Then a second CE at gain of 10 or 11, again pushing the impedance limits but not impossible.Īnd a final stage emitter follower running say 150mA class A into a low ohms resistor and capacitive coupled to the 4 ohm speaker. 2N2222 has quite high Hfe at such low signals. It may not be possible to meet the 50k input impedance with 3 2N2222, but you could try the first CE stage with RE 100k and RC 270k (gain of 2.7) and say 470k for RBH and RBL. So it seemed more a challenge of trying to get near those specs with 3 transistors, and audio quality was never mentioned, if at all important the only thing mentioned was 10mV in and 300mV out. I also assumed (in line with that thinking) that the OP meant "3 stages" of 2N2222, meaning of course 3 transistors in the design (although he allowed for paralleling some output transistors).
I took the original question as a "classsroom challenge" type of thing where everything has to be pushed to the limit to barely meet the specs. I guess that's the end of my Sunday sermon. (I do have some knowledge, which I'm glad to share with others.) That's why I hang out here! to try to fix my ignorance. Regarding my ignorance, yes, I freely admit that I am ignorant of a lot of aspects of electronics. Now, you could have replied more fully, or you could have said "Don't bother me anymore!", at which point I would have respected your wishes.īut if you're going to give people answers to questions, as happens here, it's better to give an explanation, rather than just say "Do this" or "Do that" without explaining why you should do this or that. Since you brought this up in this public forum, all I can say is that while you did provide me some information, for which I am grateful, I found it very frustrating trying to get answers to questions from you, as your replies were invariably only 4 or 5 words, and I kept having to ask you more questions. I still have them in my inbox and outbox.
Regarding my PMs to you, yes, I recall a whole string of them a while ago when I was researching on of your circuits (a boost converter running on 3 volts, which is still an intriguing circuit to me, even though I never got it to work as well as you claimed it did). RB, if you're reading this, do you agree that your solution wouldn't provide a high enough input impedance?) (According to my textbook, you can only expect to get about 3KΩ with a CE amplifier.) While an emitter follower would probably work, it wouldn't be the first choice, as it has no gain (well, unity gain). To get 50KΩ input impedance, they'll need to use either a CC (aka emitter follower) or a Darlington stage as you suggested. Regarding the input impedance, I guess I overlooked that aspect of the O.P.'s requirements, so I owe you an apology.
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