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Class A amplifier?

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Alright friends,

I've built the following circuit, save the "bass boost" which is SW1 in series with R7 and C6. I was wondering if someone could provide me with the theory of what is actually going on in this circuit. I am familiar with most electrical components and electronics in general. Thanks a lot.

**broken link removed**


P1 = 10K Log.Potentiometer
R1,R2 = 33K 1/4W Resistors
R3 = 33R 1/4W Resistor
R4 = 15K 1/4W Resistor
R5,R6 = 1K 1/4W Resistors
R7 = 680R 1/4W Resistor
R8 = 120R 1/2W Resistor
R9 = 100R 1/2W Trimmer Cermet
C1,C2 = 10΅F 63V Electrolytic Capacitors
C3 = 100΅F 25V Electrolytic Capacitor
C4,C7 = 470΅F 25V Electrolytic Capacitors
C5 = 47pF 63V Ceramic Capacitor
C6 = 220nF 63V Polyester Capacitor
C8 = 1000΅F 25V Electrolytic Capacitor
D1 = 1N4148 75V 150mA Diode
Q1 = BC560C 45V 100mA PNP Low noise High gain Transistor
Q2 = BC337 45V 800mA NPN Transistor
Q3 =TIP31A 60V 4A NPN Transistor
Q4 = TIP32A 60V 4A PNP Transistor
SW1 SPST switch
 
It is an extremely simple class-AB audio amplifier. C2 is shown with backwards polarity by mistake.

Q1 and Q2 are voltage amplifiers. Q3 and Q4 are complimentary emitter-follower current amplifiers that have their idle current adjusted by R9.
D1 is attached to the output transistors to adjust their bias current that changes when their temperature changes.
R6 provides AC and DC negaive feedback.
C5 reduces high frequencies so that the negative feedback does not cause oscillation.
Speaker coupling capacitor C7 and the speaker connected to the positive supply instead of to ground bootstraps R8 so that the base of Q3 can be driven above the supply voltage so that the output swing is the highest.
 
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