Adding input to a radio (non-pc at all)

[DanFraser]

I have an old-ish car, with an old-ish radio/cassette player. I'd like to keep the radio/cassette as it is the original and it fits in with the look of the car much much better than any gaudy LED-fest head unit you can buy now.

Problem is I have an iPhone :) I have a cassette adaptor but being a tidy freak I hate the wire being all over the place. So I've ordered a dock that never came with the phone originally (3G) in lovely dashboard black that has a 3.5mm audio jack on the back. This I can then attach somewhere on my dash. Unfortunately the radio/cassette does not have any form of input other than the cassette tray. An FM transmitter thing wouldn't be suitable though as charging will be wired into the cars live feed (bought down to 5v obviously).

So my idea is, open up the radio/cassette and find a point where I can solder on the audio wire from the dock preferably aligned somewhere on the LW band so that when I switch to that band on the radio it's unknowingly ignoring the aerial and playing the audio from the iPhone. However I'm having trouble finding starter resources for radio wiring and I am now wondering if any of you guys would be able to give me a jump on this?

[Psycogeec]

what you asked doesnt seem as possible as you asked it.
the tuner on the FM side brings in "energy" via the antenna, tunes out specific frequencies of energy, then pre-amps it then amps it. the tuner itself selects the specific frequencies, so for this plan you have, to come close, you would (like) need a switch to disable the tuner itself, or disconnect the tuner pre-amp, and feed your signal into the amp or pre-amp just after the tuner.
feeding into the pre-amp right after the tuner would be way-too-hot signal, which means you have to go past the preamp, to the amp, and even i couldnt find where the one starts and the other one ends :-)

then leaving the pre-amp on, connected would mean any tiny signal flying around would be easily amplified, as that is its purpose, so you would spend a lot of time "debugging" to try and clean everything up. then you would have to match the input signal to the amplification with attenuation, and then tune the attenuation and all , and it would just be like recreating the amplfyer in there for the one purpose to serve another purpose.

you could also feed direct into the magnetic head CONNECTIONS on the cassette side which would be much more accessable, and end up in more or less the same situation, of the preamp being for very small signal levels, but it is more doable after attenuation, and more simple to track down and wire without destroying everything.
right behind the magnetic cassett head is a couple of very acessable wires , that go to the casette pre-amp, jumping onto those would be more easily testable at least. a simple resisterd attenuation of the headphone or line output out of the other device would get you started in this mod quick.

FM transmitters all suck except for very special ones i have found that output very high levels, there is one called "Tmic" it is a mono mic and line input transmitter runs off a 9v or other 7-10V sources. it is the only one that can override radio stations when traveling. all the others get walked on by strong stations, and dont have enough volume.
To reduce wiring , why not just stuff one of these behind the dash and power it with regulated power from the 12v?

another way is to direct connect any cheap fm transmitter to the antenna, but you didnt want to do it the simple way :-)
there are many cheap FM transmitters available with 12v power input already, making them easy to wire behind the dash, "send" thier transmission more directally into the antenna and they work wihout to much noise, most of them still having volume (or gain) issues on the transmitted signal.

for like $89USD and some good shopping you can get a MP3 playing car radio that will take MP3 Cds or 16gSDHC chip MP3 and take an AUX 3.5mm direct.
i cant see tearing into an old radio to attempt to make this type of connections any more, when CHINA :-) has had all that stuff done for us now for 10+ years :-)

could you have picked something easier :-) start with IPHone , build world around it :-)

i use the TMIC in one car, and a simple AUX in the other, with the Tmic it is no wires going across the dash anymore, with the AUX it is one Roll-up cord (retract) , stays pretty clean finnaly. Watch movies, run the gps and phone or whatever.
many many simple radios for cars now have line input , even if it is on the back with an RCA input.

course i suppose it still didnt mater what i did, because just like the computer, the stereo and the toaster :-) stuff had to plug-in somewhere, and wireless means one more transmission and more use of power again. , so i guess it wont even be perfect till its bluetooth or something, and that doesnt ever have any problems does it :-)
and of course there are car radios now you can just feed blutooth too.