70/40 Watts Hi-Fi amplifier
70/40 Watts Hi-Fi amplifier
Here is a circuit of the world best Hi-Fi amplifier you may never have to replace by a better one. The high output, good specification, and small size make this 70/40 watts hi-fi amplifier more versatile.
Circuit description of 70/40 watts hi-fi amplifier
The 70/40 watts hi-fi amplifier circuit is build around transistors, configured in various modes. The signal to be amplified is given to base of transistor T1 configured as differential amplifier with T2. Transistor T3 is used to maintain the current of differential amplifier.
Transistor T4 with T5 forms a cascaded pair derived directly by transistor T1. For better result transistor T6 and T7 again configured as cascaded pair and provide constant current source to cascade pair T4 and T5 in this amplifier circuit.
Temperature coefficient of transistors T10 and T11 is compensated by transistors T8 and T9 which act like diodes. Transistors T10 with T12 & T14 and transistors T11 with T13 & T15 form a triple Darlington pairs.
The current through T4 and T5 is kept at a low value of about 6mA because the output of this circuit consists of triple Darlington pairs. The small change in the VBE of T10 and T11 changes output current of hi-fi amplifier greatly.
In order to prevent distortion in the 70/40 watts hi-fi amplifier when capacitive loads are connected to the output, coil L1 is used. Fuse is used to prevent DC voltage across the speaker and is connected in series to speaker. The total gain of this amplifier circuit is approximate 32 and is value is calculated by (R7 + R8)/R8.
PARTS LIST
Resistors (all ¼-watt, ± 5% Carbon)
R1, R7 = 100 KΩ
R2, R3, R9 = 1.2 KΩ
R4, R5, R6 = 2.7 KΩ/2W
R8 = 4.7 KΩ
R10, R13, R16, R18, R19 = 100 Ω
R11 = 3.3 KΩ
R12, R17 = 680 Ω
R14, R15, R22, R23, R24, R25 = 1 Ω/2W
R20 = 10 Ω/2W
R21 = 1o Ω/1W
VR1 = 100 Ω
Capacitors
C1 = 1 µF/polyester
C2, C3 = 25 µF/25V electrolytic
C4, C8, C9 = o.1 µF polyester
C5 = 10 µF/60V electrolytic
C6 = 4.7 µF/10V electrolytic
C7 = 56 pF ceramic disc
Semiconductors
T1, T2, T3 = BC546B
T4 = BC558B
T5, T11 = 2N4033
T6, T10 = 2N3019
T7 = BC548B
T8, T9 = BC147B
T12 = BD140
T13 = BD139
T14 = 2N3055
T15 = MJ2955
ZD1 = 3.3V 400mW zener diode
ZD2 = 3.9V, 400mW zener diode
Miscellaneous
L1 = Coil having 20 turns of 20 SWG over thin pencil
F1 = 3.5 Ampere fuse
SPECIFICATIONS |
Output power (1 KHz, o.7% THD): 73W into 4-Ω and 44W into 8-Ω |
Offset Voltage: Less than ±40mV |
Input impedance: 100 KΩ |
Harmonic distortion : 0.015% |
Intermodulation distortion (70W): 0.02% |
Frequency range: 10 Hz – 30 KHz, ±2dB |
Signal-to-noise ratio (out = 100mW): Over 72dB |
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