Introduction: AUX IN and Bluetooth for Every Car Casette Player!

Picture of AUX IN and Bluetooth for Every Car Casette Player!

If you have an older car, with a cassette player in it, I KNOW you'd want it to be able to play the music from your phone. You might have even tried different ways to do that and neither one was perfect.

This one is. It's the best way to do it. I'm not bragging, I'm stating the facts. I hate to see a good amplifier (the car player is also an amplifier, a good one, too) rendered obsolete because people can't connect their phones to it.

But you need to know your way around with a soldering iron. If you do this right,, not only you'll get crystal-clear AUX IN sound (on any cassette player!) but you can also upgrade it to a Bluetooth-connected sound system! Read on and do it, it's worth it.

If you're afraid of ruining your car's tape player, buy a used one and work on that (just get its anti-theft code with it). They're cheap now and still put out around 40W of good quality sound. The sound settings will still work. You'll make yourself a cassette player that puts out solid sound from you phone using a cable or a Bluetooth connection.

Step 1: Car Cassette Players. If Only Those Had AUX IN ...

Picture of Car Cassette Players. If Only Those Had AUX IN ...

Well, they could have had it but back then phones as music sources weren't the norm at all, you know. So nobody thought about that. Maybe a few. But the norm was most of the old car cassette players had no AUX IN.

If you're like me, the owner of an old car that had a factory fitted cassette player you would long for a stereo input jack enabling you to play all that music you have in your phone. Or drool whenever you saw a phone streaming music over Bluetooth to the new car's sound systems. Yep, I've been there.

All sorts of AUX IN devices sold over the internet tricking some CD output of some car players but those were newer than mine so I didn't bothered with those. Besides, many users reported low quality playback using those devices.

So here's how I did it. I consider it the best way there is. I gathered this information from a lot of sites with different procedures. Zero noise, perfect digital quality, no volume degradation, on the contrary you get additional signal gain so your music is now loud and clear. But you have to be skillful with the soldering iron. And you have to have some understanding of what we're doing. Also, a multimeter is mandatory. So here goes.

Step 2: Here Goes Nothing ...

Picture of Here Goes Nothing ...

First of all, be aware of the PIN code of the car player. You have to have it. Because if you don't, the next time you put the player back into the dashboard it won't work without it. At all.

So, get the cassette player out of the car. Open it. It'll look like this, or similar. Take a photo using your phone. Carefully take the tape player part out. It's mostly mechanical stuff, with springs and levers. But it also has micro switches with wires. (and a reading head). Some are depressed and some are not when a tape is in so try the mechanism with a tape and see how the switches state change (also, take photos...). Make a note of it all.

Take it all out, (make photos of every step) you can cut the wires but label the pairs for each micro switch and the ones that power the small electric tape motor. Those switches tell the radio it has a tape and it changes the source from radio to tape. Then, cut the wires and solder a normal switch (the kind that stays pressed when push it and you have to push it again to release) to those wires in order to change the source just by pressing it. Great. Now we have a switch that tricks the player into playing a cassette that doesn't exist anymore. We'll take care of that soon.

For now try and find a place for your switch so that you can access it. I re-used the eject button for that and didn't ruined the car player's look. I advise you do the same.

Step 3: The Hunt for AUX IN Lines

Picture of The Hunt for AUX IN Lines

It's a hunt, but an easy one. You already saw where the tape head ribbon (or wires) connects to the mainboard. It's a connector, visible here. Follow the traces from it and it will ALWAYS go to a preamplifier integrated circuit. This small IC (also visible here) amplifies the weak signal from the tape head to deliver a proper volume to the main amplifier.

Once you found that integrated chip, search Google for its datasheet. In that you'll see the stereo OUTPUTS of that chip (usually left out, right out and ground). Make a note of those. Those pins are the ones you'll use for the AUX input. Let me repeat, we need the stereo OUTPUTS, not INPUTS. Many people on the internet mistakenly used the stereo inputs, ending with horrible sound quality. So don't make that mistake.

In fact, once you find those OUTPUT pins, the best way is to de-solder the entire IC from the board. We don't need it anymore, there's no tape head to be amplified anymore. And the phone's stereo output is louder than its output anyway. So take it off and throw it away. Solder a stereo IN jack to those wires and place it in a hole somewhere on the player's faceplate. Or place as a very ugly wired connector dangling out of the cassette door. Your choice. I did it different, you'll see it soon.

You could leave the IC on the mainboard but you'll get noise. A lot. Because that IC still receives power from the player and it has internal noise, despite the lack of signal from the tape head.

The easiest way is to take a nail clipper and cut the power pins of the preamplifier IC, check the datasheet for that. Then, it'll be silence. I recommend this way, it's less work.

Step 4: Feast Your Ears

Picture of Feast Your Ears

Now that you have a switch and a stereo input jack, it's time for a test. Place the player intro the dashboard, input the code if necessary and turn it on. Radio should be unchanged. Now press the switch. The player should indicate "TAPE". Connect you phone and play a song. If you did it right, pure digital sound will flow, making you wonder why did it take you so long to do this. You'll discover new life in those tired factory-fitted car speakers, believe me.

If you hear nothing, check the following - is the car player indicating "TAPE"? If not, you messed up the wires from the micro switches. If it does, and you still hear no sound with the phone connected, you messed up the stereo OUT pins of the preamplifier IC. Taking photos of the entire process is the only way to go back to the drawing board. In fact, this instructable is made out of my "backup" photos of the entire process.

As you see, I got creative in placing that switch and stereo connector. This is a SEAT car player I modified for my brother. Try to do the same, it's more work but everyone will think that car tape player had those factory-fitted.

If this is all you wanted, stop here and enjoy your connected phone music. Despite the required cable connection, it's simple to do and reliable. Make a photo of your achievement and let me know you made it.

But I wanted more. I wanted Bluetooth connection. The next step is for the brave ones.

Step 5: Bluetooth Car Music on a Budget

Picture of Bluetooth Car Music on a Budget

Bluetooth enabled car players are expensive. Or they come with an expensive car. It shouldn't be like that, but it is. Well, I wanted it cheap. So I found a good stereo Bluetooth receiver in one store. It must be a reputable brand, cheap Chinese stuff sounds horrible, believe me, I tried. So in my case, a Philips AEA2000/12 fit the bill. And the sound quality was great. It was powered by a small 9V power supply.

I opened it up to see it's actually using a 5V regulator (7805) that can easily take 12V but first I replaced the 10V rated capacitors around it with higher voltage ones. So now it works on 12V.

Remember the power wires from that electric motor? Measuring voltage on those lines with the player in TAPE mode revealed it was a 12V one. Good! Here's the power supply ready! And it turns on only when the player is put in TAPE mode (using the switch). Just perfect.

I soldered my stereo AUX IN wires from the earlier steps (with a multimeter I found better soldering points than those small IC pads) to the output of this Bluetooth receiver and powered it with the electric motor's wires (mind the polarities). I placed everything inside the player (we do have the space now). One quick pairing and the sound coming out of my car with me standing outside was all the rage of the evening. I measured about 25 meters range for my connection. I only need about 2-3m so I was extatic.

I can connect to it with any android/Windows/IOS phone and tablet. The sound is perfect. No hum, no static. It's way better than the FM stations I get on the radio side.

The last photo shows my brother's setup, he purchased a different Bluetooth receiver powered from USB 5V so I sacrificed a car power supply to power it from those electric motor wires. Insulate it well, you don't want it to touch anything in there.

My Bluetooth receiver uses Bluetooth 2.1 EDR standard, my brother's is 4.0 with auto connect. On mine, I have to manually connect each time (cumbersome, I know, but there are apps for that) but I got 25 meters range! His setup self connects to his phone but only has about 3-4 meters range. Bluetooth 4.0 has a shorter range but increased data speed. For music 2.1 is enough, but higher is always better. You can use any brand, but it has to be a good one. Test it before using it for this project.

That's about it. If you have questions, just ask, I'll try to answer them.

Comments

SankarA2 (author)2017-11-14

Hi Caludiopolis, Awesome work! I found a similar work in youtube but in a non-English language which I unfortunately couldn't understand. After reading your post, i was so excited to fix my car (2000 Jetta - premium iv a non-monsoon radio system by Calrion - PU-1666A). I followed your steps and was looking for preamp ic. I believe the attached pic is the correct IC - please confirm. The data sheet of this IC (http://html.alldatasheet.com/html-pdf/19668/PHILIPS/TEA0675T/1003/4/TEA0675T.html) found from google says pin 1 and 24 are OUT A and OUT B - and 16 is GND. These pins are very tiny and so I wanted to solder them from the back of the board. On my search to find the correct pin, I noticed pin 1 and 24 are not connected to anywhere. I'm now confused if I'm looking at the correct correct IC. Please confirm. In your steps you mentioned, cut the wires from tape switches and connect to normal switch. I'm not sure if I really need this switch if tape is left inside but power cables are disconnected? If you say yes, then I would like to know what wires needs to be connected to this new switch. It's not clear enough in your description. Please explain. I wonder, if the power to the preamp is disconnected how would the AUX sound connected to output pin would be pushed to power amp? Your help would very much be appreciated.

claudiopolis (author)SankarA22017-11-15

Hi. If those pins do not seem connected, they still might be. Their traces could run under the IC and escape to some via's on the other side of the board. Your preamp seem very complex given the task. If I were you I would start from the final amplifier. There are two input pins (Stereo L and R) on that amplifier that must go to this preamp. Use a multimeter or continuity tester from each pin on this preamp to each pin of that final amplifier IC. There are two channels (pins) you need to identify (The amplifier IC datasheet will tell you if it's right or left), the ground is common and can be taken from anywhere.

The switches are on the cassette mechanism and have wires to the mainboard. When a tape is inserted, some are opened, some are closed. You need to replicate the same thing with just one switch by connecting them to this switch (should have 6 pins with NO/NC states) so that when you switch it on, the board thinks it's having a tape inserted and switched the source. After that, the entire tape mechanism is not needed anymore, just this switch.

If you just leave a tape in it, you would have no radio until you eject it. Or, the preamp could jump on radio when it doesn't detect signal from the tape. Replacing the entire tape mechanism with one switch IS the best way to do it.

Any AUX signal connected to the output of the preamp IC would go to the power amp and get amplified. You don't need power to that preamp. You could unsolder it completely and just use those output traces.

Look, I did say you need to be skilled with electronics to do this conversion. The title "for every car casette player!" doesn't mean "by everyone".

SankarA2 (author)claudiopolis2017-11-15

Hi, Thanks for your response. Though it seems bit complex, it's not super complex. Moreover the way you described in the original post seems pretty easy for anyone do it. I have a great passion in learning electric and electronics though i'm a mathematician and computer engineer. This is going to be my next project and I'll get it right. Your last line actually got me going now. Thanks again for your quick response and help.

TimC15 (author)2017-07-23

Hi claudiopolis, great instructable, really informative. Like Coffeecat84+ I, too am working on a Ford 5000 RDS EON but have come across a noise/connection issue. Everything is identical to his pictures and the IC has been cut but I'm getting what sounds like a heartbeat when I connect my phone (Samsung Galaxy S7 Edge). I've tried the phone with other AUX devices and it works fine. All the cables I've tried are working with my phone, my daughters tablet and other AUX devices. My daughters tablet works perfectly with the AUX IN that I've fitted to the 5000 RDS. The really weird bit is that if I connect my phone to the socket remove the ground cable and then reconnect it the heartbeat sound disappears and it all works perfectly. Any insight or ideas would be greatly appreciated.

claudiopolis (author)TimC152017-07-25

Hi Tim,

Sounds like you're having ground loop noise. Different devices use the ground differently, that would explain the difference.

You need a ground loop insulator.
That would make any noise go away.
It's a passive filter you need to put between your phone and your stereo input.

Here's one:
https://www.hills.com.au/hall-research-hall-research-gli-35mm-3-5mm-stereo-audio-ground-loop-isolator-and-filter

Cheers,
Claudiu

paulgabriel.cristea made it! (author)2017-05-10

Hey! I made it, and added a Home button functionality, and a mic, so now it behaves just like a headset, but amplified through the car system! Thanks a lot man!

https://www.instructables.com/id/Smartphone-WIRED-Connection-to-Old-Opel-Tape-Playe/

AllOuttaBubbleGum (author)2017-04-25

Excellent write-up. I am going to do this on a vintage 1989 Camaro factory cassette radio. Any chance you would do a write-up on adding pre-amp outputs to units that do not have them?

Thanks. I'm not sure I get the question. You mean adding pre-amp INPUTS ?

Sorry, I mean line-level outputs to feed an external amplifier. Taking the pre-amp level signal before the internal amp to external jacks.

I see. Well, what's wrong with feeding the external jacks from the same line you're feeding the internal amp? Assuming you need a signal from your phone, that is. This instructable should also apply for external amps as long as you extend the input lines made here to some DIY external RCA's in the back.

Yes, I thought about that but I thought it would be nice to use the volume control on the factory unit as well as the radio tuner function. It seems there must be a location to tap the internal amplifier input.

In that case, it's a matter of finding the amplifier IC inside your head unit. Once found and identified, the IC's datasheet will show you the inputs. There are only three pins you need to tap into for your RCA's in the back. Then you'll have AUX IN & radio tuner signal. Proper grounding is a must. Volume control can either be implemented inside the Internal amplifier IC or, if you're lucky, prior to that. The second option will also give volume control of the external amp.

paulgabriel.cristea (author)2017-04-24

Frumos, frumos. Chiar vreau sa fac si eu asa ceva la Astra F al meu si de aceea cautam instructables. Te anunt cand il fac si cum arata.

Mersi! Astept poze. Atentie la codul casetofonului! Iti trebuie neaparat. Altfel trebuie sa-l duci la decodat.

Coffeecat84 made it! (author)2017-03-19

Thanks! made the aux in and it sounds great. Used a ford rds5000. Couldnt find datasheets anywhere on line for the pre amp, but was able to figure out the ic pins by powering up the unit and running each pin to ground in turn with a multimeter and noting which speakers went quiet. I have very little electronics knowledge so am not sure if this tecnique was safe or advisable! I also found a ground pin on the ic using the multimeter for the jack sleve connection.
Thanks again i had previously followed another tutorial with audio input before the pre amp: the results sounded awfull! This sounds awesome!

Oh and i figured out the diff between the input and output pins of the pramp ic with the multimeter by noting which pins were connected with the tape head outputs.

I'm glad you made it. Well done!
That's one mistake almost everyone makes: to use the audio input. And I have one word of advice for you. De-solder that preamp IC completely. Or at least cut it powertrace on the PCB (you need that datasheet for that). The reason is, the IC is still powered, and it's noisy and sensitive. You'll be noise-free after that, at any volume.

Thanks for the advice, i'll look in to it. couldnt have done it without your instructable! I had a very enjoyable drive to work today listening to some great music!

You're welcome! And thanks. I know how that drive feels now.
About the preamp, you could just cut its pins with a nail clipper. If you can squeeze one in there, that is. If you find its datasheet, there's only V-in to cut.

Got the pin! I couldn't find a data sheet for the ic: The pin out for the connectors at the rear was readily available though. I used my multimeter to see which pin on the ic was connected to the supply from the car battery. I cut it with the nail clippers and now like you said the quality is perfect at all volumes. thanks again!

Great! Good job on finding the pins without the datasheet. Now that's how an AUX-in is supposed to sound.

shostakovich (author)2017-03-04

good

shostakovich (author)2017-03-04

good

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Bio: I am a graphic designer with many hobbies. I love electronics, computers, LEDs and all things tech.
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