What went wrong with this class A amplifier design?

Question

I was trying to build a normal class A amplifier;

However, no matter how hard I try, I cannot find the reason behind my output (BLUE LINE) being clipped at the negative cycle of the input (YELLOW LINE).

What am I doing wrong? Any help is appreciated but would be better if a small explanation would be offered.

This is the circuit:

This is the output:

score 4 · Accepted Answer · answered Sep 02 '23 at 14:28

4

You are forcibly feeding AC from AC source that is directly connected into transitor base, bypassing the DC bias resistors.

answered Sep 02 '23 at 14:28

Justme

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That could be it; but where should I connect the AC input to? – Yeal Takian Sep 02 '23 at 14:36
Through a capacitor, just like the output. – Justme Sep 02 '23 at 14:38
@YealTakian connect the AC through a capacitor. This will allow the base side of the capacitor to have a DC bias, even though the AC source side has pure AC. – Math Keeps Me Busy Sep 02 '23 at 14:38
@Justme Thanks, Now it seems to work near perfectly – Yeal Takian Sep 02 '23 at 14:44
@MathKeepsMeBusy, Thanks to all of you, it's working. – Yeal Takian Sep 02 '23 at 14:45

score 0 · Answer 2 · answered Sep 02 '23 at 17:49

If I read the "scope" right, that's 1 mV peak for input, offset unknown due to coupling "AC".
If I read the schematic right, the no input operating point has the emitter close to 1.8 V, same if the source was AC coupled or offset to about 2.4 V, and Q1 pretty much saturated:

What do you expect?

What went wrong with this class A amplifier design?

2 Answers2