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AM to Line in mod?

post #1 of 8
3/16/10 at 1:42am
Thread Starter 
I have a 5 year old Wally World CD/Radio brand boom box, an ihome and a zune. Notice none of these items go together

Anyways, my idea: Can I solder a 3.5 mm jack to the AM loop inside? I never use the AM radio, ever. I rarely ever use this boom box either. I was just thinking it'd be nice to have a boom box for my zune.

I didn't see an obvious way to trace the CD player lines, otherwise, i'd wire to that, and put a CD of silence in.
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post #2 of 8
3/16/10 at 2:11am
If this is a venture out of intellectual curiosity, I applaud your commitment. If this is a venture to try and decent audio, I have some nice men in white suits I'd like you to meet.

I would honestly have to say no to a direct conversion. The audio out of the 3.5mm jack meant for headphones is an unmodulated signal meant to drive "dumb" devices like headphones and speakers in order to emulate the real world pressure conditions of sound, whereas an AM signal is modulated as illustrated bellow.



Source: Wikipedia

So there's some electronics inline doing some conversion from the amplitude modulated signal to the actual signal itself.

So unless you're into really bad techno, this would seem a bit moot to me.

And if you are into bad techno, boot up a Linux box and go "sudo cat /proc/kcore > /dev/audio", it'll save you time and effort.

Not to mention this has the real possibility of damaging some of your equipment.
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post #3 of 8
3/16/10 at 2:17am
I actually did this to my old car radio. I just took a couple leads coming from an ipod headphone out and poked around the radio until one pin made music. I nearly ruined my ipod by connecting 12V to the headphone out but in the end it all worked out. Somewhere in the boombox the radio must be demodulated and converted into audio and if you solder your 3.5mm jack there, you'll get sound coming out.
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post #4 of 8
3/16/10 at 2:39am
In the old days we did this a fair bit, and the best place to tap into the amp was the outside legs of the volume control, so pins 1 & 3, as I recall it seemed to work nearly all the time, but the quaility is a little doubtfull
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post #5 of 8
3/17/10 at 1:02am
Thread Starter 
Thanks guys. My idea was this: cut a slot in the boombox, wire it up and put one of the tiny usb adapters attached to the AC in. It'd charge my zune and play it, like an Ihome Zune, except about $5. If I killed a $35 5 year old boombox, I wouldn't really care.

Forgot about the signal modulation. I was hoping that somehow wiring it up directly would work. Seeing as its a digital radio, I should look for an IC connected to the dial and somewhere near the antennae.

Alternatively, that volume wheel idea is looking better and better... except for the horrible static it makes when I change the volume :} I'll see what I can do. I'm TA-ing an engineering class, my teacher might let me sit and play with this in class.


I think my ipod'll be fine for poking around in there... [Note custom wired line out jack with potentiometer volume control to replace the dead headphone jack]. That's my backup. FYI normal: Zune 8>6 foot cable>Fiio e3>Image S4s. Stupid 10 feet of cord on earbuds.

Quote:
Originally Posted by mewrei View Post
If this is a venture to try and decent audio, I have some nice men in white suits I'd like you to meet.
Perhaps I should ask them about using that megaphone I have instead.
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post #6 of 8
3/18/10 at 2:51am
Thread Starter 

Almost done.

Well, sort of anyways. I removed the AM antennae and soldered a 3.5 mm jack to the volume wheel. I soldered to the wrong side of the potentiometer so volume is controlled by my zune, not a huge deal. Gotta redo it anyways, it makes bad contact on one side.

*bad idea here*
While I was at it, I spliced the wires from the AC in to a AC>USB adapter. I then stuck my sync/charging cable inside the boombox and now it charges and plays! Both come out under the handle which awkwardly puts my zune behind the handle while its playing. Conversely, its nicely out of the way while I'm moving. Also I turned the wireless on in my zune which means it'll auto sync with my computer while plugged into the boombox.

Need to reconnect the CD assembly. I had to remove it to glue the sync cable and headphone jack from the inside. Should probably glue the usb adapter down too.

For the $5 that USB adapter cost me, this seems totally worth it. Not quite finished, but I'm happy with it. I can finally sleep for more than 5 hours a night lol
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post #7 of 8
3/18/10 at 3:00am
Quote:
Originally Posted by Deathyak View Post
Alternatively, that volume wheel idea is looking better and better... except for the horrible static it makes when I change the volume :}
IIRC, a lot of static issues with potentiometers have to do with grounding issues or grounding isolation. Its something like that but I remember reading about how to remedy those on several projects. Might check around AMB's website, I believe that's where I picked up that info in part.

Good luck with the project, looks like you're making good headway though.
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post #8 of 8
3/22/10 at 2:22am
Thread Starter 

Good enough

Turns out the solder points on the bottom of the potentiometer were L/mono/ground

Flipped the board over and redid it from the other side, just had to make L&R beep test tones. Not hard, just irritating as the adapter kept falling out of my ipod.

SQ is well... eh Hold it about 16" in front of your head




Could look better


Charges, Syncs and plays. I'm happy
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