This is an admittedly mad project to see what might have happened if Sony had invented the Walkman earlier than they did - and made it so it took 8 track tape cartridges (which came before cassette tapes were invented).
In other words, can I make a personal 8 track player with just headphones in the style of a Walkman?
How small can I make it? Bear in mind it needs quite a bit of power to move the tape loop around inside the cartridge.
Before anyone asks what the point is, it is to see if I can do it, just like most other things I make. I accept this one is only of super-niche interest.
A couple of years ago I bought a really cool "Lear-Jet" 8 track tape cartridge player and got it working for an old car. These preceded cassette players and were unusual in that the tape runs in a continuous loop - you cannot fast-forward or rewind them like a cassette. They were the first usable in-car entertaiment device and sold mainly in the US. After doing more research I found out more:
a) The cartridges had reputation for jamming and sticking. However the internal mechanisms can usually be restored to work properly.
b) The tape moves much faster past the tape head than in the later cassette tapes. This is so the "hiss" becomes higher frequency than you can hear, necessary as Dolby hiss reduction did not come along until later.
c) Therefore, with a high-end 1970's indoor HiFi player, the sound quality can actually be very good.
d) No matter how old they are (1970's and early 80's) the actual tape itself does not degrade much. I have some that sound stunningly good against all expectations.
e) I like 70's rock!
I would recommend younger viewers to read around this subject, the history of the 8 Track player is an adventure in itself featuring people such as William Lear of Lear-Jet fame and "Mad-Man" Muntz, an early affordable TV pioneer in the US.
Everything you may want to know can be found on these pages, especially the first one:
Step 1: Step 1
Things to buy:
1) Get hold of an old cassette tape Walkman.
2) Buy an old car 8 track player. Cheap as chips on eBay. You just want this for the chassis, tape head and motor/flywheel assembly. So long as motor spins it doesn't matter if circuit board no longer works.
1) Take circuit board out of the Walkman. You are only using the audio amplifier so gently remove/cut away everything that relates to the motor drive in the Walkman. The Walkman circuit board is now uppermost in this photo - transplanted into my creation.
2) Take a very good look at how the tape head in the Walkman is connected to its circuit board. There is a ribbon cable with 3 flat "wires" in it. One is to ground, one takes the left signal from pickup head to circuit board, one takes the right channel. There may be another wire to the outer case of the pickup head itself. You are going to wire up the pickup head in the cartridge player to the Walkman circuit board in place of the Walkman pickup head. The Cartridge player pickup head is essentially a larger older version of the one in the Walkman and the wiring is the same. You need to copy the wiring arrangement you found in your walkman.
Step 2: Step 2
Keep dismantling the car 8 Track player.
Remove everything non-essential from car 8 Track player internal chassis:
You need to keep the motor, the rubber band from motor to the flywheel and the flywheel. The shaft of the flywheel spins and pulls the tape past the pickup head. The pinchwheel it clamps the tape against is not in the machine but is in the 8 track cartridge itself.
There is also a solenoid device which rotates a spindle that the pickup head is mounted upon. This (if looking from above) moves the pickup head towards and away from you in 4 steps. This is why they are called 8-Track players. The tape has 4 pairs of stereo (one for left one for right) tracks on it. The tape runs one full loop, the head moves up one click so lined up with the next 2 tracks, loop goes round one more time, tape head moves up another step (of possible 4) and so on.
I removed the solenoid in quest for the smallest machine I could make.
In this photo the motor is on the right, Walkman circuit board at top of picture edge-on and you can see a 2 X 1.5 AA battery holder to power the Walkman circuit board which is now soldered to the 8 Track player pickup head and is there to amplify the signal and send it to the headphones.
The sides of the now stripped out 8 Track player chassis have been bent down to make overall size much smaller than when it was a car player.
Step 3: Step 3
View from below.
Here you see the motor, rubber band and flywheel of the car player. Use all the space around for batteries. Car players run off 12Volts. Furthermore the 8 Track cartridge internal mechanisms need a lot more power than a cassette player tape to move the tape smoothly (without bad wow and flutter) past the tape head. You therefore need to supply the motor with 12Volts. In my case this meant a whole load of 1.2V rechargeable batteries mounted wherever there was any spare room. I used rechargeables because this beastie is likely to eat batteries.
I used a double pole switch to turn on the 3V to the Walkman circuit board and independently, the 12V to the motor.
Step 4: Step 4
Here is a view into the slot the cartridge pushes into. There is a sprung roller on the right (just visible) that comes with the car 8 Track player. This fits into a V shaped indent on the right side of the cartridge and holds it "pushed" against the tape head.
To change to each pair of tracks (4 possible positions for the tape head up and down remember) I simply made a knob and fixed it to the top of the rotating cam device that was formerly rotated by the solenoid device we have removed. When tape loops around to start point, you turn the knob a 1/4 turn to get head onto the next pair of tracks.
Step 5: Step 5
Here you can see how the Walkman circuit board has been squeezed protesting into a flat area above the motor. Glued in place (glue-gun) with layer of plastic between itself and metal structures below to stop circuits shorting out.
The last step is to fit some sort of casing around this internal structure. I modified the car player outer 2 part metal case by cutting it down and attaching to this chassis with very short self tapping screws.
I arranged for the cartridge to stick out as far as possible so I could make the player as small as possible.
Step 6: Step 6
Here it is with outer casing. On/off switch on rear. Holes cut for headphone socket and volume knob on side of the Walkman circuit board.
Strange 3 lobed knob on top surface rotates in 1/4 turns to select each of the 4 pairs of tracks on the tape.
As you can see it "fits easily in the palm of the hand" ............well almost!
Step 7: Step 7
Enjoy your warm analog 70's rock on the train (flourescent orange Led Zep cartridge just visible in the background here). Those iPod's are all so boring.
Another alternative would be to fit the head from a quadraphonic 8 Track player (arranged as 2 sets of 4 channels to give independent sound to 4 speakers). And you thought surround-sound was a new thing? An amplifier circuit with 4 channels could then feed some quad headphones. Yes these do exist and were made in 1970's with a front/rear speaker in each side of the headphones. There is an instructable somewhere on how to make some (for DVD surround-sound).
The cartridges are all available on ebay very cheap. They usually require cracking open and the mechanism sorting out. This is not too difficult after a short learning curve.