My C33 Stereo Aux Input Project

[m2pc]

I'm starting my own thread for this DIY because I believe I found a unique approach to this project, and because I still have some issues to work out.

ADDED 2008-09-17:

Features of this design include:

1. AUX-IN Jack in the stereo, accessible from the front faceplate.
2. RCA jacks on the back of the stereo, for hardwiring carPC/iPod/iPhone dock.
3. Switched, impedance matched, isolated audio circuit.
4. Fools the head unit into thinking a tape is inserted when it's not, eliminating the need for a "dummy" tape.

TODO:

There is an issue with the way I trick the head unit into thinking there's a tape inserted;
when you try to insert a real tape, the head unit won't accept it. If you hit EJECT and then try putting the tape in,
the head unit draws it in, but displays "TAPE ERROR" on the display.
Solution: I'm building a circuit to measure the resistance present on the AUX In jacks and automatically switch to "AUX IN"
mode. This should allow the head unit to play a tape when no AUX In signal is present.

It's only pictures for now; I will refine this post further as I get more information.

Audio switching/isolation circuit:


Tapping into the audio path:


Leads soldered in place:


Ground and switched +12V connections:


Ambient Light Sensor we will be re-routing to the "security" LED spot:


Carefully soldering wires to extend the light sensor:


Wires soldered where Light Sensor used to be:


Ambient Light Sensor hole enlarged for 1/8" Aux In Jack:


Finished Product:

[Bris328is]

thats nice--good job

[m2pc]

Hey thanks for the kudos!

First post updated to add project features and To-Do list.

[kirbykirbykirby]

I did this with my old C33 but did it much more ghetto just wired a aux in cable, and had it go to the cup holders.

[kirbykirbykirby]

http://rides.webshots.com/album/557529812aLFABe

[just4kinks]

Good job.

I researched doing something like this with my C43, but I wimped out because I felt like I was in over my head.

[m2pc]

UPDATE: After much research, I decided to return my head unit to stock as far as the "tape inserted" switch goes, since disabling it was causing problems with being able to use a tape (I'd like to retain that feature).

I found a chip on the main PCB I may be able to tap into for a better aux-in signal (Thanks to dirtyguido). It's a chip marked "TDA7328D" which is a stereo audio signal processor. Datasheet is here: http://www.datasheetcatalog.org/data...ics/mXytuz.pdf

My new plan is to intercept pins 6, 7, 16, and 17 and automatically switch my audio signal into that path when an AUX IN signal is present. That way, the head unit can be set to any source (AM/FM/WB/Tape/CD) and the AUX In will take over the signal.

I also plan to ditch the mechanical relay and employ an analog switch IC, such as this one: CD4066 (Datasheet here: http://www.datasheetcatalog.org/data.../109222_DS.pdf)

[dirtyguido]

bascially here's what I do on them...

Desolder pins 9 and 13, and connect sheilded audio cable L and R respectively to them. Connect ground to chassis ground. I disable tape function in favor of the aux in.

If you want to keep the tape function, which it seems you do, all you need is a couple relays, where you would switch between the aux in and the tape to those pins. I leave the tape mechanism alone on them and yes, you do need to insert a tape, doesn't matter if it's blank or not, because the audio is no longer coming from the tape deck pcb. If that makes sense. If you want to pickup a preamp signal,(for aftermarket amps) pins 22 - 25 would be your center conductors of your RCA cables, common ground.

Now, your plan of intercepting the audio between whatever source and having the aux override it, would require cutting in between pins 16 and 17, and pins 6 and 7 on the other channel. BUT you would need some sort of sensing circuit for the aux in to switch it. Another way to do it, look at parts express, they have certain 3.5mm audio jacks that have a built in switch in them that activates when they have a plug inserted into them,

Take care,

George

[m2pc]

I redesigned the circuit to switch itself in and out of the main "pre-amp" loop on the TDA7318D IC. It looks like there's already some capacitors soldered on the board that lead to those pins, so I shouldn't have to do any surface mount desoldering/tapping in.

This should allow me to select ANY input (AM/FM/CD/Tape) and the AUX IN signal will take over. This means I can re-connect the tape sense switch and retain full use of my tape deck!

Schematic is attached.

[isocuda]

this Brilliant setup needs a step by step...

I was gunna just solder some connections direct to the channel inputs and make an input jack...

but After seeing someone took the time to figure out the chip connections and such, which may be well over my head it would be great if I knew what parts to buy at RadioShack, and where most of the connections actually are

[m2pc]

Hey guys, bringing this one back from the dead.

Today I cracked open my C43 stereo in the M3 and went to town.
I was able to isolate the audio signal as planned, right at the stereo processor chip.
I have a hacked setup with the stereo coughing up wires out the tape slot currently, while I put the finishing touches on my auto-AUX-in switching circuit.

Preliminary tests yielded AWESOME sound, with no "muddied" sounds like my previous design.
This bypasses the tape circuit which is designed to cut out high frequency sounds.
We're now injecting audio right into the heart of the system.

More to come soon on this project!

[m2pc]

Image of audio tie-ins to C43 stereo:

[Dominic49]

hawt. let us know how it goes

[theruined]

could you possibly follow up with any more pics/info on the C43 project as I'm trying to mod one myself but get stuck at the wiring - what I'm trying to do is a take off of Jcrowell's guide, minus the C33 part, wherein lies the problem.

I'm trying to follow the above pic but it doesn't really make any sense as I have limited experience with electrical wiring...

[dorkymood1]

Is the radio with WB an c33 or c43 ?. In your firsr post you call it a c33 and in the last post you call it a c43. My other question is what cd deck works with the radio with the WB band? Any help would be appreciated. I tried realoem to try to figure out what radio I have but could not figure it out. Thanks in advance.

[m2pc]

Sorry, I started with a C33 (the one with the WB) but that car was totalled so I started hacking my new car's stereo (C43, the one without the WB but with RDS).

Both are similar, and the connections are almost identical. I've been running for a few months with a broken switching circuit, which only allows me to listen to the AUX input while the car is running, which is not as I planned obviously. However the sound is very clear without any of the distortion/quality degradation you get tapping into the tape deck circuit.

Once I get the openOBC project done, I will go back and focus on this more. It has huge potential.

[DerekVa]

Sorry, I started with a C33 (the one with the WB) but that car was totalled so I started hacking my new car's stereo (C43, the one without the WB but with RDS).

Both are similar, and the connections are almost identical. I've been running for a few months with a broken switching circuit, which only allows me to listen to the AUX input while the car is running, which is not as I planned obviously. However the sound is very clear without any of the distortion/quality degradation you get tapping into the tape deck circuit.

Once I get the openOBC project done, I will go back and focus on this more. It has huge potential.

Any update on this?

-D

[gte619n]

I'd also love to wire directly into my C33's audio circuit. Any chance we could get an update on this? Thanks!

[NJDave]

Yes, "M2PC" ... please update us on your final Alpine C33/C43 AUX modification (going through the main Audio Signal Processor), with full schematic, photos, and text description of what worked.

I've had my C33 apart ... just waiting to be AUX modified through the Audio Signal Processor (TDA7318D)!



Thanks

[JDStrickland]

I installed a wired FM Modulator. I was excited when I buttoned everything up, it sounded good and I put the Aux Jack where it makes good sense. Now, as I drive around town, the modulator is showing its failings.

I would like to get my Aux Input to go directly into an audio channel, or get a FM Modulator that actually works. The one I have was only $16.40 -- I won the auction on eBay. I think this is a product where spending more money leads to greater satisfaction.

How come one could not piggy back on the audio from the CD Changer Input? Then one would only need to unplug the Aux source to listen to the CD, or empty the CD changer to use the Aux source.

[MParallel]

...How come one could not piggy back on the audio from the CD Changer Input? Then one would only need to unplug the Aux source to listen to the CD, or empty the CD changer to use the Aux source.

That solution has been used for years through an interface like Dice or Dension. You can get an extra module that even makes you switch between the original changer or the aux channel.

[JDStrickland]

I was in my local BMW dealership today, and the guy behind the counter said there is no interface for my car because it is too old. If you have a link, I'd appreciate it...

[NJDave]

I installed a wired FM Modulator. I was excited when I buttoned everything up, it sounded good and I put the Aux Jack where it makes good sense. Now, as I drive around town, the modulator is showing its failings.

I would like to get my Aux Input to go directly into an audio channel, or get a FM Modulator that actually works. The one I have was only $16.40 -- I won the auction on eBay. I think this is a product where spending more money leads to greater satisfaction.

How come one could not piggy back on the audio from the CD Changer Input? Then one would only need to unplug the Aux source to listen to the CD, or empty the CD changer to use the Aux source.

What has this got to do with the thread subject:
"My C33 Stereo Aux Input Project"?

Please consider posting CD Changer issues elsewhere.

[flyfishvt]

I just finished this mod. I soldered a headphone jack onto the tape player board just like the picutes show. Then with the cover off I pushed on the mechanism that grabs the tape (no tape actually inside) and fooled the unit into thinking there was a tape in it. Then I ran a headphone extension cord to the cup holder and BINGO. I just plug my MP3 player into the cord and use the cassette tape player circuit as if there was acutally a tape in there. I can switch it back and forth from tape to CD to radio and the sound quality is excellent.

The only thing I have left to do is install a female headphone jack in the cup holder like I did on my 325. Everything is now completely out of sight under the arm rest. No cords getting tangled in the shifter or running all over.

[NJDave]

[QUOTE=flyfishvt;23119172]"... I just finished this mod. I soldered a headphone jack onto the tape player board just like the picutes show ... I can switch it back and forth from tape to CD to radio and the sound quality is excellent.


Could you explain further the term "tape player board"? Does this mean you wired up to the larger main circuit board (to the TDA processor chip), or you wired up to one of the smaller circuit boards mounted to the separate tape drive mechanism on top of the main circuit board?

Also by mentioning you can "switch back" from tape to CD to radio ... does this mean you've incorporated a relay set to do this? Please explain this "switching" method more.

Thanks.