Instructables on modding an old school cassette player boombox to play your iPod.
Instructables on building a charger for your iPod.
These are all great Instructables. Unfortunately, I ran into some snags and wanted to add a few more features. So, my Instructable covers how I solved some of those problems. I hope this will help others who've run into similar snags or want similar features. Lastly, I had many "do-overs" with this mod and wanted to motivate other modders not to give up on their projects. If you have the courage to tear apart something you just modded, you'll end up with something you can be proud of.
I started with a Sony CDF-8, an old school combo cassette tape, CD, AM/FM radio boombox. What I wanted in the end is an integrated iPod docking cradle that would both recharge the iPod and play through the docking connector Audio Line Out. I wanted to add a compartment where the old tape mechanism resided. Lastly, I also have a Motorola SLVR L7 iTunes phone so I wanted to add an aux Line In jack.
I've broken this Instructable into segments based on the features I added and the things I learned. I've skipped over most of the basic stuff since the above Instructables do a great job of explaining all of that.
Sorry, I didn't write this Instructable for newbies. The details aren't included. I glossed over things assuming the reader had some previous modding experience. You'll note most of the photos I've included are after the fact. I didn't take any before photos since I wasn't planning to make an Instructable. Without the photos I couldn't include details needed for a neophyte to tackle this mod. Therefore this is more about Hints and Tips rather than a true step by step.
Step 1: HINT - HOW TO FIND a "CLEAN LINE IN"
Here's a hint to make your hunt easier. Most of these boomboxes have a mechanical selector switch that switches the source from the CD player, radio or cassette tape to the main amplifier. Find this selector switch.
After you find the switch, flip the main board over and locate the correct pins for the cassette tape player. I was lucky, mine were labeled.
The switch is dual pole, one side for the left channel, the other for the right. Follow these traces to a spot where you can solder on some leads. Mine happened to end up on two jumper wires on the parts side of the main board which makes soldering real easy. On my mod, I wanted to run this "clean line" to both the iPod and an Aux. Line In. Therefore, I wired a pair of leads to this spot. Where do these leads terminate? One L&R pair can be soldered and heat shrunk to the 1/8 stereo line in jack, the other L&R pair to be wired to the iPod, See STEP 3.
Why is this line "clean?" Because it bypasses the cassette tape player's preamp and associated circuitry, which was designed for a tape head not the headphone output of an iPod. If you connect your iPod to these lines and adjust the iPod volume, chances are you'll get a much cleaner sound than using the "cassette-tape-head-method." Booya!
Step 2: HOW TO INTEGRATE AN IPOD DOCKING CRADLE
1/16" Acrylic sheet - Tap Plastic 2'x2' $7.00
Acrylic cement - Tap Plastic $3.40
1 iPod 30 pin Connector - Sparkfun http://www.sparkfun.com/commerce/categories.php - DEV-00704 $4.95
1 1/8" stereo jack - Radio Shack - 274-249 $2.99 Optional
Here's another hint. Buy the Sparkfun docking connector! In fact, don't buy the model I bought, they have a new one called the PodBreakout, DEV-08295, $14.95 which makes soldering these little buggers much easier. I mentioned "do-overs." I don't remember how many mistakes I made with this connector (DEV-00704). Several times I accidentally broke off the internal pins after installation. I ended up having to pull out pins from pins I knew I wasn't going to use to replace the ones I broke. By the way, if you do get model DEV-00704, I found it much easier to pull the pin out of the connector body, solder and heat shrink the wire and then replace it back into the body. There's less of a chance of soldering two adjacent pins together.
Don't think you can cut corners by using an iPod connector from one of those off brand iPod chargers. I bought two of these and found they only contain the pins for charging your iPod. They do not have the pins for the Left and Right Audio Line Out (pins 2, 3, 4). iPod Docking Connector Pinout Save yourself some heartache, just buy the Sparkfun docking connector...
At this point, pull out the cassette tape mechanism. Mine had four screws and two connectors. Now you have lots of space for a docking cradle.
The fabrication of the iPod docking cradle is straight forward. Basically, you are building a "box" out of 1/16" acrylic sheet. Find a location for the cradle. I have an iPod Nano 2G so even with its case, it was slim enough to fit where the mechanical cassette tape buttons used to be.
After you've chosen a suitable location, mock up the box in cardboard then transfer it to the acrylic sheet. Cut it out and glue it together using the acrylic glue. Cut a hole in the bottom so the docking connector will fit snugly in the hole. Glue this in place only after you're 100% sure all connections are working correctly, see below steps.
I had to grind down some plastic bits inside the boombox enclosure which wasn't easy because it was hard to get a big file into a tiny space. In the end, I used a cardboard nail file that was broken in half. A Dremel would have helped but I don't have one.
I also had enough room to install and On/Off switch (red button) and a stereo Line In jack (see STEP 4, below). Before gluing to the boombox you can spray paint it like I did.
Step 3: HOW TO RESOLVE THE IMPEDANCE MATCHING PROBLEM
2 Audio Isolation Transformers - Radio Shack Radio Shack - 273-1380 $2.99
Scrap of perfboard
Okay, here's the biggest hint of the entire mod. In STEP 1, I found a clean line. However, after I wired up the docking connector to test it, the Audio Line Out (Pins 2, 3, 4) Pinout signal was waaaaaay overdriven. I tested it with the headphone output and it sounded fine at about 1/2 iPod volume. However, the volume doesn't work when you use the Audio Line Out from the docking connector. The sound was absolutely gross. Back to the internet for some research I went.
On the internet I ran across some black magic called "impedance matching." Here's a link for some information. http://hyperphysics.phy-astr.gsu.edu/hbase/audio/imped.html Turns out, the Audio Line Out from the iPod is high impedance while the headphone output is low impedance. I figured the cassette tape circuit is designed for low impedance since it sounded fine with the headphone output connected. I needed to figure out how to lower the impedance of the iPod's Audio Line Out. I first tried to insert a simple headphone volume control in between the Audio Line Out and "clean line." All that did was made an overdriven signal less loud but still gross.
Then, I came across this device at DAK Industries. Impedance thingy It takes a low impedance circuit and matches it to a high impedance circuit via an isolation transformer. I wondered if I could reverse that principle.
Back to Radio Shack. I found these audio transformers and bought two of them (one for each channel). I used these "backwards."
I wired and heat shrunk the 8 ohm windings of the transformers to the "clean line" found in STEP 1. The bigger 1K ohm windings I connected to the docking connector (pins 2, 3, 4) Pinout. The grounds can be wired per the diagram. I mounted the transformers on an old piece of old perfboard. Then I modded one of the cassette mechanism brackets to mount the transformers. Lo and behold, the transformers worked! Booya!
Remember I was talking about do-overs? I finished up all the soldering, wiring and reassembled everything. I thought I was finished with the entire project. Not so! I powered up the boombox and eeeeeeeeeeeeeeeeeeeee - audio feedback! When I plugged in the iPod, the feedback disappeared. That meant I had a no load audio feedback loop. Doh! I wanted to drop kick the darn thing. Did I have the courage to tear it all apart to try to fix it? Not courageous, just stupid.
After taking it all apart again, I stripped off the shrink tubing, desoldered the connections and basically started all over. I reconnected it in different configurations. Nothing was working. Finally, I figured it out. Remember those two jumper wires I found on the main board, where I found the "clean lines?" I decided to cut them. Lo and behold, it worked! What I had done is cut out the preamp circuit. The circuit was causing a no load feedback loop.
In fact the sound was better than before. No hiss or humming, very clean. Booya!
Step 4: HOW TO BUILD AN IPOD CHARGER
1 push on/push off switch - Radio Shack - 275-617 $2.49
1 5V Fixed 7805 Regulator - Radio Shack - 276-1770 $1.59
1 10uf Capacitor - Radio Shack - 272-1025 $0.99
1 100uf Capacitor - Radio Shack - 272-1028 $1.29
1 Diode - Radio Shack - 276-1104 $0.89
2 50K ohm resistors - Mouser Mouser Industries - 270-49.9K-RC $0.11
2 75K ohm resistors - Mouser - 270-75K-RC $0.11
heat shrink tubing
The first question is where to get the 5 volts. I decided to look at the circuit that drove the cassette tape motor. After ripping out the cassette tape mechanism, I fiddled with it trying to determine how it worked. Boy it looks complex!
The mechanism has many levers and springs but it is fairly simple. The play lever pushes down the tape head carriage and a reed switch that activates the audio and motor circuit.
Like Instructable Sony boombox I wanted the ability to turn on/off the iPod charging circuit. So I bought a Push On/Push Off switch at Radio Shack. It's the red button in the photos. I measured 10 volts on the motor circuit and confirmed that it turned off when the Stop cassette button was pushed (which disengaged the reed switch). Sure, there are many 5 volt circuits on the main board but those circuits did not sync on and off with the cassette tape audio circuit. Plus, the circuit connection was easy, since both the reed switch and the motor circuit were both routed through a single connector on the main board.
The next challenge was to convert the measured 10 volt to 5 volts. I started with this Instructable. Super Simple I searched the internet further and found this circuit and decided to use it. 5 Volt Regulator Build
Another trip to Radio Shack, a scrap of old perfboard, some soldering and blam, a regulated 5 volt source that could be used to recharge the iPod.
I used the connector that powered the motor and reed switch. I wired the output to the iPod docking connector (pins 16 and 23) Pinout.
I modified the cassette mechanism mounting bracket to hold the new 5 volt regulated charging circuit.
In STEP 3 I mentioned the "do-over". Well at that time, I found the iPod wasn't charging! It was getting the 5 volts but the iPod charging bolt would come on then disappear. That meant the iPod was running on battery while docked! Doh! Back to the internet for more research, I went. I found that newer iPod firmware requires a small voltage on pins 25 and 27 in order to charge. Why oh why!? Like I said, I wanted to drop kick the thing. Persistence yields perfection.
Hint - There is more than one way to charge an iPod. In STEP 2 I mentioned I bought two iPod chargers. I pulled out a VOM to analyze these chargers since I knew both of them actually charged my iPod. I found something interesting. One charger used an AA battery as a power source. The other used a wall wart. Both had different charging circuits. The battery powered charger used the typical 5 volt USB type power (pins 16 and 23). The wall wart version used the 12 volt Firewire circuit (pins 19/20 and 29/30). The Firewire version was more attractive, since it didn't require any additional components. Simply connect 12 volts to pins 19 and 29. However, I didn't have a 12 volt source on the main board. The power supply circuit of the boombox had only an output rated at nominal 9 volts. So I took apart the USB style charger and found a bunch of resistors configured in a simple voltage divider circuit.
These resistor (50K ohm, 75K ohm) values aren't available at Radio Shack so I ordered them from Mouser...and waited anxiously for UPS. After getting the four resistors I created a small subBoard.
I soldered and glued this board to the main charging circuit board and wired it up.
I tested and found it didn't charge! I jiggled the docking connector and found I mounted the docking connector too low. The charging circuit pins were not making good contact with the iPod. Doh! I had to break the glue bonds on the cradle (again) and reinsert the connector into the cradle. Success! It was finally charging.
Lastly, solder and heat shrink the connections to the red Push On/Off button that was mounted in the docking cradle in STEP 3. You use the wires that were connected to the reed switch mentioned earlier. Remember, that reed switch activated the audio circuit and the motor circuit (which now acts as an iPod charging circuit).
You should now have a docking cradle that charges your iPod and plays music through the boombox! Booya!
Step 5: MAKE a COMPARTMENT WHERE THE CASSETTE TAPE MECHANISM EXISTED
1 blue LED diode - Frys - 149mcd 3.8Vf @20mA
1 330 ohm resistor - Radio Shack - 271-1315 $0.99
some 28awg - 24awg wire
1/16" Acrylic sheet - Tap Plastic Tap Plastic 2'x2' $7.00
Acrylic cement Tap Plastic $3.40
First you need to cut away all the unnecessary plastic. On the cassette door, most of the plastic is used to hold the cassette tape in place. This is the fun part. With pliers, wire cutters, Exacto knife, saw and sandpaper, remove all plastic bits except for the hinge nubs and doorstop nubs.
I fabricated a spring loaded latching lever that holds the door shut. I stole a spring from the cassette tape mechanism.
On the boombox's front panel, cut away all the plastic but leave a piece of plastic that will act as an anchor to hold the door shut. Make rough measurements for a 5 sided box. Transfer these measurements to cardboard templates. Mock up a compartment in cardboard first. Make your mistakes on the cardboard templates. When satisfied, transfer the cardboard templates to the 1/16" clear acrylic sheet. Cut out the pieces. Fit one piece at a time taking time to trial fit over and over again. Start with the top piece, then fit the bottom, then the sides and the last part is the back piece. If you want a real professional looking installation, sand the exposed edges of the acrylic to a smooth finish using finer and finer grades of sandpaper. Use plastic polish (from Tap Plastics) to finish it off. Use acrylic cement for final assembly.
Now that I had a clear compartment, I had the idea to add a blue LED to light it up. I decided to power the LED with the motor circuit (9v) instead of the regulated 5 volt circuit I created. Why? I figured drawing more power from the motor circuit it would "help" the 7805 regulator. If I used the 5 volt side, it would have loaded the 7805 even more, causing it to heat up even further.
I bought a blue LED (specs. 3.8 Vf, 20 mA) at Fry's. Using this LED Calculator I came up with a 330ohm resistor, using the measured 10 volt motor circuit. The LED circuit is simple. Wire the resistor in series with the diode and use heat shrink on everything. Hot glue it to the inside of the boombox. Aim the light so that it will light up the compartment.
The final step is to simply zip tie all the loose wires for a neat appearance and reassemble the boombox. Booya! You're done! Feels good, doesn't it?
Final Shout Out - Kudos to all for contributing to this site! I never realized how much effort it took!