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Two sound recorders to one speaker question.

Discussion in 'Electronic Basics' started by w2aew, Oct 3, 2005.

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  1. w2aew

    w2aew Guest

    The problem is likely because the low impedance output of the unuised
    recorder is essentially shorting the speaker. One possible simple
    solution (if you can tolerate a small volume degradation) is to put a
    8-ohm resistor is series with each output. This will attenuate the
    signal at the speaker (because of the divider from the in-use device,
    and the 8-ohm shunt of the unused device), but should maintain the
    audio fidelity.
     
  2. redbelly

    redbelly Guest

    If the (-) outputs of the recorders are isolated from one another, then
    you could wire the two recorder outputs in series with each other.
    Then connect the speaker across the combined output.

    Mark
     
  3. Rubicon

    Rubicon Guest

    Hello,

    I have a couple of 10sec sound recorder boards from toys that I wish
    to connect to a single speaker. At the moment I have a breadboard with
    a 16F84 PIC powering each board seperately via transistors before
    triggering its PLAY connection, waiting a specified time period for
    the sound to play then shutting it down. The problem is that the
    boards have their own speaker connections running back to a gob-top
    chip and if I have them both connected to an 8ohm 0.25 watt speaker
    the playback sound is degraded. Connected seperately to the speaker
    they're fine but with even only one wire from either of the other
    boards speaker connections hooked up then the sound degrades powered
    up or not.

    The only way I can think of to solve this is a couple of PIC
    controlled 5V DPDT relays, one for each pair of speaker wires. That
    seems messy and though small the relays make an audiable click
    especially when mounted.

    Can anyone suggest another hopefully less complicated way to stop this
    from happening?

    Any help is always appreciated.

    Cheers,

    Andrew.
     
  4. w2aew

    w2aew Guest

    I would imagine that the audio preamp on the unit(s) has some AGC
    (automatic gain control), so you probably aren't over-driving the input
    too badly. If the audio playback is distorted or 'clipped', try
    reducing the audio level from your soundcard. The only real potential
    problems with this setup are the potential to overdrive (covered
    above), or the detrimental affects of the electret mic bias on the
    sound card output. But, since you said that it is working, I suspect
    that the sound card output is ac coupled and rejects the mic bias. So,
    if it isn't broken... ...don't fix it!
     
  5. Rubicon

    Rubicon Guest

    Thankyou both for replying.

    I've tried the 8ohm resistor method and it worked well the audio being
    much less garbled with a little drop in volume. I haven't yet tried
    the other suggested method but I will at some point soon.

    I'm entering the audio from mono WAV files from my computers soundcard
    via a stereo cable and mono adapter to the electret mic (removed)
    connections on the boards. Though it does work is there anything wrong
    with this method or something I can do to improve it?

    Cheers,

    Andrew.
     
  6. Jasen Betts

    Jasen Betts Guest

    from those symptoms it sounds like the little chips have H-bridge output
    stages, that means that opposite signals are tens out each speaker wire...
    one DPDT relay would be enough
    build your own from scratch ?

    <http://www.atmel.com/dyn/resources/prod_documents/doc1456.pdf>

    three ICs and a little other stuff (mostly resistors)...

    you'll be able to recycle the microphone and speaker from your existing
    setup

    but I see you're using PICs - there may be something similar on the microchip
    site.


    Bye.
    Jasen
     
  7. clicker

    clicker Guest

    Try putting a 1 k resistor in line with each sound recorder. This
    worked for me. It does cut the volume a bit but the sound quality was
    fine.

    Pete
     
  8. Rubicon

    Rubicon Guest

    Once again thanks,

    Andrew.
     
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