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| 3 stages power amplifier project |
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| magic:
Try to figure out a resistor value which will work equally well within 1V of each rail ;) Furthermore, more impedance here → more open loop gain. Less distortion too, because operating current of the VAS doesn't vary as much with output voltage. |
| Lucky-Luka:
--- Quote from: magic on December 23, 2019, 11:49:19 pm ---Try to figure out a resistor value which will work equally well within 1V of each rail ;) --- End quote --- I know that for you the answer is obvious but not for me :'( You mean that resistor doesn't exist? |
| Lucky-Luka:
Hi all The voltage across the Vbe multiplier determines the quiescent current of Q1 and Q3, right? How can I decide the right current of the current mirror? It has to be greater than the base current of Q2 when maximum current is flowing in Q1 (14V/10ohm=1.4A) so that even Q5 can work properly (right?), but how much greater? Happy holidays |
| magic:
A few mA is common. Can't go too high or the VAS transistor will overheat, can't go too low or it will fail to drive the output stage or produce distortion if it is barely sufficient. Increasing too much also seems to cause distortion, perhaps due to falling output impedance of the VAS and its active load. Experiment until you get the performance you want. |
| Lucky-Luka:
After the last stage was done (more or less) I've tried to add a CE stage. Something went wrong maybe. The currents on the output resistors changed. What is going on and what should I do? Q2 base current should be it's collector current (same value as in the stage without CE) divided by Q2 beta right? I fear this relation alone isn't enough in order to find the right I1... |
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