How do I construct a basic amplifier circuit?

Ok so here it is:

I am in an electronics class where i have to build a solar powered alarm that will sound when the sun comes up at 900Hz for a time of 9 seconds. I have constructed this fine but my problem is building an amplifier circuit for the speaker. We are useing 8 omh speakers and my instructor says that we can only use basic components. (for example NPN transistors, resitors, voltage reg., capacitors) I need the simplest amplifier circuit you can think of.

Thanks alot

5 Answers

  • 1 decade ago
    Favorite Answer

    The circuit mentioned above neglects important features of an amplifier design. You need input current control, biasing to keep the thing in a linear operating range, etc.

    Here's link to a schematic that is a good bit more complete. You can use easy-to-find 2N2222 transistors instead of trying to find those BC108's if you like.

    Note that the input goes to the capacitor and to ground (same as the transistor emitters) -- the original author neglected to show the ground connection -- it is assumed.

    Pay attention to the polarity of the 10uf capacitors.

    It won't be loud, but you never did say how loud it needed to be...

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  • semdot
    Lv 4
    1 decade ago

    Speakers run off current so you need current amplification. For the simplest amplifier, you run your signal through a large capacitor (>100uf) to a NPN transistor base. Connect the NPN collector directly to VCC around 6V (assuming a 1 W speaker, 8V/8ohms = 1 watt, but you do not want to run at max rating). Connect the speaker in series between the NPN and ground.

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  • 1 decade ago

    Common Emitter, AC coupled. Bias the base and collector such that you are safetly in the foward active region, use DC blocking caps, then connect the input to the base and the output to the collector.

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  • 3 years ago

    without examining each and all of the above hyperlinks, i could advise utilising ultrasonics - as utilized in automobile reversing sensors and those little instruments architects carry with them to straight away diploma a room length. Radar is yet another selection yet a great way far greater durable.

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  • 1 decade ago

    Connect your source to Vin, and your ouput to Vout. Any way you cut it, this will give you some sort of amplification.

    If you want to get picky, you can look into adding capacitors to increase your gain at your particular frequency, and picking your resistors for maximum power transfer.

    You can construct this circuit for a quick and dirty amp though.

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