How to build Amplifier of acoustic frequencies with preamplifier

Technical characteristics:
Tendency of catering: 15V
Force of expense: 4,2Wrms in the 4W
Minimal signal of entry: 94mVp-p with preamplifier, 0,65Vp-p without the preamplifier.

Circuit diagram

Parts:
R1 2,2KW
R2 330KW
R3 4,7KW logarithmic potentiometer
R4 330W
R5 1KW
R6 1,5W
C1, C6 100nF polyester
C2 100mF/25V ilektrolytjko's
C3, C7 1mF/25V electrolytic
C4 1000uF/25V electrolytic
C5 10uF/25V electrolytic
Q1 BC547
U1 TDA2002
LS1 Loudspeaker.

Notes:
Proportionally the resistance of loudspeaker changes the force that it can give the amplifier:
LS1 Force of expense
2W 6,5Wrms
4W 4,2Wrms
6W 3Wrms
8W 2,25Wrms