microcontrolled pre for a GC power amp

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The diodes can be something like 1N4007.
R1 and R2 depend on the choice of pas transistor.
Let me try to explain my understanding of how it works. Let’s start by assuming very little current is drown, say a few hundred milliamps. The voltage drop across R2 will be very low, thus the voltage difference between the base and emitter of the pas transistor will be to low to turn it on. As we increase the current drawn by the load the voltage drop across R2 increases and so does the voltage difference between base and emitter. When this difference exceeds the base emitter on voltage the transistor will start conducting. R1 limits the current to the pas transistor and prevents it from “stealing” to much current from the regulator when it switches on causing the drop across R2 to decrease turning the transistor of and so on. At least that’s what I think it’s there for, I’ve seen schematics both with it and without it.
 
Got some feedback from my teacher to day.

he explained the circut to me(not that it helped much..), and he got it the way that the current sharing transistor wont do much good as only a small current will flow through, and most of the current will still have to go through the regulator..
 
yeah, well i do question him, but then again, he's supposed to know what he's talking about, though i find that teachers suprisingly often dont.

I dont quite see the logic he uses when explaining. he say's ohms law (whatever that is ;), but i'm sceptic. he really isn't good at teaching stuff. everything i'v learnt this year exept for a litle microcontroller basics i'v learnt here and reading on datasheets.. schools..
 
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