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

Picture of Adding a Line in to a Boombox With a Tape Player

** 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

Picture of 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.

Picture of 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.

Picture of 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

Picture of 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 !!

Picture of 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 !


PhillS11 (author)2017-12-03

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.

TheRealAnubis (author)PhillS112017-12-06

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!

PhillS11 (author)TheRealAnubis2017-12-09

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.

TheRealAnubis (author)2017-03-12

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!

rauloinstructables1 (author)2017-01-29

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.

I'm glad you liked it!

So many boomboxes, so few line in's. :)

drewoj (author)2013-06-18

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.

TheRealAnubis (author)drewoj2013-06-19


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!

drewoj (author)2013-06-18

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

drewoj (author)2013-06-18

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

fdebord (author)2012-10-15

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.

fdebord (author)2011-11-27

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!

TheRealAnubis (author)fdebord2011-11-28


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!

eli2k (author)2010-01-09

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?

TheRealAnubis (author)eli2k2010-01-11


I believe it was a Toshiba IC - TA2068N

Hope that helps..

Also, I put the ground to the system board ground..

lukethedog (author)TheRealAnubis2011-10-24

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.

TheRealAnubis (author)lukethedog2011-10-25


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!

ab727 (author)2011-10-11

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.

TheRealAnubis (author)ab7272011-10-12

Hmmmm... Is there any way you could get me some closer shots of the boards?

Without seeing those, I would recommend looking for an IC that you can find the specs for online. I would say you can even try to de-solder the wires on the tape head and try it that way, but I didn't have any luck with that. The signal needs to be so low for that, and any mp3 player, even on its lowest setting makes the sound distorted.

You could follow the wires from the line out jack and see if they lead to an IC.

After you find the sound IC, you may want to disconnect the cassette motor (or put a switch on it like I did) to cut down on line noise.

ab727 (author)TheRealAnubis2011-10-15

I have just posted my instructable. Here is the link

It would not have been possible without your excellent write up. Thank you.

TheRealAnubis (author)ab7272011-10-18

I'm glad you got it working!

Thanks for mentioning my instructable in yours. I'm going to download it later and read the whole thing.

ab727 (author)TheRealAnubis2011-10-18

How can I have not mentioned your name. Yours was the one that gave me the whole idea in the first place!

ab727 (author)TheRealAnubis2011-10-13

Thanks for the reply.
Sadly, I was too impatient and decided to start on my own just a few minutes after writing to you.
When I cut the wire #5 and connected my wire, a strange thing happened. The sound was produced, even without any power source. I guess it was drawing power from the iPod. The sound was clear, not loud but can easily be heard in a room.
There were 2 wire sets connecting board #3 and cassette board. One had 3 and the other had 4 wires.
I cut the set with 3 wires.
When I attached the wires no sound was produced but when I accidently touched a wire to the radio board (#3) there was sound!
Finally, by luck and no knowledge, I got the result.

I am uploading photos for an instructable right now. Shall be posting a link to you as soon as I finish the right up.

I regret that although I did succeed I do not know the reasoning of the thing. So it was all by a random chance.
Thanks for writing the reply.

Best regards

xtian5 (author)2010-10-01

Can you put a mic into the line in and record with the tape recorder. I just got a similar tape/CD player but it won't record external sound like the old ones. I tried putting a microphone into the headphone jack, but that wouldn't work either. I was thinking of trying to add a line in so I make simple scratch tapes of playing guitar and singing. I could probably go out and find an older boombox for $5 that already has the feature but where's the fun in that.

TheRealAnubis (author)xtian52010-10-03


Good question !

I didn't think it would work because the hookup is actually the preamp for the tape player - this would be like trying to play and record the tape at the same time, or something like that.

Given that, I found a cassette and tried it - It did not work for me. If you could locate the radio or cd circuit, that would probably work.

Let me know if you get it going !

jerkey (author)2009-09-20

Great instructable! I have done this myself a few times, and I recommend finding the audio signals coming from the radio or CD circuit. If you are lucky, they will be Red and White for Right and Left. Cut one, and that speaker will go silent - cut the other, and then hook those four wires (two red and two white) to a switching headphone jack from radio shack. Such a jack has five wires - Left in, Right in, Left out, Right out, and Ground. If you are lucky, the red and white wires you cut will reach the place you install the jack. When nothing is plugged in, the CD or radio will function as normal, but when you plug in, the jack automatically disconnects the CD player or radio. You will have to add a wire for ground from the jack to ground on one of the boards, you can usually tell Ground because it is the most prolific trace on the board. keep in mind: if you use the audio wires from the CD player, it might not work unless the CD player thinks it's playing a disc. Same with the tape wires. If you are having trouble finding the Left and Right signals here's a hint: if the boombox has a physical switch to select between Tape and Radio etc, the Left and Right wires are definitely there! Good luck and don't give up until you get it!

TheRealAnubis (author)jerkey2010-05-02

That sounds like a great way to do it as well !

I've always wondered if there was a way to trick the CD player into running without a CD in it....


soultron (author)2010-03-13

Great write up! I see how it works, but it still shows how little experience in this. I'm stuck until I find a schematic, or I guess I could try and hunt out the right leads... My box is much older than yours.

TheRealAnubis (author)soultron2010-05-02

With a little trial and error, you should be able to find it !

What is the model number and brand ?

samuraiclinton (author)2010-02-02

After reading this, I could easily manipulate a radio to only accept external line-in devices.

I think manufacturers of future ghettoblasters could save money omitting the radio feature.

I could go on for hours explaining why external devices such as MP3 players and other stuff are more beneficial and better for the environment!  But I'm keeping this comment short with that statement since DIY projects can also save the environment as well.  I even made a homemade advert on YouTube to make a point on why to visit

Thanks for the video link !

Very cool...

I agree that modifying items to extend their life and usefulness is the way to go.  It's a good creative outlet, and it is also a fun hobby.

bensmith8302 (author)2009-07-16

I did the same thing to my Sony jam box. Its very interesting that mine has the same circuit board as yours. Thanks so much for the help!

Ben, Glad I could help ! Most of the newer boxes already have an aux in jack, but not the older ones, and I'd much rather do and 'upgrade' to the old one rather than buy a new one.

sphynx88 (author)2009-04-13

great right up,

just to be sure I am understanding this (ic):

Before the wires were connected Tape Head > Certain Point on circuit board.
Tape Head> Phone Jack> Certain Point = static
Now they go from Tape Head > Phone Jack > IC


TheRealAnubis (author)sphynx882009-04-14

Hi, The first unsuccessful attempt was wired to the circuit board that the tape head connected to. I left the tape head connected just in case I wanted to actually play a tape, so the connection was piggy-backed on top of the connection on the circuit board. Once that didn't work, I went directly to the IC. So the tape head is still hooked up, and the connection from the Phone Jack goes directly to the IC. I just left the failed step in because it shows that you may need a super low signal to go to the tape head as opposed to the IC. Hope that helps !

maxpower49 (author)2008-11-03

could you just cut the wires going to the motor do you need the toggle switch

TheRealAnubis (author)maxpower492008-11-10

I added the toggle in case I wanted to play any cassettes. If you are positive that you will never play a tape again, then you can just cut the wires. A quick trip to the local thrift store can yield some great tapes for .25 cents each, and in a pinch (like when your mp3 player runs out of juice) it's handy to have a few around just in case.

mondaymonkey (author)2007-09-27

Good instructable. Me, being lazy, have made the simplest solution to amplifying Ipod ect. Take a old pair of computer speakers, the ones that divive their power from a wall outlet, not a USB. Simple, and not bad sound if you avoid loud volume. If you want bass, this isn't for you:P HEY, I have an old comp and home, half decent, about 933 Mhz processor, and 256 ram (almost as good as the laptop im workin on now) any one got any good ideas how to soundproof so i can listen to music without a hum?

Sounds like a quick and easy solution! As for the hum, I'd try a high quality sound card in the system. I am (unfortunately) using the onboard sound in my system, and it's very noisy. Good luck!

waterppk (author)2007-06-23

Hey, I was going to do this but i realized that my boombox has a separate board that sends the radio signal from the tuner (radio) board over to the amplifier/tape deck board. It sends over +/- power to the tuner board and then the tuner board sends back R/L audio. They are labeled exactly as +/R/L/- on a four conductor flat cable that runs between the tuner and the amplifier/ tape deck. I simply cut a stereo headphone cable leaving me with the four wires (red/green/two gold) to solder on to the R/L/- going into the amplifier/tape deck board. [ TIP: if you are ever trying to solder headphone cabling you need to BURN OFF the colored insulation with a lighter. Take the four ends of the internal wire and burn just the tips clean with the lighter, they will then be down to copper and solderable]. If you have questions message or e-mail me at

TheRealAnubis (author)waterppk2007-06-24

Hi, What brand was your boombox ? It would have been nice if Sony had labled their boards in a similar fashion. I considered soldering a headphone cable directly in, but I figured that I would have 2 problems. 1. The cord would get caught on stuff all the time. 2. Sooner or later the jack would get a short in it, and then I would have to open up the box and solder another one on. That's why I went with the input jack mounted through the body of the unit. Hopefully, it will mean a longer life and less hassle. Glad to hear that you got yours working, and hopefully you won't run into the problems I listed above.

mdmoose29 (author)2007-04-26

i tried doing this same thing a few months back... after i took it apart it wouldnt even turn on again. very strange since i hadnt messed with the wires yet... never did figure that out. But I'm glad to see you had a better go at it than me.

TheRealAnubis (author)mdmoose292007-05-18

Maybe you pulled out a power wire or something ? Sometimes after a while you can go back and look at it and figure it out. I've had that happen a few times !

leevonk (author)2007-04-26

uhm,.. so all one needs is the last step it seems... just solder the audio input wires to the IC right..

TheRealAnubis (author)leevonk2007-05-18

Yes, the last step is what worked for me. The reason I left the other part in is because there are other people that have had success doing it the tape head way.

marquoise (author)2007-04-28

Great instructable, I'm gonna go out and get an old tape player and turn it into an MP3 amplifier. Junk stores are full of decent tape player units. Love the way you documented the project too. Showing us your whole process, problems included, rather than just the end result.

TheRealAnubis (author)marquoise2007-05-18

Thanks ! Let me know how it goes... I have several units that I have collected from here and there. I was thinking about trying the tape head idea again on a different brand just to see if the same thing happens...

Punkguyta (author)2007-04-27

What did you do to your boom box? Kick it around?

About This Instructable




Bio: 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 ... More »
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