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

[utc_pyro]

Wow, looks good. I must confess I am a little terrified now looking at those solder points on the radio. Can you recommend what equipment I will need to accomplish the task when I get mine?

 

Thanks again for doing this, awesome work!!

 

-Jason

 

It wasn't THAT bad of a job on the radio. It took a lot less time then making the board. I just used an adjustable temp ~25W iron turned all the way up and some fine soilder. 6 out of the 7 points are actually on pads, so they are easy to work with. Only the +8V point is a pain due to taping into a via.

 

Routing the wires on the back of the board out the case is a PITA though, thinner wire is a MUST.

[mars_volta]

Sweet! Cant wait for test results.

[utc_pyro]

See the pics. I have it installed on my home system, and it actually sounds decent. There is a little something in the sound that I cant ID, but I dont like though.... I'll have to see what shows up in the sweeps. I think it might be the opamp in this board, but I have several to choose from. Also I have yet to do the loudness kill. The only error I've found on the board so far is I did the "linear" curve on the POT wrong. One little snip and some extra soilder should fix that though.

 

I'll see what kind of sweeps I can do a little later tonight. I need to hack up a cable to work with the aux in.

 

Also, if any one wants to design there own board, the 8V rail is actually 8.5V or so, and the max signal at the points we're picking it up from is ~.2v rms. Thus a gain of 10 is all that's needed from the pre-amp.

[mars_volta]

Does it sound 'flat'? I built an 8 channel mic pre amp years ago and it sounds great, but 'thin' or 'flat' or 'solid state'. Not warm? LOL. I never bothered to rework it.

[utc_pyro]

Kind of... I have a hard time describing it because I cant put my finger on the sound. It's a lot less dynamic then the audio coming in from the xbox though playing the same CD. The CD is over driven though, need to find something pre-loudness war to try on it. "Crunchy" is a good way to describe it....

 

I'm going to go run the xbox's analog outputs though my board and see how that sounds. That way I can tell if it's my circuit, or the OEM radio. I'm not sure how the xbox's analog outputs sound though, I've had it on digital it's entire life.

 

Edit: Ran the board with the xbox as the input and a CD from 1987, and it actually sounds pretty good, but ONLY with the gain at the minimum. Anything past that causes clipping. Though I guess that's somewhat reasonable, the x-box is outputting 10-20db higher then the OEM radio. Time to try other opamps.. First up: OPA2132PA

 

Edit 2: Insted of trying opamps, I changed the source: I used an MP3 cd in the player. Strangely enough, it sounds a lot better then non-compressed CD's . Also, just using my meter, I found that the level coming off the board is 1 Vrms when using the MP3 function, and it does not clip at 40!

 

So in this case, Crunchy = slight clipping and sh*tty CD DAC.

 

So, maybe I DO need to use a DC-DC converter, OR maybe no boards are needed at all . I need to hook up the ground to see what happens straight off the volume control chip.

[ean611]

It's worth comparing the CD player raw output with the final output of the OEM radio.

 

The CD player on the OEM radio outputs line level on the ribbon cable, and you can easily tap into that and listen to it.

[mars_volta]

Hmm. Sounds like too much gain no matter... Swap a decimal somewhere?

[utc_pyro]

Swap a decimal somewhere?

 

Heh, close. Forgot a "1+" in the gain equation .

 

I'm making some test CD's right now to tune in the gain on this thing, then it's time for sweeps.... I think I need to make a daughter board to run that +/- 12V dual rail dc-dc converter I got off ebay on the thing. I'm sure it would sing with a 24V differential.

[ean611]

utc_pyro, google "roomeqwizard"

 

It should be on Home theater shack, and is a great program for sound test tone generation and analysis

[utc_pyro]

It's already on the computer in the last pic (I use it to tune my sub eq), but to get the gains right I need to use that CD I burned last night. The aux in has the possibilty of being driven too hot, leading to an inacurate representation of the loudness curve. Thus I'm going to use the CD player as the level refrenve before doing the sweeps. Hopefully I can get it all done tonight before I head out of town.

[beanders]

Great Job!

 

I have been following this thread for a while. I did something similar for my Yaris. It sounded great, but suffered from electrical noise. Alternator whine, turn signal, etc. all were putting noise into the signal.

 

For now, I am simply using the factory head unit with my circuit installed, but not in use.

 

So have you installed it in the car and hooked it up to an amplifier?

[utc_pyro]

My AUX input isnt working for some reason, so I have yet to get sweeps... Those will have to wait until I get back from FL. BUT, I did find out some important info:

 

On the 07+ radio, the points I found put out a true 2vrms already. It's actually set up perfectly so the signal goes right up to max amplitude with EQ turned all the way up, but it never clips!

 

So, that said, my board is NOT NEEDED if your amps can take a 2vrms signal (typical home audio level) and be happy. I'm still going to try the V1 boards with an off board +/- 12V supply though, and maybe develop a V2 with one integrated one.

[ean611]

wait, the 07/08 Radio has Line level (2vRMS) output? I'm confused, is that with loudness built in or removed?

 

Without the loudness removed, the 2vRMS has slightly less value...

 

EDIT: I'm confused, because I tried tapping a few points on the board, and when hooked up to an amp, did not produce a usable signal. I'm very interested in which VIAs produced this.

[Zimm]

So here is a question then. I have a JL e1400D amp pushing my sub. Would I be able to get away with simply tapping these points and feeding the amp directly with them? I know 2Vrms is on the low end of the spectrum for line level signal but would it be enough?

[Zimm]

Also, where are you attaching the shields/grounds for the channels. You ID'd the locations to tap for the signal but what did you do with the shield wire for each channel?

 

I did a little research and it looks like most lower end head units output 2Vrms normally. This means amps should work fine with this signal so long as it is clean and isolated.

 

Thanks again for all the work on this project. Most people would never dream of tearing open their car stereos!!

[utc_pyro]

wait, the 07/08 Radio has Line level (2vRMS) output? I'm confused, is that with loudness built in or removed?

 

Without the loudness removed, the 2vRMS has slightly less value...

 

EDIT: I'm confused, because I tried tapping a few points on the board, and when hooked up to an amp, did not produce a usable signal. I'm very interested in which VIAs produced this.

 

This was pre-loudness kill. I want to run some sweeps before I kill it so I can do a true before and after. I tested this with a CD with test tones scaled to a "1" (max) amplitude, my meter, and listing to it as I adjusted the gain. The signal at "flat" settings is ~1.7v rms, but goes to ~2.4v rms when one turns up the corresponding mid/bass/treble.

 

I was confused as well, seeing as some of the opamps down the line in the "amp eq" section have gains greater than "1" and your past experience. It seems to work just fine though on my home system. The points I took the signal from are on page 2, post 27 of this thread.

[dr_sharp]

Any updates?

 

How did the FE go? Judging by your proven competence in this thread, I think you wasted your time if you studied for it... I remember being very upset about the amount of time I wasted that day (and night before)

[dr_sharp]

This was pre-loudness kill. I want to run some sweeps before I kill it so I can do a true before and after. I tested this with a CD with test tones scaled to a "1" (max) amplitude, my meter, and listing to it as I adjusted the gain. The signal at "flat" settings is ~1.7v rms, but goes to ~2.4v rms when one turns up the corresponding mid/bass/treble.

 

I was confused as well, seeing as some of the opamps down the line in the "amp eq" section have gains greater than "1" and your past experience. It seems to work just fine though on my home system. The points I took the signal from are on page 2, post 27 of this thread.

Are you certain on those solder points? I have my board out ready to solder on some RCA connectors to go straight to my amp.

[dr_sharp]

For anyone interested, I took some pictures of the disassembled stereo. You pretty much have to take the entire unit apart to get to the location that utc_pyro has notated as the nodes for low level speaker outputs. Its not difficult, there are just alot of screws.

[mars_volta]

Take the back, front and bottom covers off. Cant wait for results. I'll be tearing into mine soon.

[dr_sharp]

I just soldered to the "FL" connection from post 27 of this thread. I got usable audio. Unfortunately, I have no way of measuring the signal's amplitude. I don't yet know if it will work with my amps, I hooked the single channel up to an altec lansing computer speaker set since I don't have my amps fully wired yet... I had to turn the pc speaker up very high and I had to turn the head units volume up to about 20 to get good audible volume. Going to go ahead and solder the rest. I *might* have the amps in by the end of today.

 

[edit] Got usable audio from all 4 points. Still concerned about voltage level, though. Very quiet compared to what I know the pc speakers can do.

[utc_pyro]

With the line out points without an extra amps (working on one, dont worry), you'll have to "relearn" what volume level is OK to turn the radio up to. At 40 it goes up to full usable amplitude with any EQ setting. This is equivalent to ~65% on most OEM and aftermarket car radios.

 

That said, at 20 it's at about the same level as the other components on my den surround sound system. Home audio tends to use lover levels then car audio does though, as there is typically a lot less electrical noise to overcome. Well, unless you live next to a Aluminum or Steel mill.

 

I got the Aux-in fixed on my board, but I have more pressing issues at the moment then sweeps.... I think I may have nuked my 5EAT

 

Edit:

One more thing. If your amps do not have decoupling capacitors, you'll need to add one inline with each point. That or pick up a line driver, most of those are decoupled and will bump the levels up to a "usable" ~7vrms.

[dr_sharp]

OK, I was able to hook up my amps today and I was actually impressed with the volume that I got out of the signal. At 4V sensitivity, it was not very loud. I turned it to about 2-3V sensitivity and it was much, much louder. I only had 1 stock speaker hooked up in open air and it was actually impressive. If I had turned sensitivity to the full 0.25V level I'm sure it would have blown the stock speaker, even at half oem unit volume. If you have an amp that can go down to 1V sensitivity, you'll be fine. If you can go down to 500mV or 250mV sensitivity, even better.

 

I know what you're saying about the volume levels. In this case, since we know that no clipping is occuring, you can immediately turn the HU up to full volume and then adjust the sensitivity on the amp accordingly. Generally it is rule of thumb to turn HU to 2/3 or 3/4 volume and go from there, but that's only because every HU on the market (even high end aftermarket ones) will clip when pushed to near limits.

 

Now I did find one thing that bothered me... my amps are no longer functional. I was getting signal from 1 channel bleeding into the other... I guess 4 years of thrashing followed by 4 years of hibernation took it's toll on them. So, I'm now considering the Kappa Five amp. It is 75Wx4 + 300x1 at 2ohms. Not quite up to power specs I was looking for, but Harmon companies are known to underrate their products. The JBL amps that this will replace had been tested to produce the full advertised 360WRMS power at 12V supply voltage... meaning that when the car was turned on (~14V), you get a bit more power than advertised.

 

I have 1 last question for you utc_pyro. How did you determine the locations of these outputs? Were they conveniently labeled in schematics or did you have to do some reverse engineering to find them? Or did you just randomly search the pcb for signals until you found something usable?

 

Thanks for the help, you saved me from having to buy a cleansweep/3sixty,etc.

 

Sorry to hear about the tranny. Hope its not too bad! Do what I did and get yourself a spec.B as graduation gift to yourself

[utc_pyro]

Lol, the GT was more of the graduation gift to my self. I was sick of borrowing my mom's Forester every time I needed to pick up anything but the smallest piece of furniture, and my other car was starting to show signs of impending doom. I think I know what's up with it though, I just have to mess with it after work tomorrow. I'm crossing my fingers that I just overfilled it yesterday when I flushed it.

 

On the '05-'06 radio, everything was laid out in the service manual for the line out mod. All I had to do was compare the one with the sub amp to the one without, and find the unpopulated points. The '07-'09 radio I had to follow traces and check depop'd points until I found a workable set. I had the pinout of the M62490FP, so I knew what pins the audio came off at.

 

The loudness kill was the complex part (I haven't tried it yet). I measured all the components in the "loudness" RC network and put them into PSPICE. I then compared that to several common loudness circuits to figure out how it worked, and devised a way to kill it without messing up volume control. That took things I picked up in a few 300 level classes to do, but a non EE with basic electronics knowledge could probably figure it out with a weeks research online.

 

And to your earlier question about the FE: Unsure about it. I was thinking it was going to be a lot worse then it was, but I do wish I studied more of the general stuff. Subject matter from classes four years in the past does not come back as easy as one might like....

[mars_volta]

Any more testing on this? I have time tomorrow to do it.