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Picture of Convert a radio tape player to an MP3 Boombox
C:\Documents and Settings\Daddy\My Documents\My Pictures\instructable\MP3 Boombox 003c.jpg
My family and I like to listen to music when we're outside playing with the kids or swimming in our small above-ground pool. We had a couple of old CD/Tape/Radio Boomboxes but the CD players didn't work and the old analog radio tuner was often hard to lock in on a decent radio station. After reading some of the instructables here, I thought maybe I would try to modify an old tape boombox to hook up an old MP3 player. That way I could load the exact music we want to hear and the radio would be digital tuning with favorite stations saved.
So here goes...
 
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Step 1: Open the box

Picture of Open the box
C:\Documents and Settings\Daddy\My Documents\My Pictures\instructable\MP3 Boombox 004.jpg
We start by opening up the old tape player. There are screws in the back of the player that have to be taken out to open it up. Different players will have screws in various places, but this one only had four screws, one in each corner. (If you take out all the obvious screws from your player and it still won't come apart, be sure to check in the battery compartment. Sometimes there might be a screw or two in there as well. Also, note that some times, as in my case, you will have to press Eject to open/release the tape door since, at least on mine, it latched a part of the cassette mechanism and ended up keeping the front half from coming completely loose.)

Once its opened up, you'll need to find and remove any screws that hold the cassette mechanism in. Also, locate the tape play/record head since we'll use the wires coming from it as the input from the MP3 player.

Step 2: Desolder wires and unscrew cassette mechanism

Picture of Desolder wires and unscrew cassette mechanism
Here is the top side of the tape head where the wires *were* attached. I've already desoldered the four wires from it (positive and negative wires for the left and right channels).
To desolder the wires, just plug in the soldering iron and let it get fully heated up. Then just hold the tip of the iron to the solder pads while gently pulling on the wire. When the solder heats up enough to melt, the wire will come loose.
Follow the wires to where they attach to the electronics board in the player; it may be labeled there as to which is left and right.
I've also already desoldered the two wires from the tape player drive motor. We'll use those wires to power the MP3 player.
This picture also shows the headphones jack on the top of the player. We will "repurpose" that jack later on for use as the input.
You can also now remove any screws holding the cassette mechanism in so it can be removed.

Step 3: Remove the cassette player mechanism

Picture of Remove the cassette player mechanism
This picture shows the cassette mechanism laid over upside-down. Note that there is a "leaf switch" which actually turns the power on to the motor when you press any of the buttons on the player (play/rewind/fastforward, etc). We'll "repurpose" a switch on the old radio portion for use as a power switch for the MP3 player.
The grey and white wires in the lower-center of the picture are the ones that were attached to the tape player head. You can't see it here, but the board where they attached was labeled "L. Ch." and "R. Ch." for Left Channel and Right Channel.
With all the screws out and wires desoldered or cut, you can remove the cassette mechanism from the player.

Step 4: Remove the electronics board to get to its back side

Picture of Remove the electronics board to get to its back side
C:\Documents and Settings\Daddy\My Documents\My Pictures\instructable\MP3 Boombox 010.jpg
C:\Documents and Settings\Daddy\My Documents\My Pictures\instructable\MP3 Boombox 012.jpg
Take out any screws that may be holding in the board and in my case, there were also three clips holding the bottom of the board in. I had to press in on these clips one at a time and gently pull the board up a bit to pass the clip. Once it is free from the case back, you can access the back of the board to make some changes and attach some wires.

Step 5: Prepare for the input from the MP3 Player

Picture of Prepare for the input from the MP3 Player
C:\Documents and Settings\Daddy\My Documents\My Pictures\instructable\MP3 Boombox 013.jpg
In order to play an MP3 Player through the boombox, the plan is to hook the headphone output of the MP3 player to the tape head wires. One could just buy a 1/8 inch stereo phono plug from a place like Radio Shack and let that plug hang out of the boombox to hook to the MP3 player, but I didn't want to spend any more money on this project that I had to and didn't like the idea of having the wire hanging out and all, so I decided to re-use the headphones jack in the old boombox. The jack was soldered into the circuit board such that it poked through the top of the case so I didn't want to completely remove it and have to come up with a way to attach it.
To use the jack, I knew I needed to disconnect it from the rest of the audio circuit. To disconnect it with it still in place, I actually used a small screwdriver to scrape through the circuit traces so the headphone jack would no longer be really attached to anything. See the notes in the picture for other details.

Step 6: Setup a power switch for the MP3 Player

Picture of Setup a power switch for the MP3 Player
C:\Documents and Settings\Daddy\My Documents\My Pictures\instructable\switch front.jpg
This switch was for changing between AM and FM on the boombox radio. Since we'll be using the radio on the MP3 player, we won't be needing it. I decided to "repurpose" the switch as a power switch for the MP3 Player. Again, I needed to disconnect it from the circuitboard, so I used the small screwdriver again and scraped a groove through the traces. I took the two white wires that were attached to the "leaf switch" (from step 3) and soldered them to the switch here. I did go ahead and bridge the traces to "hardwire" the onboard radio to FM, but I don't expect to be using the boombox's radio, only the one in the MP3 player.

Step 7: Hook it up and try it out

Picture of Hook it up and try it out
C:\Documents and Settings\Daddy\My Documents\My Pictures\instructable\headphones jack front.jpg
Ok, I think we're all done, so we will now hook up the MP3 player and see how it works before putting it all back together.

Does it work? Will there be sound?

Hurray, it works!! There was a lot of distortion though and I had to turn the MP3 player all the way down to "1". It is still a bit strong with a little distortion though. It is probably because the headphones output of the player is still much stronger than the output that the tape head had.

I have an idea though. When I was figuring out the old tape player's headphone jack (which I "repurposed" as the input from the MP3 player), I saw that while the normal output of the tape player went straight to the speakers, the headphones output was routed through a couple of resistors (one per channel) to drop the strength of the output down to headphones level (to not blow the headphones...*or your ears*).
I'll try re-routing the MP3 input through those resistors and see if that helps. The second pane below shows them.

Step 8: Move the input wires to resistors

Picture of Move the input wires to resistors
jack back.jpg
MP3 Boombox 041.jpg
Now we'll move the old tape head audio wires from the headphones jack over to those resistors in hopes of cutting down the strength of the signal.

Will it work? See the next step :)

Step 9: It didn't work, so now add bigger resistors

Picture of It didn't work, so now add bigger resistors
la3220.jpg
LA3220 datasheet.jpg
TA7769.jpg
TA7769 datasheet.jpg
Ok the 150 Ohm wasn't enough; the sound is still distorting a bit. I'll try adding larger resistors in series. For testing I just soldered them in just sticking out until I find the right size. I first tried adding 470 ohm resistors. After trying it, it didn't seem to make much difference. Next I tried 3000 ohm resistors, but still hardly any change. Next I'll try 10k ohms.

Update 10-07-07
Adding resistors didn't seem to be helping; then I got a suggestion from another great Instructables user, unknownuser2007 He suggested that instead of trying to use resistors to drop the level of the headphones output of the MP3 player, I could try bypassing the cassette head preamp IC like he did in his instructable. A great idea!! Thanks unknownuser2007!

The tape head wires (which I am using as the input from the MP3 player) are attached to the circuit board and traces ran from there to an LA3220 IC chip (see second pic). I looked up this chip on at a great Data Sheets website (see third pic) and found that it is an Equalizer Amplifier that is apparently acting as a preamp for the tape head.
There's another IC, an LA7769 (fourth/fifth pics) whose output goes straight to the speakers. This IC is apparently the main, higher power amplifier for the speakers.
"OK", I thought. "Great; its just what I need to amplify the headphones output of the MP3 player! I'll just move those input wires straight to the input of that IC".
Well, it worked, but then the sound was very loud all the time, even with the MP3 player's volume set at its lowest setting of "1"...bummer..so close!!

Well, one last idea....see next step

Step 10: Victory!!

Picture of Victory!!
I looked at the traces going to the volume control and they went through lots of capacitors and resistors and was very confusing.
I decided, what the heck, I'll just move the wires to the output side of the preamp, the LA3220 (pins 2 and 13), just for fun. Who knows, it just might help and if it blows something, too bad; I'm gettin' tired of fighting it.

Turns out, that was the trick! Now I have good volume control, no distortion; its great!
Hurray!! Thanks again unknownuser2007!
I can now plug the MP3 player, or any other device with a headphones output, into the MP3 Boombox and play it for all to hear. Yay!!

Now on to my next project where I will try to make a power supply to do away with the need for batteries for the MP3 player. Remember the power wires that originally went to the tape player motor? I'll try to do another Instructable for making a power supply to reduce that 7 volt motor power down to 1.5 volts for the MP3 player.

I hope this instructable might help anyone wanting to do something like this. I wanted to include my troubles I ran into along the way. Good luck!

In His name, HappyDad
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Bill Bob3 years ago
hey a question about 6 wires coming from a cassette tape player head. This is on a 1999 gm delco car radio. I want to hook up to these wires to hook in an mp3 player. BUT, BUt - it's got 6 wires , not just the three that I've gootne to work with on other units like this. DOES ANYONE know how to figure out which three wires I need to tap into ??????
Kaiven3 years ago
I found pins 2 and 13 on my la3220 ic on my ghetto blaster... This may be the only solution I have left! But I still don't know where to attach ground? And are pins 2 and 13 corresponding to left and right? (or vice versa) I just need to know where ground is, any help appreciated!
Kaiven Kaiven3 years ago
Wait a sec... I found ground to be pin 1. But it doesn't work. And on the IC, pins 2 and 13 are output... so why would connecting the input from the MP3 work when connecting to the output? hmmm....
vader0ne3 years ago
I always tap off the volume control on the older recievers dont know about the newer ones,but wouldnt think there will be much diffrence...
mode15 years ago
can you tell me more about wires coming to that headphone output, can you tell which wires where goes? sorry for bad english
vincze5 years ago
Can't i just connect a 3.5mm jack to the wires going from the tape thingy to the board?
HappyDad (author)  vincze5 years ago
Hi Vincze, I think the output of the wires there would be too low; it seems it needs the pre-amplifier to be strong enough.
dman9775 years ago
Just a suggestion for "HappyDad" & those who have the same MP3...

Would it be possible to wire in a USB port and trim down the 7 volts to 5 with a few diodes? I have used those MP3 players before, and they have a built-in USB port on them. Sounds like it could work in theory, I just don't know (because I cannot try myself) if the player would go into MASS Storage Mode. If it doesn't, then you could run the player from the USB power.

Good luck.
HappyDad (author)  dman9775 years ago
Sounds like a good idea dman977, thanks!
etchasketch5 years ago
step 10Victory!!
I looked at the traces going to the volume control and they went through lots of capacitors and resistors and was very confusing.
I decided, what the heck, I'll just move the wires to the output side of the preamp, the LA3220 (pins 2 and 13), just for fun. Who knows, it just might help and if it blows something, too bad; I'm gettin' tired of fighting it.
CAN you provide a pic for us tech impaired?.....can you email one
please !
bezzymares@yahoo.com
HappyDad (author)  etchasketch5 years ago
Hi etch, sorry I'm just now getting back here.  I don't have the schematics any more.
sljubic5 years ago
Try to solder input wires directly onto volume knob slider contact midle one and you can easier adjust input level
jackbomber5 years ago
 I avoided the soldering and wiring( as I'm not electrically proficient) by buying a cassette adapter for about 5 bucks. cool instructable though. this is much cleaner than having the adapter wire hanging out the front. 
 you could have saved yourself a lot of trouble if you had connected to the main volume pot in the first place. Its about the oldest trick in the book,works everytime:)
sjlammer5 years ago
You can easily get a panel or chassis mount 3.5 mm jack from a place like allelectronics.com
qnzfinest6 years ago
can i use an ipod for this project???
yes you can!!!
pokey3026 years ago
I am trying to do this to an old Panasonic RX-DS18 but i am running into some problems. 1. I can not isolate the headphone jack for some reason. I have everything scraped away from it on the board but it’s still picking up sound (frustrating). 2. What source are you using for the wiring schematics? My radio does not have any manual switches so i am having a difficult time trying to figure out where to solder in the mp3 connection so it will bypass the pre-amps. 3. Thank you so much for the informative post. I can't wait to get mine up and running!
HappyDad (author)  pokey3026 years ago
Hi Pokey302, Sorry you're having problems. You might want to try the idea that jsmirnio99 below had. That seems like a simpler idea. On problem number 1, be sure to check both sides of the circuit board; sometimes there might be traces on the other side that need to be cut. On problem number 2, I just googled for wiring diagram for . Good luck :)
I am unable to go with the other idea because everything is digital including volume. I put the old radio back together minus the tape player. Think ill go with a different radio. (i have many to choose from) I haven't given up yet!
jsmirnio996 years ago
One of the easiest ways to add an input to any audio system is to use the existing volume control. You connect the new input to the center (wiper) arm of the controls and then still vary the volume with the knob. If you use a special 1/8" jack that disconnects one set of contacts when a plug is inserted you are all set. Plug in the jack and the new input is amplified. Unplug, and the system reverts to normal. (8~)
HappyDad (author)  jsmirnio996 years ago
That's a brilliant idea, jsmirnio99! I'll have to try that. Much simpler that what I did and would probably work much better. I bet that the volume control is likely on the pre-amp side of the circuit so that would probably work really well. Thanks!
patcroy6 years ago
Hi! I am a auto mechanic not an electronic guy. I was wondering why one could not just buy one of those cheap cassette adapters plugins for MP3. And to eliminate the tapedeck noise just open the tape deck electric motor circuit. Wouldn't it be cheap, quick and effective? Pat from Waltham PQ
Phil B6 years ago
One option would be to use capacitors to couple or connect the output from the MP3 player to the chosen inputs on the boom box circuit board. A capacitor allows the audio signal (a type of alternating current) to pass while blocking an overload from too much voltage (DC). Different sizes of capacitors may be used, but a 1 microfarad capacitor should work without distortion. They are usually electrolytic (polarized), so pay attention to what is + and -.
Great!!! I'm gonna do that with my car radio. Thanks. Hey
Jeddychan6 years ago
hey guys, I'm trying to make this for myself, but Ive gotten snagged on some things... I'm pretty sure I found the right schematics for my IC, but I don't know where I should hook up my left channel and right channel wires (aka headphones with the speakers cut off). Heres the schematics. If someone could help me Id really appreciate it. =D
heres the picture
IC.bmp
Could you shut the MP3 player inside the cavity where the tapes used to go, for total portability?
110100101106 years ago
in the part with the resistors - add resistor from each channel to ground instead of using higher value resistors use resistors about the same as the existing ones (smaller for lower volume) and equal on the 2 channes
damasta7 years ago
or you buy an mp3/cd tape (so you don't have to modify your player)
Sandisk1duo7 years ago
did you check the voltage of the motor? it might be close to 1.5v if not, you can get one of those variable regulators at radioshack, they are easy to set up and they are reliable, need help? Tell me! P.S. gr8 instructable
HappyDad (author)  Sandisk1duo7 years ago
Hey Alex, thanks! Yeah, I checked the motor voltage, it is about 7 volts. So I do plan on using one of those voltage regulators to drop it down to 1.5v. thanks again!
Your welcome!
DoubleM7 years ago
I read your instructable thinking"what if my old mp3 player will be different then yours,I will mess it all"but when I saw your final picture,the mp3 player is THE EXACT SAME!Maybe I'll try this!
HappyDad (author)  DoubleM7 years ago
Hey MM, yeah cool! It works great. I've also used my PDA as the player and hooked the headphones plug of it to the project. Its really handy. Hope it works for you too. Good luck!
bootdsc7 years ago
This is a great way to add an audio input for old devices that lack this ability. I have done this before on a radio just like yours sept i fully removed the amp and used it to make amplified headphones to help with the crappy output volume of my ipod shuffle. great Instructable!
HappyDad (author)  bootdsc7 years ago
Cool, sounds great! Thanks, bootdsc!
HappyDad (author) 7 years ago
Hey CameronSS, cool! I wish they would have had a sale here when I got it! Great deal!
CameronSS7 years ago
You have to pay $7 for a Harbor Freight multimeter? Our Harbor Freight has them on sale virtually all the time for $1.99. The set of leads is worth that...
idogis17 years ago
going to start this, tell ya how it turns out
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