The Schematic Diagram is a basic MOSFET amplifier. Output power is 100 Wrms under 8 ohms or 160 Wrms under 4 ohms with distortion is 0.001 %. Bandwidth at -3 db is from 4 Hz to 100 Khz .
Input sensitivity is 1.2 volts. The gain of 27DB is archived by R7/R6. It may be modified by changing R7 value. Transistors T5 and T6 makes the second differential stage. Transistors T3 and T4 works as a current mirror source. They push the second differential stage to drain equal current. Doing so we get a high gain and an excellent linearity. Output MOSFET transistors works in AB class, their quiescent current is set at 100 mA trough P1. For setting quiescient current, you must set P1 in minimal resistance, place a multimeter in mV DC range on R14 or R15 leads, turn slowly the screw until you read a 33 mV value, which correspond to a 100 mA quiescent current.
F1 and F2 works as an elementary output short-circuit protection. The power supply must have a value between 45 and 55 Volts DC (positive and negative). One heatsink with a thermal resistance less of 2° C / W is required.
All resistors are 1% metal film 1/4 watt. Before connecting a speaker to the amplifier output, connect a multimeter to the output and look on DC output voltage. This level must not be greater than 50 mV. If it is so, check all amplifier for error. Also, change T2 with another device and check again. This amplifier is very simple to build and low cost.
Part List
C1 = 2,2 µF-100 VC2 = 330 pF-100 V
C3 = 100 nF -100 V
C4 = 100 µF 63 V
C5, C6 = 18 pF
C7 = 100 nF
R1, R3 = 47 K
R2 = 2K2
R4, R5 = 3K9
R6 = 1 K
R7 = 27 K
R8, R9, R11 = 100 ohms
R10 = 10 K
R12, R13 = 470 ohms
R14, R15 = 0.33 ohms 5 watts
R16 = 10 ohms 3 watts
T1, T2 = 2N5401, ZTX558, BC556B
T3, T4 = BF470, MJE350, 2SB649
T5, T6 = BF469, MJE340, 2SD669
T7 = IRF540, IRFP240, 2SK1530, 2SJ162, BUZ900DP, BUZ901DP
T8 = IRF9540, IRFP9240, 2SJ201, 2SK1058, BUZ905DP,
P1 = 2K5 trimmer
F1, F2 = 3 A
power supply
One 2x40 volts 225 VA transformer is exactly what we need for one mono amplifier. For a stereo amplifier, one 2x40 volts 500 VA transformer is required.
Use at least 4x6800 µF 63-80 V reservoir capacitors. The more caps you use, the better the ripple rejection.
4K7 5W resistors are used to discharge reservoir capacitors once mains is set off.
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