![]() ![]() I still need to understand how bootstrap works to better define the values of the resistors and capacitors, but it seems to increase the overall gain, and the oscillations of the output power This was causing oscillations in the power across the speakers Added a bypass capacitor to the emitter of the first stage to increase the gain.Increased output decoupling capacitor to 1000uF.Reduced the amplitude of the input signal to 100mV.Replaced second stage transistors with what I had available (2n3904 & bd139).(Or got the same results with a much more complicated circuit :-)) Maybe it is unrealistic, but I assume I can get it by using multiple resistances in parallel.Īfter reading the various comments and answers, reasearching online and a lot of experimentation, I think I have made some progress. Thanks to the suggestions I have updated the circuit replacing the Q2 transistor with a Darlington pair and reducing the common collector emitter resistance to 2 ohm. I could buy a pre-designed kit of course, but what's the fun with that. Do I need to increase the gain of the first stage and change the transistor?.Can I actually build an (educational) amplifier with this approach?. ![]() Of course I am missing a few things, but the purpose of this exercise was to start small and then build my way up. It is clearly not enough to drive the speaker. If now I add a load R L = 8 ohm after the C out capacitor I have the following V out and current across it: The choice of the 16 ohm resistor was dictated by the the input impedance for the common collector Z in = beta * RE_2 (is this correct?) The model for the power transistor is (downloaded). Now I would like to add the second stage (common collector) and I came up with this: The model for the 2N2222 transistor is the following. I have sized the various components following this tutorial. I am a mechanical engineer and I am just learning about electronics so please bear with me. The idea is to start from a common emitter amplifier to amplify voltage and then add a common collector (emitter follower) amplifier to amplify power and deal with impedance matching. I am trying to design an amplifier for a 1 W 8 ohm speaker for educational purposes. ![]()
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