Need help hacking car stereo. (I've done the hard part already!)

I'm trying to hack an auxiliary input into my car stereo. My car is a 93 Saab 9000. The goal is to keep the stock setup. The origin of this hack is a similar hack for the radio in the 9000's successor -- the Saab 9-5, and you can find instructions for that HERE.

So the idea is that you hijack the audio signal between the cassette player head and the processor/amp in the car stereo. You effectively loose the cassette player, unless you install a switch, blah blah blah.

Not a few ground rules before we go on...not to appear crabby or anything, I just want to stay on topic

1 - I realize I could just install an after-market stereo. This, however, seems easier and cheaper for sure. The car's audio setup is a little complicated, and so adding an after-market stereo requires well over $100, and it's hardly plug and play. I should be able to do this mod for rougly the cost of an audio cable, so a substantial savings. An after-market stereo would surely sound better, but only if I upgraded all the speakers to match the new head unit. cha-CHING!

2 - I also realize that hard-wired FM modulators are a good option, and if I can't get this working that's probably the way I'll go. But I am going to do this mod on my dad's car (It's well documented for his, and proven to work) and so I wanted to try it this way on mine too.

Next up, here is a picture of my stereo (Click to make it bigger). Or rather, the cassette circuit board on my stereo.




Ok -- here's where I've gotten so far. I thought I could hook into the solder pads called "R-Out" and "L-Out" -- but those solder pads have a capacitor dangling off them on the other side, and I didn't know what leg of the capacitor I'd need my audio to pick up on. So I started looking at that "1 4 3 2 G" thing. That's a ribbon cable that goes straight to the cassette deck head. I decided to jack in there.

So I hooked my grounded audio cable in at ponts "1" "2". 1 is the left audio channel, 2 is the right audio channel, and then I hooked the ground for the audio cable to The point on the far left of the picture called "ZERO II" (It would probably work with "G" as well, but that's not where I have it.)

now the dilemma!

It doesn't really work. I have to turn the iPod all the way down, and then it's still really loud. If I turn the iPod up just a little, it distorts like wild.

As I type this I realize that perhaps it is because the level that a cassette head should be putting out is tiny. I probably need to intercept the audio signal elsewhere on the board, where the level that the car radio would be expecting to see would be similar to the headphone output level of an iPod.

But I'm a little lost. :duh2: so...what do you think?

The problem could be solved with a small voltage divider circuit for each input, the signal from the Ipod is far too high for a low level input that would come from the cassette head. Something like this, where the Ipod is on the left and your cassette input is on the right, duplicate the top part of the circuit for each channel, this should drop the level. http://www.arrl.org/news/features/1999/0701/2/figure1.pdf
Norm

The output voltage of the ipod may be to much at the point you connected.

You know what is incredible is it's extremely easier to trace the circuit on the picture than on the actual board. I guess my camera created more contrast between the shades of green than really exists.

Looking at it a little closer, it looks like I jacked in at about the earliest point I could in the signal path. Well Then the signal goes a bunch of places, and eventually into that microprocessor. Then it goes out, and for the "L" and the "R" it goes through a capacitor, and the cap is labeled "L Out" and "R Out" -- and then it goes to that ribbon cable at the right side of the board, and out to the radio.

So I don't know anything about how a cassette player works, but I think maybe I am grabbing the signal where it is supposed to be really really weak, and then when it goes through that microprocessor the signal gets boosted to an output level signal, and then it flows into the radio where it gets boosted to a speaker level output.

So, unless somebody has a better idea, I think maybe I'll try moving where I jack in, and I'll move to the "L Out" and "R Out" spots, and I'll go *after* the capacitor, because I'm trying to skip as much signal processing as possible on the iPod output, because it's already at a output level.

Does that sound plausible? Because I'm literally making this up as I go.

I know it's not what you're looking for but why not just use one of the cassette adapters that have a phono plug for the input? Seems like it would be a lot easier and you don't lose the use of your cassette player if you want it.

Dividing down the ipod output sounds like the best bet, though it would sound better if it had a line out. You might also have to mess with the equalization to get it to not sound weird. Those cassette adapters sound like crap. FM modulators (the wireless kind, I've never heard of a wired one) are also crap if you drive near cities where there is a lot of interference. Basically if you can't get this to work, go for a new head unit, I'm sure you can connect it up to your old speakers somehow. I'm pretty happy with my old jvc mp3/cd player which has a front panel aux input, a huge plus when I bought it but in fact I just burn my mp3's to cd's, so no external crap plugged in with wires in the passenger compartment. I'd only use the aux in if I were on a road trip with a friend who had an ipod or something like that, and was going to sit there with it and operate it. The couple of times I've driven like that (friend using laptop or cell phone plugged into cig lighter) it's been messy enough that I really wouldn't want to deal with it and drive at the same time.

These days instead of cd/mp3 I'd go for at least dvd/mp3 but there are also some units that will let you directly plug in an SD card or USB memory stick.

paulr inline modulators piggy back with the antenna connector are are less prone to interference.
http://autospeed.com/cms/A_2335/article.html
Norm

I was using a cassette adaptor, but they're juts a pain. Every so often I have to reach my finger in and jiggle the cassette.

If I put a new head unit in I have to re-do the wiring to the back speakers, because the way the car is set up there is an amp under the passenger seat to drive the rear speakers, well you can't make that amp work with an aftermarket head unit.

I can put in an inline FM modulator, and that's option number 2, but that's a $15 or $20 option, and I really already have all the stuff on hand to do it this other way, so why spend $20 when I can do it for $0?

So there isn't a really clean place to bring the wire out of the stereo. I need to drill a little larger hole in the stereo casing, and then the stereo sits in a cage within the car, and I have to drill a hole in that. But I'm busy for the next day or 2 -- booked solid busy, so for now I have the volume knob removed, and the cord is coming out the front of the deck. It is not pretty at all!

I know it would sound a little better out of the line out instead of the headphone port of the iPod, but since I'm using an iPhone and not an iPod, the headphone port has the advantage of the fact that calls will go through it (Calls will not go through the line out) -- so if I use the headphone port not only can I play music through the car's speakers, but I can take my phone calls through the speakers hands free.

http://www.installer.com/

This site might have something useful in a direction not talked about before. Typically their harness assembly installs between the radio and CD unit.

mike

Saaby, I don't have the exact answer you need, but you are on the right track. The tape heads put out an extremely weak signal, with a very special EQ. Reducing your aux signal for the tape head input is a poor way to go particularly from a signal/noise standpoint, and it WILL sound awful without the right EQ, which can be difficult to duplicate.

Agreed you need to find where the tape signal is amplified to aux level, and inject there, with some isolating resistors inline. This is probably just a matter of tedious examination and reverse engineering of the circuit. The board labels might be misleading, just because they say "right out" doesn't necessarily mean what you think. The head wiring has to go to a preamp chip with the proper EQ built-in from some Rs and Cs. The place I would look is on the output of the first IC the head goes to. You can probably look up the function of the IC from the code on top. It's more difficult if dozens of functions have been integrated into one huge chip, which is a high probability.

double post from system freeze.

I love to speculate. So this post is juts speculation.

Where I have patched in is PRE-that chip. But where I want to patch in is POST that chip, and as best I can tell, I am patching into the "last stop" on the tape board. After it runs down a ribbon cable and into the radio mainboard.

Ok, here is why I have not given up hope -- he was talking about the 9-5, not the 9000, which has a totally different stereo, but a member over at the Saab board said the following:

The tape pre-amp input, expects 388mv PtP current... guess what MP3 players put out? Yup, same thing!

Click to expand...

So there you go, like we have determined here, I just have to get to the spot where the current is at 388mv PtP. Technically this would be a good time to have a multi-meter, but the way the radio mounts in the car it's really virtually impossible to do any testing with the radio in place anyway, so it's like trial and error. I don't care if I "Mess the radio up" because I am only messing the tape module up, and the only thing I am using it for anyway is to hook through my iPhone, which I can do through a in-line modulator if all else fails.

It's just that there are no EEs driving 9000s any more! They've all upgraded to the 9-5, and that's why it was over 2 years ago that somebody figured out this hack for the 9-5, and we're just now realizing it might work on other radios too

Thanks for the help. I'll quit speculating and get to work moving the connection points!

That would be a voltage, not a current. The figure of 388mv peak-peak is only a ballpark figure. There's no absolute standard, and you can adjust the output level of the player/iPhone. A tape head might put out a couple of millivolts.

A typical meter is useless looking for audio signals because they don't have high frequency response like audio, and digital readouts are too slow. That's what o-scopes are for. Or schematics. Your best bet is just to reverse engineer the wiring to find the mix/control point for the preamped tape audio, hoping it's not hidden inside a huge multifunction chip.

When injecting (mixing) the iPhone audio into the circuit, isolating resistors are recommended - just 1k or so in the signal wires to the injection point will do.

It's working! Now I just need to figure out if I can make the player think there is a tape in there, when there really isn't.

I just jacked into a different spot on the circuit board, the place I originally thought about jacking into, but wussed out on

Saaby said:

If I put a new head unit in I have to re-do the wiring to the back speakers, because the way the car is set up there is an amp under the passenger seat to drive the rear speakers, well you can't make that amp work with an aftermarket head unit.

Click to expand...

There are two options there, actually. You can get an adapter that will convert the amplified output of the new head unit to a line level that can drive the amp. The other option is to just get a special jumper wire to bypass the factory amp. Crutchfield.com more than likely has the adapters you need to use the factory wiring with an aftermarket head unit. That's the way I'd go personally. You will certainly get a better sound quality out of it.

But how much money to I want to put into a sound system for a 15 year old car with 183,000 miles. Even if it is a Saab which I adore.

Saaby said:

It's working! Now I just need to figure out if I can make the player think there is a tape in there, when there really isn't.

I just jacked into a different spot on the circuit board, the place I originally thought about jacking into, but wussed out on

Click to expand...

That is another problem. Maybe there's another point to inject that is always on - even perhaps at the volume knob.
Or maybe there's a leaf switch that detects the tape dropping in. Good luck.

I think you can hack your way into that rear channel amp from another head unit at least as easily as the stuff you're doing now.

Saaby said:

But how much money to I want to put into a sound system for a 15 year old car with 183,000 miles. Even if it is a Saab which I adore.

Click to expand...

You can buy a head unit for not a whole lot of money and you can always move it to your new ride when you dump this one.