first item on the page is designed for boosting the output of MP3 players up to 2v RMS. It's not a high-end 4v signal but I think it will give me a little more gain if I need it.


Oh, ok, I thought you wanted to boost the signal from inside the headunit. That sounds like a nice, easy one to install, and much cheaper than the 10v competition driver they sell.

Also, some good news, I think I found a way to bypass the loudness feature! I thought the loudness components were inside the chip, but it seems the boosted frequencies are done via external resistors and capacitors. I may be taking my headunit apart this weekend and finding out, stay tuned!
 
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tschanrm said:
Also, some good news, I think I found a way to bypass the loudness feature! I thought the loudness components were inside the chip, but it seems the boosted frequencies are done via external resistors and capacitors. I may be taking my headunit apart this weekend and finding out, stay tuned!

yeah that was what i was talking about. the external RC circuit just acts as a filter for the signal. when the loudness is off, it doesnt go through the filter, so i would seem that bypassing this circuit would make the signal the same whether loudness is on or not.

i dont have time to take my unit apart this weekend....so let us know whatever you find out :D
 
OK, here's how to disable the loudness contour on the head unit:

You will need a fairly fine tipped soldering iron for this final step, because this involves removing SMD components, and bridging an SMD gap. You will also need to make two very small leads, about the size of a SMD resistor. These will be used to bridge the gap of two of the SMD parts you remove.

First, disassemble the unit, as shown in Chuyler's post, or my original first post. Once apart, you will look on the main board.


1. Flip the board so it is on it's backside. Look by the black mark:



2. Desolder the two SMD components, the C220 capacitor, and one resistor next to it. (shown below) DO NOT REMOVE RESISTOR R217!
3. Bridge the resistor gap as shown in the picture below:


4. Flip the board back over and look right by the volume chip.
5. Desolder the two SMD components, one capacitor, and one resistor next to it. (shown below)
6. Bridge the gap as shown in the picture, and pay close attention to which smd pads are connected together:


7. Reassemble

Your Done! If all went well you should now have a loudness free stereo!
 
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It should be the same as before, only now with no loudness contour below 3/4 volume level. I tested the HU when I didn't bridge the gaps in this post:

http://www.msprotege.com/forum/showpost.php?p=2626120&postcount=30

The only difference between that test and now is that I bridged those smd pads together. Hopefully in a week or so I'll be able to retest the HU again on a something better than an onboard soundcard (for more accurate results).
 
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