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Modifying OEM head unit for un-eq’d line out


utc_pyro

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STEP BY STEP GUIDE ADDED ON PAGE 15

 

Purpose:

I just bought a 2006 Legacy GT wagon two weeks ago, and a 2008 outback radio off eBay with dual climate control. I want to upgrade the audio in the car, but retain the good functionality and looks of the stock head unit. As has been found by the ones who use RF 3sixty.x's that the stock head unit applies quite a bit of EQ to output of the audio, and not quite how I'd like it to do so.

Thus, I want to modify the stock head unit with a line (or close) level output bypassing as much as the factory EQ as possible. A DSP based line out converter is a no-go as I want to retain use of the OEM volume control. If anyone has the service manual to this radio (or has any clue were to find one) it could make this a LOT easier. Another plus would be to get phone input capability like in the old 2006 radio, but it's more of a secondary concern. Most of internals are shared between the two designs, so the functionality may still be there hiding.

Research/dissecting:

Popping the radio open, I found two areas of interest in the radio to get a clean line out signal. The first in the audio pathway is the SRS WOW chip. Looking at the front of the PCB, the clip is in the lower right corner next the radio tuner, and labeled "(s) WOW 2195 JRC A6008C". This IC cross-references with a "NJW1142M", looking that up one can see that it’s the SRS processor. The second is the M62490FP as found in the 2006 radio, a digital volume control/fade/balance/tone control chip tailored to car use. Looking over at the board layout it appears to be very similar from this point to the speaker terminals as in the 2006 radio, thus one can use the old repair manual for reference.

The 2006 service manual can be seen in this post: http://legacygt.com/forums/showthread.php?t=51886 It gives detailed information on the audio flow through the M62490FP back.

So, one can look at those to get a rough idea of the audio path through the system:

[source audio] => SRS WOW chip => Volume/fade/loudness chip => "amp eq" => AMP

So, it’s known that the audio will be garbed before the "AMP EQ" stage at least, but it may take further work/digital tweaking to disable the rest of the EQ.

Looking at that audio path that's left, it's going to be more difficult to decipher how the CPU is actually adjusting the volume and adding further EQ. Both the SRS WOW chip and the M62490FP "volume control" chip can adjust the volume, bass, treble, and mid range, with the SRS WOW chip having fairly fine grain control according to the speck sheet. The "volume control" chip is the only one with true loudness control, and this is tweakable by modifying some external components. It is also possible for the CPU to apply an EQ/Loudness curve of sortes to the signal through software by adjusting the bass/sub-bass/mid/treble/sub-treble dynamical with the volume setting.

Question:

So, anyone have an idea on how the duties are split between each chip? I don’t have easy access to a scope to run test anymore as I just graduated and they locked me out of the labs at the local University.

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Have you consider using a JL Audio cleansweep.

 

With a Cleansweep one cannot use the factory volume control. The stock head unit applies a "loudness" factor and bass killing EQ to the output that varys with the volume setting. A JL Cleansweep can fix this at one volume setting only, and you'd have to use it"s volume control. Also, for the same price I could get a RF 3sixty.1 with full time-alignment and 10 band EQ.

 

Not to mention I just got my B.S.E.E. Might as well put it to good use and save $200.

 

I've had some luck figuring out how to kill the loudness on the M62490FP presuming no additional digial loudness is being applyed. It appears that the factory radio keeps loudness enabled all the time (it's set digitally through the chips's serial interface), so there is no easy way to just turn it off. BUT, one can keep it from functioning.

http://i50.tinypic.com/fxfamh.jpg

This is an excerpt from the M62490FP's data sheet showing the loudness portion of the circuit. When loudness is on (all the time in our case), switch B is closed and switch A is open. BUT, if you look at the circuit diagram, internally the two would be the same (resistor going to Vref). The only diffrence is Switch B connects pin 7 to an RC network across the volume control. Cut the trace going to pin 7, and no more loudness on that channel.

 

http://i50.tinypic.com/o0atj7.jpg

This is the same area on the actual scematic for the 2005/2006 radio. As I stated before, this older radio is identical to the newer one electrically from this chip to the amplifier. Interestingly, this diagram shows pin 7 being "Vol1" insted of the loudness control, but the scematic matches up with the data sheet other wise, so I looks like cutting the trace off of pin 7 will infact disable loudness.

 

Getting a workable audio output from this chip is easy, see here:

http://i46.tinypic.com/15f5guc.jpg

Just have to find a Via to tap into and cut the trace leading to the amp EQ section.

 

So some progress at least in killing the EQ. If digital EQ/loudness is being applyed is still up in the air though. Any imput on this would be much apreciated though, particulary if any one has actually sniffed the serial/i2c busses in the radio or ploted the frequency responce between modules.

 

The phone input is looking to be thoroughly deleted form the design though, at least in the way previously done. I'm digging around on the board but can't find any signs of the original input circuit used on the 2005/6 radios still being in place. I need to trace the I/O's of the CPU further to see if I can find any supporting transistors for a "mute"/tell-on input.

 

Does anyone have the pinout of the Satellite Radio/Navigation plug on the back of the radio by chance? That could help ALOT figuring out a way to do a phone input.

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Excellent work... and congrats on your BSEE... always good to see engineers on this forum, who are willing to dive DEEP into this stuff! (BSME here, though I know enough EE and CS stuff to get me in trouble! Haha!)

 

Incidentally, would you happen to have schematics that you can share? Personally, I'd love to have a set for the 2006 radio (ie, my car!)

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Nice work! Subscribing. I replaced my 05 unit with 09 "HK" unit. I got the OEM HK amplifier as well, but haven't hooked it up yet. I am worried I may need to get OEM HK speakers for it to "match". Being able to kill teh loudness crap I could go with any amp/speakers easily...
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It seems you already have most of this figured out. I have actually done this in the past to another brand OEM radio (Mazda), and the RC network for loudness was the only component altering the signal, ie. no further digital loudness. This was confirmed through before and after frequency response plotting. I presume Subaru uses a similar system.

 

As far as where to tap into for line level outputs, the board most likely has through holes connected to the volume chip's outputs (which you circled) which are not being used. Just solder into those and you should be good.

 

Congrats on your degree! (fellow EE)

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Thanks all on the degree congrats.

 

Incidentally, would you happen to have schematics that you can share? Personally, I'd love to have a set for the 2006 radio (ie, my car!)

 

I do have the schematic for the 2006 radio (that's actually what the clips are from). www.mcwiggin.com/subaru/0505cqef1560l.pdf Credit to mcwiggin's thread on were I got that from. The audio path past the SRS WOW chip is almost identical, so that's how I'm able to use it in my application in the 2008 radio.

 

It seems you already have most of this figured out. I have actually done this in the past to another brand OEM radio (Mazda), and the RC network for loudness was the only component altering the signal, ie. no further digital loudness. This was confirmed through before and after frequency response plotting. I presume Subaru uses a similar system.

 

That's what I'm hoping that Panasonic did with this unit. Sniffing the serial and I2C data going to the two audio chips, then intercepting and modifying those signals is more work then I want to put into this project. With enough time and money it could be done, but both are in short supply for me now that I've bought this car.

There is another stage of EQ down the signal path (one can see it in the diagram below), but it's not something I need to worry about as nothing changes userinterface wise from there out. If I had OEM nav, it would be as its audio is feed directly into the amplifier stage in the 2005 radio. Hopefully no issue here though.

 

http://www.mcwiggin.com/subaru/Block.png

(Again, credit to mcwiggin for the image, I can't get to tinypic from work. This is again the 2005/2006 radio, so just look at IC206 right)

 

As far as where to tap into for line level outputs, the board most likely has through holes connected to the volume chip's outputs (which you circled) which are not being used. Just solder into those and you should be good.

 

 

That's what I was thinking. I didn’t look too close for a good point to solider on my audio output wires last night, but I'll probably do that when i get home. There are four output capacitors going to the "amp EQ" stage that might be easy to solider to, and it would provide decoupling for me so I wouldn't need any additional circuitry. These are "C1, C21, C61, C81" on the old board, and located on the bottom of the PCB. I'm hoping the output level here will be high enough that I can drive external amps directly, but I have most of the stuff sitting around to build a small amplifier if need be.

Speaking of that, on the Mazda radio you did, were the output levels off the volume control circuit high enough to run an external amp?

Also I've had a little progress on the phone input. Pin 88 still goes to a similar resistor pack on the 2008 radio as the 2005/6, but I'm not sure if it has the same use. There IS an external mute wire though on the 20pin SAT/NAV connector. Pin 8 is mute, and MAYBE pin 19/20 can be repurposed as a phone input as this appears to be the audio input from the navigation system. Anyone know if the nav system mutes the music when it is giving directions? I don’t have much hope though seeing as that portion of the radio is so similar to the old one (feeds direct into the amp), but as SOMETHING is till hooked into the differential input on the volume control chip, it's possible.

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Don't want to burst anyone's bubble, but I've done quite a bit of hacking of the OEM radio. (Literally, I attempted this project in my lab a couple of years ago).

 

The output pins that you are looking at do not have the drive strength of line level. I've tapped multiple sections of the circuit to feed into amps, and none has the voltage and drive strength for even a high-Z input.

 

If you want this to succeed, you'll need a line-level amplifier to sit between the pins you have selected, and the output to your amps.

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If you want this to succeed, you'll need a line-level amplifier to sit between the pins you have selected, and the output to your amps.

 

Yes, but it will depend on the input and gain range of your external amp. Obviously the stock amp makes do with the supplied voltage level.

 

Otherwise, like you said, you simply need a line driver.

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Don't want to burst anyone's bubble, but I've done quite a bit of hacking of the OEM radio. (Literally, I attempted this project in my lab a couple of years ago).

 

The output pins that you are looking at do not have the drive strength of line level. I've tapped multiple sections of the circuit to feed into amps, and none has the voltage and drive strength for even a high-Z input.

 

If you want this to succeed, you'll need a line-level amplifier to sit between the pins you have selected, and the output to your amps.

 

Do you happen to remember what the actual signal strength was at those points? If so I'd be able to know what gain to build a amp for. If I use the power rails provided by the radio I should be able to get 5vrms out of just an op-amp at full volume. That appears to be in the acceptable range fore car audio (I'm a HT guy, this car stuff is new to me).

 

So, an amp with a 10db gain or something for the output of the volume control chip? Dang it I need a scope, I'm not going get the SQ how I want it without one... Any one have suggestions on a cheap one? Maybe even a cheapy China handheld or USB based software one?

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Alright, I have some more progress on this. I managed to get some pictures of the points of intrest on the board. My good cam is dead and my old cam is going bizerk, so we're stuck with images from my Droid.

 

http://i45.tinypic.com/1zl8vhw.jpg

This is the volume/fade/balance/tone/loudness control chip. The thin red lines are were one needs to cut the trace to disable loudness. Fairly simple here.

 

http://i49.tinypic.com/332tpwo.jpg

Here took a few minutes longer, but are the decoupoling capacitors between the volume chip and the "amp EQ" section of the audio path. One should be able to tap in right before or after this point to get audio for a pre-amp/linedriver. This area is on the back of the PCB near the volume control chip.

 

If one cannot read the text on the picture, here is a key to what capacitors to tap into. The volume control side is on the right, "Amp EQ" on the left.

C1 = Front Right

C21 = Rear Right

C75 = Front Left

C81 = Rear Left

 

To those of you with 2005/2006 radios, it will be the same except C75 will be C61.

 

No progress on a phone input though. It appears that it has been completely removed from the board as the volume control chip no longer has pins 2,3, 34, and 35 hooked up. The path of the "nav audio" does seem to have changed though, so it may be possible to tap into that.

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utc_pyro

 

I don't remember how weak they specifically are, as I discarded hat I had when I abandoned the project in exchange for aftermarket radios. Nothing beats my old Eclipse CD8053, but this was before the dual HVAC kit had been figured out, so I had a bigger project to complete...

 

I did test the weak signal with an amp. I will say the signal is weak enough where there is no suitable amount of gain the amp can do to adjust for any listen-ability.

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A little off-topic, but normally I see people take pictures with their "camera" and then post crap from their cellphones. Cellphones are not cameras!

 

But, more to the point, utc_pyro - Your droid pics are excellent. FINALLY someone who knows how to use a cellphone camera! Proof that if you know how to use it, a cellphone can be an acceptable camera... but people, please stop posting blurry crap from your cellphones and get a real camera (or learn how you use your crappy one).

 

Rant over.

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I've found a few more interesting things out about the radio. There appears to be a version of the radio with a subwoofer output, just like the old version used in some outbacks. I have no idea if/were this mystery radio is used, but the capability is there. On i85, Pins 4 and 8 are used for woofer +/- (yes, pin-8 is reused).

 

Looking over i88, some thing have change about it as well. The HVAC Tx/Rx are pretty much the same as they were before (hence how we can use these radios with our older cars), but there appears to be a level shifter right on the daughter board now. This section was previously locaten next to the mirocontroller. "Nav Signal -" is now straight to ground, "Nav signal +" still exist, and connects to something around the 20-pin connector. Ignition and ground are still the same. Not sure about the other two wires though.

 

The schematic that is tossed around about the 20-pin connector is WRONG. I've yet to figure it all out, but it does not match the 2008 radio. There are singularity in the supporting circuitry, but the arrangement of the pins is quite different.

 

Again on the 20-pin connector, has any one yet tried the Subaru Media Hub or the bluetooth module with the older radios? I have not found much info on them as of yet, but the media hub should work based on other people's work on getting Satalite radio to work and the PAC making the I-Pod/AUX input for subaru radios across the time gap. There should be a "call mode" hidden in this thing as well accessed through the 20-pin connector, but it may be what happens when one hits the mute line.

 

I'm working on a simple design using a quad-opamp for a signal increase coming off the points posted above. I'll post it up after I select my opamp and run the Spice on it.

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utc_pyro, assuming your quad op-amp design works, do you have the equipment to test if the output from the volume control chip is un-eq'd? I can point you in the right direction of some analysis software and hardware (inexpensive) if you need to do some audio analysis.
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I was originally going to try and run Room Eq Wizzard through it, a program I've used in home theater to tune systems. It would probably freak out a bit as the levels won’t be what it expects though. Also it’s calibration is tied to a SPL meter, so it may not be that accurate.

Any suggestions would be much appreciated though.

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Would this help you?

http://www.zelscope.com/

 

That actually might. I'll look into it. The only thing I'm unsure of is if it will give me the voltage info I need for larger signals (setting the amps up to avoid clipping and such).

 

Also attached is a pinout of the 20-pin I found through digging on russian sites. I'm still going to check this diagram out, but it actually matches what I saw last night (unlike the other one floating around). It appears that the radio can take the "nav" audio from two sources, backing up what I found last night.

 

I wonder what standard the "Bus" is based on and if it's posible to find some information on it. Also any one have a clue what "B/U" is?*

 

*Edit: B/U = fused battery connection from HU. There is a 5a self resetting poly fuse on the board that feeds this pin, it's used to supply power to bus accessories like the Sattalite tuner, Media Hub, Bluetooth, ect.

sub_20pin_audio_bus.JPG.4f99b3c88c34d9f780f6111084d023db.JPG

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roomeqwizard is a good program for analysis. Trick is you're going to need some pro grade gear to interface with it, because it's only as accurate as your weakest component (A/Ds or D/As)

 

Hum, ok. So how would you suggest going about this? I have not attachment to RoomEQWizzard by the way, it's just a program I used a few times in the past.

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Roomeqwizard is fine, I was more referring to using good equipment outside of it. For instance, I use an Alesis io2 combined with a DBX reference Mic for calibration. Along those line, I would suggest pro audio gear for your calibration.

 

Specifically, you want something USB (read, digital) to avoid your PC's A/D and D/A converters. You also want that device to be high grade.

 

I'm very interested in the results, as I poked around before, but I've got to ask, why not just get the JDM dual HVAC kit and go aftermarket? Sound quality is going to be a lot higher on an aftermarket radio than the OEM. If you want sound quality, you're going to end up aftermarket one way or the other.

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I found an easier place to pick up the audio then attaching to existing components. There is a set of four pads between the Volume IC and the “amp EQ” stage that’s used for the subwoofer amp in version equipped with it. Pic is attached, look at the orange area.

Here is a key for what channel is on what pad:

R237 = RR

R238 = FR

R239 = FL

R240 = RL

I haven’t checked what side of the pad to attach to yet, I’ll update on that later. One will need to have decoupling capacitors after these points though.

Also I’ve analyzed the first part of “Amp EQ”, it’s just a low-pass filter/buffer that should not interfere with anything if one leaves it in place.

Roomeqwizard is fine, I was more referring to using good equipment outside of it. For instance, I use an Alesis io2 combined with a DBX reference Mic for calibration. Along those line, I would suggest pro audio gear for your calibration.

Specifically, you want something USB (read, digital) to avoid your PC's A/D and D/A converters. You also want that device to be high grade.

Alright, I guess it's time to upgrade the radio-shack SPL meter and no-name USB sound card. It works fine for tuning my HT sub with a DSP1124P, but I've never tried full-range with it.

I'm very interested in the results, as I poked around before, but I've got to ask, why not just get the JDM dual HVAC kit and go aftermarket? Sound quality is going to be a lot higher on an aftermarket radio than the OEM. If you want sound quality, you're going to end up aftermarket one way or the other.

Actually I was considering that yesterday after stopping by the Subaru dealership and seeing how much the media Hub was. For the price they want for just that thing one could buy a decent double din head unit with Bluetooth audio functions built in, time alignment (negating the need for a 3sixty.x), and a properly driven line out. But in the end I keep coming back to this for a few reasons, as listed below.

1) Poor user interfaces. No aftermarket head units I've ever found offer the ease of use while driving as an OEM unit. They all have too many small buttons, too many functions, or touch screens. Though nothing could be as bad as some of the aviation GPS's I've dealt with for operation in a moving vehicle, any need to look down or explain to a passenger how to operate it is a safety hazard in my opinion. The OEM unit has the perfect blend of functions on the face. Not iPod-retarded-user simple, not Garmin aviation GPS complex. For complexity I can get a DSP EQ to tune the system with a laptop while parked, I don’t need access to this at all while moving.

2) Blending with the interior. As above, all of the designs are not thought out from a tasteful and useful perspective. They are designed to draw teenagers attention and have "rice" appeal. No thanks, not for me. Also the few "OK" looking ones have an obsession with blue lighting. That won’t blend with the night-vision conscious red interior at all. I have no tolerance for "Bling", it's not going in or on my car. When I'm done the only thing that one will be able to see different in the car will be the tweeter pods on the door sails (will look near stock) and the lump of the CAS box in the back.

3) Theft. If it looks stock, no one will even consider breaking into the car to steal it. I like the ability to park in a rough area of town (Free parking FTW!) and not have to worry about my car being messed with.

4) Cops. I've never gotten a ticket in my 9 years of driving, and I attests part of that to having inconspicuous vehicles on the outside (don’t think it's worth pulling me over) and inside (when they come up to talk to me in the cases they skip part 1). I look about 5 years younger than I actually am, anything at all that might bring to mind the following terms will get me screwed: "teenager", "irresponsible", "bling", "flashy", "loud", "fast", "rap", "Boom". Really anything other than "Well behaved, unremarkable, god fearing, middle class white boy".

5) Technical challenge. Just about anyone can install a "system" in a car using off the shelf components and instructions. There were some people I went to highschool with that were literally retarded that would put them in for extra money. These same types of people could probably even build a system that sounded fairly good. What they can't do is perfectly integrate an aftermarket system into the OEM controls with good sound quality and user transparency.

I always have some sort of technical challenge that I put before myself, this is one of the current ones. It's something I really enjoy doing, and has the side effect of keeping my mind sharp for future professional opportunities that may call on my past "hobby" experience. It's been about a year and a half sence I've analyzed analog circuits like this in a class. Working through the OEM radio diagrams to figure out what it's doing to the signal is a great refresher. Same with my booster amp, a great refresh on my analog electronic skills.

When I finish the radio modification, few people will even have a clue that I've done it. My roommate will from the mess, and my girlfriend will due to the time I put into it. The others won’t know on won't notice, but I don’t care. I'll have the experience that I've gained working through this that might open doors in the future, the personal satisfaction of accomplishing my goals, and a temporary ease to the "Must Build Something!!!" itch. Well, at least until it gets warmer and I install the rest of the sound system.

easy_subaru_lineout.JPG.25d8cdf07e57723f975947afaa396e68.JPG

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I'm very interested in the results, as I poked around before, but I've got to ask, why not just get the JDM dual HVAC kit and go aftermarket? Sound quality is going to be a lot higher on an aftermarket radio than the OEM. If you want sound quality, you're going to end up aftermarket one way or the other.

 

My answer....

 

/rant on

 

I absolutely despise 99% of the aftermarket offerings. That must be absolutely the worst market when it comes design. It's full of horrid designs, both cosmetically, appealing to low-class teenagers, and ergonomically to aliens with extra pair of hands and eyes... How about simple power off button!?? Or maybe that volume control that should not double as a menu navigation knob that sucks you into overly complex menus you can't (and definitely shouldn't) navigate when you drive!?

 

I understand an aftermarket option might be the best choice when the best SQ is concerned, still the tradeoffs in look-and-feel are not worth to me. I recently replaced an abhorrent aftermarket Pioneer unit in my wife's car (bought the car used and it came with it). Trust me, I looked high and low to find a unit with sensible interface, particularly with ONE TOUCH POWER OFF on the volume knob. These don't exist in the aftermarket!!! Ended up buying a double din OEM Nissan Pathfinder head unit, coupling it with an aftermarket (Pac) Ipod interface. Not an ideal combo, but at least is easy to use and does not look like it was pulled out of Startrek spaceship console.

 

/rant off

 

Sorry for the rant, but I don't understand why there are no decent looking aftermarket options. Well it seems there is a couple, Nakamichi and McIntosh, but they don't have or have limited Ipod integration and other shortcomings (side note: I don't particularly care for Ipod, in fact I somewhat hate Apple for the semi-monopoly, but having my entire music collection in one small package to use in car is attractive, I don't use it outside the car anyway).

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