AUX IN and Bluetooth for Every Car Casette Player!

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

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 ...

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 ...

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

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

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

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.

2 People Made This Project!

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46 Discussions

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FlorinN10

25 days ago

Hi . excellent instructions. I have a PIONEER KEH-P3600, a legacy from my father-in-law (resting in peace), which I would like to transform into an audio unit in his memory. but it's a lot different. I leave the pictures, and I can wait for opinion.

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claudiopolisFlorinN10

Reply 24 days ago

Hi Florin. Yes ... it's different. Probably an aftermarket unit. With CD-changer control. Perhaps dual-headed, too. I wouldn;t try to convert it. Too complicated. Even if you trick the microswitches, the logic is still there as there are too many sound options on those buttons. Better stick with the car's default player (the cheaper ones work best for this instructable).

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FlorinN10claudiopolis

Reply 24 days ago

multumesc. ai dreptate, prea complicat. as fi vrut sa profit de performantele audio ale lui, pe langa faptul ca acum multi ani, in tinerete, mi-a incantat calatoriile cu vechea mea Dacie. poate o sa il folosesc asa cum este , intr-un sistem de boxe.
multa sanatate si spor .

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HencoS1

Question 5 months ago

Hi claudiopolis. Thank you for the great guide. I did this to my Audi Symphony radio and I'm glad to say that is working( well sort of). I have a slight problem which I do not quite understand. I used a male-female AUX cable so that I can hide the cable somewhere out of sight. For some reason though if I skip or pause a song I need to plug out from the female end and reinsert untill I get a connection again. Any advice on fixing this problem?

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claudiopolisHencoS1

Answer 5 months ago

Does your player defaults to radio when that happens? What does the display show?

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HencoS1claudiopolis

Reply 5 months ago

Nope. It still stays on tape mode. Attached I added a video of what it does.

I AUX cable I used was dirt cheap though and I don't know whether that might cause the problems. The left and right channel audio inside te aux was also incorrect.

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claudiopolisHencoS1

Reply 5 months ago

Video does not work. I think your problem is preamp-related. You still have it there, active. (And the tape player, too?) Your unit seems to have some background noise cutout feature. When you skip or pause, it thinks there's a gap like in between songs on a tape. So it mutes the output despite the new song starting. The reconnection causes a "pop" noise that makes it think a new song starts and resumes playback. Try removing the preamp chip. And browse your unit settings for any noise-cutout feature, it has to go. The ground is the same in the entire car.

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HencoS1HencoS1

Reply 5 months ago

Does not matter which device I use. Same problem with all of them. Though for some reason when playing anything from YouTube I do not get the same results. I can pause and play as long as it is withing about 2 sec, and I can skip through the videos and start playing something else without any issues. I tested with my standard music player and with Google Play music and it stop working immediatly when I pause or skip.

Regarding the comment on testing the AUX. As soon as I plug in to the 'radio' I can hear a popping sound, also when I touch the ends of the AUX. And the cable I use to plug in has never given me problems. And still doesn't when using it on other radios, so I can only think that the cheap AUX (which I plug into) is possibly the problem.

But thank you very much for the advice. I'll first replace the cable that is soldered to the radio an see whether that fixes the problem. If not I'll cut the power to the IC. And hopefully after that my problems will end. But the sound quality is amazing. Never thought it would be that good.

Highly appreciate all the effort and willingness to help.

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claudiopolisHencoS1

Reply 5 months ago

Have you tried other music source? A table, another phone? Same thing happens?

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HencoS1claudiopolis

Reply 5 months ago

Danm wish the video worked. It shows exactly what happens. But the phone also 'looses' connection with the AUX if I can say it like that. When this problem occurs, I should then plug out from the female end and start the music on my phone again and give it a second or two until it realises there is an AUX cable plugged in and only after that I can plug back into the female end and the music wil start playing as it should.

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claudiopolisHencoS1

Reply 5 months ago

Two scenarios can happen in your case.
1. Weird cable. Change it, all the way to the car player. Use another. Take the player out of the dash and confirm with a multimeter that every pole on that jack goes to the right signal insertion point, without any interruptions. Ground can be tested by checking continuity between the stereo jack's ground and the car ground (metal door lock, for instance) or the car player's outer metal shell.If that's no happening, you're not using the right ground.
2. Take the preamp IC out. At least cut it's Vcc IN with a nail clipper so that it's not operating. If the problem persists, it's hidden in some noise reduction feature of your player. Put a switch on the line and live with it. Or, find the main amp inputs and solder there. It's up to you. Judging by the sound quality, I think it's worth the trouble, isn't it?

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claudiopolisHencoS1

Reply 5 months ago

I saw the video. Turn the car unit on (with no phone connected. Test your aux input by touching that female jack with your fingers. If things are OK you should hear a noise (static/pops/whatever) That means the car player is live and awaiting signal. If that's happening, then it;'s your phone. Or cable. Modern phones have a 4 poles jack (for microphone input). It's been known to work unreliably with some simple 3 poles jacks. There are many a bit too short, or unable to be fully inserted because of some phone cover and so on.

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HencoS1HencoS1

Reply 5 months ago

Do you think it is possible that it might be a ground problem? I soldered the left, right and the ground on to the IC. I did not desolder the IC as I did not have any noise, and the sound from the tape immediately cuts out when I plug the aux in to my phone.

Reason for thinking it might be a ground problem is that the tape plays in reverse but if I insert the aux in to the female end (just enough for the ground connection) the tape starts playing as it should. (Hope my explanation is clear)

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ttemple2

1 year ago

claudiopolis, I loved reading this ible! I decided to give it a go, but (always a but) my deck is older and spartan compared to yours. For reference, it's from a 1994 Jeep Cherokee. Chrysler Radio model P56007214 (made by Mitsubishi). I am posting a pic of the unit with tape removed. I can not find a preamp chip anywhere. I have located the AM receiver and tape motor chips, but that's it. I am not expecting you to know everything about all radios, although it would cool, however, just by the pic can you tell anything at all about where I should be looking?

Looking forward to your reply. Thank you.

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ttemple2claudiopolis

Reply 1 year ago

Thank you, sir! Actually, I am a member of that forum and have read that post many, many times. The problem is, my model of radio has a lot of bleed through when adding an aux to the pins that others use. Unless you know of a way to eliminate that extra noise?

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claudiopolisttemple2

Reply 1 year ago

Noise on cars' AUX comes usually comes from:

1. Unshielded/RF noise-generating alternator. That noise varies as you rev the engine. Only a car service can get rid of it. They need to change the alternator's filter capacitor

2. Dried capacitors inside your radio. Look for bulged or leaked ones, those need replacing. That noise is constant.

3. Ground loop noise. You need a ground loop filter between that AUX and your signal source (phone). Your car and your signal source handle grounds differently.

In your case, it may also be because your signal still goes thru the tape head preamp (every tape player has one, the tape head's signal is way too weak to feed a proper amplifier chip). Follow the traces from your tape head. It goes directly to that preamp chip. Always does. A multimeter set to continuity helps. That chip must be disabled as in my instructable and the AUX signal applied to its OUTPUTS.

Let me know how it goes.

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ttemple2claudiopolis

Reply 1 year ago

It's not going that well. This unit seems to be configured entirely different from most others. New pics show a small board that is connected to the tape deck part of the radio. I had to go macro to see the markings. I highlighted the areas that look like to be relevant. I inset a macro of the only area that looks like a R, L, channel, but I don't know.

Your thoughts?

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