AUX in on a Stock '05 Head Unit w/o Silent CD (The Project)

[zcarmob]

Right now I have the + of the op amps that the audio is feeding just danlging.. The resistors are on the - side of the op and feed the line in audio. It sounds good.

 

Made a really simple setup to switch the radio into call mode when I turn on my satellite radio using the output it provides for FM modulation. It runs 5v down this to trip the accessory which disconnects your stock antenna. I simply attached a resistor and to the +5v and then to the base of a transistor allowing it to connect the call to ground.. This could be done with a relay too.. but this was easier with what I have on hand.

 

 

I am having an issue though.. There is a hum in the background so somewhere noise is getting into the system. Its only audible when there is no audio playing but it is audible. Possibly adding back the capacitors will filter out this noise. The other issue is I am sure I am doing the wrong thing with how the audio is fed to the volume chip... If someone could guide me as to what is the right thing to do that would be great.

 

What is the problem you are having with the volume?? The volume should work with the way you have it hooked up.

[Deer Killer]

if you don't match the impedances and use filters as designed, you risk letting the magic smoke out. And electronics don't work after the magic smoke leaves.

[mcwiggin]

Update:

Ok- Added the resistors. Everything works as expected. Its pretty slick. I turn on my sirius receiver and the head unit goes into call mode and tunes start playing. Turn off the sirius receiver and the head unit goes back to whatever state it was in before.

 

I have one remaining issue.. There is still a whine in the system. I did something wrong in finding a suitable audio ground. Using the stereo body as a ground turned out not be a clean enough ground for audio use. I need to figure out where I can find a clean ground so that I can eliminate the engine whine.

 

Besides that.. I am pretty excited. The sound is clear and clean as would be expected.

 

If anyone has ideas where I can find a suitable audio ground (hopefully w/o disassembling the whole head unit again) please let me know.

[jazzymt]

You're gunna need a ground loop interupt... Seriously - there is simply no other way to avoid that noise if your audio source causes it...I've seen people try everything & a GLI is all that ever worked.

 

Nice work btw.

[Deer Killer]

Update:

Ok- Added the resistors. Everything works as expected. Its pretty slick. I turn on my sirius receiver and the head unit goes into call mode and tunes start playing. Turn off the sirius receiver and the head unit goes back to whatever state it was in before.

 

I have one remaining issue.. There is still a whine in the system. I did something wrong in finding a suitable audio ground. Using the stereo body as a ground turned out not be a clean enough ground for audio use. I need to figure out where I can find a clean ground so that I can eliminate the engine whine.

 

Besides that.. I am pretty excited. The sound is clear and clean as would be expected.

 

If anyone has ideas where I can find a suitable audio ground (hopefully w/o disassembling the whole head unit again) please let me know.

 

The right way to do it is the use the ground pins above the pins above the pins you tapped into. GLI or not if you're attaching your audio device's output to body ground on one side it's going to be noisy.. Also you're going to be missing bass as the actual audio ground is floating. What I suggested above is "sorta" what you're doing but using the on-board filtering..

[mcwiggin]

Which pins are you referring to as the ground pins? Audio is not my specailty when it comes to electronics. I am much more at home with digital logic circuits. Luckily there you can do some pretty nasty things and still get away with it because you just need to get the 1 or 0 across..

[Deer Killer]

as labelled R- and L-

[mcwiggin]

I tried grounding to those pins but the audio went away all together. I am doing something wrong. If you look at the block diagram of the volume chip the + and - are both inputs to an op amp inside the chip. I am actually running the audio through the - lines right now. I know I have done something wrong but I am not sure what the right way is to connect the audio.

 

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

[Deer Killer]

Don't ground those pins! None of the input audio connectors should be grounded to body either.

 

The only thing grounded should be the logic select, if you're using that.

 

Just use R+/R- and L+/L- as your two channels. Tie L- and R- together if you're using something with a common audio -, like a headphone output jack.

[drcaveman]

Great I am glad to see such progress, way beyond my Mechanical Engineering knowledge.

 

DrCaveman

[Jon in CT]

It seems like there are many lumps in the circuit between CN402 and IC206:

 

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

 

http://www.mcwiggin.com/subaru/audioplan.jpg

 

You're trying to ignore as many as possible. Maybe that isn't a good idea. Maybe, instead, you need an Aux Box with circuits that duplicate what the headunit does to the handsfree phone audio input between its arrival at the connector and its input into IC206.

 

The Aux Box circuits would look like this:

 

http://i16.tinypic.com/2wogn01.jpg

 

The only problem is that the service manual never provides the inductance value for the coils. Maybe you could measure it and let us know what it is.

[zcarmob]

Can't you just connect the R+ to pin 4 of CN402 and the L+ to pin 8 of cn402.

Then connect the R- and L- to pin 6 on cn402.

With those connected then remove c403 and c405 capacitors.

That should work right?

The Radio/CD does not have a negative into IC206.

[Deer Killer]

;948751']

The only problem is that the service manual never provides the inductance value for the coils. Maybe you could measure it and let us know what it is.

Well, theoretically it's "ok" to skip that, it's a low-pass filter anyway. The cap is much more important as it at least provides some de-coupling from the input..

[zcarmob]

Anyone think my suggestion in post #37 will work?

[Jon in CT]

Anyone think my suggestion in post #37 will work?

It won't work.

[zcarmob]

Any reason why it wouldn't???

[NutBucket]

It won't work because pins 8 and 4 represent Signal + and Signal - of a mono circuit. You can't feed Signal + into both sides of an amplifier.

[NutBucket]

Ok, upon some further consulting there is a bit of misinformation floating around here. If you notice on IC, the signals into the pins of interest are labeled L+ and L-. If I'd paid attention I would have immediately identified them as differential signals. So, what zcarmob posted in #37 works, sort of. You see, L+ and R+ are tied together. You'd still lose stereo. What you need to do is tie one input from CN402 to R+ and the other to L+. Then, ground both L- and R- to signal grougn. Tie the signal ground from the auxiliary source to that same signal ground in the radio. Now we've effectively converted the differential input to a single ended one. A bit crude, but we're talking about audio signals here. By doing this, we eliminate the need for any sort of auxiliary adapter and noise filters. We'll just use what's already provided.

 

And we were wondering what value L606/L605 were? Well, they're not really inductors per se. They're beads, or EMI filters to help prevent any sort of alternator whine and what not. They are not filters designed to isolate vocal frequencies.

 

I plan on trying this sometime this week when I have some time at work.

 

Any thoughts?

[zcarmob]

Pins 2 and 3 of IC206 are for Right + and -.

Pins 35 and 34 of IC206 are for Left + and -.

 

On cn402 pin 4 and 8 go to 2 capacitors each then they split into R+, L+ and L-, R-. All have seperate traces to IC206.

 

Pins 2 and 3 are connected to the same transistor in the chip also Pins 34 ansd 35 are connected the same way.

 

if you remove c403 and c405 capacitors. then you will only Right + going to pin 2 and Left + going to pin 34. you could jump it over to pin 35 so both go to the Positive pin on IC206. The negative Left and Right will be taken care of with hooking it to ground.

 

Then if you ground pin 2 on CN402 then that will put the radio in call mode and sound should come through the speakers in stereo.

[NutBucket]

Sounds about right to me. Time to get soldering;)

[zcarmob]

you mean desoldering

[zcarmob]

The trigger is to ground pin 2 on cn402

[NutBucket]

Well, both. Gotta remove then jump;)

[Deer Killer]

Ok, upon some further consulting there is a bit of misinformation floating around here. If you notice on IC, the signals into the pins of interest are labeled L+ and L-. If I'd paid attention I would have immediately identified them as differential signals. So, what zcarmob posted in #37 works, sort of. You see, L+ and R+ are tied together. You'd still lose stereo. What you need to do is tie one input from CN402 to R+ and the other to L+. Then, ground both L- and R- to signal grougn. Tie the signal ground from the auxiliary source to that same signal ground in the radio. Now we've effectively converted the differential input to a single ended one. A bit crude, but we're talking about audio signals here. By doing this, we eliminate the need for any sort of auxiliary adapter and noise filters. We'll just use what's already provided.

That's what I said 9 posts ago.. Also tying the L- and R- does not make it into a non-differential signal!! The ground still floats.

 

And we were wondering what value L606/L605 were? Well, they're not really inductors per se. They're beads, or EMI filters to help prevent any sort of alternator whine and what not. They are not filters designed to isolate vocal frequencies.

Inductors are inductors. The filter frequency depends on the impedance of the circuit, which I cannot guess at. EMI filters don't filter magic EMI signals, it's all electricity and magnetism...

[NutBucket]

You're right, tying L- and R- doesn't make it non-diff. Tying it to signal ground just means we can use the diff input with a single-ended source, like you said. I didn't read fully either;)

 

From what I could find online, I found a very similar part number for a Murata part that is an EMI filter in the form of a SMT chip....unless I'm not remembering right from earlier in the day. I'll have to look it up again tomorrow since I think I left the datasheet open on one of the computers at work.