Hi, I just found this interesting schematic and I just wondered if my theory about how this amp works is right or not.
I like this schematic because of it's input stage with two current sources.
If I understand it correctly Q9 en Q4 act like current sources, so when no input connected there will flow following biasing current:
I(bias) = (4.7V - 0.7V)/1820 * Hfe(Q4)
When the input signal (Vi) increases, Vb(Q3) will decrease and
Ic(Q3) will increase. The current through the biasing circuit doesn't change so the current through the base of Q5 will increase.
Q7 and Q8 give the signal a phase shift of 180 degrees that we need for the negative feedback.
When Vi decreases, Ic(Q3) will decrease and Ib(Q6) will raise, etc...
I'm just wondering if C9 is placed over there to prevent that the bias voltage will drop when Ic(Q3) decreases or has this capacitor another function??
thanks,
HB.
I like this schematic because of it's input stage with two current sources.
If I understand it correctly Q9 en Q4 act like current sources, so when no input connected there will flow following biasing current:
I(bias) = (4.7V - 0.7V)/1820 * Hfe(Q4)
When the input signal (Vi) increases, Vb(Q3) will decrease and
Ic(Q3) will increase. The current through the biasing circuit doesn't change so the current through the base of Q5 will increase.
Q7 and Q8 give the signal a phase shift of 180 degrees that we need for the negative feedback.
When Vi decreases, Ic(Q3) will decrease and Ib(Q6) will raise, etc...
I'm just wondering if C9 is placed over there to prevent that the bias voltage will drop when Ic(Q3) decreases or has this capacitor another function??
thanks,
HB.