This topic contains 1 reply, has 2 voices, and was last updated by  mwpeters75 1 month, 3 weeks ago.

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  • #3420


    Hi all,

    The Lectron system is truly versatile ! In no more than a few minutes is it possible to construct a 3 stage amplifier which has surpringly good audio reproduction.

    There are 2 circuits here and it’s up to you which one you prefer ! The 2nd circuit only differs in the fact that a red wire is connected to form a closed feedback loop.

    The first amplifier has a bigger gain but might distort the sound.

    The 2nd has lower gain but reproduces the sound more adequately.

    Here are the 2 setups :

    I’ve included some oscillogram pictures with measurements. The blue is the input measured at the wiper of the potentiometer. The yellow is measured at the junction between the lamp and the emitter of the top transistor (where the feedback loop is connected)

    Waveforms in Vrms on transfo  Waveforms in Vpp on transfo

    The next oscillograms are measured at the speaker terminals (yes, I had to open the speaker box).

    Waveforms in Vrms measured on speaker  Waveforms in Vpp measured on speaker

    Who can calculate the power output of our little amplifier by reading the oscillograms ? It’s not that hard !




    • This topic was modified 1 month, 1 week ago by  mwpeters75.
    • This topic was modified 1 month, 1 week ago by  mwpeters75.
    • This topic was modified 1 month, 1 week ago by  mwpeters75.
  • #3438


    Hi Frank,

    Thanks very much for the new circuit!

    From my recollection, the formula P=E/I comes to mind but I don’t see any current value for calculation purposes.  Another learning opportunity for me!

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