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May 15, 2018 at 22:56 history edited jonk CC BY-SA 4.0
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May 15, 2018 at 4:24 comment added jonk @WillisBlackburn And yes, I believe the output can sustain about 9Vpp (4.5Vp.) However, keep in mind this is an educational circuit, doesn't include current limiting, doesn't manage the BJT Ohmic resistances, pastes in a simple cap to create a dominant pole roll-off when other ideas might be better applied, and is quite inefficient as it is a class-A. Probably someone better than I (I'm only a hobbyist) should do a fuller exposition.
May 15, 2018 at 4:22 vote accept Willis Blackburn
May 15, 2018 at 4:20 comment added jonk @WillisBlackburn My fault in poorly communicating. The closed loop gain is perhaps 15.8, and fixed. Since the output shouldn't be driven to more than 4.5 Vp, this means the input should not be more than about 250 mVp. If it is, then the output will begin to clip and the distortion becomes much more noticeable. The input to Q3 is limited to 50mVp (100mVpp). But the signal goes into Q4, not directly into Q3. I separated the gain calcs into two parts and probably confused you by doing so. My apologies.
May 15, 2018 at 3:18 comment added Willis Blackburn Could you help me understand what the gain of 15 (or 15.8) really means? If the input is just 100mV peak to peak and the output 9 volts peak-to-peak then isn't the gain 90? In other words once the NFB comes into play does the amp still attain a 9V swing between Q1 and Q2?
May 15, 2018 at 2:20 history edited jonk CC BY-SA 4.0
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May 15, 2018 at 2:00 history edited jonk CC BY-SA 4.0
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May 14, 2018 at 18:52 history edited jonk CC BY-SA 4.0
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May 14, 2018 at 17:40 history edited jonk CC BY-SA 4.0
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May 14, 2018 at 17:17 comment added jonk @WillisBlackburn Added a note on open and closed loop gain.
May 14, 2018 at 17:17 history edited jonk CC BY-SA 4.0
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May 14, 2018 at 12:05 comment added Willis Blackburn Thanks for the detailed explanation! I realize now that I had everything completely backward. I did think it might be okay that the base of Q3 is restricted to about 1.4V, because it's the current that matters, not the voltage. But then I couldn't figure out where the voltage amplification came from. Now I understand, it comes from Q1 and Q2. In my initial attempt, the output stage was an emitter follower, and I was still thinking of it as a current amplifier, but here the output stage isn't an emitter follower.
May 14, 2018 at 9:14 history edited jonk CC BY-SA 4.0
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May 14, 2018 at 8:57 history edited jonk CC BY-SA 4.0
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May 14, 2018 at 8:49 comment added Solar Mike Thorough and illuminating... +1
May 14, 2018 at 8:43 history edited jonk CC BY-SA 4.0
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May 14, 2018 at 7:33 history edited jonk CC BY-SA 4.0
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May 14, 2018 at 7:28 history edited jonk CC BY-SA 4.0
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May 14, 2018 at 7:04 history edited jonk CC BY-SA 4.0
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May 14, 2018 at 6:57 history answered jonk CC BY-SA 4.0