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Help: 18Khz+ Amp and Speaker Impedance matching

Discussion in 'General Electronics Discussion' started by louarnold, Dec 18, 2012.

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  1. louarnold

    louarnold

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    0
    Dec 5, 2012
    I have a circuit that generates a range of sine-wave signal frequencies using an LTC6903 chip.
    I need to drive a speaker - the small PC speaker will be fine - up to 20KHz. I don't know how to design the impedance matching circuit or the amplification portion. It would help to run it of +/- 12V.

    Alternatively, with the proper impedance match again, I can input the signal to one of the inputs of a 50W per channel Sony audio amplifier (some 30 years old now).

    What should I do and how should I do it?
     
  2. davenn

    davenn Moderator

    13,837
    1,952
    Sep 5, 2009
    Hi there

    yes you could run it into that amplifier say an aux input
    just be aware of the signal level from the signal generator keep it very low
    impedance matching for something like that isnt hugely critical, its going to work regardless

    Altermatively, if you just want a small signal level to a small speaker, google LM386
    its an audio amplifier chip ~ 0.5 - 0.8 W outpu, you could use it to drive an old say... external PC music speaker etc :)

    Dave
     
  3. louarnold

    louarnold

    14
    0
    Dec 5, 2012
    I tried this on the bench with a +5V supply to the osc. chip. The open circuit output (AC coupled) is between +/-2.5V. However, when I connected a PC speaker to it (even through a unity gain 741 Op Amp at +/-12V), the signal level dropped to nothing (sharp positive and negative spikes). I felt the problem was the impedance mismatch. The chip output impedance is 45 ohms and the speaker is 8 ohms. Can you comment on this?
     
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