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

[SVXdc]

The V2 boards will be the cheap, simpler, build-install-and-go type board. ... no RCA inputs, etc.

You meant "no RCA output jacks" (which I'm guessing means the board will just have solder pads for people to connect wires to their own cables with whatever plugs or jacks they wish to use, right?).

[mars_volta]

Subscribed. I have the "Must Build Something!!!" itch. I'm installing a Motorola T605 bluetooth kit for music and have been thinking about a Re-Q. This would be much better as I could run my old school fosgates again!

[utc_pyro]

You meant "no RCA output jacks" (which I'm guessing means the board will just have solder pads for people to connect wires to their own cables with whatever plugs or jacks they wish to use, right?).

 

Both actually. The input will not be an RCA jack set like the already posted board, and the output wont be ether. Both will just be an edge connection point were one can use whatever wire they want. Most would probably just cut an RCA cable in two and use that for the output though, as it's cheap and simple.

 

V0.9a of the board can be seen attached below. I changed the ground to one that I can switch with jumpers, corrected the RCA inputs, and revised the layers that some of the wires are on. Green is the bottom layer, red is the top. I'll be ordering these tomorrow (today now?) night if I don't find any more errors.

 

I'm going to use these boards for testing and setting the gains, and then I'll make the final schematic/PCB file/parts list for the V2 boards and post those here for any one else wanting to make one. Might also be useful for those wanting just to install a sub, they could just build half the V2 board, install it and go.

 

The V1 board is a 2"x3" board, using the pad2pad service for fabing.

[mars_volta]

No cutting of traces? Just tap left and right from the board? Does this affect the stock output? Say if I just run this into my sub and leave the other speakers stock for now...

 

 

I am willing to bet this head unit is as clean as any from crutchfield. That may not have been true 15 years ago.

[utc_pyro]

You only need to cut traces to remove the loudness, and that's optional. I'll starting to think loudness will be a little more involved, but I need to sit down with pspice and try it.

 

Stock output will not be changed if you don't do the loudness disable.

[mars_volta]

Ok. Sorry for questions...

 

If I don't cut the loudness, at least my new sub out will be 'non EQed' right? I don't care that the stock speakers still get EQed. If I do cut the loudness traces, then all outputs are now 'flat' and don't change according to volume?

[utc_pyro]

if you don't cut the loudness trace, the sub will only have the "loudness" eq on it. There are two stages of EQ, and the second is the worst for bass. If you do disable loudness on the stock speakers, it I may take the "life" out of the sound unless you manually adjust the bass/treble to compensate.

 

Again though, I need to sim this and then try it.

[mars_volta]

Got it. I will be in my radio this week adding a aux-in switch , and may do some playing with this. Thanks!

[SVXdc]

You meant "no RCA output jacks" ...

Both actually. The input will not be an RCA jack set like the already posted board, and the output wont be ether. ...

Ah, I missed that on your earlier board layout.

 

I don't see any advantage to using RCA jacks for the input to your board. Since you'll be soldering the other ends of the wires into the HU, a smaller (and less expensive) header should be fine going into your board, or even soldering the wires directly there too.

 

As for the outputs, if I were building one for myself, I'd have RCA jack "pigtails" hanging out the rear of the HU (so no need for output jacks on the PC board either).

[utc_pyro]

I don't see any advantage to using RCA jacks for the input to your board. Since you'll be soldering the other ends of the wires into the HU, a smaller (and less expensive) header should be fine going into your board, or even soldering the wires directly there too.

 

As for the outputs, if I were building one for myself, I'd have RCA jack "pigtails" hanging out the rear of the HU (so no need for output jacks on the PC board either).

 

That's exactaly how the V2 board will be. There will be no provisions for RCA jasks, just a place to soilder in your own "pigtails" or bare wire. The V1 board is more for my own testing, my first install, and maybe an install for one other person (I want to dissect a HK head unit). Thus the RCA in and outs, it lets me wire my "pigtales" right up to the stock radio and

 

 

 

BIG UPDATE ON THE LOUDNESS!

Ah pspice... I hate that GD program but my hacked version of multisim is no longer working. It brings back too many memorys or working in labs until 3AM trying to get analog circuits going on fried equipment. But it's useful in this audio hacking stiff.

 

Attached is the pspice for the "loudness" circuit in the 2008(?) radio. I used my multimeter an LCR meter to test all of the components between the input stage and the bass/mid/treble stage to model how it works.

 

http://i40.tinypic.com/20sf7s7.jpg

PSpice schematic of the loudness compensation circuit.

 

First off, the loudness may not be that bad. At some valued for the digital pot, things looked fairly good. At others, it looked BAD. Ether way though, there is a nice boost in the bass below 100hz, so anyone looking to just do a sub install should be in good shape leaving it as is.

 

Second, I could never nail down the value of the internal digital pot. If any one has an idea how to do this, please let me know. This will let me more accurately model the audio path. Setting it up as a 300K pot seemed to give the most realistic results.

 

Third, the 2005 service manual is WRONG about the component values. It never looked remotly right untill I measured them and put those actual numbers into the simulator.

 

http://i43.tinypic.com/fk9lkp.jpg

Figure 2. What the loudness compensation looks like using the measured values with a 300K internal pot.

 

Fourth, one cannot cut the trace I talked about earlier in this thread. It will actually mess with the volume control. The internal "pull up" to Vref is ~168K ohms, too high to be used on it's own unless the digital pot is in the 1M range. This will require more modifications, but I have a solution.

 

New loudness kill procedure:

(This works on all 05-09 USDM head units with auto climate control)

Remove, or cut the traces to the following capacitors: C207, C201, C307, C301.

These are all on the bottom of the board on the drivers side.

[Guest]

New loudness kill procedure:

(This works on all 05-09 USDM head units with auto climate control)

Remove, or cut the traces to the following capacitors: C207, C201, C307, C301.

These are all on the bottom of the board on the drivers side.

 

Are you saying cutting these traces will kill loudness for good and get clean signal to an amp without any special board?

[utc_pyro]

Are you saying cutting these traces will kill loudness for good and get clean signal to an amp without any special board?

 

 

Not quite. This will remove the loudness compensation from the output of the volume control chip (M62490FP), but there is another stage of EQ after that chip and before the stock amp. The whole point of this is to intercept the signal between the volume control chip and the second stage of EQ to send to an external amplifier. The signal levers at that point are quite low, thus the need for the board I designed.

 

You could also use an off-the-shelf 4-channel line driver to do the same thing as my board, and tap into the same place on the board. It wont sound quite as good as this setup, and will have a little more noise, but will still be significantly better then using a speaker level LOC.

[Guest]

Nah, I am most definitely interested in your board (if it works with 09 "HK" unit).

 

What is the "another stage of EQ"? Bass/mid/treble adjustments?

[utc_pyro]

No, that's something we want to keep. I'm referring to this:

 

http://i41.tinypic.com/245lp5i.jpg

 

That entire block of op-amp hell is the second EQ stage. The clips with "Rch" and "Lch" on them are 4-channel opamps. So 14 total op-amp channels messing with our audio. Good reason to bypass it!

[SVXdc]

BTW, where does the built-in 5th-channel subwoofer amp get its input signals -- pre- or post-EQ/loudness/etc.?

 

 

(for those joining us late, the sub out is only present and working on 2005-2006 MYs

EDIT: Oops, only on radio model P-203UE )

[utc_pyro]

The sub amp (if equipped) picks up the audio right after the M62490FP volume control chip. So this is post loudness, pre "amp eq", and uses the exact same pads I'm going to. In the 2006 radio It just uses a resistor network, and probably introduces a lot of cross-talk between the channels. I haven't figured out that part of the '08 radio yet, but there is better isolation between the channels.

 

The 5th channel amp is only included in the radios in VDC Outbacks (and maybe the '09 HK unit) that have the sub in the rear corer of the cabin. Thus, it wont be applicable to most users here. There are still the places for the components on the board though, so one can trace how it would be used.

 

Speaking of the '09 HK unit, I may need one to do testing at some point. I have my '08 head unit I'm working on now, and the '06 unit in my car, so that's all I'd need to make sure it works on all of them. Any one want to lend me one to dissect

[SVXdc]

Thanks. So do you see any indications that the 2005-2006 sub amp has better low frequency response than the main speaker outputs? I'm working with someone who wants to connect a powered sub, and wants to try connecting a LOC to the sub output.

 

The 5th channel amp is only included in the radios in VDC Outbacks (and maybe the '09 HK unit) that have the sub in the rear corer of the cabin. Thus, it wont be applicable to most users here.

I know that only a few particular Outbacks had the rear cargo speaker, but I'm fairly sure that the same HU model number was used in many different Legacy and Outback 2005-2006 models. So the amp components should be populated on that HU in any car it was installed in (whether or not the car had the rear subwoofer speaker). [ADDED: Wrong! See replies]

 

In cars with the h/k system, the HU is similar to those in 2007-2008 -- it only has 4 speaker outputs. Those are fed directly into the h/k underseat amp, which then generates the eight output channels (4 door speakers, 2 tweeters, and single- or dual-voicecoil sub). See amp's harness pin-outs here.

[utc_pyro]

I have a normal 2005-2006 radio as well. The sub amp is NOT populated in the normal 2005-2006 radio, only the special MP3 comparable one (easy way to tell). More specifically, have them look at the top. If it says "CQ-EF1561" the there is no sub amp inside. If it says "CQ-EF1560", it has one.

 

If the radio is the "CQ-EF1560", then it will have better low frequency response then the main outs. The loudness circuit is holds the low end solid until sub 20hz, so the death of the bass is later down the audio chain.

[SVXdc]

What are the model numbers printed on the fronts of those respective versions?

 

n/m -- found them:

 

P-203UE is CQ-EF1560 (has MP3 CD capability and sub amp)

(according to Jon [in CT], this "was used only in the 2006 spec.B and Outback VDC models")

 

P-203UH is CQ-EF1561 (no MP3, no sub amp)

 

Both have "Onstar" (phone audio input) and audio Steering Wheel Controls (SWC) capability.

[CTATV]

subscribed

[mars_volta]

FWIW, I have both the stock 05 GT radio and the MP3 cd radio.

[Guest]

Speaking of the '09 HK unit, I may need one to do testing at some point. I have my '08 head unit I'm working on now, and the '06 unit in my car, so that's all I'd need to make sure it works on all of them. Any one want to lend me one to dissect

 

That can be arranged. I'll pm you later.

[utc_pyro]

V1 boards ordered. Should be here in two weeks. It took a few extra days because I had to pull out my OLD laptop to place the order on. Apparently Pad2Pad does not like win 7 x64 on a macbook....

 

If all goes well, V2 boards (general user) will be available in early may. I want to test before ordering those.

[ean611]

utc_pyro, you didn't try xp mode?

http://www.microsoft.com/windows/virtual-pc/download.aspx

It's free for Windows 7 pro and Ultimate. That should allow you to run any XP app natively without digging out an old machine.

[utc_pyro]

Tried that... also tried runing as admin and a bunch of other things. I think my laptop is just messed up and needs a clean windows install. Pad2Pad crashes all the time on it, romraider won't work well, WinIDS crashes, and the Xilinks FPGA tools don't work quite right on it.

 

Never has problems in OSX or Ubuntu, so I'm betting on softwere vs hardware.

 

On topic though: is there enough demand for a extra simple "I just want to add a sub" board to design one? It'd be smaller, have half the components, and only require 5 soilder points to the radio? Still a kit, but a lot simpler.