Hello again,
I just built and tested my first 2 stage BJT amplifier.
I'm using it to drive a small 8 ohm speaker. For these reason, I used an emitter follower as output stage, and a common emitter as first stage. But I would like to do it better now.
Here is the circuit, and the waveforms (CA coupling). Yellow is the input signal. Blue is Q1 output. Magenta, the speaker's voltage.
The first thing I see wrong is the strange clipped output waveform, which I suppose is due to the grounded speaker terminal. I think voltage can't drop below 0 V because there's no negative power source in the circuit, but in the second waveform image I used a 10 timer higher frequency, and the output gets closer to a sine wave, and aparently going below 0 V (but I'm not 100% sure about this because I forgot to check it in CC coupling mode). Also it gets bigger in amplitude, and don't really know why, as the 220 uF capacitor should be high enough to let the low frequency pass by. In fact, if I raise frequency even more, the output ends up looking very much (but not 100%) like a sine wave.
Can you give me some directions??
Thank you!!