Adding Aux Input to Sony Stereo

Discussion in 'The Projects Forum' started by bockyPT, Dec 25, 2012.

  1. bockyPT

    Thread Starter New Member

    Dec 25, 2012
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    Hi there,

    I have a Sony HCD-EP303 Stereo that has radio, CD and cassete players, but no Auxiliary input. So I'm adding one.

    [​IMG]

    I have opened it to check what it looked like, then I got the service manual. I'm not sure if it's legal to post it here, but some of you may "have it" laying around...

    Anyway, I found that the IC that receives the outputs from the 3 sources and sends them to the amp has two unused input pins (L+R) that, according to the IC schematic in the manual, are connected internally.

    See here, pins 12 (L1) and 19 (R1) are not connected:

    [​IMG]

    And the IC schematic:
    [​IMG]

    So... This sounds like the perfect place to wire the new input, if the PCB isn't shorting them with L2 and R2 (I don't have the stereo with me right now). However, I have no idea if I can just connect the output of an MP3 player (or something else) to it. Are the voltages compatible? Do I need some kind of decoupling capacitor or something? The CD, cassette and tuner inputs have 0.1uF capacitors in series as you can see.

    Also, would it be better to just intercept the signal from, say, the CD player and have my signal use the same circuit? It could be done with those 3.5mm stereo ports that close one circuit when no jack is present and connect the jack to the circuit when inserted, disconnecting the original circuit.

    Thanks!
    F S
     
  2. tracecom

    AAC Fanatic!

    Apr 16, 2010
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    I guess that the inputs are not directly connected together inside the IC, and that those double arrowheads indicate some sort of selection circuit, but I don't really know anything about the IC. I do notice that the other audio inputs are connected to the IC with .1 μF caps, so I would think that an MP3 player should also be capacitively coupled, probably with mylar film caps. Good luck.


    ETA: If you look at page 9 of the datasheet for the IC ( http://www.google.com/url?sa=t&rct=j&q=&esrc=s&frm=1&source=web&cd=1&cad=rja&ved=0CDcQFjAA&url=http%3A%2F%2Fwww.datasheetcatalog.org%2Fdatasheet%2Fsanyo%2Fds_pdf_e%2FLC75392M.pdf&ei=3vbZUK33IZCw8ASl54GICA&usg=AFQjCNFYhiiRBURQHLppsm8NyniPIf_oDw&sig2=kdcsN0kpHW7g9WpqADEKRw&bvm=bv.1355534169,d.eWU, )it seems to indicate that the input selection is made by applying the correct digital code to the IC. If that is correct, then you will need to not only connect the MP3 play to the unused pins, but also find a way to tell the IC to select it.
     
    Last edited: Dec 25, 2012
  3. bockyPT

    Thread Starter New Member

    Dec 25, 2012
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    Indeed, it's not as simple as I was hoping. I guess my best bet is to intercept the signal coming from the CD/Tuner/Cassette and replace it with the aux in.
     
  4. tracecom

    AAC Fanatic!

    Apr 16, 2010
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    I might just sacrifice the cassette function and connect the MP3 player to where the cassette was, i.e., pins 11 and 20. But maybe you don't want to give up the cassette function.
     
  5. bockyPT

    Thread Starter New Member

    Dec 25, 2012
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    I'm planning to intercept the signal further up, where it comes from the cassete board to the main board via a ribbon cable. If I use a 5-pin 3.5mm jack I can have both functions working: if no jack is present, the circuit is connected as default. When a jack is inserted, the cassette output is disconnected and instead the MP3 signal is fed to the board.

    This is what I'm taking about:
    [​IMG]
     
    Last edited: Dec 25, 2012
  6. tracecom

    AAC Fanatic!

    Apr 16, 2010
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    Be sure that the first time you try the MP3 player, you have the volume control on the MP3 player set to minimum volume, and then turn it up gradually.
     
  7. bockyPT

    Thread Starter New Member

    Dec 25, 2012
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    0
    Sounds wise, thanks.
     
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