In Part I and part II about the paX amplifier we developed a complete error-correction power amplifier. In this accompanying article the protection system is described, that is constructed on a separate small circuit board that can be mounted directly on the speaker binding posts. We will also discuss the Safe Operation Area for the output devices and how it is modeled in the protection system.
Resistors
(0.25W metal film)
R1 = 10kΩ
R4,R9 = 12Ω
R5,R12 = 9kΩ1
R6,R13 = 6kΩ19
R7,R11 = 2kΩ0
R8,R10 = 536Ω
R14,R15 = 270Ω
R16,R22 = 3kΩ9
R17 = 36kΩ
R18 = 523Ω
R19 = 16kΩ
R20 = 56kΩ
R21 = 18kΩ
R24,R25 = 22kΩ
R23 = 3.9kΩ 1W
Capacitors
C1,C2 = 100nF ceramic
C3 = 330µF 6.3V
C4 = 22nF ceramic
C5 = 33µF 10V
C6 = 4.7 µF 25V
Semiconductors
D1,D6-D11 = 1N4148
D2,D5 = zener diode 18V 0.5W
D3,D4 = zener diode 12V 0.5W
J2 = Dual color LED
Q1 = 2SC2910
Q2 = 2SA1208
Q3 = BC546B
Q4 = BC556B
U1 = MCT6 (Fairchild)
U2 = UPC1237 (NEC) or NTE7100 (NTE Electronics)
Miscellaneous
J6 = header 2 x 1 pin
J7 = 2 x 3 pin DIL flatcable header
RL1 = Amplimo LS relay
DIL socket 2 x 4
SIL socket 1 x 8 pin
PCB, order code 071086-1
Informative articles
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