Adding a Line in to a Boombox With a Tape Player


Introduction: Adding a Line in to a Boombox With a Tape Player

About: I usually end up doing an instructable because I have to figure out how to do something myself. I just get pictures during the process, and if it works out, BOOM, an instructable!

** As with all the instructables, you take your item / health / whatever into your own hands when attempting ! Be mindful of high voltages on the main power board, the hot soldering iron, etc. Being careful and patient will bring you success. **

This is my first instructable, but I've been doing this sort of thing for a long time !

I know about the cassette adapters, but all the ones that I have tried cause too much background noise.

With this in mind, I decided that I wanted to add a line in to an old boombox that has seen better days, but still sounds good.

I found this baby left for dead on a job site, so I took it and cleaned it up (goof off plastic safe formula), fixed the cd lid, and now I want to add a line in so that I can use it with my mp3 player.

The reason is simple. Now I use an FM transmitter, plugged into a cigarette lighter adapter (which is plugged into the wall), and I hook my mp3 player to the FM transmitter (with an adapter from the 3/32" jack to 1/8") and then tune the radio on the boombox to the transmitter's station.

Besides being bulky, it picks up a lot of static and interference.

The white boombox in the picture was going to get the line in install, but after taking it apart I didn't want to chance breaking it to find the signal from the FM board (or even the CD player).

Step 1: Disassemble

Sony (and many other brands) makes it easy to take their products apart by stamping an arrow by the screws that you need to remove to get the unit apart.

This boombox is model # CFD-S36

I took out all the screws indicated, and that got the front chunk (which holds the speakers) off.

Then I followed the next set of arrows and the unit split into 2 more parts.

Step 2: Locate the Wires From the Tape Head, and See How the Mechanisim Works.

The wires coming from the tape head were easy to spot on this boombox. At first, I thought that since the player had a power button I wouldn't need to press play to get the sound to go through the system, but I found a leaf switch under the board that has to make contact before sound will play through the system.

From there I was thinking about hooking up a toggle switch for the leaf switch, and a toggle switch to cut power to the tape player motor. In many cases the motor causes background noise.

After shopping at Radio Shack for an hour I revised my plan to just a single toggle to cut power to the motor. Pushing play will take care of the leaf switch !

The smallest toggle I could find was a micromini toggle switch, part #275-624 at $2.99
I decided to use a closed circuit 1/8" stereo phone jack, part # 274-246 at $2.99

I'm not sure if feeding a signal back into the tape head will cause any damage, but it may use up some of the signal that I want to be amplified, so the closed circuit switch is the way to go.

The tape head is connected until you plug something into the jack, then the only thing connected is what you are plugging in.

Step 3: Drilling the Holes and Mounting the Hardware.

After looking for a good place to put the toggle switch and phone jack, I decided to go under the carry handle (when it is down). Since this player comes apart in three main chunks, putting them anywhere else could cause a problem if I have to take it apart again.

I located a place that would have clearance inside, and under the handle, then drilled the holes.

This plastic was really thick, and the jacks wouldn't go all the way through, so I used a larger bit to do a type of countersink on each hole, making the hole larger on the topside, and thinning the plastic so that I could fasten the jack and the toggle with the supplied hardware.

Step 4: Hooking Up the Hardware

After both items were mounted I unplugged the connector that goes to the leaf switch and to the tape player motor. I separated the motor wires, cut the red wire and hooked it up to the toggle switch.

The next step is to de-solder the wires coming from the tape head and connect them to the phone jack, then connect the wires from the phone jack back to the board that the tape head wires were soldered to.

The tip of the line in jack is the Left positive, the next band down is the Right positive, and the rest of the jack is the ground.

The picture of the back of the phone jack box shows the diagram, and I have the area on the right labeled as follows:

1 = Ground
2 = Left Board
3 = Left (head)
4 = Right (head)
5 = Right Board

I soldered all the wires in place and tested the system:

Step 5: It Doesn't Work.... Maybe... Wait.. Success !!

The sound is terrible ! It's all broken and fuzzy with distortion.

I tried turning the volume on the mp3 player to 1 and it was still distorted.
Next I tried another mp3 player - with the same results.

I checked the wiring again and it was all fine.

Then I started to comb the boards for a line in or L, R marking. All attempts at getting a signal through sounded distorted.

I didn't want to add a resistor to each channel because of possible sound quality issues, so I decided to check the IC on the tape player board.

I went here:

and discovered that the IC was a system preamp for the tape deck.

I got the datasheet and found 2 pins that gave a really good sound for input.
(pins 18/Right and 20/Left)

It was a tough solder either way, but I chose to tap the wires on the top of the IC.
It went pretty well and the wires are pretty stable. If I get a chance to get a hot glue gun I'll add some to make sure the wires stay put.

I left the toggle for the tape player motor, since it does kill some noise.

After that I put the box back together and plugged my mp3 player into it. It sounds great !

It ended up that the closed circuit phone jack didn't get to be fully used (nothing is connected when there is nothing plugged into it). That's OK, though, because it was the only type Radio Shack had at the time !



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    50 Discussions


    Question 5 months ago


    1 more answer

    Hola, estoy usando Google translate para intentar responder a tu pregunta.
    ¿Estás diciendo que no tienes todo el sistema, solo las partes de las imágenes?
    No tuve suerte usando el cassette desde el cabezal de la cinta. Terminé obteniendo una hoja de datos para el IC y encontrando las entradas allí. Ese IC en su imagen parece que podría ser el indicado, pero no puedo leer el número en él.

    Did this with an old Technics box. Works ok with the line-in feed onto the output lines of the pre-amp chip, but doesn't sound completely clear, almost like certain frequencies are being clipped by something. I might try shifting the ground and see if that helps. It's not easy to get to though, as it's buried under the CD mechanism.

    2 replies

    Yeah, sometimes you have to dig a little to get it to work right. Also, make sure the signal you're putting in is very low if possible - usually when you hijack an input, it's looking for a weaker signal... Good luck!

    Another hour or so tracing back towards the power amp, and I came across 2 terminals marked "tp-r" and "tp-l" Have a wild guess what they stood for! Never mind, lesson is to have a proper look at the board before you start. Works great now.

    Hello 2017!

    Just because this instructable is now 10 years old doesn't mean it's not useful!

    I check the comments now and then, and update things that aren't clear.

    Good luck wiring up those old boomboxes - I'm seeing more and more of them around with dead cassette decks (likely belts), or CD players - so now you can get them super cheap!

    We're not alone in this world! I was wondering about adding an input to my old boom box. Finding this guide was great, but finding out that my boom box was the same as yours was incredible! Thank you! Indispensably helpful.

    1 reply

    on the subject of the belt breaking and autostop turning it off.. i wasn't sure how autostop worked, so I assumed it worked like your''s must, so I unplugged the motor and it still works fine I tried to listen for the motor noise you mentioned but I could not tell the diff with or w/o the motor running (during silence between tracks) there is some noise but not from this motor. I don't need to play tapes, I have tapes, just will never play them again... i'll leave it disconnected.

    1 reply


    Glad you got it going! This little rig has worked well for me, and it kept another boombox out of the dumpster.. Glad to hear that you didn't have to keep the motor running and / or put a new belt on the tape drive to keep it playing!

    Just thought about this... correction, I hit play on either tape deck and it's enabled... makes sense...

    Yo, TheRealAnubis... you the Man (or Woman)!!! I knew this could be done! I just didn't want to figure it out myself!! I've been in software dev for almost 20 yrs but roots are in electronics.. I did this mod to a vintage JVC boom box model PC-XC30. I wrote down the numbers of the ICs I could see and luckily the most accessible one was the cassette preamp! the chip is LA3246, this one is for dual tape deck boxes, but the technique is the same. found the preamp out on pins 4 & 17, top soldered the new audio in to those on the IC and audio common to gnd in the unit. Works like a charm. I just hit play on the right side tape deck and listen to music from my tablet. That is until the tape drive belt breaks and it auto stops. Then I'll need to think.

    thanks much! Drew

    it did work pretty well. i hooked the cables on the amp (IC302), on the pins 8 and 13 if i remember correctly. i don't want to open the thing again to check...
    if those don't work you can to hold the cables on different pins until you get a signal, and then solder them in place. this is what i did, but be careful though...
    the ground is important too. it worked best in my case with the ground cable from the cinch socket soldered on the outside of the metal bracket where volume control is located (the main ground on the board didn't work for some reason).
    the signal is amplified so much that you have to make sure that the volume is set to zero on the boombox, and as low as possible on your source. you then turn 'on' the radio and you should be able to hear your favorite tunes coming out this amazing little device!

    hope this helps.

    Hey, thanks for the tutorial, this is pretty cool. i was thinking of doing that on an old panasonic boombox, and was amazed to find something about such a conversion online...

    The thing has both an amplifier and a preamp... Where do you reckon is the best place to hook the cables?

    Thanks a lot!

    1 reply


    I'd try the amp. It's more likely to take a regular signal from a headphone jack. I would think that the preamp would be for a much weaker signal.
    I could be wrong, but I'd check the chips on the amp board for a winner!

    Hey, thanks for the guide. I'm trying to do something similar to a stereo shelf system (tape/CD/tuner). What was the part number for the IC, or can you link directly to the datasheet? The stereo I have is using LC75392 IC chip, the cassette deck uses TA8189N for its preamp, but not sure how to approach this yet. If you soldered the left/right leads to the preamp, where did you solder the ground pin to?

    3 replies

    I see it has been sometime since you put up this instructable. But, I am curious. Did you just put the MP3 output (via the connector) directly to the IC chip ? Or did you still use the imput from the tape head ? It seems like you can bypass that part and just goto the chip.

    Thanks for anymore info. Great stuff, thanks for taking the time to put this together. I am sure that took more time then the addition of the (AUX) port.


    Yes, the tape head idea didn't work out. I left it in the instructable because it was my original plan, and because it could possibly save some time for the next person if they decide to go that way instead of looking for the IC. The signal from the Mp3 player, even at its lowest came through distorted. I believe that the signal from the tape head is very weak. The final version has the input going straight to the IC.
    So to get it to work, I press play on the tape player (this powers up the boom box) and toggle the motor off to remove excess noise. Then you plug in the Mp3 player and enjoy!

    Thanks for the comment!

    This is a very old instructable and I just hope you would be interested in my comment/problem.
    I have an old Philips cassette+radio player. It does not have a line-in but it does have a line-out.
    I want to connect my iPod shuffle to it. I don't much care about the radio/tape.
    I do not have much knowledge about electronics (bio student)

    I opened it up and I found this.
    There are three boards - #1, #3 and the board under the cassette player.
    Wire #2 connect Board #1 to speakers. Board #1 also has line out.
    Board #3 is radio board and has the radio needle and also the volume wheel.
    Wire #4 connect the power to Board # 3. Only board #3 has power supply.
    Red Blue Wire #5 connect board #3 to Board #1.

    So board #1 is connected to speaker and cassette board by wire # 2& #5
    Power is connected to Board #3
    A lot of other wires connect board #3 and cassette board.

    Now. I was wondering if I could just cut Wire #5 and attach it to a cut 3.5mm connector wire could it all work. I don't want the radio/cassette player just the mp3 player.

    Please help.

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