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Sound amplification decreases when connecting a capacitor

  1. Jun 27, 2013 #1

    An electronics newbie here..

    I'm trying to produce sound using a 555 timer. When I tried using the schematic(attached file), a definite sound came. But when I removed the capacitor C2 in the circuit, the sound (amplitude) actually increased! Why does this happen? Why then, do we use a capacitor before the speaker?:confused:

    One more thing.. Why do we need the resistor R2 from the transistor to the ground? When I removed the resistance, it doesn't seem to work. Why is that so? Isn't the emitter terminal connected to the ground through the speaker??:uhh:

    Thanks in advance :smile:

    Attached Files:

  2. jcsd
  3. Jun 27, 2013 #2


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    Did you try a larger capacitor?
    The capacitor gives zero average current in the speaker, so the voltage there oscillates around zero. At the same time, it limits the current flow, if the voltage differences are too large or the frequency is too low.

    R2 is needed to discharge the capacitor, if the transistor is not conducting. Otherwise, C2 just gets charged and afterwards nothing happens any more.
  4. Jun 28, 2013 #3


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    The capacitor blocks DC so that current through the speaker coil averages out to zero. It is not a good idea to allow DC through a speaker coil for a prolonged period, it can weaken its response. But for a cheap speaker, who cares?
  5. Jun 28, 2013 #4


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    R2 provides a necessary direct current path through the transistor.
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