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TECH: How to add an AUX input to your stock Radio

Discussion in 'The Hokey Ass Message Board' started by Radio Joe, Oct 9, 2008.

  1. Radio Joe
    Joined: Jan 9, 2007
    Posts: 306

    Radio Joe
    Member

    Here is a cheap and easy way to add an auxillary input to most stock radios so you can listen to your ipod, MP3 player or XM radio through your stock radio.

    In order to do this yourself you need to have the ability to solder and some basic electronic skill is helpful.

    First- Your radio must work. If your radio doesnt work now, adding things to it wont make it work later. Fix it, have it fixed or use another radio.

    Next you will need the service manual for your radio. These can be found on ebay pretty eaily for between $3.00 and $20.00. The service manual will help you find the location to connect your AUX input.

    Lets look at a basic radio block diagram (Below) Yoru radio has a tuner section which connects to the amplifier section through a Volume control (a picture of the volume control schematic symbol is below). to use your MP3 player on this radio, you need to break the connection between the tuner section and the volume control. See the picture below
     

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  2. Radio Joe
    Joined: Jan 9, 2007
    Posts: 306

    Radio Joe
    Member

    After breaking the wire, you would connect the MP3 player to the volume control. If everythign was done right, you will hear your MP3 player (Or other source) through your stock radio.

    This is all great in theory, but how do you adpat this to your radio? Lets find out:

    first thing you need is a test AUX source. I recommend an older portable FM radio, tape deck- Something you wouldnt miss if you accidentally broke it. WARNING- testing by connecting an AUX source to your radio in the WRONG place could blow out your AUX source. BE CAREFUL! I cant be held responsible if you blow out your iPod.

    Connect your test AUX source to a headphone style extenion plug (radio shack number 42-2387A (see picture)

    On the other end of the cable (not plugged into your MP3 player) you will see three sections. These are the ground, left and right channel. We will be using the ground and left connection for testing. connect a lead to the section closest to the connector body- This is the ground lead (Black wire in picture) connect another wire to the last section further from the connector body (green wire in the picture) Set this all aside and you will be using it later to verify you have found the correct connection point for your AUX input.
     

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  3. monsterflake
    Joined: May 13, 2003
    Posts: 3,763

    monsterflake
    Member

    how much would you charge to do it for me?
     
  4. Radio Joe
    Joined: Jan 9, 2007
    Posts: 306

    Radio Joe
    Member

    Now it is time to look at your schematics- Now you may look at it and think "What is all this stuff- Im so lost" thats okay. You dont need to understand all of it. LOOK FOR THE VOLUME CONTROL. Once you have found the volume control you only need to figure out which lead it the input to the volume control. This is where you will break the connection. On transistorized radios, this should be easy- on tube radios it will be a little harder.... This is why you set up the test AUX source in the earlier step.

    Below is a few examples of some radio schematics. you can see I marked the area where the circuit should be broken and labelled each side. The labels will be important coming up.

    The first schematic is a transistorized AM only radio- Pretty straight forward

    The second is a transistorized AM/FM radio- AM/FM radios use a switch to connect the proper tuner section to the volume control. You will break the circuit between this switch and the volume control.

    the third is a tube radio with a fairly simple connection location- You may need to test a connection on both sides of the capacitor- Try a connection at location "3" and at location "7" and use whichever provides better sound. Look at the schematic to see where locations "3" and "7" are in relation to the volume control.

    the Forth is a difficult tube radio where you would need to do some experimenting. Basically pick a location close to the volume control and test- if it doesnt sound good, move a little further back in the circuit and try again.
     

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  5. Radio Joe
    Joined: Jan 9, 2007
    Posts: 306

    Radio Joe
    Member

    So now you have determined the proper location in the schematic to connect the circuit. Now its time to test if you are right.

    Identify the area you found in the schematic in your radio and disconnect this location. If you turn the radio on, you will get no sound from it.

    touch the disconnected points together and make sure that the sound comes back. If it doesnt- you have probably disconnected something else or broken something. fix it before proceeding.

    pull out your test AUX source now. Connect the ground to the radio chassic (black wire from earlier picture) and connect the green lead to the radio on the volume control side of the break. If you look at the schematics in the previosu step, I have labelled this side as "B"

    Press play on your AUX source and if you were right you should hear music from your radio. Turn up your radio and listen. Does it sound good? if so, you are ready to start buttoning up. If not you will need to find a new connection point.
     
  6. Radio Joe
    Joined: Jan 9, 2007
    Posts: 306

    Radio Joe
    Member

    So now you are excited. You know it works and want to get it ready to put into the car. The next step is to create a connection point that will allow you to listen to the radio and will interrupt the tuner when you want to listen to the AUX source.

    Run to radio shack and purchase a headphone jack part number 274-246. This connector will allow the situation described above.

    Your aux source (iPod, MO3 player ect) has stereo output- A left and right output. Your radio however only has one speaker. We have to combine the laft and right channels of your AUX source into a mono signal that your radio can use. DO NOT JUST WIRE LAFT AND RIGHT CHANNELS TOGETHER! this could damage your AUx source. Instead we will add two 3.3Kohm resistors to the circuit to to combine the channels.

    In the schematic below, you will see how the resistors are connected to the headphone jack and you will also see the labels on the lead similar to the previous schematics.
     

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  7. stude_trucks
    Joined: Sep 13, 2007
    Posts: 4,755

    stude_trucks
    Member

    Cool, I like this post. This might come in handy for me later when I get around to finally putting a radio in my truck. Next problem will probably be just hearing it over all the noise from the truck. :)
     
  8. Radio Joe
    Joined: Jan 9, 2007
    Posts: 306

    Radio Joe
    Member

    Below is a picture of a headphone jack with the resistors and wiring connected to it (sorry its a little blurry)

    So if you connect the wire labelled "B" on the headphone jack schematic to the location labelled "B" on the radio schematic and do the same with location "A" on both schematics. I usually use about a 2 to 3 foot wire lead between the radio and the headphone jack so the jack can be mounted in the dah somewhere.

    Note- You must use shielded wires between the radio and the headphone jack. If you dont, noise and crosstalk can happen in your radio. This will degrade sound quality.

    SO- now everythign is connected and its time to test it. DO NOT PLUG ANYTHING INTO THE HEADPHONE JACK RIGHT NOW. Turn the radio on. The radio shoudl work as normal.

    Plug the AUX source into the headphone jack. Your radio shoudl stop producing sound.

    Now turn on the AUX source (press play)- You should here your AUX source through the radio. If so you have successfully added an AUX jack to yoru radio.

    ENJOY!
     

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  9. Radio Joe
    Joined: Jan 9, 2007
    Posts: 306

    Radio Joe
    Member

    And Finally here are some troubleshooting tips for common problems:

    *When the aux is plugged in, it plays at full volume and wont turn down.
    ----You made your input connection on the wrong side of the volume control. Look at the schematic and the radio and determine the correct location and change it.

    *Unplugging the AUX source does not return the radio to working condition.
    ----- You have made an incorrect connection on the headphone jack. Review the connections and make changes

    *No sound from the radio with the AUX plugged in and playing.
    ----- The ground wire from the headphone jack is not connected to the radio ground (Chassis). Connect this terminal to ground (usually done with the shield of the shielded wires used)

    Any questions? Let me know.
     
  10. Radio Joe
    Joined: Jan 9, 2007
    Posts: 306

    Radio Joe
    Member

    Monsterflake- I usually charge $90.00 to do this.

    That breaks down as $15.00 PARTS, $60.00 for 1 hour labor, $15.00 S&H
     
  11. Thirdyfivepickup
    Joined: Nov 5, 2002
    Posts: 6,088

    Thirdyfivepickup
    Member

    as one of my good customers in NC would say...

    "do what now?"

    Damn, this is a great idea. Too technical for me. If I could do it all with a hammer and pliers I might try!
     
  12. Awesome thread, sorry i missed it the first time around!
     
  13. zman
    Joined: Apr 2, 2001
    Posts: 16,562

    zman
    ALLIANCE MEMBER
    from Garner, NC

    hell yeah. awesome...
     
  14. 49anglia
    Joined: May 10, 2008
    Posts: 160

    49anglia
    Member

    I dont get what you've done with the resistors to join the 2 channels.

    Can you explain where in the circuit the resistors go?

    Ive just converted an old valve radio from positive earth to negative earth, replaced a few capacitors and converted it to stereo with an MP3 input (need another radio for the second cahnnel though)

    I wont need resistors in my set up but a friend wants me to put MP3 leads into his mono radio's so need to bridge both channels.
    I just dont get from your diagrams where abouts in the signal circuit the resistors are.

    Thanks.
     
  15. 49anglia
    Joined: May 10, 2008
    Posts: 160

    49anglia
    Member

    Ah, its ok, i understand now.


    Thanks.
     
  16. banjorear
    Joined: Jul 30, 2004
    Posts: 3,779

    banjorear
    Member

    Damn, that is slick. Good job.
     
  17. Gruizer54
    Joined: Apr 23, 2001
    Posts: 85

    Gruizer54
    Member

    Way cool, I'm an electronics engineer and I never thought of doing this. I'm gonna give it a go when i get out to the garage. Thanks Joe!
     
  18. 49anglia
    Joined: May 10, 2008
    Posts: 160

    49anglia
    Member

    You know you can do stereo too.

    Take out the volume knob, this is probably the on/off switch too. Measure the resistance so you know its value and buy the same switched potentiometer with the same value but in stereo.

    If you unlucky you might not be able to get a switched stereo pot in the right value. In that case get any switched stereo pot, and 2 mono pots of the same make and the right resistance and swap the tracks over.

    Swap in the new volume pot and run your MP3 input lead to it (i just disconected the radio altogether).

    Run one chanel signal out into your origional radio's amp section then run the other chanel into an IDENTICAL radio's amp section.
    Run one speaker from each radio.

    You can add a second switched power out from the main radio to turn the second hidden (im mounting mine up behind the dash) radio on at the same time. Can also add power outs for electric ariels etc at the same time if you wish.

    I now have stereo MP3 valve radio that looks identical to the stock mono valve one.
     
  19. haroldd1963
    Joined: Oct 15, 2007
    Posts: 1,154

    haroldd1963
    Member
    from Peru, IL

  20. Radio Joe
    Joined: Jan 9, 2007
    Posts: 306

    Radio Joe
    Member

    Hey everyone- Sorry I missed this when it popped back up in March- If anyone needs any info just let me know.

    49angelia is right- That is one way to run a second channel from your radio. That will give you stereo from your MP3 player. BUT if you are removing the tuner part completely, I would suggest just running the Mp3 player on a small amplifier and leave the radio unhooked. Its alot easier.

    I used to add stereo to old AM/FM radios by adding an FM demodulator chip and a second audio channel.



    -Joe-
     
  21. mp3 to straight amp? got a wiring diagram for that hookup?
     
  22. Radio Joe
    Joined: Jan 9, 2007
    Posts: 306

    Radio Joe
    Member

    I dont have one but could draw one if you need it. Basically all you need is atleast a 2 channel amp and an adapter from your local radio shack. The adapter converts headphone jack to RCA jacks. plug the headphone style into your MP3 player, plug the other end up to the amp and use the volume control of the MP3 player to control the volume of the system.

    Basically you end up with a stand alone system you can pull out of the car when you need to.
     
  23. jamesgs4
    Joined: Aug 22, 2007
    Posts: 253

    jamesgs4
    Member
    from denver

    well..................you shoulda done a search:rolleyes:
     
  24. Merc cruzer
    Joined: Feb 26, 2009
    Posts: 275

    Merc cruzer
    Member
    from Colorado

    Radio Joe,

    By way of a background the Caps and Resistors have all been replaced and/or tested in my 53' Merc 6 volt pos ground radio and I have installed the jack and it works great. By way additional protection, does anyone make a 1/8" cord with some sort of serge protection to protect the signal source ( CD player, ipod, Iphone or android etc)? I haven't found one so far.

    Thank you,

    Roy
     
  25. I'd like to know about the surge protector as well. Great thread, can't wait to do it to my 53.
     
  26. David Gersic
    Joined: Feb 15, 2015
    Posts: 2,151

    David Gersic
    Member
    from DeKalb, IL

    Most "surge protectors " are just a metal oxide varistor (MOV) across the inputs. You can buy them for pennies from Jameco, Mouser, DigiKey, etc.. See:

    https://en.m.wikipedia.org/wiki/Varistor

    for more on how they work.
     
  27. Merc cruzer
    Joined: Feb 26, 2009
    Posts: 275

    Merc cruzer
    Member
    from Colorado

    With this in mind, I thought it was getting too complicated, so I decided to take the project to the final phase and go bluetooth/airgap (probably a misuse of the term even though the operational range is up to 30'). This little device I have pictured here just plugs into the jack and rather than having a cord between the cell phone, I-pod etc. and the radio jack, it is now wireless (bluetooth). It works great and in the event there is a power surge, the only thing lost is the bluetooth receiver (less than $15.00) and your phone, I-pod etc. is fully protected. The unit is 1" Wide X 2" Tall X 1/4" deep.

    Mpow 2.jpg Mpow.jpg Mpow 1.jpg

    I found it on e-bay:
    http://www.ebay.com/sch/i.html?_nkw=Mpow+MBR1&clk_rvr_id=1208817190165&adpos={adposition}&rlsa=kwd-132201631583&geo_id=10232&MT_ID=7&crlp={creative}_2416792&cmpgn_id=44216767&query=mpow+MBR1&keyword=Mpow+MBR1&device=c&crdt=0&ad_grp=3799928895&ul_noapp=true
     
    Last edited: May 1, 2017
    clunker and Chris like this.

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